Question

) In muskrats, short hair is recessive to long hair and brown coat is recessive to black coat. (Both are autosomal.) You cross a true-breeding short-haired black muskrat to a true-breeding long-haired brown muskrat. Let L= long and l= short, and let B= black and b= brown

. A) Diagram this cross, showing the genotypes of the parents and the F1.

B) Now you test cross the F1. Diagram this test cross, showing the genotypes of the F2 produced.

C) If the hair length gene and the coat color gene are linked by 5 map units (m.u.), what percentage of the F2 (from part B) will have long hair and a black coat

? D) Now you have a different long-haired black muskrat you call Smitty that you got from an independent source. You test cross him. Amongst the progeny are short-haired black, short-haired brown, long-haired black and long-haired brown kits (muskrat babies). However, you find that the vast majority of the progeny are either long-haired black or short-haired brown.

i. What is Smitty's genotype?

ii. Assume that Smitty’s parents were true breeding. What were their genotypes and phenotypes?

Answer 1

A.

Short-haired Black × Long-haired Brown

llBB × LLbb

	Lb	Lb	Lb	Lb
lB	LlBb	LlBb	LlBb	LlBb
lB	LlBb	LlBb	LlBb	LlBb
lB	LlBb	LlBb	LlBb	LlBb
lB	LlBb	LlBb	LlBb	LlBb

In F1, all offsprings will have same genotype LlBb and same phenotype Long-haired Black.

B.

Test cross means cross between a Homozygous recessive individuals to a heterozygous individual.

LlBb × llbb

	LB	Lb	lB	lb
lb	LlBb	Llbb	llBb	llbb
lb	LlBb	Llbb	llBb	llbb
lb	LlBb	Llbb	llBb	llbb
lb	LlBb	Llbb	llBb	llbb

C.

Hair length gene and coat color gene are linked by 5m.u.

Linked Genes are usually inherited together because they are physically close to each other. Long hair and black coat allele are together in F1 offsprings.One of the  parent in F2 has long hair and black coat allele together. 1 map unit is equal to 1% recombinant Frequency. So 5% F2 offspring will have long hair and black coat..

D.

i. Smitty 's genotype is LlBb .

because large numbers of offspring shows their parents genotype. Short- haired brown is the testcross individual(Homozygous recessive).And offsprings are not all long haired and black coated. so smitty is not Homozygous. His genotype must be LlBb.

ii.

Smitty 's parents genotype and phenotype was,

LLBB ( LONG HAIRED BLACK) and llbb( short haired brown)