ch 7: sex determination and sex chromosomes Flashcards
(23 cards)
heteromorphic chromosomes
XY
mosaics
somatic cells show two different genetics lines
primary sexual differentiation
only gonads where gametes produced
secondary sexual differentiation
overall phenotype of organism, clear differences in organs like mammary glands and external genitalia
Pseudoautosomal regions (PARs)
share homology with regions on X chromosome-meiosis
Male-specific region of the Y (MSY)
non recombining region of Y, still some homology with X
Sex-determining region Y (SRY)
critical gene controlling male development (includes TDF)
Testis-determining factor (TDF)
transcription factor
heterochromatic
regions lacking genes
Paternal Age Effects (PAE)
paternal age associated with increased risk of congenital disorders with genetic basis
primary sex ratio
proportion of males to females conceived in population
secondary sex ratio
proportion of each sex that is born
-easier to measure, but doesn’t account for the disproportionate embryonic or fetal mortality
dosage compensation
always 2 of all chromosomes, except sex chromosomes, males hemizygous
barr body
-number of inactive X chromosomes
highly condensed structure lies against nuclear envelope of interphase cells and stains positively using DNA dyes
number of Barr bodies
=N-1
(N being the total number of X chromosomes present)
lyon hypothesis
inactivation of X chromosome occurs randomly in somatic cells early in embryonic development
-once inactivation occurs, all descendant cells have same X chromosome inactivated
imprinting
- gene from one parent is expressed while the other parents is silenced
- EX: brown and blue eyed parents with brown eyes child
X-inactivation center (Xic)
major control region on X chromosome, genetic expression occurs only on the chromosome which is inactivated
XIST
-part of Xic that is a long noncoding RNA
-recruits a protein complex that silences transcription at epigenetic level by spreading over and coating X chromosome to be inactivated
hermaphrodite
contains testes and ovaries
-can self-fertilize
-ratio of X to autosome still determines sex
temperature-dependent sex determination (TSD)
sex determined by incubation temperature of eggs during stage of embryonic development
extrachromosomal inheritance
influenced by the parent contributing the most cytoplasm to the embryo
-dont follow typical mendelian patterns
