Sex Chromosomes & Sex Linkage Flashcards
not every organism has ____
sex chromosomes or even separate sexes
monoecious
in many plants and animals, every individual is both male and female
1 individual makes both male and female gametes
dioecious
organisms where there are separate males and females
all vertebrates are …
dioecious
in lower vertebrates however, males and females are not high differentiated
if sexes are not highly differentiated, then
there may be no special sex chromosomes
species with highly differentiated sexes also have differentiated _____
sex chromosomes
sex in humans is typical of …
placental mammals, in its biology, genetics, and cytogenetics
XX makes
females
XY makes
males
nonsex chromosomes are called
autosomes
humans have __ pairs of autosomes and __ pair of
autosomes, sex chromosomes (either XX or XY)
the X is …
big and metacentric
centromere near the middle
the Y is …
small and acrocentric
centromere very close to the end
X and Y act as a …
pair of homologs
even though they look different
what happens to X and Y in meiosis?
form a bivalent but only at the tips
psuedo-autosomal regions
Y pairs with X only in these regions on the tips
non-recombining region
male-specific region
located between the tips of the Y chromosome
do X chromosomes in the female recombine with each other?
yes, just like a normal pair of autosomes
they make a “normal” bivalent where recombination can happen anywhere along the length
chromosomal sex determination ensures..
equal numbers of males and females
SRY gene
found only on the Y chromosome on the short arm
near the end of the non-recombining region of Y
responsible for initiating male development
TDF
testis-determining factor
SRY makes
TDF protein
in the presence of TDF….
the testis-determining facror turns gonads into testes instead of ovaries
is SRY a dominant gene?
yes, only one copy makes you male
is SRY a pleitropic gene?
yes, it has multiple effects
testes make…
testosterone and other androgens
all are male sec hormones
male sec hormones cause…
the body’s organs to develop male characteristics
androgen insensitivity syndrome
AIS
no receptors for androgens
sex-limited traits
secondary sex characteristics
sex-limited traits include all…
of the typical physical differences between men and women
sec limited traits can be produced…
in either sex, just by male or female hormones acting during development
the signal for sex-limited traits to develop comes from…
steroid hormone balances
the genes that control the growth of sex-limited traits are …
distributed all over the chromosomes
sex-linked traits are caused…
by genes of the sex chromosomes
genes on the X chromosome
more than 1000
random set of genes for varied functions
similar to a typical autosome
the human Y has…
150-200 transcription units (majority not protein-coding)
codes for 30 different proteins
11 function in the testes (all in male-specific region)
hemizygous
situations where a diploid has only one allele for a gene
due to a deletion of one homolog, for example
males are hemizygous for …
most of the genes of the X chromosome
they only have 1 copy
exceptions to hemizygous males
small number of genes in psudo-autosomal regions have 2 copies
males get …
all the recessive genetic disorders on the X is they inherit only one recessive allele
sex linked genetic disorders
about 100 X-linked diseases
most are recessive due to alleles on X-chromosome genes
almost all occur in males
males can only get an X from…
their mothers
males can only pass an X to their…
daughters
sons cannot get an x-linked disease from…
their fathers
sons can only get an x-linked disease from…
their mothers
