Lecture 7

Question 1

determine if X, Y or autosome

Answer 1

Reciprocal cross
Cross 1: affected female x normal male
all females carriers but heteroz, all males affected
Cross 2: normal female x affected male
all offspring normal b/c males get mothers X
If same outcome for both crosses, autosomal
If different outcomes for the crosses, sex linked

Question 2

ZW traits

Answer 2

father –> daughter

Question 3

X inactivation

Answer 3

• No matter how many X chromosomes were present, only one active and the other barr bodies
• Occurs randomly in each gene (maternal or paternal) - some mutant, some not = x linked mosaic (sweat glands present or absent)
• After early embryonic development (makes it different to Turner’s syndrome)
• Once off, stays off but reverses in the oocytes (not a change in the DNA)

Question 4

XIST (X inactivation specific transcript) what is it?

Answer 4

a gene locus on the X which is only transcribed from the INACTIVATED X - produces interference RNA (heterochromatin). It is cis acting - only has an effect on the chromosome from which it is produced.

Question 5

Sex influenced traits

Answer 5

the phenotypic expression of the trait is influence by the sex of the individual (eg. pattern baldness: in females the dominant trait is not baldness))

Question 6

Sex limited traits

Answer 6

phenotype limited to one sex but can be passed to offspring by either sex (eg. precocious puberty, daughters wont express it)