In cats, orange coat color is determined by the b allele,...

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?

Key Concepts

Genotype-Phenotype Relationship in Heterozygous Conditions

The genotype-phenotype relationship in heterozygous conditions occurs when an individual possesses two different alleles for a trait. In some cases, this can result in a mosaic or intermediate phenotype, as different cells express different alleles, leading to a pattern or a mix of traits.

Punnett Square Analysis

Punnett square analysis is a fundamental tool used in genetics to predict the possible genotypes and phenotypes of offspring from a cross between individuals. By organizing the alleles from each parent into a grid, one can visualize and calculate the probability of various genetic outcomes, which is especially useful when dealing with X-linked inheritance.

X-linked Inheritance

X-linked inheritance refers to the transmission of genes that are located on the X chromosome. Because males and females have different numbers of X chromosomes (males being XY and females XX), the expression of X-linked traits can differ between the sexes, leading to unique patterns of inheritance not seen in autosomal traits.

Sex Determination in Mammals

Sex determination in mammals is based on the chromosomal composition of the individual, typically with females having two X chromosomes and males having one X and one Y chromosome. This difference underlies the distinct genetic outcomes in male and female offspring when it comes to X-linked traits.

Transcript

00:01 In order to answer this question, let's talk about inheritance.

00:04 It says in cats, the dominant ovaleal for the ex -link orange gene is required to produce orange fruit.

00:10 So according to this information, in females, when you have the homozygose dominant, you're going to get an orange female.

00:22 And when you get the homozygoseb excessive, you're going to get the black female.

00:32 Okay, a black female cat.

00:34 And when you get the heterozygous like this, you're going to get a tortoise shell.

00:42 A tortoise cat.

00:44 Now in males it is easier because males only have one x chromosome.

00:50 So in this case you have either this or this.

00:56 This is going to be an orange male and this is going to be a black male.

01:00 Now it says, approximately 90 % of the same, called tortoiseshell cats are females.

01:09 Then it says explain why tortoise shell cats are nearly always female and this is because in order to produce a tortoise shell you need one dominant allele and one ovalial and as this trait is ex -linked it means that this gene is at the x chromosome then you need two x chromosomes.

01:27 Okay, one x chromosome to have the dominant of allele and one x chromosome to have the recessive ovale.

01:33 So this is why females can be tortoiseachial and males no, because they don't have two x chromosome, they only have one x chromosome.

01:42 The next question says what types of crosses would be expected to produce female tortoise shell cats? so if you want female tortoiseshell cats, it means you want this...

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