Exam 1: Lecture 5 Flashcards
what is the gene that encodes protein TDS
SRY
during which stage we haploid
meiosis/gametes
during which stage are we diploid
fertilization/zygote
heterogametic mean
sex produces 2 different gamete types with 2 different sex chromosomes
T/F: most mammals have 2 sexual phenotypes: m and F
true
when is having 1 sexual phenotype advantageous?
when the environment is stable and no genetic variation is needed
what is the pairing region for in X and Y chromosomes
the X and Y chromosomes pair during meiosis bc small region of shared homology
A male with a recessive mutation on his X chromosome means what
No counterpart on the Y so not able to make working gene so any defective genes on his X they become pseudo dominant and will express (phenotypically)
Y carries no balancing genes so susceptible to defects
hermaphroditism
both sexes in same organism
monoecious
both m and f reproductive structures in the same organism
dioecious
either m or female reproductive structures but not both in 1 organism
XX-XO system:
dosage system. 1 X is the threshold to be a male
ZW-ZZ system:
females are heterogametic
why is the Y seen as a “flip switcher”
default is female but if get an Y, switch is made to male
the pseudoautosomal regions are located where on a chromosome
at the tips
how does the heterogametic sex differ from the homogametic sex
gametes of teh heterogametic sex have different sex chromosomes; gametes of homogametic sex have the same sex chromosome
turner syndrome:
XO
klinefelter syndrom
XXY, XXXY, XXXXY, XXYY
single Y will be male no matter number of Xs
androgen-insensitivity syndrome
caused by defective androgen receptor
where is the SRY gene located on a chromosome
short arm of Y chromosome
y linked characteristics
- only present in males
- all male offspring will exhibit the trait
- Y chromosome lost DNA over time
- sex determination in SRY
x linked characteristics
mutation in a gene of the x chromosome causes phenotype to be expressed in males (hemizygous for the gene mutation)
mary lyon
cell line will have same x chromosome inactivated throughout
mosaicism
different tissues have mom or dad x chromosome active
Xic
x inactivation centers are counted; xist is turned on and its RNA product coats one of X chromosomes
can xic be undone?
yes; during meiosis (recurring cycle in female development)
what are the 2 important recessive x linked disorders?
red-green color blindness and DMD
