Question

biology exam 6
complete the following punnett square to answer questions 8 - 12.
a litter of kittens were born to a mother cat that has long hair. long hair is a recessive trait for cats. in the litter of kittens, half the offspring have short hair and half the offspring have long hair. the father is unknown.

1. name and describe the type of cross shown above. (2pts)
2. are the offspring with the dominant trait heterozygous or homozygous dominant? what is their genotype? (2pts)
3. what is the genotype of the unknown parent cat?
4. what is the phenotype of the unknown parent cat?
5. suppose the genotype of the unknown parent cat were homozygous dominant. what would be the phenotype of the offspring as a result?

Explanation:

• Question 8: A test cross is used to determine the genotype of an individual with a dominant phenotype. In this case, since the mother has long hair (recessive, genotype \(ll\)) and half the offspring have long hair (\(ll\)) and half have short hair, it's a test cross. The cross is between the unknown parent (with dominant - phenotype trait, short hair) and the recessive - parent (long - haired mother).
• Question 9: Offspring with the dominant trait (short hair) get one recessive allele (\(l\)) from the mother (\(ll\)). So their genotype must be \(Ll\) (heterozygous).
• Question 10: Since half the offspring are \(ll\) (get \(l\) from mother and \(l\) from father) and half are \(Ll\) (get \(L\) from father and \(l\) from mother), the father's genotype is \(Ll\).
• Question 11: The dominant allele (\(L\)) determines short hair. So the phenotype of the unknown parent (\(Ll\)) is short hair.
• Question 12: If the unknown parent was \(LL\) (homozygous dominant), all offspring would get \(L\) from the father and \(l\) from the mother (\(Ll\)). So all offspring would have short hair.

Answer:

• 8: This is a test cross. A test cross is a cross between an individual with a dominant - appearing phenotype (unknown genotype) and a homozygous recessive individual. Here, the mother is homozygous recessive (\(ll\), long - haired) and the cross is to determine the genotype of the unknown (short - haired) parent.
• 9: The offspring with the dominant trait (short hair) are heterozygous. Their genotype is \(Ll\).
• 10: The genotype of the unknown parent cat is \(Ll\).
• 11: The phenotype of the unknown parent cat is short hair.
• 12: If the unknown parent cat were homozygous dominant (\(LL\)), all of the offspring would have short hair.