Meiosis SL Flashcards
outline the stages of meiosis briefly
Before meiosis, homologous pairs of chromosomes go through DNA replication, producing 2 identical sister chromatids.
Meiosis 1:
Cell divides and homologous pairs of chromosomes are separated
Meiosis 2:
Cells divide again and sister chromatids split, each sister chromatid is now referred to as a chromosome.
What is a bivalent?
A pair of homologous chromosomes.
What is a synapsis?
The pairing process that results in a bivalent
Describe crossing over and when does it happen?
It occurs after synapsis
It is when two non sister chromatids (one chromatid from each of homologous chromosomes) form a “junction”
At this junction they break and rejoin with each other, which allows them to exchange alleles
This leads to formation of chromatids with completely new and different alleles
This also leads to genetic variation in gametes.
What is a chiasma (plural: chiasmata)
It is the “junction” or position in which crossing over happens on 2 non sister chromatids
Explain what random orientation is and how it results in genetic variation in gametes:
During metaphase in meiosis 1, homologous chromosomes line up at the equator preparing to be pulled to different poles.
Each chromosome from a bivalent is pulled towards an opposite pole
The orientation in which the chromosomes are lined up at the equator is completely random
Therefore there are multiple ways these bivalents can line up resulting in multiple possibilities of which chromosomes get pulled to which pole and separated to which gamete
What is disjunction?
The process in which bivalents separate to different chromosomes during meiosis
This reduces the diploid nucleus to a haploid nucles in the daughter cells.
When can non disjunction happen?
Anaphase 1 or anaphase 2
What is non disjunction? What does it result in?
It is when chromosomes fail to separate correctly during mitosis
This can result in an abnormal number of chromosomes
More specifically, can result in an extra copy of a certain chromosome or no copies of a certain chromosome
DONT FORGET TO STUDY DISEASES RELATED TO NON DISJUNCTION AND TRISOMIES
DONT FORGET TO STUDY DISEASES RELATED TO NON DISJUNCTION AND TRISOMIES
