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In domestic cats, two gene loci that control different aspects of coat colour have the following alleles - VCE - SSCE Biology - Question 6 - 2009 - Paper 1
Question 6
In domestic cats, two gene loci that control different aspects of coat colour have the following alleles. Gene locus for black coat colour B : black fur b : bro... show full transcript
Worked Solution & Example Answer:In domestic cats, two gene loci that control different aspects of coat colour have the following alleles - VCE - SSCE Biology - Question 6 - 2009 - Paper 1
Step 1
A. kittens could be brown with white spots.
Answer
This statement is true. Given that one parent is BbSs (which can pass either a b or B allele and an S or s allele) and the other parent is BBSs (which can pass a B allele and either an S or s allele), it is possible for the offspring to inherit the b allele from the first parent and the S allele from either parent, leading to brown kittens with white spots.
Step 2
B. kittens have a one in two chance of having no white.
Answer
This statement is correct. The BbSs parent can contribute either S (white spotting) or s (no white spotting) alleles to the offspring. Since the second parent is BBSs, there are two possibilities for the S locus: it can pass S (resulting in white spotting) or s (resulting in no white spotting). Therefore, there is indeed a one in two chance the kittens will have no white.
Step 3
C. kittens could have far more white than either of the parents.
Answer
This is true as well. If a kitten inherits the S allele from both parents (SS), they will exhibit more white spotting than either parent. The homozygous genotype for S (SS) leads to more white on the coat than the heterozygous genotype (Ss) seen in the parents.
Step 4
D. kittens would have a one in two chance of being homozygous dominant at both loci.
Answer
This statement is false. The only way to be homozygous dominant at both loci (BBSS) is to inherit a B from both parents and an S from both. However, since the BbSs parent can contribute either B or b and either S or s, the probability of being BBSS is not one in two but rather less than that due to the presence of alternative alleles.