Intro to Cytogenetics Flashcards
What is the most important phase of mitosis in cytogenetics?
metaphase
What are the two critical phases in meiosis?
- recombination which occurs in prophase I
- reduction division (anaphase I)
what is reduction division?
reduction by 1/2 of the original number of chromosomes
what is crossover?
exchange between homologous chromosomes resulting in a reassortment of the genes/alleles present on each chromosome
During meiosis II how many chromosomes does each daughter cell get? are there pairs?
23; no
What is the net result of nondisjunction that occurs in meiosis I and not in meiosis II?
4 cells with a chromosomal imbalance
-2 disomic gametes and 2 nullsomic gametes
What is nullsomic?
cells that are missing chromosomes
gametogenesis (includes spermatogenesis and oogenesis ) are a combination of
mitosis and meiosis
How many functional gametes are produced at the end of spermatogenesis?
primary germ cells–>spermatocytes via mitosis
4 per spermatocyte
How many functional gametes are produced at the end of oogenesis?
primary germ cells–>oocytes via mitosis
1 per oogonia
Why don’t oocytes become ovum until ovulation?
primary oocytes are formed by 3rd month of gestation, reach prophase I and pause until ovulation
Why is there only one functional oocyte formed?
at the completion of meiosis I, two daughter cells are produced one secondary oocyte and one polar body
after meiosis 2, you get one ovum and one polar body
What is the difference between a secondary oocyte and a polar body?
secondary oocyte received most of the cytoplasm and will go on to become an ovum
polar body didn’t get much cytoplasm and will go on to degenerate or produce 2 more polar bodies
When is meiosis completed in the female?
during fertilization
What prompts the fusion of the male and female pronuclei?
penetration of sperm head and release of second polar body
Describe the differences in the frequency of gamete production in males and females.
Males: primary spermatocytes produced throughout life; gametes produced continuously
4 equal gametes per gametocyte
females: all primary oocytes present at birth
gametes made once a month
1 gamete per gametocyte
Which sex is homogametic and which is heterogametic?
females; males
What is the TDF?
testis determining factor
What is SRY
sex determining region og Y
What is the pseudoautosomal region of Y?
region on the short arms of the X and Y chromosomes that engages in recombination
What is the default sexual development? what triggers it?
female; absence of TDF/SRY
What does presence of TDF/SRY do?
leads to differentiation of gametocytes to testes and inhibition of Mullerian ducts–>degeneration of Mullerian ducts
proliferation of Wolffian ducts
Are the protein produced by TDF initiates the male developmental pathway the only factors determining sex?
No
Is it possible to have functional TDF/SRY with a female genotype?
yes; there are also males with XX and females with XY;
