Meiosis

Question 1

Meiosis def

Answer 1

Type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes.

Question 2

Similarities and differences between meiosis and mitosis

Answer 2

Both begin after the cell has progressed through the G1, S, and G2 phases of the cell cycle. Both have the same phases, prophase, metaphase, anaphase and telophase.
Meisiosis involves two divisions, meiosis 1 (two cells with n) and meiosis 2 (4 cells with n) and mitosis only has one.

Question 3

Stages of prophase 1

Answer 3

1. Leptotene- chromosomes contract, visible
2. Zygotene- chromosomes condense, homologous pairs pair up and begin synopsis.tetrad
3. Pachytene- chromosomes become shorter and thicker synaptomal complex develops
4. Diplotene- centromeres of the paired chromosomes move apart. Homologous pairs remain attached at chias,tats. Result of crossing over
5. Diakinesis- synaptonemal complex completely disappears

Question 4

Metaphase 1 def

Answer 4

Homologous pairs of chromosomes align along the metaphase plate. Microtubule from each pole attach to each chromosome of the homologous pair.

Question 5

Anaphase 1

Answer 5

Separation of homologous chromosomes. The two chromosomes of a pair are pulled toward opposite poles . Sister chromatids remain attached and travel together.

Question 6

Telophase 1 def

Answer 6

The chromosomes arrive at the spindle poles and cytoplasm divides

Question 7

Interkinesis def

Answer 7

Period between meiosis 1 and 2 where the nuclear membrane reforms around the chromosome clustered at each pole, the spindle breaks down and the chromosomes relax

Question 8

Prophase 2 def

Answer 8

Events of interkinesis are reversed: chromosomes recondense, spindle reforms and nuclear envelope breaks down.

Question 9

Metaphase 2

Answer 9

The individual chromosomes line up on the metaphase plate, with sister chromatids facing opposite poles.

Question 10

Anaphase 2 def

Answer 10

The kinetochores of the sister chromatids separate and are pulled apart to opposite poles. Each chromatid is now a distinct chromosome.

Question 11

Telophase 2 def

Answer 11

The chromosomes arrive at the spindle poles, nuclear envelope reforms, cytoplasm divides and chromosomes relax, no longer visible.

Question 12

Sources of genetic variation in meiosis

Answer 12

Each original cell produces four cells.
Chromosomes number is reduced by half
Cells produces are genetically different from one another and from parent cell.
Genetic differences result from crossing over and random separation of homologous chromosomes.

Question 13

Crossing over def

Answer 13

Crossing over takes place in prophase 1, Initiated in zygotene. Refers to the exchange of genetic material between two non sister chromatids. Crossing over is the basis for intrachromosomal recombination, creating new combinations of alleles on a chromatid.

Question 14

Random separation of homologous chromosomes def

Answer 14

Occurs during anaphase 1 after their random alignment in metaphase 1. When the chromosomes pairs separate in anaphase, the separation is random and many different outcomes are possible.
Shuffles alleles on different chromosomes into new combinations.

Question 15

Spermatogenesis def

Answer 15

The production in a male animal takes place in the testes.

Question 16

Spermatagonia def

Answer 16

Diploid cells produced by spermatogenesis

Question 17

Primary spermatocyte def

Answer 17

Spermatagonium entered into prophase 1, diploid because the homologous pairs have not yet separated. Each primary spermatocyte completes meiosis 1, giving rise to two haploid secondary coermatocytes that undergo meiosis 2, producing two haploid spermatids.

Question 18

Spermatids def

Answer 18

Formed after meiosis 2. Haploid, 4 produces, mature and develop into sperm.

Question 19

Oogenesis def

Answer 19

Production of female gametes in animals. Takes place in ovaries.

Question 20

Oogonia

Answer 20

Diploid primordial germ cells divide mitotically to produce oogonia.

Question 21

Primary oocytes

Answer 21

Diploid cells in prophase 1. Each primary oocyte completes meiosis 1 and divides.

Question 22

Secondary oocyte def

Answer 22

Haploid cell. Most of the cytoplasm is allocated in one of the two haploid cells- the secondary oocyte.

Question 23

First polar body def

Answer 23

The smaller cell, haploid but only contains a small part of the cytoplasm. May not divide further.

Question 24

Ovum def

Answer 24

Meiosis 2 occurs and again cytokinesis is unequal resulting in a larger cell- ovum. The ,ature female gamete.

Question 25

Second polar body def

Answer 25

Smaller cell. Only a small amount of cytoplasm, the rest went to the ovum.