Question

Two short-tailed Manx cats are bred together. They produce 3 kittens with long tails 5 short tails and 2 without tails. From these results, how do you think tail length in these cats are inherited? Show the genotypes for both the parents and the offspring to support your answer.

Answer 1

Answer and Explanation:

There are three phenotypes, so it seems that this an example of incomplete dominance, with the short tail being the intermediate form between long-tail and no-tail. Incomplete dominance is a condition where neither of the alleles completely dominates over the other one. Dominant alleles cannot completely cover up the recessive alleles. Descendents possess an intermediate phenotype between the two parental phenotypes and not the dominant one, which would appear if this would be the case of complete dominance.

Available data:

• Two short-tailed Manx cats are bred together.

• F1: 3 kittens with long tails, 5 short tails, and 2 without tails.

The T gene might express the tail trait. T allele expresses long the tail and is dominant over t allele which expresses the absence of the tail.  

So, homozygous dominant individuals, TT, are long-tailed animals

homozygous recessive individuals, tt, have no tail

Heterozygous individuals, Tt, are short-tailed animals, the intermediate form.

Cross: Two short-tailed Manx cats are bred together

Parental)  Tt    x    Tt

Gametes) T   t   T   t

Punnet Square)  T        t

                   T    TT     Tt

                    t     Tt       tt

F1)  1/4 TT = Long-tailed animals

     2/4=1/2 Tt = Short-tailed animals

     1/4 tt = untailed animals

The ratio 3:5:2 of the progeny in the example is close enough to the Mendelian ratio 1:2:1.

Answer 2

Answer:

This is a case of incomplete dominance. Consider the genotypes below:

LL - long tailed

Ll - short tailed

ll - no tail

The parent genotype is Ll. This means they have the ability to produce offspring with either of the 3 given phenotypes depending on the combination of alleles that get passed down. The cross would be the following way:

        L             l

L      LL           Ll

l       Ll             ll

There's a 25% chance of long-tail, 50% chance of short-tail and 25% chance of no-tail.

Hope that answers the question, have a great day!