Mitosis and Meiosis Flashcards
What are sister chromatids?
Chromatids that are found on the same chromosome joined by the centromere.
Where can the telomeres be found?
On the end of the chromatids.
How can you distinguish the p-arm from the q-arm?
The p-arm is usually shorter than the q-arm.
What is the purpose of telomeres?
To protect the chromosome.
What is the purpose of the centromere?
To link the sister chromatids.
What types of centromeric placement is there?
Metacentric
Submetacentric
Acrocentric
Telocentric
In the M-phase there are different subphases in the cell cycle. Which?
Prophase Prometaphase Metaphase Anaphase Telophase and Cytokinesis
What happens in prophase?
Solenoids and therefore chromosomes condense even more. The nuclear membrane also breaks down.
Spindle fibres appear.
What happens in pro metaphase?
The spindle fibres attach to the chromosomes.
What happens in metaphase?
The chromosomes are lining up randomly in the middle of the cell. The randomness is important here. Homologous chromosomes do not line up.
What happens in anaphase?
The kinetochore fibres or spindle fibres pull the sister chromatids to opposite poles as the centromeres divide.
One sister chromatid is now a chromosome.
What happens in telophase?
The spindle fibres disappear.
The nuclear membrane starts to form again and the chromosomes decondense.
What happens in cytokinesis?
The cytoplasm divides and 1 cell become two new cells.
How many chromosomes and chromatids can be found in a mother cell in prophase?
46 chromosomes and 92 chromatids.
How many chromosomes and chromatids can be found in a newly made daughter cell who has just been formed from mitosis?
46 chromosomes and 46 chromatids.
What are homologous chromosomes?
Chromosomes that have the same DNA sequence and therefore the same genes.
Can homologous chromosomes differ?
Yes the genes on the homologous chromosomes may be of different variants called alleles.
How do sister chromatids differ to homologous chromosomes?
Sister chromatids have identical DNA with the same alleles.
How do sister chromatids differ to non-sister chromatids?
They have the same genes but may have differently alleles.
What is the product of meiosis?
Four non-identical cells with half chromosome content of parental cell. 1 diploid (2n) goes to 4 haploid (n).
What different phases can be found in meoisis 1?
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
What happens in prophase 1?
Spindle fibres appears
Chromosomes condense
Homologous pairs find each other
What happens in metaphase 1?
Homologous chromosomes align at the middle by random. This means that the paternal chromosome of one homologous chromosome pair might be pulled to the left, whereas the paternal chromosome of another homologous chromosome pair might be pulled to the right. This contributes to genetic diversity.
Something else happens in metaphase 1 which is special for just meoisis. What?
Recombination where crossing over where there are maternal and paternal crossovers. This is where the homologous pair ‘switches’ parts of the genes on the chromatids resulting in newly formed chromatids. This contributes to genetic diversity.
What happens in anaphase 1?
The homologous pairs are separated and move to different poles.
What happens in telophase 1?
The chromosomes decondense. The nuclear membrane reforms. The spindle fibres disappear and the cell is ready to divide.
Two new daughter cells are formed. How many chromosomes can be found in each of them?
23 chromosomes in each. (n) haploid
How many chromatids can be found in each of them?
46 chromatids in each.
What happens in prophase 2?
Nuclear membrane disappears
Spindle fibres appear
Chromosomes condense
What happens in metaphase 2?
The chromosomes align. (No more homologous chromosomes!)
Here crossing over also occur.
What happens in anaphase 2?
This is is similar to in mitosis anaphase where the sister chromatids separate and are pulled to opposite poles.
What happens in telophase 2?
Chromosomes decondense
Nuclear membrane reappears
Spindle fibres disappear and cells are ready to divide.
Forming 4 new cells.
Four daughter cells have now been formed. How many chromosomes can be found in each of them?
23 chromosomes (n) haploid.
How many chromatids can be found in each of them?
23 chromatids.
So briefly what happens in meiosis 1?
Homologous pairs of chromosomes line up and separate.
Briefly what happens in meiosis 2?
Chromosomes line up (not homologous) and chromatids separate.
What phenomenons in meiosis 1 and 2 contribute to genetic diversity?
Random assortment of chromosomes (how they line up in metaphase)
Crossing over
How long does spermatogenesis take?
60 days
What are the products of meiosis from an oocyte?
1 egg and 3 polar bodies.
What is nondisjunction?
When in anaphase 2 if two sister chromatids do not separate and two sister chromatids instead go to the same pole. This results in 24 chromosomes in one daughter cell and 22 in the other one.
What is aneuploidy?
When a human has 47 chromosomes instead of 46.
Or if one has 45 chromosomes instead of 46.
When does mitotic nondisjunction occur?
When the first mitotic division of the zygote occurs. (Post zygotic division). This leads to non-mosaic karyotype.
What happens if mitotic nondisjunction would occur later in cell division?
You would have two cell lines. Some that are normal 46, N and some that are aneuploidy. This leads to a mosaic karyotype.
What is mosaicism?
The presence of two or more cell lines in an individual.
This can be throughout the body or tissue limited.
What does the degree or severity of the mosaicism depend on?
When it happens in mitotic division. Early in preembryogensis or later.
What is the risk of aneuploidy if nondisjunction happens in meiosis 1?
100%
50 % of trisomy
50% of monosomy
What happens if nondisjunction happens in meiosis 2? What is the risk of aneuploidy then?
50% risk
25% of trisomy
25% of monosomy.
