Cat worksheet: use in combination with the cat photosprovided in the module to practice your dihybrid crossskills

**refer to text sections 9.4 & 9.5 to help youduring this exercise**

1. Look at the photographs of domestic cats found in thismodule and take a look at the information on Mendelian traits thatcontrol the appearance of cats’ coats found below:

1. Coat uniformity is controlled by genes at the P locus:genotype (P--) = white patches of fur & genotype (pp) = solidcolored fur

1. Hair length is controlled by genes at the H locus:genotype (H--) = short hair & genotype (hh) = longhair

KEY: P-- means PP or Pp, and H-- means HH or Hh: you’llneed to choose one or the other

1. Use the information about these two genes and thepictures of cats to answer the questions that follow.

Questions:

1. What does the gene at the H locus control? Which alleleis dominant and which is recessive?

Hair length, H is dominant while h isrecessive.

1. What does the gene at the P locus control? Which alleleis dominant and which is recessive?

Coat uniformity, P is dominant while p isrecessive.

1. Look at the photos of cats and figure out all thepossible phenotype combinations an individual cat could have forthe two traits of hair length and coat uniformity. Use words, notletters to describe these phenotypes (i.e. solid colored long hair,solid colored short hair, etc..).

First cat: Solid colored long hair

Third cat: Solid colored short hair

Third cat: White patches short hair

Fourth cat: White patches long hair

1. For each of these genes, how many alleles does anindividual cat have? In other words how many alleles that determinehair length and how many that determine coatuniformity?

Two

1. Choose four cat photos and fill in the blanks below foreach. This helps you practice translating what you see (phenotype)into genotype.

1. Cat #1 phenotype: Solid colored long hair

genotype: pphh

1. Cat #2 phenotype: Solid colored short hair

genotype: ppHh

1. Cat#3 phenotype: White patches short hair

genotype: PpHh

1. Cat#4 phenotype: White patches long hair

genotype: Pphh

1. Now choose any two cats and designate one male and theother female. Both are heterozygous for hair length and coatuniformity.

1. What are the genotypes of each cat?

Male: PpHh

Female: PpHh

1. What are their phenotypes?

Male: White patches short hair

Female:White patches short hair

1. Write the genotypes of all the gametes that each ofthese two cats can produce. (NOTE: this can be tricky at first, ifneeded refer to your dihybrid cross Amoeba Sisters video in thePreLab to see an example of how it’s done).

1. Male’s gametes:

1. Female’s gametes

1. Now you’re ready to take the gametes you’ve createdabove and construct a dihybrid cross Punnett square to predict thephenotypic and genotypic outcomes of possible offspring (kittens!).Use the space below to construct your Punnett.

*Text section 9.5 & figure 9.5A are a good referenceto use as you construct your Punnett. Doublecheck your gametes tobe sure they each contain only ONE allele (alphabet letter) foreach trait.

1. Using the possible phenotype combinations you listed inQuestion 3, write down the number of individuals in each categoryyou expect to see based on your Punnett square. Can you expressthis as a ratio? (see fig 9.5A text)

1. Does a Punnett square show expectations for a wholepopulation or just for one family? Explain your answer in relationto the cats in the photos and the Punnett square you justmade.