Download Ernest Just - CPO Science

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Date:
10.1
Ernest Just
Ernest Just was a pioneer in the study of cells, fertilization, cell division and the effect of ultraviolet rays on
chromosomes.
A strong work ethic
Teaching and learning
Ernest Just was born on
August
14,
1883,
in
Charleston, South Carolina.
His father was a dock
builder. He died when
Ernest was only four years
old. Ernest’s mother was a
school teacher. She instilled
in him a love for learning.
After his mornings at
school, Ernest worked in
farmers’ fields to help his
mother support the family,
which also included a younger brother and sister. This
tradition of hard work and long hours would remain
with Ernest over his productive life.
Upon graduation from Dartmouth in 1907, Just took a
teaching position at Howard University in Washington,
D.C. In time, Just would be named head of the biology
and physiology department. He also served as a
member of the medical school faculty. While juggling
all of these responsibilities, Just managed to find time
to earn a Ph.D in experimental embryology from the
University of Chicago in 1916.
A boarding school standout
Ernest and his mother decided it would be best for
him to attend Kimball Union Academy in Meridan,
New Hampshire, a boarding school that specialized in
preparing serious young students for a successful
college experience.
Before he left for New Hampshire, Ernest worked
after-school and summer jobs to earn money to pay
for boarding school. He proved himself an outstanding
student while at Kimball Union. He excelled in his
classes, was editor of the school newspaper, and
served as president of the debating team. To top it off,
Ernest completed the four year program in only three
years. He graduated as valedictorian of his class.
Ernest was also the only African-American student
enrolled at the school during his time there.
Becoming a scientist
In 1903, Just entered Dartmouth College. He decided
to become a research biologist and specialize in
cytology, the study of cells. Ernest earned a degree in
zoology. He was the only person in his class to
graduate magna cum laude (with great honor).Once
again, he was the valedictorian of his class. In
addition, he received special honors in botany,
history, and sociology.
Excellence in research
During his summers, Ernest traveled to Woods Hole,
Massachusetts, on Cape Cod. There he did extensive
research on marine animal reproductive systems at
the Woods Hole Oceanographic Institute. In 1915,
Just won the first awarded Spingarn Medal, given by
the National Association for the Advancement of
Colored People. He was only 32 years old.
Just completed thousands of experiments and
published over 50 papers during his twenty summers
in Woods Hole.
Worldwide acclaim
Just was honored again when he was invited by a
group of Germany’s top biologists to the Kaiser
Wilhelm Institute in Berlin. He was the first American
ever to be invited to study there.
His success at the institute led to invitations to Naples
and Sicily to work in marine biology labs there. Seeing
a great deal of opportunity in Europe, Just lived there
for many of his later years.
Just’s book, The Biology of The Cell Surface,
published in 1939, was a ground breaking work. It
outlined the importance of the outer layer of
cytoplasm in the cell, which he named endoplasm.
In 1941, after a long battle with cancer, Just died.
Reading reflection
1.
Look up the definition of each boldface word in the article. Write down the definitions and be sure to credit
your source.
2.
Imagine that you knew Ernest Just when he was growing up. Write a brief description of him as a young
person.
3.
Research marine biology and give a brief description of it for your class.
4.
Research: What were some additional reasons that led Ernest Just to move to Europe?
5.
Do you think it was easy for Ernest Just to excel as he did?
Name:
Date:
Mitosis and the Cell Cycle
10.1
Write the name of each stage of the cell cycle next to the correct letter. Describe what happens in each stage in
the spaces below the diagram.
a.
______________________________________________________________________________
b.
______________________________________________________________________________
c.
______________________________________________________________________________
d.
______________________________________________________________________________
e.
______________________________________________________________________________
Name:
Date:
Phases of Mitosis
10.1
Use the diagram below to help you identify the phases of mitosis on the onion root tip slide. Sketch what you see
under the microscope for each phase.
Pictures of slides under a microscope
Sketches of your slides
Name:
Meiosis
Explain what happens in each step of the diagram below.
Date:
10.2
Name:
Date:
Working with Ratios
11.1
For comparison purposes in science (and in many other fields), it is often useful to simplify a numerical result
into a ratio. Most people find that whole number ratios are the easiest to interpret. For example, the ratio 5:4 is
quicker to read, write, and understand than the ratio 2.5:2, even though these ratios are equivalent:
5
2.5
--- = -------4
2
One Friday night, Jerod went out to dinner and a movie with his family. His parents ended up spending $82.40
for dinner, and it cost $45 for everyone to see the movie. What is the ratio of the money spent for the movie to the
money spent on food? Please give the answer as a whole-number ratio.
1.
2.
3.
4.
5.
Write the given information as a ratio. Here we want $ movie: $ food; $45: $82.40
$45
Write the ratio as a fraction: ---------------$82.40
$45 ÷ $45
1
Divide top and bottom by the smallest number: -------------------------------- = ------------$82.40 ÷ $45
1.831
Round the decimal (when there is one) to the nearest whole number: 1.831 ≈ 2. The fraction from step #3 is
rewritten as 1/2.
Write as a ratio: 1:2.
The whole number ratio of the money that Jerod’s family spent on the movie to the money they spent on
food is 1:2.
Part A: Rewrite each as a simple whole-number ratio.
1.
67 : 128
2.
15.8 : 2.6
3.
15,007 : 33,045
4.
322.8 : 89
5.
203 : 1,088
Part B: Answer each with a simple whole number ratio.
6.
Theresa’s doll collection has only brunette and blonde dolls. Eight of the dolls are brunettes, while twentyfive of them have blonde hair. What is the ratio of blondes to brunettes in this doll collection?
7.
In Herbert Hoover Middle School, there are 1,285 students. Eight hundred six of the students are girls, while
479 are boys. What is the ratio of girls to boys?
Page 2 of 3
8.
After it rained one Saturday, Gail and Terry decided to collect earthworms. They planned to sell them 11.1
for fishing bait. Deciding that they could charge more money for the larger worms (those over 7
centimeters long) they began counting and sorting. Of the 356 worms they had collected, just 82 of them
were over 7 centimeters long. What is the ratio of short worms to long worms?
In some situations, this method for writing whole-number ratios does not provide enough information. In the
example of Jerod going out with his family for dinner and a movie, if only the estimated whole-number ratio
(2:1) is given, we might believe that his family spent twice as much money on food as it did on the movie. Maybe
this estimate is enough, if only a very general idea is needed. But if Jerod’s parents would like a better idea of
how they spent their money (maybe for budgeting purposes), they might use the following approach (note that
the first three steps are the same as with the first method):
1.
4.
Write the given information as a ratio. Here we want $ movie: $ food; $45: $82.40.
$45
Write the ratio as a fraction: ---------------$82.40
$45 ÷ $45
1
Divide top and bottom by the smallest number: -------------------------------- = ------------$82.40 ÷ $45
1.831
Round the decimal part of the fraction from (3) to the nearest tenth. 1.831 ≈ 1.8
5.
Write the decimal from (4) as a mixed number, and reduce to lowest terms if possible. 1.8 = 1 8/10 = 1 4/5
6.
Rewrite the mixed number from (5) as an improper fraction. 1 4/5 = 9/5
2.
3.
7.
1
Replace the decimal part of the fraction in (3) with the fraction from (6). Here, that gives --------- , which means
9--“the reciprocal of 9/5”; in other words, 5/9.
5
NOTE: The result in this step will always be either 1/fraction (in which case the reciprocal is required), or
fraction/ , in which case the fraction is being divided by 1, and the result is the fraction itself.
1
8.
Write as a ratio: 5:9
The whole number ratio of the money that Jerod’s family spent on the movie to the money they spent on
food is 5:9. This means that for about every $5 the family spent on the movie, they spent about $9 on food.
Part A: Rewrite each as a simpler whole-number ratio, using the method of rounding to the nearest tenth as
shown in the last example.
1.
167 : 108
2.
5.8 : 12.6
3.
3,450 : 5,007
4.
32.28 : 112.5
5.
2,043 : 888
Page 3 of 3
Part B: Answer each with a simple whole-number ratio.
11.1
6.
Sonya’s troll collection has only red-headed and purple-headed trolls. Seventy-seven of the trolls have red
hair, while just forty-six of them have purple hair. What is the ratio of red-headed trolls to purple-haired
trolls in this collection?
7.
In Everett Middle School, there are 508 students. Two hundred seventy-seven of the students are boys, while
231 are girls. What is the ratio of girls to boys?
8.
Tim and Rocco were asked to clean out their little brother’s toy box. While they were doing this, they found
that many of their own markers were mixed in with their brother’s. They sorted them into two piles, and to
their surprise, only 17 of the 109 markers actually belonged to their brother. What is the ratio of Tim and
Rocco’s markers to their little brother’s markers?
Name:
Date:
11.1
Gregor Johann Mendel
Mendel, the father of genetics, did not receive credit for his discoveries until after his death. Today, Mendel is
recognized as a pioneer for his insights into the mechanics of heredity.
Early Childhood
Two Peas in a Pod
Johann Mendel, the son of
a farmer, was born in 1822
in Austria. Mendel loved
nature.
He
worked
alongside his father caring
for plants in their fruit tree
orchard and garden.
Mendel’s mother hoped her
young son would become a
teacher or priest. His father
anticipated he would take
over the farm. The future
would hold many careers
for Mendel - teacher, priest,
and scientist.
Educating Mendel
Mendel learned a great deal both in and out of the
classroom. Home provided a natural setting to
understand plants and the value of hard work.
However, Mendel also excelled in school. A teacher
recommended that Mendel continue his education.
His father hesitated, but his mother supported the
idea. So, eleven-year-old Mendel went to school
nearly 13 miles away. Afterward, he went on to high
school. Tuition was a strain. To save money, his
parents rationed the food they sent him in order to pay
for his schooling.
In 1838, Mendel’s father was injured and unable to
work. Mendel became a tutor to earn money to study
at Olmutz Philosophical Institute. In 1841, Mendel’s
father sold the farm to his daughter’s husband. The
proceeds were divided among the children. Mendel’s
younger sister shared her portion to pay for his
education.
Mendel met Professor Franz who was both a scientist
and monk. After finishing his two years at Olmutz,
Mendel wanted to attend the university. Professor
Franz suggested joining a monastery in Brunn to help
relieve Mendel’s financial stress. In 1843, Johann
joined the Augustinian monastery, became a priest,
and took the name Gregor.
In a monastery setting, one would think that Mendel
would be secluded from the outside world. However,
monasteries were centers of learning. The monastery
suited Mendel well. It was here that he conducted his
famous pea experiments. Mendel’s approach to
explaining his results was unique. He used math to
defend what occurred naturally. This was a novel
approach in the field of biology.
He started his experiments in 1856 and grew over
24,000 plants during the next eight years. His garden
was small to house so many plants and he was forced
to hook them up onto anything he could find. He
fondly referred to his plants as his “children.”
Mendel discovered that traits do not blend, but rather
there are dominant and recessive features. His
tireless work led to the creation of two important
principles—the Law of Segregation and The Law of
Independent Assortment.
Mendel’s paper was published in 1866, but most
ignored it. It was not until 1900 that his work gained
respect, as scientists used microscopes to
understand cells and chromosomes.
A kind Mendel
In addition to conducting experiments, Mendel was a
teacher. He was unable to become a permanent
teacher after failing the teacher’s exam several times,
but remained a temporary high school teacher for
many years.
In 1867, he was elected abbot. As monastery
demands increased, he was forced to give up
teaching. He gave his last month’s teaching pay to the
three poorest boys in his class. With an abbot’s salary,
he also repaid his younger sister by paying for his
nephews’ education including medical school for two
of the boys.
Mendel, an avid weather lover, later became a
weather watcher and record keeper. Mendel died in
1884 at the age of 61. The Mendel Museum of
Genetics at the Abbey of St. Thomas in Brno in the
Czech Republic is a tribute to Mendel and his
scientific achievements.
Reading reflection
1.
Why did Mendel join the monastery and how did he benefit from this decision?
2.
Research: A punnett square is a graphical tool showing all possible combinations of alleles from the
parents. Who is responsible for developing the punnett square?
3.
Research: Mendel was always fascinated by the weather. Even before becoming an abbot, he kept
weather records. As a weather watcher he studied temperature, air pressure, wind speed, air moisture,
rainfall, and snowfall. He made graphs and charts to study the weather and patterns. Technology has
improved greatly since Mendel’s time. What types of technology are available today that help
meteorologists study and forecast the weather?
4.
Research: Mendel studied seven traits when performing his pea experiments. List the seven traits he
studied.
5.
What was unique about Mendel’s approach to explain his pea experiment results?
Page 2 of 2
Name:
Date:
11.1
Walter Sutton
Walter Sutton discovered the connection between inheritance and chromosomes, a concept we take for granted
today. This connection set the stage for the development of modern molecular biology.
Beginnings of innovation
Walter Sutton was born in
Utica, New York on April 5,
1877. When Walter was
ten, his father, William Bell
Sutton, a successful county
judge, decided to move
west with his family and
open a ranch in Russell,
Kansas.
Walter Sutton and his four
brothers slowly became
accustomed to ranch life.
About half of their ranch was grazing land for cattle,
and the other half planted with rye, barley, oats and
potatoes. Walter especially enjoyed figuring out how
to operate and maintain the many pieces of farm
equipment on the Kansas ranch.
Sutton’s interest in farm machines and obvious
mechanical skills made the study of engineering a
natural choice for him. After graduating high school,
he enrolled in the University of Kansas School of
Engineering in 1896.
Trying times prompt a shift in interest
The summer of 1897 was tough for Sutton. He spent
the months between school semesters caring for his
family, all of whom had come down with typhoid fever.
His younger brother John died from the illness.
When he returned to school in the fall of 1897, Sutton
switched from engineering to biology and premedical
studies. One of the first professors he encountered in
the program was Clarence McClung. Sutton
volunteered to help McClung with some last minute
work he needed to complete, and they soon became
friends.
A close relationship with a mentor
In 1898 Sutton went back to the ranch to help with the
harvest. He had become familiar with grasshopper
reproductive cells while working with McClung, and he
decided to dissect various species he was finding
mixed into the grain during harvesting.
One particular grasshopper species was bigger than
the others. When Sutton examined dissected tissue of
the grasshopper, he observed very large cells under
his microscope. He prepared some samples and sent
then back to McClung, with the recommendation they
begin using this species (Brachystola magna, the
“Lubber” grasshopper) for future experiments.
Even though Sutton was only a second year student,
McClung and several other faculty members quickly
agreed with Sutton, and considered his findings
important to the study of reproductive cytology and
morphology. Soon, cells from the Lubber
grasshopper were used by labs all over the world.
With these cells, McClung was able to identify the
chromosome responsible for sex determination in
sexual reproduction.
Building upon past success
Sutton received his undergraduate degree from the
University of Kansas in 1899, and his masters degree
in 1900. In 1901 he left Kansas for Columbia
University in New York City. There Sutton received a
graduate fellowship in zoology.
In 1902, Sutton wrote a paper after hearing about the
work of Gregor Mendel involving heredity with pea
plants. In this paper, Sutton provided evidence that
chromosomes carried the cell’s units of inheritance.
While studying his grasshopper cells, Sutton
observed that chromosomes occurred in distinct pairs,
and that during meiosis, the chromosome pairs split,
and each chromosome goes to its own cell.
In 1903 he published a paper announcing his
discovery that chromosomes contain genes, and their
behavior during meiosis was random. Despite these
ground breaking discoveries in genetics, Sutton
remained committed to his goal of becoming a
practicing physician. Upon receiving his doctorate of
medicine from Columbia, he moved to Kansas City,
Kansas and practiced general surgery until his death
in 1916.
Reading reflection
1.
Look up the definition of each boldface word in the article. Write down the definitions and be sure to credit
your source.
2.
Imagine that you knew Walter Sutton when he was growing up. Write a brief description of him as a young
person taking care of his family during the summer of 1897.
3.
How did Sutton’s two graduate school papers help to expand our understanding of genetics?
4.
Research: How is the X chromosome involved with sex determination?
5.
Research: Who was Gregor Mendel and how was his work related to Walter Sutton?
Name:
Date:
Genetics Vocabulary
1.
2.
11.1
Use the following terms to complete each sentence: genes, codominance, incomplete dominance, traits, and
allele.
a.
__________ are segments of DNA that carry hereditary instructions and are found on chromosomes.
b.
Different forms of a single gene are called __________.
c.
__________ is when a recessive and a dominant trait mix or blend.
d.
In horses, when a pure red horse and a pure white horse mate to have offspring, the offspring’s fur color
is a mixture between red and white. This is an example of __________.
e.
Hair color, eye color, seed shape and plant height are examples of __________.
Put the following notes under the correct heading in the table.
Phenotype
Genotype
Recessive
Dominant
•
stronger allele that may mask a weaker allele
•
physical appearance or genetically inherited feature
•
a trait that will appear in the offspring if one of the parents contributes it
•
a weaker allele
•
a trait that must be contributed by both parents in order for it to appear in the offspring
•
PP, Pp or pp
•
purple flowers, white flowers, black rabbits
•
genetic make up or the combination of alleles
•
the appearance due to the combination of alleles present
Dominant, Recessive and Codominant Traits
1.
Shade red all of the genetic combinations in which the dominant trait will appear and shade blue all of the
combinations in which the recessive trait will appear.
r
r
R
Rr
Rr
r
rr
rr
p
p
P
Pp
Pp
P
Pp
Pp
S
s
S
SS
Ss
S
SS
Ss
Page 2 of 2
2.
Shade red all of the combinations in which CODOMINANCE has occurred.
R
W
R
W
RR RW
RW WW
R
R
R
RR
RR
W
RW
RW
R
R
3.
If RR is the genotype for red flowers, what is the genotype for white flowers?
4.
What is the genotype for red flowers with white stripes?
11.1
R
RR
RR
R
RR
RR
The Story of Gregor Mendel
Use the following words to fill in the following passage: punnett, phenotype, recessive
trait, Gregor Mendel, genotype, traits, genes, alleles, dominant trait, and codominance.
Our story begins in a monastery in Austria in the 1800’s. __________, the “father of
genetics,” conducted many experiments on his garden plants. He was particularly
interested in studying pea plants because of their short growing time and many varieties.
Mendel noticed that certain ________ in pea plants were passed on from parents to
offspring. He also noticed that sometimes a trait seemed to disappear in between
generations. He wanted to find out why.
After many experiments, in which he crossed plants with different traits, he noticed similar results. He noticed
that sometimes trait showed up and other times they did not. For example, when he crossed a true-breeding
purple-flowered plant with a true-breeding white-flowered plant, the first generation of plants were all purple.
White flowers had disappeared! Mendel called the trait that always showed up the __________. He called the
trait that did not show up the __________. When he allowed the plants of the first generation to self-pollinate, the
next generation had 75% purple flowers and 25% white flowers.
He concluded that each plant had two sets of instructions for each trait, one from each parent. Today we know
that ________, found on chromosomes, determine traits. Each gene has two or more different forms called
________.
When studying genetics today, we can set up __________ squares. The squares contain the possible allele
combinations that might occur when crossing two pea plants. The inherited combination of alleles (PP, pp or Pp)
is called the __________. The organism’s appearance, such as flower color is called the __________.
It was later discovered that in certain organisms neither trait was dominant and a mixing or blending of the
dominant and recessive trait occurred. In this case, both traits are present. This is called __________.
In 1864, Mendel published his results, but unfortunately it wasn’t until after he died that he was recognized for
his work on genetics.
Name:
Date:
Probability
11.2
Probability is the likelihood that a certain event will occur. Technically, that is the ratio of the number of
favorable outcomes (a favorable outcome means that the event occurs) to the number of total outcomes possible.
To make the probability easier to understand, the ratio may be simplified (reduced), or even written as a percent.
1.
John is rolling a number cube that has the letters A, B, C, D, E, and F written on each face.
a.
What is the probability that he will roll a vowel?
Since there are two vowels (A and E), the probability of a favorable outcome is 2. There are six total
outcomes (A, B, C, D, E, or F). The probability of rolling a vowel is, 2/6 (or 1/3), or as a percent, 33.3%.
b.
What is the probability that he will roll a “Z”?
Since there is no “Z” on the cube, there is no chance of rolling one. The probability of rolling “Z” is 0.
2.
Kaya is spinning two spinners, each with equally divided sections. One has the letters A, B, and C, and the
other has the numbers 1, 2, 3, 4, 5, and 6. Spinning each spinner just once, what is the probability of spinning
a C on the first spinner and an even number on the second spinner?
First list all the possible outcomes in an organized way. A table is a good way to do this:
First Spinner Outcome
A
B
C
Second
1
A1
B1
C1
Spinner
2
A2
B2
C2
3
A3
B3
C3
4
A4
B4
C4
5
A5
B5
C5
6
A6
B6
C6
Outcomes
Outcome
There are 3 “favorable outcomes,” C2, C4, and C6. There are 18 possible outcomes.
3
1
The probability of spinning a “C” and an even number is ------ , or --- = 16.6%.
18
6
Notice that the number of possible outcomes (18) can also be found by just multiplying the number of possible
outcomes from each spinner [3 (from A, B, C) × 6 (from 1,2, 3, 4, 5, 6)].
Page 2 of 2
11.2
Please answer by giving the original ratio of favorable outcomes to total outcomes, then the simplified ratio, and
finally the percent.
1.
Kaya’s friend Jonah spins the same spinners. What is the probability that he will spin an “A”?
2.
Scottie is selling chances for a raffle drawing for his soccer team. Just one grand prize will be given to the
winner of the drawing. Each member of the team has 25 tickets to sell, each with a different number on it.
There are 20 players on his team. Scottie’s grandmother buys all 25 of his tickets. If all of the tickets are
sold, what is the probability that Scottie’s grandmother will win the grand prize?
3.
Natalie’s little brother is playing with her calculator. Her calculator only has the numbers 0 through 9, four
function keys (+,-, ×, ÷), the = button, and the on/off button. He randomly pushes one button on the
calculator. What is the probability that he pushes each of the following:
4.
a.
a number?
b.
one of the four function keys?
c.
the “=” or on/off button?
d.
any button that is not a number?
Ryne is blindly pulling slips of paper with letters of the alphabet written on them from 2 different bags. Each
bag contains two letters. The first bag contains two X’s, and the second bag contains one X and one Y.
a.
How many outcomes are possible?
b.
What is the probability that he will choose two X’s?
c.
What is the probability that he will choose two Y’s?
Name:
Date:
Punnett Squares
11.2
A punnett square helps scientists predict the possible genotypes and phenotypes of offspring when they know the
genotypes of the parents. The phenotype is the physical appearance of an organism and the genotype is the
inherited combination of alleles.
In rabbits, black fur is dominant to white fur. If you cross a BB male with a Bb female, what are the possible
genotypes and phenotypes of the offspring?
To solve the problem, write the alleles of one parent across the top and the alleles of the other parent along the
left side. Then, fill in the squares. Each box represents one of the possible genotypes of the offspring.
B
B
B
BB
BB
b
Bb
Bb
BB appears in 2 out of 4 squares. This means that there is a 50% for a genotype of BB. Bb also appears in 2 out
of 4 squares, or 50%. The genotype BB (two dominant alleles) will produce only black rabbits. The genotype Bb
(one dominant and one recessive allele) will also produce black rabbits, because the dominant trait hides the
recessive trait. Therefore the phenotype of the offspring will be 100% black. It is easier to interpret a punnett
square if you fill in a table like this one:
Genotype
Phenotype
Chance
BB
Black fur
50%
Bb
Black fur
50%
Page 2 of 3
11.2
1.
In pea plants, tall height is dominant to short height. If a TT pea plant fertilizes a Tt pea plant, what are the
possible genotypes and phenotypes and the chances for each?
T
T
T
t
Fill in the table:
Genotype
2.
Phenotype
Chance
Having dimples is a dominant trait in humans. If the mother and father both are Dd for dimples, what are the
possible genotypes and phenotypes of their children?
D
d
D
d
Fill in the table:
Genotype
Phenotype
Chance
Page 3 of 3
3.
Suppose a man with no dimples marries a woman with Dd for dimples. What are the possible
genotypes and phenotypes of their children?
d
11.2
d
D
d
Fill in the table:
Genotype
4.
Phenotype
Chance
Phenylketonuria (PKU) is a genetic disorder in which a person cannot use the amino acid phenylalanine. It is
carried by a recessive allele. Individuals with PKU must follow a strict diet that is low in phenlyalanine.
Let PP = normal, Pp = carrier, and pp = PKU.
Suppose a man who is a carrier marries a woman who is also a carrier. What are the chances that they will
have a child with PKU?
Fill in the table:
Genotype
Phenotype
Chance
Name:
Date:
More Punnett Square Practice
11.2
A punnett square helps scientists predict the possible genotypes and phenotypes of offspring when they know the
genotypes of the parents. The phenotype is the physical appearance of an organism and the genotype is the
inherited combination of alleles. This skill sheet will give you additional practice in using punnett squares to
solve genetics problems.
In rabbits, black fur is dominant to white fur. If you cross a BB male with a Bb female, what are the possible
genotypes and phenotypes of the offspring? What is the percent chance for each type?
Solution:
1.
B
B
B
BB
BB
b
Bb
Bb
Genotype
Phenotype
Chance
BB
Black fur
50%
Bb
Black fur
50%
In cabbage butterflies, White wings are dominant to yellow wings. If a Ww butterfly is crossed with a ww
butterfly, what are the possible genotypes and phenotypes of the offspring and the percent chance for each?
W
w
w
w
Fill in the table:
Genotype
Phenotype
Chance
Page 2 of 3
2.
In dogs, there is a hereditary type of deafness caused by a recessive gene. Two dogs who carry the
gene for deafness but have normal hearing are mated. What are the possible genotypes and
phenotypes of their offspring and the percent chance for each?
D
11.2
d
D
d
Fill in the table:
Genotype
3.
Phenotype
Chance
In guinea pigs, short hair is dominant over long hair. If a short haired SS guinea pig is crossed with a long
haired ss guinea pig, what are the possible genotypes and phenotypes of their offspring and the percent
chance of each?
S
S
s
s
Fill in the table:
Genotype
Phenotype
Chance
Page 3 of 3
4.
Can you curl your tongue up on the sides? Tongue-curling in humans is a dominant genetic trait.
Suppose a man who is Tt for tongue-curling marries a woman who is also Tt for this trait. What are
the possible genotypes and phenotypes of their children and the percent chance for each?
11.2
Fill in the table:
Genotype
5.
Phenotype
Chance
In guinea pigs, rough coats (with lots of swirly cowlicks) are dominant over smooth coats. If an RR guinea
pig is crossed with a Rr guinea pig, what are the possible genotypes and phenotypes of the offspring? What
are the chances of each?
Fill in the table:
Genotype
Phenotype
Chance
Name:
Date:
Incomplete Dominance and Codominance
11.3
When Mendel studied pea plants, he happened to select traits that were determined by two alleles where one
allele was completely dominant over the other allele. For instance, for flower color in peas, purple flowers are
dominant and white flowers are recessive. But some patterns of inheritance are different than the ones Mendel
discovered. In this skill sheet, you will get some practice with two other patterns of inheritance called incomplete
dominance and codominance.
When a red snapdragon is crossed with a white snapdragon, the next generation will have all pink flowers!
Because red and white blend, this is an example of a pattern of inheritance called incomplete dominance (see
example below). In incomplete dominance, the phenotypes of the two alleles blend—just like mixing paints.
In codominance, an organism that has both alleles of a gene displays both phenotypes at the same time. For
example, a cross between a black cat and a tan cat results in a tabby cat.
1.
2.
A cross between red-flowered snapdragons and white-flowered snapdragons produces offspring with pink
flowers. Let R = red flowers and W = white flowers.
a.
What is the genotype of a plant with a phenotype of red flowers?
Answer: RR
b.
What is the phenotype of a plant with a genotype of RW?
Answer: pink flowers
Suppose a pink-flowered plant is crossed with a pink-flowered plant.
The punnett square to the right shows the possible genotypes of the
offspring. Use the punnett square to answer the questions below it.
a.
What are the possible genotypes and phenotypes of the
offspring?
Answer: RR = red flowers; RW = pink flowers; WW = white
flowers
b.
What ratio of the offspring will have pink flowers?
Answer: 1:2
c.
What percent of the offspring will have red flowers?
Answer: 1/4 = 25%
Page 2 of 2
11.3
1.
2.
3.
A tabby cat is crossed with a tan cat. Use punnett square A to answer
the questions below.
a.
What is the pattern of inheritance in this example?
b.
What are the genotypes and phenotypes of the parents?
c.
List the possible genotypes and phenotypes of the offspring.
d.
What ratio of the offspring will have tabby fur? Tan fur? Black
fur?
e.
What are the chances, in percent, that the parents will have a
kitten with black fur?
f.
Suppose two cats with tan fur have kittens. What are the possible
genotypes and phenotypes of their offspring?
There are three possible genotypes and phenotypes for wing color in
a species of moth:
RR = red wings; RY = orange wings; YY = yellow wings.
Use punnett square B to answer the following questions:
a.
What is the pattern of inheritance in this example?
b.
What are the genotypes and phenotypes of the parents?
c.
What percent of the offspring will have red wings? Orange
wings? Yellow wings?
d.
Moths lay lots of eggs! Suppose the parents produce 1,200
offspring. Predict how many of those offspring will have orange
wings.
e.
Suppose out of the 1,200 offspring, 950 have orange wings. Is
this possible? Why or why not?
f.
Challenge: Suppose two moths, each with orange wings, produce offspring. Make a punnett square of
the cross. List the possible genotypes and phenotypes of the offspring and their ratios.
In a fictional species of mice, one gene determines fur color. Let B =
black fur and W = white fur. Use punnett square C to answer the
following questions.
a.
True or false: The offspring would have a variety of phenotypes.
b.
Suppose the alleles in the examples show incomplete
dominance. What would you expect the offspring to look like?
Explain your answer.
c.
Suppose the alleles in the example show codominance. What
would you expect the offspring to look like? Explain your
answer.
Name:
Date:
Multiple Alleles and Polygenic Traits
11.3
Multiple Alleles
Some inherited traits involve more than two alleles of a single gene. In humans, for example, three alleles (A, B,
and O) determine blood type. A person can have only two of the alleles, but there are three different ones found
in the human population. The A and B alleles are equally dominant. A child who inherits and A allele from one
parent and a B allele from the other parent will have type AB blood. The O allele is recessive to both A and B
alleles. A child who inherits an A allele from one parent and an O allele from the other parent will have a
genotype of AO and a phenotype of Type A blood. Use this information to complete the tables below. Then
check your work using the chart found in Section 11.3 of your student text.
A
A
B
O
AA
AB
AO
B
O
Genotype
Phenotype
Chance
AA
Type A blood
1/9 = 11%
A man with type A blood marries a woman with type B blood. They have ten children together. All of the
children have type AB blood. What do you suppose are the genotypes of each parent?
Solution:
The father must be either AA or AO. The mother must be BB or BO. If one parent had the recessive O gene, we
would expect that some of the children would have type A or type B blood. If both parents had the recessive O
gene, we would expect that some children would have type A, type B, or type O blood. Since all ten children
have type AB blood, it is likely that the father is AA and the mother is BB.
Page 2 of 3
11.3
Use your tables from page 1 to answer the following questions:
1.
A man with type A blood marries a woman with type B blood. Their first child has type O blood. What do
you know about the genotypes of the parents?
2.
One parent has type AB blood while the other has Type O blood. Which two blood types could their children
have?
3.
A child is born to a woman with type O blood. If the child also has type O blood, what are the three possible
genotypes of the father?
4.
A woman with type O blood gives birth to a child with type A blood. What are the three possible genotypes
of the father?
5.
If both parents have Type AB blood, what blood types are possible in their offspring?
Polygenic traits
Polygenic traits are inherited characteristics where more than one gene is involved in determining the phenotype.
Most of the traits you learned about earlier involved just two possibilities: attached or free earlobes, can or cannot
roll tongue, etc. Polygenic traits involve several possibilities. Hair color in humans is a polygenic trait. Eye color
is, too. Height is also a polygenic trait, but nutrition during childhood also plays an important role in determining
height. Even if your phenotype for height is six feet tall, without proper nutrition you won’t reach that height.
Kernel color in wheat is an interesting polygenic trait to study. There are two genes that work together to
determine kernel color. Dark red kernel plants are AABB. White kernel plants are aabb. When you cross a dark
red with a white, the combination looks like this:
AB
AB
ab
AaBb
AaBb
ab
AaBb
AaBb
The AaBb offspring have kernels that are an intermediate color—a medium pink. What happens if you cross two
AaBb plants? Fill in the table below to find out.
AB
Ab
aB
ab
AB
Ab
aB
ab
AABB
AABb
AaBB
AaBb
Page 3 of 3
11.3
How many different colors of wheat are possible when you cross two plants with the AaBb genotype for kernel
color? Use the table on the previous page to answer the question.
Solution:
There are five different colors possible. The darkest red occurs when all four alleles are represented by upper
case letters. With three upper case alleles, you get dark pink. Two upper case alleles give a medium pink, and one
upper case allele results in light pink. The fifth possible color is white, represented by no upper case alleles.
6.
When you cross two wheat plants that are AaBb for kernel color, which kernel color is the most likely result?
What is the percent chance of getting this kernel color?
7.
When you cross two wheat plants that are AaBb for kernel color, what is the percent chance of getting a light
pink kernel color?
8.
What is the percent chance of getting a pure color (either dark red OR pure white) when you cross two wheat
plants that are AaBb for kernel color?
9.
A dark pink kernel plant (genotype AaBB) is crossed with a light pink kernel plant (aaBb). Make a punnett
square of the cross and list the possible genotypes and phenotypes of the offspring.
aB
ab
AB
aB
Genotype
Phenotype
Chance
10. Suppose three genes control a single inherited trait. If the genes are represented by Aa, Bb, and Cc, what are
the possible combinations of alleles that one parent could contribute to its offspring?
Name:
Date:
12.1
Rosalind Franklin
Rosalind Franklin was a physical chemist whose data helped solve the structure of DNA. She is also known for
her research on coal and carbon during World War II and for her celebrated work on viruses.
A child who liked reasons and facts
Rosalind Elsie Franklin was
born in London, England on
July 25, 1920. She came
from an educated and
socially conscious Jewish
family. Her father was a
banker and her mother
actively volunteered in the
community.
As a child, Franklin didn't enjoy playing pretend
games. Instead, she liked reasons and facts. Franklin
attended St. Paul's Girls' School in London—one of
the few girls' schools that taught physics and
chemistry. By age 15, Franklin knew she wanted to be
a scientist. However, her father didn't support higher
education for woman and wanted Franklin to become
a social worker. Franklin's mother and aunt convinced
her father to pay for college.
Wartime research
In 1941, Franklin graduated from Newnham College,
Cambridge. World War II was underway when
Franklin began working for the British Coal Utilization
Research Association in 1942. Through air raids,
Franklin courageously bicycled each day to her job.
She studied the physical structure of coal and carbon
to find a more efficient way for England to use these
resources. At the young age of 26, Franklin published
five papers on the subject. In 1945, she earned a
doctorate in physical chemistry from Cambridge
University.
From 1947 to 1950, Franklin joined the Laboratoire
Central des Services Chimiques de l'Etat in Paris.
There, she mastered a special x-ray technique called
x-ray crystallography.
X-ray crystallography and DNA
Franklin returned to England in 1951 to work as an xray crystallography expert at King's College in the
University of London. Franklin was assigned to study
the structure of DNA. She was under the impression
that only she would be performing this research.
However, Franklin soon discovered that another
scientist, Maurice Wilkins, was also assigned to the
project. Unfortunately, Franklin and Wilkins had
difficulty getting along.
To make matters worse, female scientists at King's
college were treated differently than the men. They
were not allowed to eat lunch with the men in the
common room and were not invited to join in afterwork
discussions.
Photo 51 and the DNA puzzle
Because of the strained relationship between Franklin
and Wilkins, Franklin conducted her research alone.
Franklin was growing very close to solving the DNA
structure. She suspected that DNA had a helical
shape, but wanted more evidence to support her
theory. Wilkins was growing impatient with Franklin.
James Watson and Francis Crick were two other
scientists from the Cavendish Laboratory of
Cambridge who were also searching for the structure
of DNA. Without Franklin's permission, Wilkins
showed Watson her DNA data. This included a
stunning picture Franklin labeled “photograph 51” that
showed DNA's double helix structure. This
information helped Watson and Crick solve the DNA
puzzle.
Viruses and RNA
In 1953, Franklin left King's College and began her
renowned work on viruses at Birkbeck College.
Between 1953 and 1958, Franklin published 17
papers on the topic. Her research helped to establish
the link between RNA and protein. Up until her death,
Franklin also conducted research on the poliovirus.
An untimely death
Rosalind Franklin died at the age of 37 on April 16,
1958, of ovarian cancer. Four years after her death,
the Nobel Prize for medicine and physiology was
awarded to Watson, Crick, and Wilkins. Despite
providing key data about DNA's structure, Franklin did
not share in the prize. The Nobel Prize can only be
given to living recipients and shared among three
winners. Many wonder if Franklin would have
received the prize if she had been alive.
Reading reflection
1.
What career obstacles did Rosalind Franklin face as a female scientist?
2.
Describe Franklin's research during World War II that earned her a doctorate in physical chemistry.
3.
How did Franklin contribute to solving the structure of DNA?
4.
Why was Franklin not awarded a Nobel Prize, despite providing key data about DNA's structure?
5.
What other important research did Franklin conduct during her final years before her death?
6.
Research: Using the library or Internet, find out what contribution Franklin made to the 1958 World's Fair in
Brussels.
7.
Research: Using the library or Internet, find out which university recently changed its name in honor of
Rosalind Franklin.
Page 2 of 2
Name:
Date:
James Watson and Francis Crick
12.1
On February 28, 1953, Francis Crick entered the Eagle Pub in Cambridge, England and excitedly announced,
“We found the secret of life.” James Watson and Francis Crick cracked the puzzle that several other researchers
tried so hard to solve—the structure of DNA. The two researchers were an unlikely pair with different
educational backgrounds and a 12-year age difference. However, their enthusiasm for science and strong wills
led to one of the greatest discoveries in molecular biology.
A whiz kid on Quiz Kids
James Dewey Watson was
born in Chicago, Illinois on
April 6, 1928. He was a
very intelligent child who
enjoyed spending his free
time bird watching. By age
12, Watson starred on the
popular radio show of the
1940s, The Quiz Kids. On
the
show,
young
contestants
answered
difficult questions. Watson
finished high school in 2
years and entered the University of Chicago when he
was only 15 years old. In 1947, Watson graduated
with a degree in zoology (the study of animals).
In 1950, Watson earned a doctorate in zoology from
Indiana University. Although Watson still had a strong
interest in ornithology (the study of birds), he pursued
research in genetics and microbiology. Between 1950
and 1951, Watson went to Copenhagen, Denmark
where he studied bacterial viruses.
A first glimpse of DNA
In the spring of 1951, Watson attended a conference
in Naples, Italy. Watson met Maurice Wilkins, a
researcher from King’s College in London. At the
meeting, Wilkins presented photos of DNA using a
special x-ray technique called x-ray crystallography.
To Watson’s eye, Wilkins’ blurry picture of DNA
showed a regular, repeating pattern. This first glimpse
of the molecule marked the beginning of Watson’s
quest to find the structure of DNA.
Two great minds team together
After the Naples conference, Watson tried to talk his
way into Wilkins’ research lab. However, Watson was
denied entrance because he didn’t know much about
x-ray crystallography. In October 1951, the 23-year
old Watson began working at the Cavendish
Laboratory in England where there were many x-ray
crystallography projects underway.
Already working at the laboratory was a researcher
named Francis Harry Crick. Crick was born on June 8,
1916 in Northampton, England. In 1937, he received
his degree in physics at University College, London.
He then began his doctorate degree, but stopped at
the outbreak of World War II in 1939. During the war,
Crick designed mines for the British Admiralty.
In 1947, Crick left the Admiralty and decided to study
biology and organic chemistry for the next several
years. In 1950, Crick began his doctorate for a second
time at Caius College, Cambridge. Crick was part of
the Medical Research Council Unit at the Cavendish
Laboratory of Cambridge.
Newcomer Watson had much to learn about x-ray
crystallography. He was assigned to share an office
with Crick who knew a lot about the subject. Although
the two men seemed an unlikely pair because of their
12-year age difference, a strong friendship and
working relationship began. Watson’s biology
background and Crick’s expertise in x-ray
crystallography was a perfect partnership.
The race begins
By 1951, Crick had been already interpreting the x-ray
patterns of proteins. Within a few days of arriving at
Cavendish Laboratory, Watson talked with Crick about
using this technique on DNA. Crick became excited
by the idea.
Meanwhile, the Nobel Prize winning chemist Linus
Pauling had already published his model of proteins
using x-ray crystallography. He found that many
proteins spiral like a spring coil—an alpha helix.
Pauling’s next goal was to solve the structure of DNA.
Watson and Crick decided that they would imitate
Linus Pauling’s work and crack the structure of DNA
before Pauling did.
Two other scientists at King’s College in London were
also searching for the structure of DNA. One was
Maurice Wilkins, whose DNA photo Watson had seen
at the Naples Conference. The other scientist was
Rosalind Franklin. Watson decided to attend a lecture
given by Franklin to learn more about her research.
Watson returned to Cambridge with a sketchy
memory of Franklin’s presentation. Watson and Crick
created a model of DNA using this information, but it
failed miserably. Watson and Crick’s supervisor told
them to stop their DNA research, but the two refused
to give up.
Watson started his 20-year position as professor of
biology at Harvard University. In 1968, Watson also
served as director of Cold Spring Harbor Laboratory
of Quantitative Biology in Long Island, New York. The
laboratory became a key research center in molecular
biology.
Discovering the double helix
In 1968, Watson published his book The Double
Helix, which described his firsthand account of the
DNA discovery. From 1988 to 1992, Watson headed
the National Center for Human Genome Research at
the National Institutes of Health. Today, Watson
continues to give public speeches and is chancellor of
Cold Spring Harbor Laboratory.
Although Franklin and Wilkins were conducting similar
research, the two did not get along. Therefore,
Franklin mostly did her research alone. She
suspected that DNA had a helical shape, but wanted
more evidence to support her theory. Wilkins was
growing impatient with Franklin. Without Franklin’s
permission, he decided to show Watson her data. This
was the key information that Watson and Crick
needed to solve the DNA puzzle.
Watson and Crick took Franklin’s data and realized
that DNA was made of two chains of nucleotides
forming a double helix. They found that one chain
went up, while the other went down. They had also
recently learned about matching base pairs (adenine,
thymine, cytosine, and guanine) and added this
concept to their model. The matching base pairs
interlocked in the middle of the double helix, which
kept the distance between the chains constant.
Watson and Crick also showed that each chain of the
DNA molecule was a template for the other. When the
DNA strands separate during cell division, new
strands are built off of the existing strands.
On February 28, 1953 Francis Crick entered the
Eagle Pub in Cambridge, England to share in their
exciting news. He announced, “We found the secret of
life.”
A Nobel Prize is awarded
Watson and Crick’s DNA model fit perfectly with the
data and was quickly accepted. In 1962, Watson,
Crick, and Wilkins were awarded the Nobel Prize for
physiology and medicine.
Despite providing key data about DNA’s structure,
Franklin did not share in the prize. Unfortunately, she
had already died of cancer in 1958 at the age of 37.
The Nobel Prize can only be given to living recipients
and can only be shared among three winners. The
question remains whether Franklin would have been
awarded the prize if she were still alive.
Life after solving the puzzle
After solving the DNA puzzle, Watson and Crick’s
careers took them in different directions. In 1956,
Page 2 of 3
Crick remained at Cambridge for 20 years and
continued to study DNA. He made major contributions
in solving how genetic information is coded. In 1962,
Crick became director of Cambridge University’s
Molecular Biology Laboratory. He also held several
visiting professor positions in the United States during
this time. He later joined the Salk Institute for Biology
Studies in La Jolla, California.
In 1966, Crick wrote Of Molecules and Men, which
described the impact of recent biochemistry
discoveries. He also developed an interest in
neurobiology and did research on vision and the
function of dreams. Crick died in July 2004 at the age
of 88.
Name:
Date:
Reading reflection
12.1
1.
What first prompted James Watson’s desire to solve the structure of DNA?
2.
Why were Watson and Crick considered both an unlikely pair and a perfect team to solve the structure of
DNA?
3.
Who were the other researchers “racing” to find the structure of DNA?
4.
How did Rosalind Franklin’s data help Watson and Crick with their research?
5.
When did Watson and Crick receive the Nobel Prize and why were there only three recipients?
6.
Research: Describe the technique of x-ray crystallography.
7.
Research: What is Chargaff’s Rule and how did this support Watson and Crick’s double helix model of
DNA?