meiosis (genetics)

Question 1

what is sexual reproduction?

Answer 1

name: meiosis

-> production of gamates (sex cells) and fertilization

Question 2

what is a gamate?

Answer 2

a sex cell; sperm cells in males and egg cells in females. Haploid.

Question 3

what is fertilization?

Answer 3

the formation of a zygote by the joining together, or fusion, of two gametes (diploid)

Question 4

what is a zygote?

Answer 4

a cell produced by the fusion of two gametes

Question 5

what are somatic cells?

Answer 5

body cells, where mitosis happens

Question 6

gamates are sex cells, where does it take place?

Answer 6

take places in the ovaries and testes, and sex chromosomes are the 23rd pair of humans

Question 7

what are autosomes?

Answer 7

other chromosomes that are not sex chromosomes!

Question 8

meiosis is known as the “power of reduction,” what is it (without saying the process)? (4)

Answer 8

2-stage cell division

resulting daughter cells (gametes or spores) have half the number of chromosomes (haploids)

formation of gametes is called gametogenesis.

takes place in the testes and ovaries.

Question 9

what are the 3 goals of meiosis?

Answer 9

-> reduction in chromosome numbers
-> recombination
-> fertilization

Question 10

in general, how does fertilization happen?

Answer 10

haploid sperm cell (n=23) unites with haploid egg cell (n=23) to form a diploid zygote (2n = 46). Zygote then begins to grow, divide (mitosis), specialize, and mature.

Question 11

what are homologus chromosomes?

Answer 11

matching pairs of chromosomes, similar in size and carrying information for the same genes

-> signifying meiosis (stage 1)

Question 12

what are the stages of meiosis?

Answer 12

interphase (DNA being duplicated)

meiosis 1: (homologus chromosomes are divided) (REDUCTIVE DIVSION, diploid to haploid

meiosis 2 (sister chromatids are being divided)

Question 13

what happens in prophase 1?

Answer 13

chromosomes shorten and thicken.

replicated chromosome (during interphase) joins the original at the centromere (2 sister chromatids, 1 chromosomes)

nuclear membrane begins to dissolve

centrioles separate and move to opposite poles of the cell

spindle fibres form.

SYNAPSIS AND CROSSING OVER OCCURS

Question 14

What is synapsis?

Answer 14

physically intertwining chromosomes

-> homologus chromosomes turn into a tetrad, and each sister chromosome interwines with another (from its matching homologus chromosome)

-> crossing over then takes place, where a piece of the chromosome breaks off and reattaches to the other chromosome (between 2 non sister chromatids, in a homologus pair)

-> increase of genetic diversity/the mix of genetic information

Question 15

what is a tetrad?

Answer 15

tetrad refers to the homologus pair of chromosomes (2 chromosomes, 4 chromatids)

Question 16

what happens in metaphase 1?

Answer 16

tetrads (pairs of homologous chromosomes) migrate toward the centre of the cell

align their centromeres across the middle of the cell.

-> NOT IN A SINGLE FILE LINE, but next to each other!

Question 17

what is anaphase 1?

Answer 17

homologous chromosomes move to opposite poles of the cell. (they split a part, so one chromosome on one side, and the other on the other side)

reduction division occurs (because now its 2 cells, with half the amount of chrosomes)

Each chromosome in the new cells consists of two sister chromatids.

Question 18

what is telophase 1

Answer 18

nuclear membranes begin to form around the chromosomes at each end of the cell
cell begins to divide

Chromosomes in the two nuclei are not identical (because of the crossing over)

Each daughter nucleus receives only one member of each original chromosome pair (started with 46 chromosomes, now you only have 26)
.
Cells are now haploid - ready to begin the second stage of meiosis

Question 19

Meiosis 2, known for?

Answer 19

-division of sister chromatids

Gamete formation

DNA does not replicate between meiosis I and II. (NO INTERPHASE)

Question 20

prophase 2

Answer 20

-> nuclear membrane dissolves
-> spindle fibers form

Question 21

metaphase 2

Answer 21

-> chromosomes line up on the equator of the cell in a single file line

Question 22

anaphase 2

Answer 22

-> spindle fibers retract, and the centromeres divide
-> the non-identicle sister chromatids begin to migrate to the poles of the cell

Question 23

telophase 2

Answer 23

-> nuclear membrane begins to form around the chromosomes

Question 24

cytokinesis

Answer 24

Cell division is complete. Four haploid and genetically different daughter cells (gametes) produced.