Meiosis Flashcards
what is meiosis
nuclear cell division which produces gamete cell
what are the two important functions of meiosis
results in a haploid nuclei which is necessary to maintain the diploid number of chromosomes after fertilisation
creates genetic variation among offspring
what is the process of meiosis (before, meiosis I, meiosis II)
Before meiosis -
PROPHASE
starts with primary oocyte or spermatocyte (2n = 46 chromosomes, diploid)
DNA then replicates in testes or ovaries and its DNA becomes 92 chromatids/two sister chromatids (2n x 2).
Meiosis I-
stages are:
METAPHASE - 92 chromatids align in the middle of the cell
ANAPHASE - chromosomes are pulled a part by spindle fibres at their centromeres
TELOPHASE - two cells with 46 chromatids in each of them is formed
Meiosis II-
stages are:
METAPHASE - 46 sister chromatids align in the middle of each of the cells
ANAPHASE - chromosomes are pulled a part by spindle fibres at their centromeres
TELOPHASE - four cells with 23 chromatids in each of them is formed (four haploid daughter cells produces)
what are the two types of genetic variation
crossing over
independent assortment
what is crossing over, when does it occur and how does it give rise to genetic variation
what is it:
crossing over is when chromosomes swap their chromatids that touch at a chiasmata
when does it occur:
during meiosis I
how it gives rise to genetic variation:
produces chromosomes that contain new combinations of alleles from both parents
what is independent assortment of chromosomes, when does it occur and how does it give rise to genetic variation
what is it:
when chromosomes randomly line up at the equator of a cell and are then divided
when does it occur:
during meiosis I
how it gives rise to genetic variation:
chromosomes can line up in over 8 million potential genetic combinations (2 power of 23) different combination each time so they are split differently each time
