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CHAPTER
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CHROMOSOMES,
GENES AND
INHERITANCE
34-1 Laboratory lnvestigation:
Human Heredity
34-2 Ghromosomes and Genes
34-3 Sex-Linked Traits
34-4 Sample Sex-Linked and Blood Type Problems
34-5 Sex-Linked and Blood Type Problem Set
Ch 34 Chromosomes, Genes and lnheritance
33
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Cfropter 34
Cfi.romosoffLes, $erces arcf Infteritance
you try to do sometfi.ing 1egond afiat gou
fiorte a{reo"dy mastered, you usi$ neoer Brod.
'Un{zss
Ralph Waldo Emerson
34-1
Laboratory lnvestigation
Human HereditY
-YouObjectiu"
will determine
which traits you posses from a list of described traits. You will
then be expected to determine which members of your family also possess these
traits and wjll fill in pedigree diagrams for your family, for each trait.
To determine whether you can taste PTC, perform the following taste test:
a. Find the petri dish marked NoRMAL PAPER, WITHOUT PTC.
I l
your
for about 8
paper
tongue
on
strip
Taste 1 piece of this by placing the
seconds. This will allow you to compare the normal taste of clean paper to the
taste of PTC. I I Throw the tasted papers in the garbage can when finished.
t I Don't set them on the lab tables' t l
b. Now taste a piece of PTC paper taken from the petri dish marked PTC PAPER.
Taste it in the manner described above. lf you can taste this chemical, you will
taste a considerably strong bitter taste. There will be no mistaking this taste.
1 lf your PTC paper does not taste much different to you than the normal
paper WITHOUT PTC, then you are unable to taste it due to certain inherited
1
genes in you and your family. Discard all tasted paper.
I
l.
Ch 34 Chromosmes, Genes and lnherhance
34
Most of the other traits are easy to determine by
observation. You will need your lab partne/s help
in two of the cases. ln a person with an 'unattached
ear lobe" the lobe of the ear hangs free from the
face.
Examine the diagram carefully.
t
I
Examine both of your ears to determine which you
have. t I
Attached ear lobe
Unattached ear
lobe
Some people can roll their tongue as
shown in the diagram. Some cannot.
To test for this trait, you are not to use
your fingers to help roll your tongue.
Examine the drawing on this page and
try
this. t
l
Tongue roller
This trait, as well as the others, are determined by
certain dominant and recessive genes. Some
individuals have a relatively straight thumb.
Others have a thumb thal angles 45o angle at the
joint. This is called a "hitch hikels thumb." Which
do you have?
Non hitch hiker's
thumb
I Hitch hike/s thumb
lf you examine the hair of your partner,
you will find that the hair forms a whorl at
the crown. This whorl will either be
clockwise or counter-clockwise. Which
do you and your partner have? (See the
diagram.)
@
Counterclockwise
hair whorl
Ch 34 Chromosomes, Genes and lnherhance
35
$
Clockwise hair whorl
Create a chart like the one below and fill in the information. The way to tell if a trait is
dominant or recessive is to determine how many in your class have the trait. The trait
that the majority of people have is usually the dominant trait.
Number in your
class with each
THAIT
trait
Genotype
ls the trait dominant
or recessive?
of trait
fi
PTCTASTER
orTt
tt
NON-TASTER
TONGUE ROLLER
NON_ROil FR
ATTACHED EAR LOBE
UNATTACHED LOBE
HII-CH HIKER'S THUMB
NON.HITCH HIKER'S THUMB
CLOCKWISE HAIRWHORL
@UNTER.CLOCKWSE HAIR WHORL
On the chalk board you will find a chart similar to the one above. After you have
determined which traits you possess, place your results on the chalk board with a tally
mark after the appropriate trait. I
1
Examine the chart on the chalk board when most of the class have entered their tally
marks.
t
I
1. How can you determine, from your chart above, which traits are dominant and which
are recessive?
Fill in the third column in your chafi showing .dominance and recessiveness.
I
I
ln the last column of the chart, the genotype is given to you for PTC tasters and nontasters. You fill in the genotypes for the remaining traits. Determine which letters to use
according to the standard rules for assigning symbols. Make your letters clearly so it is
obvious which letters are capitals and which are lower case letters. t
1
Ch 34 Ghromosomes, Genes and lnheritance
36
DETERMINING HOW SOME OF THESE TRAITS HAVE BEEN
PASSED TO YOU FROM OTHER MEMBEHS OF YOUR FAMILY
To be done at home.
Pick any 3 of the 6 traits that you worked with in this lab and see if you can determine the
genotypes and phenotypes of other members of your family. lf you cannot obtain
information about your natural mother or father, your teacher can assign arbitrary
phenotypes for parents so you can complete the assignment.
You will need to determine which characteristics are present in some of your relatives ab
shown on the chart. By deduction, you are to determine the probable genotype of as
many relatives as possible. lf you would like to take home some PTC taster papers to
check members of your family, arrange this with your teacher.
I
t
When at home, check as many members of your family as you can, for your 3 chosen
traits. Record what you are able to determine. I I
For each trait, determine the following:
2.
See if you can determine your genotype for each trait by examining natural parents
and sisters and brothers or other relatives. Provide all available information on each
relative and explain how you determined your genotype. lf you can't determine your
genotype, explain why.
3.
List the phenotype and genotype (where possible) of each parent, bother, sister or
other natural relative available.
I'\
i
I
5
at
'\. \
i
r{i
,.t
\
;
t
Ch 34 Chromosomas, GenEs and lnheritance
37
34-2 Chromosomes and Genes
1. Where in the cell are chromosomes found? Where are the genes located?
Objectlve
You will be expected to know that genes are located on chromosomes. Be able to
describe whai happens to the genes and chromosomes during sex cell formation
(meiosis).
Chromosomes
As the 19th century was coming to a close, biologists had
observed chromosomes appearing in the nucleus of cells as
they began to divide. lt wasn't until 1902 that Walter Sutton, a
graduate student at Columbia University, provided evidence
that the genes were located on or in the chromosomes.
He believed ihat the parallel behavior of the chromosomes and
genes was not coincidental and hypothesized that the genes
must be on the chromosomes.
Chromosomes occur in pairs. This can be shown by a simple exercise. Photograph the
chromosomes in the nucleus of a human cell. Print a large photo of the 46
chromosomes. Use a scissors to cut out each of the 46 chromosomes. Arrange similar
chromosomes together and we find that each chromosome has what appears to be an
identical twin. lt is the same length and shape. This is true for all but one pair, the sex
chromosomes.' One member of this pair is shorter than the other. The four pairs of
chromosomes at the left illustrate the
ffi%@ffi$qt,ffi#$*ry*
##
Pair.
a
tall plant can
that
For example, in pea plants you learned
have one'gene for tailness and one for shortness. Sutton's
hypothesiJ states that the tall gene (T) is located on one
chromosome and the short gene
(t) is on the other I
€
#l
K
e
*
## \r
tr
I
chromosome. Examine the drawing at tl're'right. t I These
&
two genes for height are called alleles. Allele-s are pairs of
corrdrp.onOing genes fof.a tr:ait that are located at the game position on each member of
a piir of chromosomq-s. T and.t are alleles for height in pea plants. Other allele
'cO-rnninations
aie TT and tt. Geries for other traits are located above and below the T
gene on each chromosomes. They are also paired alleles'
2.
What is an allele?
Ch 34 Chromoemes, Genes and lnheritance
3. Draw a pair of chromosomes and place the genes for brown and blue eyes on the
chromosomes to show how alleles are positioned. Label the position of each gene
with an arrow.
4. How many pairs of chromosomes are found in human cells? Are all
pairs
represented by two identically shaped chromosomes? Explain.
Gene Location and Separation at Sex Gell Formation
The genes for one trait are located on a pair of similar chromosomes. What happens to
these genes when the cell divides to form sex cells? ln the last unit you learned that
cells in the human testis divide by meiosis. The cell containing 46 chromosomes
divides in two steps, creating sperm cells each with 23 chromosomes. To understand
what happens to the genes during meiosis and sex cell formation we will examine the
formation of sex cells in the pea plant anther. We will follow only one pair of
chromosomes. The same thing happens to all other pairs. The cell diagrammed on the
next page has chromosomes with genes T (tall) and t (short) on them for height. Study
the changes that take place from step to step so you can answer the questions that
follow.
Photo ol human chromosomes
Continued on the next page >>>
Ch 34 Chromosomes, Genes and lnheritance
39
Meiosis
in
Pea
'#
1ffi'#)
#
4
*@*
'ff
d'
Sperm cells
Notice that each step and change is represented with a numbered arrow.
5.
ls the parent plant tall or short? Explain how you decided.
6. What changes took place
7.
in step 1?
ln step-2 lhe chromosome pairs line up on the spindle fibers as the cell starts to
divide the first time. What changes lollowed in steps 3 and 4?
B. The two new cells
next divide again in step
steps 5 and 6?
Ch 34 Chromosom€s, Genes and lnheritance
40
6.
What changes can be observed in
L
Of the four sperm cells formed, what fraction contain a gene for tallness and what
fraction contain a gene for shortness?
Cells in the ovule of the plant undergo the same process when egg cells are formed.
10. lf four egg cells are formed in the ovary that are identical
to the sperm cells in
genetic type, what genotypes and phenotypes gre possible for offspring in a cross
between these two plants? Give the fractions predicted for each genotype and
phenotype.
34-3 Sex Linked Traits
Objectlve
When you have completed this program, you should be able to describe how
chromosomes determine your sex and how colorblindness, muscular dystrophy
and hemophilia are passed from generation to generation. You will be expected
to apply these principles in solving sex-linked genetic cross problems.
Did you ever wonder why more men are colorblind than women? The reason is that
these genetic traits are linked up with maleness. This program is designed to provide
you with the understanding to be able to solve problems involving sex-linked traits.
You will have opportunity to practice sample problems. Your understanding and ability
to apply these principles will be evaluated with two sets of home assignment problems
that follow.
BEFORE GOING ON, PLACE YOUR PAPER OVER THE ANSWERS.
1. When a cell nucleus is photographed, the chromosomes look something like the
drawing below.
.-
\ \,1 ir.S=*Yr{\} Jr*}L
What are the individual units that are found on each chromosome that determine
hereditary traits?
1. Genes
Ch 34 Chromosomes, Genes and lnheritance
41
2.
Human body cells contain how many chromosomes?
Each egg or sperm cell contains how many chromosomes?
2.
g.
46,
23
Each body cell contains 46 chromosomes or 23 pairs of chromosomes. lf the
chromosomes from the photograph in 1 above were paired up they would look like
the drawing below.
II )(X x,t N' II [[
ffi
11[ hh
xk ru tt
IX XX
\l\
\\
II ff rn ilil tl \\
Note that for each pair, the 2 chromosomes look alike except for one pair. ( The pair in
the box.) One of the chromosomes of this pair is shorter and has a curled end. This pair
of chromosomes is called the sex chromosomes. The long one is called the X
chromosome and the short one is called the Y chromosome. Human cells have 22
pairs of body cell chromosomes and 1 pair of sex chromosomes, the X and Y
chromosomes. Every female has 22 pairs of body chromosomes and 1 pair of sex
chromosomes which are both X's. (XX) Body chromosomes and the sex chromosomes
have thousands of genes on each chromosome. Every male has 22 pairs of body
chromosomes and 1 pair of sex chromosomes, one an X and 1 a Y chromosome. On
your own paper draw an X and a Y chromosome.
I
4. lf a fertilized egg received 2 X's (XX) it would result in a (male or female).
lf a
fertilized egg received an X and a Y (XY) , would it grow into a male or a female?
u
4. female,
o
-s
male
:l'
*)
{
S.
With the above information, you can verify why all populations of plants and animals
have close to 50% males and 50% females. (Remember: when sperm cells are
formed, the 2 chromosomes in a pair separate and go into different sperm cells.)
What chromosome would you find in each of 2 sperm cells formed? What
chromosome would be found in each egg cell?
Ch 34 Chromosomss, Genes and lnheritance
5.
X or Y in male sperm cells and
X only in all of the lemale eggs.
6. Now you can create a Punnett square to determine which chromosomes will end up
together in all possible offspring:
Copy this chart on to your own paper and complete
it. What fraction of the offspring are males?
What fraction females?
eggs
b.
spe rm
XI
Y
112 male and 112 female
7. Remember that the X and Y chromosomes are called "sex" chromosomes. Tbe
remaining 22 pairs of chromosomes are called "body" chromosomes. Geneticists
call them autosomes. The pair of body chromosomes below show how the genes
for eye color and height and other unidentified genes are arranged on the pair of
chromosomes.
B = brown-eye gene
b = blue eye gene
T = tallness gene
t = shortness gene
:-EE_:
What color eyes would this person have and would he be tall or short?
Notice that the genes for eye color are opposite each other on each chromosome
and are at the same level. This is true for all gene pairs for any particular trait. Note
that the genes for height are at the same level also. The other dark bands on the
chromosomes represent other gene pairs at the same levels on each chromosome.
Geneticists call gene pairs like this that are at the same levels, alleles.
7.
Brown,
tall
Gh 34 Chromosomes, Genes and lnheritance
4r
8.
The X and Y sex chromosomes present a unique situation since the Y chromosome
is much shorter than the X. lt, therefore, cannot hold as many genes on it as the X
can. This is very important to remember.
+-
Cobr blind gene
q
H
X
The diagram at the left will help you to
understand this difference. Notice that the
gene for color blindness is at the top of the X
chromosome and that the Y chromosome is
not long enough to hold a gene for this trait.
Y
The situation for the female is different since she has two X chromosomes. The
diagrams below show all the possible combinations for the color blindness in males
and females. Note that color blindness is a recessive trait (c) and that normal vision
(C) is dominant.
"H"H'H"f,
XXXX
normal visbn
lemale
normal vision
{emale canier
"Hl
cH
"H
XY
Hl
XY
normal
cobrblind
visbn
male
male
"H"H
XX
cobr blind
female
Would you ever find a gene for color blindness on the Y chromosome? Explain why.
A carrier is anv individual that carries a gene for a trait but does not exhibit the trait.
8.
No. The Y chromosome is too short to have
room at the same level for this gene. So
REMEMBER, Y chromosomes are too short
to carry either a color blind gene (c) or a
normal vision gene (C), or any other sex-linked trait.
9. To solve color blindness inheritance problems, it's best to use symbols rather than
drawing out chromosomes as done above. The above conditions are usually
symbolized by showing the X and Y chromosomes and which gene is attached to
the chromosome as follows: A normal vision female would be symbolized as XCXC
and the normal vision male would be shown as XCY. How would you symbolize the
following:
Normal vision female carrier of color blindness?
Color blind male?
Color blind female?
'
Ch 34 Chromosomes, Genes and
lnheritance
44
9. XcXc
xcY
xcxc
10. You should now be able to solve a color blindness problem. Remember that
anywhere the X goes, the attached gene goes with it. Also remember that the Y has
no color blind or normal vision gene attached to it. Try the following problem:
Cross a colorblind male with a female carrier of color blindness. First show the
genotypes of the parents and then show the genotypes, phenotypes and fraetions of
each kind of offspring.
X
Parents
color blind
carner
List the genotypes and phenotypes of allthe offspring and state the fractions of each:
xcY
xc x'
Of the females, 1/2 will be
carriers and 112 color blind.
For the males, 1/2 will be
normal and 112 color blind.
10.
11. Muscular dystrophy is an inherited disease. The gene for it is recessive and it is sexlinked as in color blindness. Under these conditions, males will inherit the trait more
often than females. This is because a male only needs to get the one recessive
gene from his parents and he will have the disease. A female will have to get a
recessive gene for the condition from BOTH parents in order to have the condition.
This fact causes males to have sex-linked conditions 10 times more often than
females.
Muscular dystrophy is a condition that affects the muscles and causes weakness
and muscle degeneration. The child that inherits M.D. eventually will not be able to
move and usually dies by the time he becomes a teenager. There is no known cure.
The disease usually begins to show up between the ages of 6 and 9.
Write the genotypes for the following people:
Male with Muscular dystrophy (M.D.)
Male, unaffected bY M.D.
Female with M.D.
Female carrier of M.D.
Unaffected female that is not a carrier
Ch 34 Chromosomes, Genes and lnheritance
45
11. XmY
xMY
xmxm
xMxm
xMxM
12. Assume you are a genetic counselor and a couple comes to you for counseling.
They want to know if there is any chance that their first baby might have muscular
dystrophy. Neither of these two have M.D. but the wife's father has M.D. What would
you advise them? Could any of their children have M.D.? Would any of the girls
born have M.D.? Would any of the boys born to this couple have a chance of having
M.D.? (Show your work on your own paper)
12. Begin by putting down what you know about
the parents. (The man and wife) They are both
normal.
xMv x
husband
xMx?
wife
The wife has an M but the ? could be either an M
or m. Her father had M.D. and that means he was
XmY. Therefore the ? in the wife must be m.
She would get the m as
follows: XmY X
father
I
XMXM
mother
I
Y
xmxM
Fr
wife
Then this wife, when croised with her husband
would pass on genes as determined using the Punnett
square:
XMY
husband
XMXm X
wife
The Punnett square will give 114 normal females (XMXM;,
1t4 lemale carriers (XMXm;, 114 normal males (XMY),
and 1 /4 ol Jhe males with M.D. (XmY). You would,
therefore, inform the couple that the chance that their first
baby might have muscular dystrophy would be 114 or a
25"/" chance.
Ch 34 Chromosomes, Genes and
lnheritance
46
13. Hemophilia is a disease which is sex-linked. Those with the disease do not have
normal clotting mechanisms in the blood which causes blood to clot when cut or
bruised. This condition is inherited and until recently, was fatal to most of those who
inherited it. The person with the disease usually died from bleeding to death from a
small cut or bruise before becoming an adult. This trait is inherited by a recessive
sex-linked gene in the same manner as the other sex-linked traits covered earlier.
It is well known to historians that hemophilia was passed from generation to
generation in the royal family of England. For example, in the 1800's, Queen
Victoria and King Albert had a son, Prince Leopold who had' hemophilia. Neither the
king nor the queen had hemophilia. What is Leopold's genotype and what are the
genotypes of the king and queen?
13.
XHXh
Queen
X
*
XHY
Kins
xtlY (Prince Leopold)
14. Since people have more than one sex-linked trait, the genotypes can become
complicated in some problems. Consider the following:
A color blind, hemophiliac husband (XchV1 and a color blind wife who does not
have hemophilia (XcHlcH) have 4 children. Use the genotypes given and figure
out the genotypes and phenotypes of each possible child.
14. The possible offspring are as follows:
1/2 color blind females carrying a gene
for hemophilia (XchXcH;, 1/2 color blind
males, normal for hemophilia (XcHV;
BLOOD TYPE INHEHITANCE
15. Each person's blood type is inherited from parents. The four blood types are type A,
type B, type AB and type O. Anytime blood is transfused form one person to another,
blood type is checked to be sure the recipient's blood is compatible. Persons with
type O blood can give blood to any other person. Those with type AB blood can
receive blood from any other person. People can give blood to or receive blood
from another with the same blood type.
Ch 34 Chromosomes, Genes and lnheritance
47
Blood types are inherited as in hybrid crosses. To do blood type heredity problems,
use the following genotypes:
Blood Type I Genotype
Type
I AA. or AO
Type
I BB. or BO
AB
TypeAB
A
B
I
TypeO | @
Try the following cross.
Cross a homozygous type A with a homozygous type B.
15.
lA lA
B IAFIAB
B IABIAB
All offspring will be type AB.
16. Cross a heterozygous type A with a heterozygous type B. What fraction of each
blood type is possible in their offspring?
16.
IA I O
B IAB
I
BO
o lAoloo
Ch 34 Chromosomes, Genes and
lnherilance
114 ol the children will be type
AB, 114 type A, 114 B, and 114
type O.
48
34-4 Sample Sex-Linked and Blood Type Problems
Obiectlve
You are expected to be able to apply the principles of sex linkage and blood type
genetics to solve the following problems.
BLOOD TYPE
1.
Put the work and answers on your own paper and
circle all answers.
Cross the following parents and show all the possible offspring:
a. Type O
type AB
X
(Homozygous)
b. Type A
Type B (heterozygous)
X
c.
2.
PROBLEMS
Type A (heterozygous)
X
Type O
A type AB woman marries a man with type B whose mother was type
their offspring would be expected to be type A?
O.
What % of
SEX LINKED PROBLEMS:
Show "/" of all phenotypes and all genotypes. Circle all answers.
3.
Cross the following:
a. Color blind man with a normal vision woman (not a carrier)
b. Color blind man with a normal vision female carrier
c. Color blind female with a normal vision male
4.
Cross the following:
a. A man with muscular dystrophy with a normal female carrier of muscular
dystrophy
b. A man with muscular dystrophy with a normal female whose father had muscular
dystrophy
5. Cross a female
hemophiliac with a normal man with no history of hemophilia in his
family.
Ch 34 Chromosomes, Genes and lnheritance
49
34-5 Sex-Linked and Blood Type Problem Set
Objectlve
You are expected to be able to apply the principles of sex linkage and blood
group genetics to solve the following problems.
BLOOD TYPE PROBLEMS
1.
Put all work on your own paper and circle
all answers.
Two parents, both with type A blood, have a son with type O blood. What are the
genotypes of both parents?
2. What To
of
any future children from the parents in problem 1 above would you expect
to have type B blood? What 7" would have type A blood?
3.
A man with type AB blood marries a woman with type A blood. The woman's
genotype is not known in that it can be either homozygous or heterozygous. lf one
particular genotype were to show up in their children, it would tell us the precise
genotype of the mother. What is this blood typelgllhe3ttspdng that would allow us
to determine the mother's genotype? Explain.
B blood claimed that a certain J. R. Wilson, a
multimillionaire oil tycoon, was the father of Mrs. Fleming's recent 4 month old baby.
The Flemings took the issue to court charging that Mr. Wilson was the father and that
he should pay $35,000.00 per year to the Wilsons for child support. Mr. Wilson's
blood type is AB. The baby's blood type is type O.
4. Mr. and Mrs. Fleming, both with type
(a) lf you were the expert genetics witness called
into court by Mr. Wilson's attorney,
how could you show that the baby could not be Mr. J. R. Wilson's?
(b) ls it possible that the baby is actually Mr. Fleming's? Explain your answer.
SEX LINKED TRAITS PROBLEMS:
The problems that follow are typical of those that appear on the unit exam. lt's best if
you show your work by diagramming the crosses. Write out both the genotypes and
the phenotypes when asked to do so. CIRCLE the answer asked for in each
problem.
5. A female carrier of color blindness married a normal vision man.
What % of their
children would you expect to be colorblind?
have a boy and a girl with normal vision.
The girl marries a normal vision man and their first son is colorblind. What are the
genotypes of the Smiths? What are the genotypes of both the Smith children?
6. The Smiths, who both have normal vision,
Ch 34 Chromosomes, Genes and lnheritance
50
7.
The parents of a boy with hemophilia both have normal clotting blood. What is the
genotype of the mother of this hemophiliac?
8.
A normal vision man with muscular dystrophy, married a woman with normal vision
and no symptoms of muscular dystrophy. The woman's father is colorblind and has
muscular dystrophy. What l" of their children could be both colorblind and have
muscular dystrophy? What % of their sons could you expect to have muscular
dystrophy?
9. A blue eyed,
colorblind, but otherwise normal man, married a hemophiliac wife with
muscular dystrophy. (Poor couple) What % of their children would you expect to
have hemophilia?
Ch 34 Chromosomes, Genes and lnheritance
51