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GENETICS PROBLEMS #2
Answer all problems on separate paper. Show all your work clearly! I can’t give you partial
credit for an incorrect answer unless I can find your error.
1.
What gene combinations can appear in the gametes of an individual with a
WwXx genotype? _________________________________
2.
In 4 o’clock plants, red is incompletely dominant to white, and busy is dominant to lazy
(a creeping vine characteristic). Following both traits, list all the phenotypes and their ratios
which result from mating 2 hybrid individuals. Your results will be the
P2 generation. Key: Use R for Red, W for White. A genotype of RW gives a pink color. Use B
for bushy and b for lazy.
3.
In human beings, brown hair is dominant to red hair and the ability to taste a certain
chemical is dominant to the inability to taste it. Diagram a cross between a red-haired taster man
(whose father was a non-taster) and a brown-haired non-taster woman (whose mother had red
hair). Show what kind of gametes can be produced and the proportions or ratios of genotypes and
phenotypes expected of their children.
4.
In humans the allele for dimples is dominant to the allele for “no dimples”; the allele for
curly hair is dominant to the allele for straight hair and brown hair is dominant to red. A dimpled
woman with curly brown hair marries a non-dimpled man with straight red hair. What are the
possible genotypes of these two people? By assuming, when there is doubt, that they are
heterozygous, predict the possible phenotypes and their proportions for the couple’s children.
5.
In man, there are 22 pairs of autosomes, and one pair of sex chromosomes. The sex
chromosomes in female are XX. In males the sex chromosomes are XY. The Y chromosome
carries very little information except sex-determining information. The X chromosomes carries
a number of genes that have nothing to do with sex, such as the gene for normal color vision, or
its alternate, color blindness. Since females are XX, all females’ eggs carry one X chromosome.
Since males are XY, some sperm carry the X chromosome and some carry the Y chromosome.
Show this in a punnet square.
XX
x
XY
What percent of the offspring are males?_______What percent females?__________
6.
In birds and butterflies, the male is XX and the female is XO (only one X). Which parent
determines the sex of the offspring? in these species? _________________
Explain.
7.
Colorblindness is a sex linked disease that is linked to the x chromosome. A female, who
is a carrier for colorblindness marries a man who is not colorblind. What i the possibility that a
BOY born to these parents will be colorblind?? Show your cross and explain your answer.
8.
Hemophilia is a sex-linked characteristic. Hemophilia is due to a recessive gene. Key:
Use H for Normal and h for hemophilia. What parental combinations would be necessary to
produce a hemophiliac son? Give all possible combinations
9.
Hemophilia, a disease in which the blood does not clot properly, is a sex-linked disease
found on the x chromosome. If a hemophiliac man has a son, will he be able to pass the gene for
the disease to his son??? Explain. To his daughter, if he has one?Explain.
10.
Is it more likely that a man inherits colorblindness than a woman? Explain.
11. A color blind father passes the gene for color blindness to:
A. all of his children
B. all of his daughters
C. all of his sons
D. none of his children
-explain
12.
Genetically, why would matings between close relatives be unsound? Explain.
13.
In cats, black coat color is due to the gene B. Its allele Y produces yellow coat color.
The genotype BY produces tortoise shell (or calico) color. This trait is sex-linked. A female
yellow cat is bred to a black male. (Note: the male is hemizygous). What will the ratio of
phenotypes in the kittens be? List the sexes as well as the coat colors.
14.
Could you produce a tortoise color male cat if no abnormalities occur?
Explain.
15.
What is the expected genotypic and phenotypic ratio of a cross between a tortoise-shell
female and a black male? List the sexes as well as the coat color.
16.
A tortoise-shell male cat is born. What are the possible genotypes of the mother and
father and what must have occurred to produce this offspring?
17.
Two parents, both with brown hair (and both heterozygous for brown hair) had four
children. The children knew that on their mother’s side of the family, their grandmother had
blonde hair. They asked what color their grandfather’s hair had been. Their mother said that
they could figure this out if they remembered that their two aunts (her sisters) both had blonde
hair. (Brown is dominant).
The grandfather’s hair was:___________________explain
A. blonde
B. hybrid brown
C. pure or homozygous brown
A scientist would write the genotype of the grandmother’s hair as___________
18.
If the leaf of a corn plant has 20 chromosomes, then the egg cell has how many
chromosomes? _______________
19.
Sex-influenced traits are not a result of genes carried on the X chromosomes, but are
autosomal genes which are expressed differently in males and females.
In the Male Aryshire Bull:
In the female Aryshire cow:
MM is mahogany and white
MM is mahogany and white
Mm is mahogany and white
Mm is red and white
mm is red and white
mm is red and white
20. Use a punnet square to mate a female mm X and a male MM. Remember this is not sexlinked, but sex-influenced. Now indicate the phenotypes of the offspring clearly indicating the
% of each color of male and female.
21.
At first, one might guess that baldness is sex-linked. It is not. It is a gene on the
autosome. Yet more men are bald than women. The reason is that the baldness gene acts as a
dominant in males and a recessive in females. Therefore, using the key :
B=bald, N-normal:
In females: NN is normal (full hair)
In males:
NN is normal
BN is normal
BN is bald
BB is bald (usually very thin)
BB is bald -very
a. Mate a homozygous female (normal) with a bald male (heterozygous). What will the
offspring be like? Indicate sex and phenotype.
b. Mate a heterozygous female (she looks normal) with a homozygous normal male. BN
female and NN male. Indicate the phenotypes and sexes of the offspring.
22.
A brown-eyed woman whose blood type is AB (and whose father had blue eyes) is
married to a blue-eyed man whose blood type is A (and whose mother is type O). What ratios of
phenotypes would you expect among their children? (Hint - use symbols other than B and b for
the eye color gene!)
23.
A man with blood type AB marries a woman who has blood type B. Is it possible that
any of their children could have blood type A? Explain your answer using a punnet square.
24.
A child has blood type O. The parents of the child have blood type A and blood type B.
Using your knowledge of the inheritance of blood type, explain how the child inherited her blood
type. Use a punnet square in your answer.
25. Sickle-cell anemia (a serious defect which causes red blood cells to be abnormal) is caused
by a recessive autosomal gene. The heterozygotes are said to have sickle-cell trait. Essentially
they are normal, unless subjected to an unusually low oxygen tension environment. There is
now a test which can determine carriers (heterozygotes). If two heterozygotes mate, what are
their chances of producing diseased children? If one out of 10 are carriers, what is the
probability that two such people will mate.
26.
Huntington’s Disease is a latent dominant gene which expresses itself late in life-thirties
or later. If a man with Huntington’s marries a normal woman, what are their chances of
producing children with Huntington’s? of producing carriers?
27.
There is a blood grouping factor known as the M, N or MN blood grouping. M and N are
co-dominant. Therefore genotype MM is Type M blood, genotype MN is type N blood and
genotype MN is type MN blood. If 49% of the population has M blood, what % has type N
blood, and what % has MN blood? What is the frequency of the M gene? What is the frequency
of the N gene?