AP BIOLOGY

HEREDITY

MULTIPLE ALLELES

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Why is the gene for a disease or disorder more likely to be found on the X chromosome than Y?
A
The X chromosome has many more genes
B
The Y chromosome has many more genes
Explanation: 

Detailed explanation-1: -Not to stir up a battle of the sexes, but the X chromosome (females have two of them, while males have one) is five times larger than the Y chromosome, and has 10 times the number of genes. That means it carries more traits-and diseases-than the Y chromosome.

Detailed explanation-2: -The study shows that essential Y genes are rescued by relocating to other chromosomes, and it identifies a potentially important genetic factor in male infertility. The Y chromosome is dramatically smaller than the X chromosome and has already lost nearly all of the 640 genes it once shared with the X chromosome.

Detailed explanation-3: -X-linked recessive diseases most often occur in males. Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease. The Y chromosome is the other half of the XY gene pair in the male.

Detailed explanation-4: -The X chromosome is about three times larger than the Y chromosome, containing about 900 genes, while the Y chromosome has about 55 genes. Female mammals have two X chromosomes in every cell.

Detailed explanation-5: -When a gene is present on the X chromosome, but not on the Y chromosome, it is said to be X-linked. X-linked genes have different inheritance patterns than genes on non-sex chromosomes (autosomes). That’s because these genes are present in different copy numbers in males and females.

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