Multiple Choice
In a cross between a homozygous normal female (XX) and a male affected by an X-linked recessive disorder (X^aY), why are there no affected females in the F1 generation?
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2. Mendel's Laws of Inheritance
Sex-Linked Genes
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In a sex-linked pedigree, if females are labeled as 'XX', how should males be labeled?
A
XXY
B
XY
C
XO
D
YY
Verified step by step guidance1
Understand that in humans, sex chromosomes determine biological sex: females typically have two X chromosomes (XX), and males have one X and one Y chromosome (XY).
Recognize that the problem states females are labeled as 'XX', which is the standard notation for female sex chromosomes.
Recall that males have one X chromosome and one Y chromosome, so the correct label for males in a sex-linked pedigree is 'XY'.
Note that 'XXY' represents a different condition (Klinefelter syndrome), 'XO' represents Turner syndrome, and 'YY' is not a viable chromosomal combination in humans.
Therefore, when labeling males in a sex-linked pedigree where females are 'XX', the correct and standard label for males is 'XY'.
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