Question

In cats, orange coat color is determined by the \(b\) allele, and black coat color is determined by the \(B\) allele. The heterozygous condition results in a coat pattern known as tortoiseshell, These genes are X-linked. What kinds of offspring would be expected from a cross of a black male and a tortoiseshell female? What are the chances of getting a tortoiseshell male?

Short answer

Answer: The chances of getting a tortoiseshell male offspring from this cross are 0%.

Step-by-step solution

Identify the genotypes

The genotypes of the given cats are: - Black male: XY (with B allele on the X chromosome) - Tortoiseshell female: XX (with B allele on one X chromosome and b allele on the other X chromosome)

Construct a Punnett square

To find the expected offspring from the cross between the black male and the tortoiseshell female, create a Punnett square using the parents' genotypes: B b +-----------+-----------+ X | XB | Xb | +-----------+-----------+ Y | YB | Yb | +-----------+-----------+

Determine expected offspring

From the Punnett square, we can determine the possible genotypes and phenotypes of their offspring: - XB female (black): 50% probability - Xb female (tortoiseshell): 50% probability - YB male (black): 50% probability - Yb male (orange): 50% probability

Calculate the probability of a tortoiseshell male

From the possible offspring genotypes, there are no tortoiseshell males (XY with both B and b alleles). So, the chances of getting a tortoiseshell male are 0%.

Key concepts

Coat Color Genetics

Coat color genetics in cats involves the fascinating interaction between specific alleles. In this scenario, the two main alleles are "B" for black and "b" for orange. These alleles are located on the X chromosome, which means they are X-linked traits. This is key because male cats inherit an X chromosome from their mother and a Y chromosome from their father, while female cats inherit an X chromosome from each parent. As a result of this inheritance pattern, males from a black or orange lineage will always express the allele on the single X chromosome they inherit, leading to either a black or orange coat. For females, however, having two X chromosomes allows for the heterozygous possibility, where one "B" and one "b" allele can result in a mixed or tortoiseshell pattern. This unique color pattern occurs when both the black and orange colors are expressed due to random X chromosome inactivation, a process known as "lyonization." Thus, coat color genetics in cats showcases a rich example of how X-linked inheritance patterns affect phenotypic outcomes.

Punnett Square

The Punnett square is a fundamental tool used in genetics to predict the genotype and phenotype of offspring from a particular cross. It is especially useful for visualizing the inheritance of specific traits, such as coat color in cats. The square is constructed by placing one parent's alleles on the top and the other parent's alleles on the side. For example, in our case:

• The tortoiseshell female has alleles represented as XX, with one X carrying "B" and one carrying "b".
• The black male has one copy of the X chromosome with the "B" allele and a Y chromosome.

To construct the Punnett square, align the female's alleles across the top and the male's underneath:

• The possible combinations are then filled in the boxes to show the genetic makeup of potential offspring.
• Each box represents a 25% chance of an offspring having that particular genotype.

This method highlights how different combinations of alleles from each parent can lead to varied outcomes in their kittens. Using the Punnett square helps illustrate why there are no tortoiseshell males in this scenario.

Sex-Linked Traits

Sex-linked traits are those genetic characteristics determined by genes located on the sex chromosomes, particularly the X chromosome. They are inherited differently in males and females due to the biological differences in their chromosome composition. In cats, coat color being X-linked serves as an example of how such traits are distributed.
For males, having only one X chromosome means they will express whichever allele is present on that chromosome, leading to either black or orange coats based on our scenario.
Females, however, have two X chromosomes, which results in a broader array of potential phenotypes like the tortoiseshell coloration because they can carry two different alleles, one on each X chromosome. This genetic arrangement means males can never be tortoiseshell since the pattern requires the presence of both "B" and "b" alleles, which is impossible with just one X chromosome.
Therefore, understanding sex-linked traits is key to predicting outcomes in genetic studies, as it reveals why certain expressions of coat color, like tortoiseshell, are unique to female cats in this genetic cross.