meiosis (genetics) Flashcards
what is sexual reproduction?
name: meiosis
-> production of gamates (sex cells) and fertilization
what is a gamate?
a sex cell; sperm cells in males and egg cells in females. Haploid.
what is fertilization?
the formation of a zygote by the joining together, or fusion, of two gametes (diploid)
what is a zygote?
a cell produced by the fusion of two gametes
what are somatic cells?
body cells, where mitosis happens
gamates are sex cells, where does it take place?
take places in the ovaries and testes, and sex chromosomes are the 23rd pair of humans
what are autosomes?
other chromosomes that are not sex chromosomes!
meiosis is known as the “power of reduction,” what is it (without saying the process)? (4)
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.
what are the 3 goals of meiosis?
-> reduction in chromosome numbers
-> recombination
-> fertilization
in general, how does fertilization happen?
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.
what are homologus chromosomes?
matching pairs of chromosomes, similar in size and carrying information for the same genes
-> signifying meiosis (stage 1)
what are the stages of meiosis?
interphase (DNA being duplicated)
meiosis 1: (homologus chromosomes are divided) (REDUCTIVE DIVSION, diploid to haploid
meiosis 2 (sister chromatids are being divided)
what happens in prophase 1?
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
What is synapsis?
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
what is a tetrad?
tetrad refers to the homologus pair of chromosomes (2 chromosomes, 4 chromatids)
what happens in metaphase 1?
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!
what is anaphase 1?
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.
what is telophase 1
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
Meiosis 2, known for?
-division of sister chromatids
Gamete formation
DNA does not replicate between meiosis I and II. (NO INTERPHASE)
prophase 2
-> nuclear membrane dissolves
-> spindle fibers form
metaphase 2
-> chromosomes line up on the equator of the cell in a single file line
anaphase 2
-> spindle fibers retract, and the centromeres divide
-> the non-identicle sister chromatids begin to migrate to the poles of the cell
telophase 2
-> nuclear membrane begins to form around the chromosomes
cytokinesis
Cell division is complete. Four haploid and genetically different daughter cells (gametes) produced.
