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Bios205-Exam 3
Sex-Linked Traits and Inheritance
9
Biology
Undergraduate 2
06/02/2009

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Term
Approx how many genes are on the X-Chromosome?
Definition
1150 genes (with diverse functions, most unrelated to sex determination)
Term
X-LINKED TRAITS
Definition
traits coded for by genes on the x-chromosome. x-linked traits use a superscripts to represent alleles (X^A=dominant, X^a=recessive)
Term
T/F- Most genes on the x chromosome are expressed in males
Definition
True. Males only receive one x chromosome so most genest on that chromosome are expressed.
Term
Hemizygous
Definition
EVERY gene is expressed!! whether dominant or recessive-- happens in males because only have one x chromosome.
Term
T/F- abnormal alleles are more often expressed in males than females
Definition
True. Because males have only one x chromosome, they express ALL genes--including recessive and abnormal alleles.
Term
Examples of Sex-Linked Disorders occurring more frequently in males:
Definition
Muscular Dystrophy, hemophilia, color blindness, fragile X-syndrome, kinky hair syndrome
Term
X-INACTIVATION
Definition
each autosomal cell in the female has one x-chromosome inactivated--controlled by a gene on the x-chromosome called "Xist". Inactivated X shows up as a "barr body" in cells.
Term
T/F- X-inactivation may increase Autoimmune Diseases in women.
Definition
True. Women havea higher incidence of most autoimmune diseases due to immune cell reaction to x-inactivation
Term
Is there any parental influence over which x-chromosome is inactivated?
Definition
Yes. The influence is outside the gene, during early development, and is called IMPRINTING.
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