Gamete Formation & Nondijunction Flashcards
What is gametogenesis?
Gamete (sex cell formation)
- formed from germ cells
- specializes into either sperm or eggs
Spermatogenesis
Sperm formation
Oogensis
Egg formation (ovum formatjon)
What are the names for various steps in soermatogensis?
- Diploid spermatogonia (og germ/parent cell)
- Primary spermatocyte (halfway through meiosis)
- 4 spermatoids (end result. They are undifferentiated sperm cells)
How do you calculate the number of possible pairings during independent assortment, according to the number of chromosomes?
2^n
What are the names of the steps during oogenesis?
- Diploid oogonia (og germ/parent cell)
- Primary oocyte (halfway through meiosis)
- 1 ova , 3 polar bodies
What type of cell undergoes meiosis
Germ cell
What is the name for an egg
Ova. Ovum plrl
What are polar bodies? What happens to them?
3 polar bodies are made during meiosis. They have nothing but a nucleus, because all the organelles went to the egg - they quickly get recycled.
When does meiosis end/ when does an undifferentiated egg cell become an egg?
Right before it becomes a zygote.
What is nondisjunction?
Mistake that occurs during meiosis. Chromosomes don’t properly split, resulting in an abnormal number of chromosomes (aneuploidy - happens in autosomes or sex cells)
Aneuploidy
Abnormal number of chromosomes
Either 45 or 47
Trisonomy
Extra chromosome that occurs due to nondisjunction (chromosome doesnt split properly)
Monosomy
Lack of a chromosome in an unfertilized cell, due to non disjunction. Very fatal due to the lack of genetic information
What are the two categories for nondisjunction?
- Failure to split homologous chromosomes, occurs during meiosis 1
- the result is that all of the gametes are irregular - Failure to split sister chromatids, occurs in meiosis 2
- results in half the gametes being irregular (often occurs in females over 35)
Result of nondisjunction disorder
Results in a lot of human genetic disorders, cells arnt able to function properly.
Changes physical appearance as well as mental challenges.
(Cases of monosomy are usually fatal)
Ex. Down syndrom- extra chromosome 21 (3 instead of 2)
Amniocentesis
Diagnosing fetus by pushing a needle into the moms stomach to get a sample of DNA. Could cause a miscarriage
Chorionic villus
Tests fetuses DNA through the vagina. Could cause a miscarriage
Why are women over 35 more at risk to have children with genetic complications
Girls start meiosis when they’re in the womb, so they create a limited amount of cells that will turn to eggs (stops at pro phase 1)
Meiosis then continues after puberty, but there still remains a set number of eggs.
As the women ages, so does the organelles, allowing for more complications.
Deletion (abnormal chromosome disorder)
Lose an allele/section of the chromosome when crossing. Could be very fatal.
ABCDEFG - ABDEFG
Duplication (abnormal chromosome structure)
Sequence reattached to an already complete chromosome
Inversion (abnormal chromosome structure)
Segment rematches in the wrong order during cross over
ABCDEFG - ABCGFED
Translation (abnormal chromosome structure)
Crossing over happens between pairs of chromosome that arnt homologous
