3. DNA Variation & Repair Flashcards
SRY Gene
codes for TDF (testis-determining factor) protein, called sex-determining region Y
Testis-determining factor (TDF)
develops male traits, around 6th week of gestation
Are X and Y chromosome homologous pairs?
Yes - even though Y is smaller and has less genes, Y still carries some of the same genes as X and there are sequences similarities throughout the Y, X and Y crossover
Pseudoautosomal regions (PAR1)
regions on X and Y chromosome that can crossover, 5% of Y chromosome but holds about half of all genes
Male-specific region (MSY)
everything on Y chromosome that i snot PAR1 and PAR2, repetitive/palindromic, 30-35% resembles X chromosome
Colorblindness
X-linked recessive
Hemophilia (factor IX disease)
X-linked recessive
Incontinentia pigmenti
X-linked dominant
Rett Syndrome
X-linked dominant, MECP2 gene, controls nerve cell development and expression of other genes
Sex-limited traits
phenotype only expressed in one sex; ovarian vs prostate cancer, heavy vs thin beard, preeclampsia
Sex-influenced traits
phenotype is expressed differently in both sexes; male pattern baldness
X-inactivation
one X chromosome (75%) is inactivated in each cell, leads to mosaicism in females
XIST gene
controls X-inactivation, completely random
Polyploidy
each chromosome set is copied, extremely fatal
Aneuploidy
wrong # of chromosomes, either more or less, could be deletion or addition of parts of a chromosome
Nondisjunction
when chromosomes improperly align during meiosis at any stage and gametes end up with wrong number of chromosomes
Nondisjunction in Meiosis 1 leads to…
all 4 gamete cells have aneuploidy, 2 with no chromosomes, 2 with extra chromosome
if fertilized, 2 are monosomic, 2 are trisomic
Nondisjunction in Meiosis 2 leads to…
2 gametes have aneuploidy, 2 gametes are normal
if fertilized, 2 are normal (euploid), 1 is monosomic, 1 is trisomic
Monosomic
only one pair of a chromosome, form of aneuploidy (-)
Trisomic
extra copy of a chromosome, form of aneuploidy (+)
Euploid
normal # of chromosomes
Chromosome notation
[Total # of chromosomes],[Sex chromosomes],[abnormalities]
Trisomy 21
Down syndrome, extra copy of 21st chromosome, least fatal
- intellectual disability, short neck, flat face
Trisomy 18
Edwards syndrome, extra copy of 18th chromosome, very fatal
- low birth weight, microcephaly, micrognathia, scrunched fists, low-set ears
Trisomy 13
Patau syndrome, extra copy of 13th chromosome, very fatal
- organs developing outside of body, cleft palates, small head
Cri-du-chat syndrome
partial deletion of chromosome 5, mild-severe, mostly males
- cat-like cry, widely spaced eyes, small head, low birth weight
Turner Syndrome (XO)
missing X chromosome (or partial missing X or mosaic) in females
- short, sexually underdeveloped, webbed necks, low set ears
Klinefelter Syndrome (XXY)
affects males, extra X chromosome
- taller than family, low muscle mass, low testosterone, breast development, small genitalia, less facial and body hair
Triple-X Syndrome (XXX)
females have extra X chromosome
- typically taller than average, X inactivation allows normal development
XXYY Syndrome
like Klinefelter, affects males, intellectual/behavioral issues
XYY Syndrome
affects males, taller than average, risk of learning disabilities, developmental delays, and behavioral issues
