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
What are the consequences of aneuploidy in autosomes?
-nullisomy (missing 1 pair) = pre-implantation lethal
-monosomy (missing 1 chromosome) = embryonically lethal
-trisomy (1 extra chromosome) = usually lethal but some exceptions
What are the consequences of aneuploidy in sex chromosomes?
-additional sex chromosome = minor problems but relatively normal lifespan
-lacking a sex chromosome: x chromosome = 99% abort, rest normal but infertile
y chromosome = not viable
When do structural rearrangements of DNA occur and what else can it be caused by?
-occur when homologous recombination happens
-can be caused by DNA-damage induced homologous recombination - any time when cell is dividing
