Lecture 7 - Chromosome Segregation Flashcards
How do you get genes from your parents?
Genes from both parents undergo meiosis and enter daughter cells. These then undergo mitosis
What can happen if you undergo chromosomes mis-segregation in somatic cells?
Cancer
What happens is chromosome mis-segregation happens in female meiosis in human oocytes?
Infertility, miscarriage, birth defects
Mechanism of chromosomes segregation - anatomy of chromosomes - what is the key features?
2 double stranded dna
Mechanism of chromosomes segregation - what is the main attachment site between sister chromatids?
Centromeres
Mechanism of chromosomes segregation - where do spindle fibres attach?
Kinetochores
During mitosis what holds sister chromatids together?
Cohesin
Do all chromosomes need to be attached to both poles? If so, why?
Yes because they cannot separate and therefore will send of wait signals until both poles are attached
What happens if both poles attach correctly to the chromatids
The cohesin is destroyed and the sister chromatids enter anaphase which means they can be pulled apart
What is the structure of cohesin?
4 subunits which form a ring structure to embrace the DNA after dna replication..
What happens to the cohesin in anaphase?
One of the subunits is destroyed by a specific protease during anaphase
When is cohesin established?
During s phase
What is the difference between mitosis and meiosis in terms of cell numbers?
Mitosis - 1x diploid cell creates 2x diploid cells,
Meiosis (two division) - 1x diploid cell makes 4x haploid cells
What is a diploid?
Chromosomes are in a pair - they are identical apart form X and Y in males
What is the difference between homologous chromosomes and sister chromatids?
Homologous - one from mother one from father and made form a pair of sister chromatids = may have a different genetic makeup
Sister chromatids - a duplicate of the same chromatids = identical
What is the main point of mitosis?
To separate sister chromatids into 2 daughter cells.
How does meiosis 1 work?
1x diploid cell = sister chromatids pair with other sister chromatids and swap genetic information. Then the 2 pairs of sister chromatids separate (e.g II and II join IIII then swap genetic information and then split back into II and II
How does meiosis 2 works?
The haploid cells have swapped genetic information and then each daughter cell sister chromatids split and form 4 daughter cells.
E.g. II and II goes to I and I and I and I.
What happens once meiosis is finished?
Two haploid cells form egg and sperm come together to make a diploid zygote
How does meiosis create diversity?
Segregation of homologous chromosomes and recombination between homologous chromosomes
How does Segregation of homologous chromosomes create diversity?
Ignoring recombination any chromosomes can go into any daughter cell with any other chromosome
How does recombination between homologous Chromosomes create diversity?
A chromosomes could have good and bad parts and they could recombine with another chromosomes which has both good and bad parts to make a fully good or a fully bad chromosomes
Meiosis stages - what happens during prophase 1?
Recombine homologous chromosomes - exchange of genes and crossing over occurs here
In prophase 1 what is the synaptonemal complex?
This stabilises homologous chromosomes pairings=ands promote recombination. It contains a recombination nodule
What are the 5 stages of prophase 1 and their morphology of SC?
Leptotene - SC starts forming
Zygotene
Pachytene - SC fully formed
Diplotene - SC disassembled
Diakinesis - chromosomes condense
What happens after the chromosomes has condensed in prophase 1?
They attaché it poles - sister kinetochores attach to the same pole
What holds homologous chromosomes together (not sister chromatids)?
Chiasmata
In meiosis 1 what cohesin is kept?
The ones at the centromeres so the sister chromatids will stay together even when the homologous pair it was exchanging DNA with goes away
What happens to make the cohesin holding the sister chromatids go away?
Kinetochores attach to opposite poles
The difference between meiosis 1 and meiosis II sister Kinetochores?
At 1 Kinetochores attach to same pole at 2 they attach to different poles
The difference between meiosis 1 and meiosis II cohesin at centromeres?
1 - protected and during 2 is destroyed
