Multiple Choice
In a sex-linked pedigree, if females are labeled as 'XX', how should males be labeled?
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2. Mendel's Laws of Inheritance
Sex-Linked Genes
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Why is it unusual for a calico cat to be male?
A
Because the calico coloration is determined by two different alleles located on the X chromosome, and males typically have only one X chromosome.
B
Because calico coloration is caused by a mutation on the Y chromosome, which males always inherit.
C
Because male cats have a higher chance of inheriting the calico gene from their fathers.
D
Because male cats are more likely to express dominant coat color genes, preventing calico patterns.
Verified step by step guidance1
Understand that calico coloration in cats is linked to genes located on the X chromosome, specifically involving two different alleles that determine coat color patterns.
Recall that female cats have two X chromosomes (XX), allowing them to carry two different alleles for coat color, which can result in the patchy calico pattern due to X-chromosome inactivation.
Recognize that male cats typically have one X and one Y chromosome (XY), meaning they usually have only one allele for the coat color gene on their single X chromosome.
Since males have only one X chromosome, they generally cannot display the calico pattern, which requires two different alleles on two X chromosomes; this makes calico males rare and usually the result of genetic anomalies such as Klinefelter syndrome (XXY).
Conclude that the unusual nature of male calico cats is due to the genetic mechanism of X-linked coat color inheritance and the typical chromosomal makeup of male cats.
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