Sex Chromosomes

Question 1

almost ____ of the genes in the X chromosome have counterparts in the Y chromosome

Answer 1

none

Question 2

the ____ of the arms of the X and Y chromosomes share a small region of homology

Answer 2

tips (telomeres)

Question 3

_____ recessive alleles are expressed in males

Answer 3

X-linked recessive alleles

Question 4

why are X-linked recessive alleles expressed in males

Answer 4

because they only have one X chromosome

Question 5

why is an X mutation seen in the males phenotype

Answer 5

because Y does not carry an allele of this gene

Question 6

Who can a father pass his X chromosome to?

Answer 6

ONLY his daughters; his sons get their X from the mother. must skip a generation

Question 7

meiosis in a female results in ____ eggs only

Answer 7

X-bearing

Question 8

Meiosis in a male results in a _____ ratio of X-bearing and Y-bearing sperm

Answer 8

1-1

Question 9

What is the expected ratio from random fertilization

Answer 9

1-1

Question 10

describe the heterozygous cross between a female carrier and a normal male

Answer 10

among progeny from a heterozygous carrier, half of the daughters and half the sons are expected to be affected

Question 11

describe the affected X-chromosome in male and his progeny.

Answer 11

his X-chromosome MUST and ONLY get passes to his daughter.
-among progeny from a normal female and an affected male, all of the daughters are expected yo be heterozygous carriers and all of the sons are expected to be normal.

Question 12

pedigree characteristics of autosomal recessive, autumnal dominant, X-linked recessive, X-linked dominant, and Y-linked traits??

Answer 12

• usually more males than females are effected
• affected sons are usually born to unaffected mothers
• approx half of a carrier mother’s sons are affected
• never passes from father to son
• all daughters of affected fathers are carriers