Topic 3 - Mitosis + Meiosis Flashcards
What is meiosis
The reduction division of a germ cell
A process that occurs in the ovaries and testes to produce haploid gametes
What is reduction division
A process that halves the chromosome number from a diploid cell to produce a haploid nucleus in cells
Why does meiosis occur
To increase genetic variation
How does meiosis create genetic variation
Alleles cross over
Independent assortment
Random nuclei form during fertilisation
What is an allele
A different version of a gene at the same loci of a chromosome
What happens in meiosis I prophase I
Nucleolus + nuclear envelope break down
Centrioles migrate to opposite poles
Chromosomes condense
Homologous chromosomes pair up forming a tetrad
Crossing over occurs
What is crossing over (meiosis)
The swapping of genes between non- sister chromatids
What is a tetrad
The group of four chromatids that occurs when homologous chromosomes pair up
What are homologous chromosomes
A pair of chromosomes.
1 is paternal
1 is maternal
How does crossing over occur
Non sister chromatids become entangled (a chiasmata)
Stress causes sections of DNA to break and rejoin from one chromatid to another
What is a chiasmata
A point of contact between two chromatids from homologous chromosomes
What happens in metaphase I meiosis I
Independent assortment
The homologous chromosomes line up randomly next to each other on the equator of the cell
Why does independent assortment cause genetic variation
As it creates random combinations of maternal and paternal chromosomes at the poles of the cell
What happens in anaphase I meiosis I
The HOMOLOGOUS PAIRS are pulled to opposite poles by spindle fibers
(The sister chromatids are still attached)
What happened in telophase I meiosis I
Nuclear envelope and nucleolus reform.
Chromosomes decondense
Spindle fibers break down
What happens in meiosis I cytokinesis I
Cytoplasmic division
Produces two diploid daughter cells
What happens on meiosis II
Mitotic division (ot contains prophase metaphase anaphase and telophase)
Sister chromatids are separated
What happens in meiosis II cytokenisis II
The cells divide to produce 4 genetically different haploid daughter cells
What are some similarities and differences between meiosis and mitosis
NUCLEAR division occurs in both
Mitosis produces TWO genetically IDENTICAL DIPLOID daughter cells
Meiosis produces FOUR genetically VARIED HAPLOID daughter cells
