Meiosis Flashcards
When does meiosis occur?
in sex cells for sexual reproduction producing gametes
What is gametogenesis?
formation of haploid gametes
What is fertilisation?
fusion of gametes to form a diploid zygote
How many stages of meiosis are there?
2
How does meiosis result in genetic variation?
crossing over during late prophase 1
independent assortment of chromosomes during metaphase 1
random fertilisation of gametes produced by genetically different parents
How does crossing over occur?
homologous chromosomes pair up to form bivalents
adjacent paternal and maternal chromatids cross over
thus when chromosomes separate during anaphase 1, chromatids carry a combination of paternal and maternal genes
What are points of crossing over in prophase 1 called?
Chiasmata
What does independent assortment during metaphase 1 result in?
Gametes having different combinations of paternal and maternal chromosomes
Why does random fertilisation result in genetic variation?
gametes are produced by genetically different parents
all gametes have an equal probability of being involved in fertilisation
What are the stages of meiosis?
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
Cytokinesis
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
How many daughter cells are made from one parent cell in meiosis?
4 gametes
What happens to the DNA, what does this mean?
DNA replication happens once
2 divisions therefore results in haploid daughter cells
What id the diploid number of chromosomes in humans?
46 (23 pairs)
What is the haploid number of chromosomes in humans?
23
What happens during prophase 1 in meiosis?
chromosomes condense and attach to the nuclear envelope
synapsis occurs (pair of chromosomes line up close together) a tetrad composed of 4 chromatids is formed.
genetic recombination via crossing over may occur
the centrioles migrate away from one another and both the nuclear envelope and nucleoli break down