Multiple Choice
Males are more often affected by X-linked traits than are females because:
3
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2. Mendel's Laws of Inheritance
Sex-Linked Genes
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In cats, the calico fur pattern is due to X-linked genes. Which meiotic error could produce a gamete that, when fertilized, results in a calico male (an XXY individual)?
A
Nondisjunction of autosomes during meiosis I in the mother
B
Nondisjunction of the Y chromosome during meiosis II in the father
C
Normal segregation of sex chromosomes during meiosis in both parents
D
Nondisjunction of the X chromosomes during meiosis I in the mother
Verified step by step guidance1
Understand that calico fur pattern in cats is linked to X chromosomes and typically seen in females (XX) due to X-inactivation, while males are usually XY and not calico.
Recognize that a calico male must have more than one X chromosome, specifically an XXY karyotype, which is a result of an abnormal number of sex chromosomes.
Identify that nondisjunction is the failure of chromosome pairs to separate properly during meiosis, leading to gametes with abnormal chromosome numbers.
Determine which meiotic error could produce a gamete with two X chromosomes: nondisjunction of the X chromosomes during meiosis I in the mother would cause one egg to have two X chromosomes.
Conclude that fertilization of this abnormal egg (XX) by a normal Y-bearing sperm from the father would result in an XXY male, which can express the calico pattern.
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