Lecture 5: Sex determination and Linkage Flashcards
Chromosome that determines sex, gene on that chromosome and protein of that gene
Y chromosome
SRY gene
TDF protein
Heterogametic
Sex produces 2 different gamete types with 2 different sex chromosomes
Monoecious
Both male and female reproductive structures in the same organism
Dioecious
Either male or female reproductive structures but not both in one organism
Grasshopper XX-XO system
XX female
XO male
Bird/reptile ZW-ZZ system
ZW female
ZZ male
X chromosome contains
Genetic info for both sexes. At least one copy is required
Pseudoautosomal regions
Regions in X and Y chromosomes that are homologous, essential for X-Y pairing during meiosis
Haplodiploidy system
Haploid set- male
Diploid set- female
Bees, wasps, ants
Turner syndrome genotype
XO
Klinefelter syndrome genotype
XXY or XXXY or XXXXY or XXYY
Turner syndrome features
XO Short stature- most common High arched palate Retrognathia Droopy eyes or lazy eye
Klinefelter syndrome features
Boys May be slightly taller Fatter around the belly Clumsier Slower development of motor skills
What happens if SRY is transferred to X chromosome
Male phenotype
Why is the Y chromosome short
Over time, it has lost DNA due to the lack of crossing over with the X chromosome
XYY syndrome
Male has extra Y chromosome, meaning he has 47 total chromosomes
Many have no appreciable characteristics, some may be taller or lack in intelligence
Dosage compensation
Inactivation of 1 X chromosome to compensate for different X dosage between the sexes
Lyon hypothesis
Suggested that dosage compensation in mammals is by inactivation of all but one X chromosomes in cells with more than one X chromosome.
This is the Barr body
Masaicism
A condition in which cells within the same person have a different genetic makeup
e.g. when different X chromosomes are inactivated in neighboring cells
Xic’s and X inactivation
X inactivation centers
If two or more are counted, Xist is turned on and its RNA product coats one of the X chromosomes- randomly determined
Additional proteins recognize the inactive X and cause condensation and permanent inactivation
This process is undone during meiosis
Common x-linked diseases
Red-green color blindness Hemophilia A Hemophilia B Duchenne/Beckers muscular dystrophy Glucose-6-phosphate dehydrogenase deficiency
Random X inactivation produces
Mosaic
X-inactivation unfavorable skewing
X-inactivation may unfavorable inactivate the WT X chromosome and cause female carriers to present phenotype
