Dihybrid Crosses Directions: Answer the following questions using your notes and your textbook. For all problems show your work using punnett squares!



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Dihybrid Crosses
Directions: Answer the following questions using your notes and your textbook. For all problems show your work using punnett squares!
1. In pea plants, tall (T) plants are dominant over short (t) plants. Complete the following

crosses and give the genotypic and phenotypic ratios of offspring.


a. TT x tt

b. Tt x tt

c. Tt x Tt

2. In pea plants, purple flowers (P) are dominant over white (p) flowers. Complete the following crosses and give the genotypic and phenotypic ratios of offspring.




  1. A heterozygous purple plant is crossed with a homozygous purple plant.


  1. A cross between two pea plants produces offspring in which approximately 50% of the flowers are white and 50% are purple. What are the genotypes of the parents?



  1. Show punnett square to support your answer.

3. A cross between two purple pea plants yields approximately 25% of the offspring

exhibiting white flowers. What are the genotypes of the parents? Show punnett square

to support your answer.

4. A widow’s peak in humans is determined by a dominant/recessive inheritance. A person who is purebred for widow’s peak is crossed with a person who is purebred for no widow’s peak. All of the offspring have a widow’s peak. Which trait is dominant and which is recessive? Show punnett square to support your answer.

5. In guinea pigs, black fur is dominant. If a black guinea pig is crossed with a white guinea pig and the litter contains a white offspring, the genotype of the black-haired parent is probably? Show punnett square to support your answer.

6. In cattle, red and white hair are codominant. The heterozygous condition is roan colored (contains both red hair and white hair)
a. Cross a red cow and a white cow. What would be the genotypic and phenotypic ratios

of the offspring be?

b. Would it be possible to have any red cattle when two roan cattle are crossed? Show

punnett square to support your answer.

7. In humans, colorblindness is due to the recessive allele (c), and normal vision is due to the dominant allele (C). Color blindness is a sex-linked trait.

a. What is the expected offspring between a normal man and a colorblind woman? Give

both genotypic and phenotypic ratios of offspring

b. A normal male is crossed with a female who is not colorblind? Would it ever be

possible to produce offspring that are colorblind? Show punnett square to support your

answer.
c. What would you expect when a colorblind man marries a colorblind woman? Give both genotypic and phenotypic ratios of offspring.

d. Is it ever possible to have a male that is a carrier for colorblindness? Explain

e. Would there ever be an instance when a female could not be a carrier? Explain

8. The chart below shows the inheritance of human blood types. There are four different phenotypes possible: A, B, AB, and O. The alleles A and B are codominant, and the O allele is recessive to both A and B.

Blood Type (Phenotype)

Genotype

Donate to:

Receive from:

O

ii

A,B,AB and O(universal donor)

O

AB

IAIB

O, AB

A,B,AB and O (universal receiver)

A

IAIA or IAi

AB, A

O,A

B

IBIB or IAi

AB,B

O,B

a. A person with IAIB is crossed with a person who is IAIA. What are the genotypic and

phenotypic ratios of the offspring?

b. A person with type AB blood is crossed with a person with type O blood. What are the

genotypic and phenotypic ratios of the offspring?

c. A person with type A blood is crossed with a person with type B blood. They have



offspring with type O blood. What are the genotypes of the parents? Show punnett

square to support your answer.


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