Download Genetics Problem Set #3

Genetics Problem Set #3
Example:
In humans, detached earlobes (D) are dominant over attached earlobes (e). If you have detached earlobes
and are heterozygous (Dd) for that trait and your partner has attached earlobes. What are the genotypic
and phenotypic ratios of this cross?
Correct Answer:
Cross: Dd x dd
D
d
Phenotypic ratio: 2 detached earlobes: 2 attached earlobes
d
Dd
dd
Genotypic ratio: 2 heterozygous: 2 homozygous recessive
d
Dd
dd
Note: Punnett squares are not always required. You may do a Punnett square anytime, but get used to
understanding the ratios of each cross. This will help you on future quizzes and exams.
1. The ability to roll your tongue (T) is dominant over the ability not to roll your tongue (t). What would be the
genotypic and phenotypic ratio of offspring if you crossed a heterozygous male (Tt) with a homozygous
recessive female (tt)?
2. A woman who can roll her tongue marries a man who cannot. Their first child has his father's phenotype.
What are the genotypes of the mother, father, and child?
3. When performing a dihybrid cross, when would you expect to get a phenotype ratio of 9:3:3:1 in the next
generation?
4. If you crossed two true breeding plants, one with red flowers and one with white flowers and all the F1
generation came out with pink flowers. You then let all the F1 generation flowers cross pollinated and in the
resulting F2 generation, the phenotypic ratio of all the offspring was 1 red flower: 2 pink flower: 1 white
flower. What type of inheritance pattern would you predict?
5. You do the same cross as in question 4, but all the F1 flowers come out red with white spots. You again let
the F1 generation cross pollinate and the resulting phenotypic ratios in the F2 are: 1 red flower: 2 red and
white spotted flowers: 1 white flower. What is the inheritance pattern of these flowers?
6. In the breeding season, male Anole lizards court females by bobbing their heads up and down while
displaying a colorful throat patch. Assume for this question that both males and females bob their heads and
have throat patches. Assume also, that both traits are controlled by single locus genes on separate
chromosomes. Now, suppose that anoles prefer to mate with lizards who bob their heads fast (F) and have
red throat patches (R) and that these two alleles are dominant to their counterparts, slow bobbing and
yellow throats. A male lizard heterozygous for head bobbing and homozygous dominant for the red throat
patch mates with a female that is also heterozygous for head bobbing but is homozygous recessive for
yellow throat patches. How many of the F1 offspring have the preferred fast bobbing / red throat phenotype
(assume 16 young)?
7. In Western Nevada, there is a creature know as a “Wild Mucker Man”. It comes in three colors: blue, silver,
and white. This trait is controlled by a single locus gene with incomplete dominance. A homozygous (BB)
individual is blue, a homozygous (bb) individual is white, and a heterozygous (Bb) individual is silver.
What would be the genotypes and phenotypes of the offspring if a blue “Mucker Man” were crossed with a
white one? What are the phenotypic and genotypic ratios in the F2?
Blood typing Worksheet
1. In humans the blood groups are produced by various combinations of three alleles IA, IB, and i. Blood type
A is caused by either IA IA or IA i; type B by IB IB or IB i; type AB by IA IB; and type O by i i. Suppose a child
is of blood type A and the mother is of type 0. What type or types may the father belong to?
2. Suppose a father of blood type A and a mother of blood type B have a child of type O. What blood types
are possible in their subsequent children?
3. Suppose a father and mother claim they have been given the wrong baby at the hospital. Both parents are
blood type A. The baby they have been given is blood type O. What evidence bearing on this case does
this fact have?
4. In humans, red-green colorblindness is an x-linked recessive trait. If a normal (no color blindness) male
mates with a normal female and have a red-green color blind boy, what is the genotype of the mother and
the father? What is the probability that if these two parents have a daughter, she will be red-green color
blind? Explain.