Question

(The Manx is a breed of domestic cat that lacks a tail.  The Manx phenotype is caused by a single autosomal gene.  Two Manx cats are bred over a period of years with several litters of kittens being produced.  Overall, the following progeny result: 12 Manx kittens and 6 kittens with tails.  Consider carefully the proportions of the two phenotypes before answering these questions:

(A)   What unusual mode of inheritance is involved in the inheritance of the Manx trait? ___________________________

(B)  (What is the genotype of the Manx cats?______________

(C)  What is the genotype of the cats with tails?_______________

(D)  Using the Punnett Square, diagram the above cross

(E)  (2 points) What are the genotypic and phenotypic ratios in the F₁generation when two Manx cats are crossed?

(F)  (3 points) A cross is performed between 2 Manx cats and 6 kittens are born.  What is the probability that 3 kittens will be Manx (tailless) and 3 kittens will have normal tails?  Use the binomial expansion formula.

*PLEASE LETTER EACH ANSEWR*

Answer 1

A. The Manx trait is caused by autosomal dominant mutation. The dominant homozygous condition is lethal, resulting in a 2: 1 ratio as opposed to the normal 1:2:1 ratio.

B. Genotype of manx cat = Aa (heterozygous)

C. Genotype of tailed cats = aa (recessive homozygous)

D. and E. Manx x Manx = Aa x Aa

f1 generation genotypes and phenotypes are as follows:

	A	a
A	AA (lethal)	Aa(Manx)
a	Aa (Manx)	aa (tailed cat)

F. p = getting a manx cat = 2/3
q = getting a tailed cat = 1/3
probability of getting 3 kittens with normal and 3 with manx trait = = 4/2187 = 0.0018 *100 = 0.18%