Download GENETICS: Introduction

GENETICS: Introduction
Terminology:
gene
allele
homozygous
heterozygous
recessive
dominant
genotype
phenotype
Practice Problems Set 1:
1.
For each of the following genotypes, give all genetically different
gametes, noting the proportion of each for the individual.
a.
b.
c.
d.
2.
WW
Ww
Tt
TT
For each of following, state whether a genotype or a gamete is
represented.
a.
b.
c.
D
GG
P
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More Terminolgy:
Gregor Mendel
Mendelian Genetics
Monohybrid Cross
P generation
F1 (filial) generation
(filial = "pertaining to offspring")
Punnett square
Complete Dominance
I.
____________________ ____________________ (early ______'s)
Austrian monk
Provided basis for modern genetics, worked with ____________
plants, (Pisum), carefully designed his experiments, and gathered
mathematical data)
A.
B.
A cross of two parents for __________ trait is a
_______________________ cross.
1.
original parents are the ______ generation.
2.
first generation offspring are the _____ (__________)
generation
A ____________________ ____________________ is a simple
method to calculate the results of a monohybrid cross.
1.
Example, EE, Ee, and ee:
UNATTACHED EARLOBES ARE A DOMINANT TRAIT
ATTACHED EARLOBES ARE A RECESSIVE TRAIT
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1a
1b
2a
2c
2b
2d
Use the diagram above
For each BOX/LETTER , LIST the PHENOTYPE (from top to bottom)
1,
List the Phenotype of the P generation (the two parents)
(there are two)
2.
In each of the 4 boxes, list the Phenotype of each of the 4 offspring.
3.
Once you have written down the PHENOTYPES of all 6 individuals, go back,
and next to each phenotype, write the GENOTYPE.
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2.
Use a Punnett square to calculate the following results:
Red flower = RR, Rr
White flower = rr
a.
Homozygous Dominant X Homozygous Dominant
b.
Homozygous Dominant X Homozygous recessive
c.
Homozygous Dominant X
Heterozygous
d.
Heterozygous X Heterozygous
e.
Heterozygous X Homozygous recessive
f.
Homozygous recessive X Homozygous recessive
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Practice Problem Set 2
Use a Punnett square to help solve the following:
1. In rabbits, if B = dominant black allele and b = recessive white allele,
which of these genotypes could a white rabbit have?
(Bb BB bb)
2.
In horses, trotter (T) is dominant over pacer (t). A trotter is mated to a
pacer, and the offspring is a pacer. Give the genotype of all horses.
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3.
In humans, freckles is dominant over no freckles. A man with freckles
reproduces with a woman with freckles, but the children have no
freckles. What chance did each child have for freckles?
4.
In pea plants, yellow seed color is dominant over green seed color.
Give the genotype of all plants that could possibly produce green peas
when crossed with an individual that is heterozygous
(Y) = yellow, (y) = green
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How to work Mendelian Genetics Problems
1.
Write a Phenotypic/Genotypic KEY of information available
BEFORE you start working the problem:
(Use allele letter given to you, for this example, will use “A” and eye color, monohybrid cross, complete
dominance)
Genotype Phenotype
__ __ = _______________
(Example):
AA = Brown eyes
__ __ = _______________
Aa = Brown eyes
__ __ = _______________
aa = Blue eyes
Write down “CROSS” with what information you have been
given before you try to solve problem.
2.
Male
Female
P1 = __ __ (__________) X
genotype
phenotype
__ __ (__________)
genotype
phenotype
THEN:
F1 =
(write down genotype and phenotype of any offspring given in problem)
3.
Construct Punnet Square, (if applicable) plug in known
values, compute blank squares.
4.
Calculate genotypic and phenotypic % and ratios from
information in filled out punnet square
5.
Answer any questions from problem.
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For those of you that desire additional information/assistance/practice with
Mendalian Genetic Problems on the WEB, here ya go:
Go to Google, type in: PUNNETT SQUARE
Here are some of the hits that I looked at that seem very good/helpful:
(there are more)
http://www.accessexcellence.org/AE/AEPC/WWC/1994/punnett.html
http://www.athro.com/evo/gen/punexam.html
http://curriculum.calstatela.edu/courses/builders/lessons/less/les4/casino/ca
s1ck.html
http://anthro.palomar.edu/mendel/mendel_2.htm
http://biology.clc.uc.edu/courses/bio105/geneprob.htm
http://www2.edc.org/weblabs/Punnett/punnettsquares.html
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Monohybrid Crosses-Complete DominancePRACTICE
DIRECTIONS: Construct a KEY, write the P and F1 generations, and, if
applicable, fill out a punnet square.
1.
In mice, brown hair, (B) is dominant over white hair (b). A brown
mouse is repeatedly mated with a white mouse, and all of their
offspring are brown. If two of these brown offspring are mated,
what fraction of the F2 will be brown?
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2.
How could you determine the genotype of the brown F2 mice in
problem 1? How would you know whether a brown mouse is
homozygous? Heterozygous?
3.
Tim and Carolyn both have freckles. (Freckles F dominant over no
freckles f). Their son Michael has no freckles. Show with a punett
square how this is possible. What is the chance of Tim and Carolyn’s
next child of having freckles?
4.
Both Tim and Carolyn have a Widow’s peak hairline, but son Michael
has a straight hairline, (homozygous recessive ww). What are all three
genotypes for these 3 individuals? What is the chance that Tim and
Carolyn’s next child will have a straight hairline?
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II. Monohybrid Crosss: Incomplete Dominance
A. First Example: Snap Dragons
1. KEY
2. Red X White
3. Pink X Pink
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Monohybrid Crosses – Incomplete Dominance
DIRECTIONS: Construct a KEY, write the P and F1 generations, and, if
applicable, fill out a punnet square.
1.
In the flowers SNAPDRAGONS, Red flower is dominant over White
flower. Flower color is an Incomplete dominance situation. The
heterozygous phenotype is PINK.
A red snapdragon is crossed with a white snap dragon. What are the
chances that there will be white flower offspring?
2.
When chickens with splashed white feathers, (recessive) are crossed with
chickens with black feathers, (dominant), the offspring have slate blue
feathers.
If two slate blue feather chickens are crossed, what is the genotypic and
phenotypic results? (give % only)
3.
A splashed white feather chicken is crossed with a black feather chicken.
What is the chance of offspring having black feathers?
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4.
A red snapdragon flower is crossed with a pink snapdragon flower. What
are the chances that the F1 will be white flowers?
5.
In # 4 above, what are the chances that the F1 will be pink flowers?
6.
In # 4 above, what are the chances that the F1 will be red flowers?
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Betta Genetics
Betta genetics can be very complicated or very simple depending on what we look at. Before I attempt to explain any
genetics however there are a few general (very oversimplified) laws of heredity you should know. To begin with, for
each characteristics every organism inherits two genes, one from their mother and one from their father. Bettas are
made up of millions of these gene pairs. An organism's genetic make-up is called it's genotype. Basically, these gene
pairs are what determine an organisms physical appearance. The physical appearance of an organism is referred to as
it's phenotype.
Each characteristic generally has a recessive and dominate form of a gene. When there are two different forms of a
gene the forms are called alleles (i.e.: the dominant allele and the recessive allele). If an allele, in a pair of genes, is
dominant, the dominant copy overrides a recessive copy. The only way a recessive gene is expressed is if there are
two copies of it. An organism with two same copies of a gene (either dominant, dominant or recessive, recessive) is
referred to as homozygous. When two homozygous organisms are crossed their offspring are all homozygous for that
trait. An organism with two different copies of a gene (dominant, recessive) is call heterozygous. When two
heterozygous organisms are crossed half of their offspring is heterozygous and half is homozygous. Confused yet?
Don't worry - you will catch on!
Lets begin with a simple dominant/recessive gene - the gene that make a Betta either a single tail or a double tail. In
Bettas, a single tail is dominant to a double tail.
This is a double tail Betta - notice the tail is split into two lobes.
His alleles are d, d
This is a single tail Betta - his tail is only one lobe. His alleles
could be D, D, or D, d
Relationships between genotype and phenotype
Alleles
Genotype
Phenotype
D
D
D
d
Homozygous Dominant Heterozygous
Single tail
d
d
Homozygous Recessive
Single tail
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Double tail
Genetics Worksheet-Betta Crazed
DIRECTIONS:
For each problem, 1st make key, then write the P generation, then punnet square,
then phenotypic and genotypic results. (Give both % and ratio) (All problems are
either Complete Dominance or Incomplete Dominance) (HINT: Complete
Dominance problems have two phenotypes, Incomplete Dominance have 3
phenotypes) Before you start with Question 1, Please read the Article: “BETTA
CRAZED”
(Use the information in the article to answer questions 1 - 8) (Use a
separate sheet of notebook paper to work these out.)
1.
Two double tailed Bettas are crossed. Determine the genotypic and phenotypic
results.
2.
Two Homozygous dominant Bettas are crossed. Determine genotypic and
phenotypic results.
3.
Two Heterozygous Bettas are crossed. Determine the genotypic and phenotypic
results.
4.
A double tailed Betta is crossed with a single tailed, Homozygous Dominant,
Betta. Determine the genotypic and phenotypic results.
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5.
Two of the F2 in number 4 above are crossed. Determine the phenotypic and
genotypic results.
6.
Have these problems been Complete Dominance, or Incomplete Dominance
Problems so far? Why? (explain your answer)
7.
In Bettas, Green body color, (G), is dominant over Blue Body Color, (g). For
Heterozygous individuals, the phenotype is cornflower blue. Two heterozygous
cornflower blue Bettas are crossed. What are the chances for Green F1?
8.
Is question #7 a Complete Dominance, or Incomplete Dominance problem?
Why? (explain your answer)
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III.
Dihybrid Cross (Complete Dominance)
A. EXAMPLES:
DIHYBRID CROSS
GENETIC Practice PROBLEMS # 1
1. Both T (tall) and H (hairy) are completely dominant over short (t) and bald (h).
If a heterozygous tall, homozygous hairy male fox bug is mated with a female which is
heterozygous tall and heterozygous hairy:
a. What is the genotype for the male?
_____ _____
b. What is the genotype for the female?
____ ____
a. Fill in the Punnett Square below and predict the number of expected phenotypes of fox
bug offspring.
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2.
In watermelons, the genes for green color (G) is dominant over striped
(g) and short shape (S) is dominant over long shape (s).
a. If a plant with long, striped fruit is crossed with a plant which is
heterozygous for the traits of color and shape,
What are the genotypes for the two parent plants?
Long striped: _____ _____
Heterozygous: _____ _____
b. What phenotypes would this cross produce?
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3.
In rabbits, spotted coat (S) is dominant to solid color (s), and black (B) is dominant to brown (b).
a. If a brown spotted rabbits are mated to solid black rabbits and all of the offspring are
black spotted rabbits, what must the genotypes of the offspring and parent rabbits be?
Males: _____ _____ Females: _____ _____
Offspring: _____ _____
a. If two of the second-generation black spotted offspring were mated, what would the
phenotypes of the third generation be?
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Dihybrid Crosses-GENETIC PROBLEMS 2
1. In the garden pea, Mendel found that yellow seed color was dominant to green and round seed
shape was dominant to shrunken. Determine the phenotypic and genotypic ratios for the F1 generation
and the phenotypic ratio for the F2 if a plant with homozygous rounded yellow seeds is crossed with a
plant with shrunken green seeds. (Y = yellow, y = green, R = round, r = shrunken) Show Punnett
Squares.
2. Tall tomato plants are produced by the action of a dominant allele T and dwarf plants by its
recessive allele t. Hairy stems are produced by a dominant gene H and hairless stems by its recessive
allele h. A dihybrid tall, hairy plant is crossed with a dwarf hairless tomato plant. Determine the
phenotypic ratio for the F1 generation. Show work. (Punnett Square).
3. Black coat color in Cocker Spaniels is dominant, while red coat color is recessive; solid pattern is
dominant, while spotted pattern is recessive. A solid black male is mated to a solid red female and
produces a litter of six pups: two solid black, two solid red, one black and white, and one red and
white. Determine the genotypes of the parents. (B = black coat, b = red coat, S = solid pattern,
s = spotted pattern) Show work.
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4. In rabbits, black color is due to the dominant gene B and brown color is due to its recessive allele
b. Short hair is due to the dominant gene S and long hair to its recessive allele s. In a cross between
a heterozygous black short-hair male and a homozygous brown long-hair female, what would be the
expected genotype and phenotype ratios of the offspring? Show work.
5. In horses, black coat color is determined by a dominant gene B and chestnut brown color by its
recessive allele b. The trotting gait is due to the dominant gene T and the pacing gait is due to its
recessive allele t. If a homozygous black pacer is mated to a homozygous chestnut trotter, what will
be the phenotypes and genotypes of the offspring? If two of these F1 individuals were mated, what
phenotypes and genotypes of offspring could they have? (Include ratios for both genotypes and
phenotypes in both generations.)
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Common Crosses Involving
Complete Dominance
EXAMPLES:
Phenotypic Ratios
Tt
X
Tt
=
3:1
(dominant to recessive)
Tt
X
tt
=
1:1
(dominant to recessive)
TtYy
X
TtYy
=
9:3:3:1
(9 dominant, 3 mixed, 3 mixed vice
versa, 1 recessive)
TtYy
X
ttyy
=
1:1:1:1
(all possible combinations in
equal number)
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IV.
Sex Linked (“X” Linked)
A. First Example = Color Blindness
1. KEY
2. Examples
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Genetics Worksheet – Sex Linked #1
DIRECTIONS:
For each problem, 1st make key, then write the P generation, then punnet square,
then phenotypic and genotypic results. (Give %).
1. (Look in your notebook for a sex-linked color blindness KEY – copy that key down
for each color blind problem) (Questions 3 & 4)
John, who is color blind, marries a carrier, normal vision girl, Mary.
b. What are the chances for color blind children?
c. What are the chances for color blind boys?
d. What are the chances for color blind girls?
e. What are the chances for normal vision children?
f. What are the chances for normal vision boys?
g. What are the chances for normal vision girls?
2. Bobby is a Color blind boy. Which parent, (FROM QUESTION 1 above), (John or
Mary, or both, or neither), passed him the allele(s) for his color blindness? Explain
your answer.
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Genetics Worksheet –Sex Linked #2
DIRECTIONS:
For each problem, 1st make key, then write the P generation, then punnet square,
then phenotypic and genotypic results. (Give %). (you will only need to do one punnet
square, and one phenotypic and genotypic results, since questions 2 & 3 are a
continuation of question 1)
Hemophilia is a sex-linked recessive human affliction. Hemophilia A is caused by
the absence or minimal presence of a particular clotting factor called factor VIII.
Hemophilia is called the bleeder's disease because the affected person's blood
does not clot. Not only do hemophiliacs bleed externally after an injury, they also
suffer from internal bleeding, particularly around joints. At the turn of the century,
hemophilia was common in the royal families of Europe, and all of the affected
males could trace their ancestry to Queen Victoria of England. Because none of
the queen's ancestor or relatives were affected, it seems that the RECESSIVE
allele she carried arose by mutation either in Queen Victoria or one of her parents.
Her daughters Alice and Beatrice were carriers and introduced the allele into the
ruling houses of Russia and Spain. Alexis, the last heir to the Russian throne
before the Russian Revolution, was a hemophiliac. The current British royal
family has no hemophiliacs because Victoria's eldest son, King Edward VII, did not
receive the allele and therefore could not pass it on to any of his descendants.
1.
A hemophiliac man reproduces with a homozygous normal woman. What
are the chances that their sons will be hemophiliacs?
2.
In Question Number 1 above, what is the chance that their daughters will
be hemophiliacs?
3.
In Question number 1 above, what is the chance that their daughters will
be carriers (= they carry the damaging allele, but their phenotype is
normal)
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V. Multiple Allelles and Co-dominance
A. First Example: Human Blood
Type
1. KEY
2.
Examples
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Genetics Review: (Multiple Alleles, X-Linked)
DIRECTIONS:
For each problem, (when appropriate) 1st make key, then write the P generation, then
Punnet square, then phenotypic and genotypic results. (Give %). (when applicable)
1.
A man of blood type A and a woman of blood type B produce a child of type
O. If the couple were to have many more children, what are the possible
blood types possible in the offspring?
2.
A woman is color blind. What are the chances of her daughters being color
blind if she marries a man with normal vision?
3.
From the following blood types, determine which baby belongs to which
parents: (All the parents are monogamous and faithful)
Mrs. Lily Munster
Type A
Mr. Brady
Type A
Mr. Herman Munster Type B
Mrs. Brady
Type AB
Baby 1 = Type O
Baby 2 = Type B
4. Mary, who is blood type AB, marries John, who is Blood type O. What are
the genotypic and phenotypic outcomes of all possible offspring?
5. A Hemophiliac man marries a carrier female. What are the chances that
their 1st child will be hemophiliac?
6. What are the chances that (question 5), their 1st son will be normal?
7. What are the chances that, (question 5), their 1st son will be hemophiliac?
8. What are the chances that, (question 5), their 1st daughter will be
hemophiliac?
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Genetics PRE EXAM Review Practice Problems
DIRECTIONS:
For each problem, 1st make a KEY, then write the P generation, then punnet square, then
phenotypic and Genotypic results. (Give both % and ratio)
1. In Snapdragons, Red is dominant over white flowers. The heterozygote is Pink Flower. A Red flower
snapdragon is crossed with a white snapdragon flower. Give Genotypic and Phenotypic results in % .
(HINT – see Key in Notes)
2. In Humans, color blindness is a recessive, sex-linked trait. Jenny, daughter of Tom and Mary, is a
normal visioned CARRIER. What are the genotypes of her parents, Tom and Mary? (Tom is normal
visioned, and Mary is normal visioned). (HINT – see Key in Science Notebook)
3. Jenny, mentioned above, marries a color blind gentleman named Larry. What is the genotypic and
phenotypic results of this cross? (Give %)
4. What are the chances of any of the offspring having normal vision?
5. Hemophilia is a recessive, sex-linked condition in Humans. Two hemophiliacs who marry cross.
Give genotypic and phenotypic results. (Give%)
6. In question # 5 above, what are the chances of any of the offspring being Normal, (non-Hemophilia)?
7. Muscular Dystrophy, as the name implies, is characterized by a wasting away of the muscles. The
most common form, Duchenne muscular dystrophy, is an X-linked (sex-linked) recessive disorder
that occurs in about one in 5,000 live male births. Symptoms, such as waddling gait, toe walking,
frequent falls, and difficulty in rising may appear as soon as the child start to walk. Muscle weakness
intensifies until the individual is confined to a wheelchair. The condition also affects the muscles that
allow us to breathe and the heart; death usually occurs during the teenage years, therefore, affect
males are rarely fathers. The recessive allele remains in the population by passage from carrier
mother to carrier daughter.
Use D and d for your alleles. (Hint, key set up just like color blindness)
PROBLEM (Number 7):
A son with Duchenne muscular dystrophy is born to a couple who both appear to be
normal. What are the chances that any child born to this couple will have Duchenne
muscular dystrophy?
8.
In cats, S = short hair, s = long hair; Xc = yellow coat, XC = black coat, XCXc = tortoiseshell
(calico) coat. If a homozygous long haired yellow male is crossed with a tortoiseshell (calico)
female homozygous for short hair, what are the expected phenotypic results?
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