Meiosis in eukaryotic cell division

Question 1

How do single celled organisms reproduce?

Answer 1

Through binary fission e.g. Amoeba, yeasts, algae

Question 2

What amount of chromosomes are present in the daughter cells?

Answer 2

Haploid gametes produce diploid zygote - then go through mitosis to grow.

Question 3

What would happen if gametes were produced by mitosis?

Answer 3

They would be 2n resulting embryos would be 4n. Need a process of cell division that halves number of chromosomes going into gametes (n), so that diploid number (2n) is retained in zygote.

Question 4

What is meiosis 1?

Answer 4

Homologous chromosomes seperate, results in haploid cells with duplicated chromosomes.

Question 5

What happens in prophase 1?

Answer 5

• Chromosomes appear already duplicated as sister chromatids (Centromere are attaching sister chromatids)
• Homologous chromosomes line up at the chiasmata to recombinant. Don’t “ignore” reach other like in mitosis.
• Spindles of microtubules grow out from the centrosome (each of which have a pair of centrioles)
• Crossing over is more likely to occur in some spots on the chromosome rather than others. Less likely in the region of the centromere, more likely at the ends.

Question 6

What happens in metaphase 1?

Answer 6

• Chromosomes line up on the metaphase plates (pairs of homologous stay together)
• Connected by kinetochore that are at the centromere, which connect to kinetochore microtubules
• Chiasmata on the metaphase plate

Question 7

What happens in anaphase 1?

Answer 7

• Homologous chromosomes separate (sister chromatids remain attached)
• New combinations of chromosomes at each side because of recombination in prophase 1
• The kinetochore microtubules rip these chromosomes apart (by shortening)

Question 8

Telophase 1 and cytokinesis?

Answer 8

• The cleavage furrow forms and the cells starts to duplicate
• Spindle starts to disintegrate
• Complete separation of the cytoplasm and the formation of new plasma membrane in cytokinesis.

Question 9

How is meiosis different from mitosis?

Answer 9

As it separates homologous chromosomes, not sister chromatids. It also does crossing over, whereby bits of homologous chromosomes are shuffled around.

Question 10

What happens in meiosis 2?

Answer 10

Sister chromatids separate, results in haploid cells will unduplicated chromosomes (end up with four daughter cells). A parallel of mitosis (start of with haploid cells and end up with haploid cells)

Question 11

What happens in prophase 2?

Answer 11

• The centrosomes with there centrioles forming a spindle apparatus (occurring in both daughter cells)

Question 12

What happens in metaphase 2?

Answer 12

Chromosomes line up on the metaphase plate (line up by their centromeres like in mitosis) kinetochore microtubules that connect through kinetochore to the centromere and non-kinetochore microtubules that don’t connect to any sister chromosomes.

Question 13

What happens in anaphase 2?

Answer 13

Sister chromatids are ripped apart at the centromere by the kinetochore microtubules and lengthening of non-kinetochore microtubules.

Question 14

What happens in telophase 2?

Answer 14

Cleavage furrow forming. Spindle disintegrated and and formation of new nuclear envelope that contains the chromosomes.

Question 15

What are the six differences between mitosis and meiosis?

Answer 15

• Chromosomes align independently vs homologous chromosomes synapse
• No chiasmata vs chiasma (form chiasmata that allows for crossing over)
• Centromeres in metaphase plate vs chiasmata on metaphase plate
• Chromatids disjoin vs chromosomes disjoin
• 2n –> 2v vs 2n –> n
• The evolutionary enigma of sexual reproduction

Question 16

What does sexual reproduction produce genetic diversity through?

Answer 16

1. Spatially variable environments e.g. climate, ecology
2. Changing environments e.g. parasites, seasons
3. Sib-Sib competition (offspring in the next generation will be competing for the same resources and thee genetically identical offspring will experience more severe competition that sexual siblings because the latter will be genetically different and will not utalize resources in identical manners)