Meiosis Flashcards
Semester 1 year 1
What happens in meiosis I?
-centrioles + chromosomes are replicated
-maternal + paternal homologues pair up
-chromosomes line up side by side
-1 complete chromosome (2 chromatids) pulled to separate poles
What is generated in meiosis I and how?
-genetic diversity
-recombination between homologous chromosomes
What happens during meiotic prophase I?
-homologues pair up
-pairing facilitated by synaptonemal complex + DNA base pairing between homologues
-forms a bivalence
What is the purpose of meiosis prophase I?
-aligns chromosomes ready for anaphase + forms synaptonemal complex
-allows genetic recombination between paternal + maternal DNA on same chromosome
When does crossing over occur?
When homologues pair up
What happens in meiosis II?
-the same as mitosis
-main difference = cells in meiosis II are haploid instead of diploid
What is the fundamental difference between meiosis and mitosis?
-mitosis = sister chromatids separate
-meiosis = homologous chromosomes separate in anaphase
What allows the difference between meiosis and mitosis?
-both kinetochores on 1 chromosome attach to the same spindle in meiosis
-avoided in mitosis
-this is done by a protein complex that’s removed after meiosis I
How many crossing overs occur per bivalent?
At least 1 but no more than 4
Where do crossing overs occur and what does the formation of a crossing over limit?
-form in DS breaks - breaks tend to form in open chromatin
-it limits more forming around it - crossover interference
What are the 2 categories of chromosome abnormalities?
-abnormalities in chromosome number
-chromosome structural rearrangements
What are the 2 types of aneuploidy?
-monosomy = 1 copy of a chromosome
-trisomy = 2 copies of chromosome
What is polyploidy?
Whole extra sets of chromosomes
What causes disorders of chromosome number?
-chromosome non-disjunction
-homologous chromosomes or sister chromosomes fail to separate in meiosis I, meiosis II or mitosis
What is the consequence of polyploidy?
Embryonically lethal
