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Meiosis - genetic variation - Coggle Diagram
Meiosis - genetic variation
Crossing over (aka recombination)
in prophase 1, the formation of homologous pairs allows for the tangling of non-sister chromosomes
the pair of homologous chromosomes has 4 chromatids (2 from each chromosome)
when the homologous chromosomes lie next to each other the chromatids can intertwine & exchange sections
chromosomes have same genes but different alleles
the chromatids of each chromosome in meiosis 2 are no longer genetically identical due to crossing over in prophase 1
Independent assortment (aka random assortment)
during metaphase 1 is up to chance which way round the homologous pairs of chromosomes (bivalents) line up on the equator
this affect which chromosome of the pair (maternal or paternal) goes into which daughter cell in anaphase
mixes up maternal & paternal so gametes have a mixture of alleles form both parents
the chromatids of each chromosome are also randomly arranged in metaphase 2 during meiosis 2
the way they are arranged determines how chromatids separate during anaphase 2, leading to further random distribution of chromosomes
during metaphase 1 there is an assortment of chromosomes
during metaphase 2 there is an assortment of chromatids
possible combos can be calculated using formula;
2^n
n = number of homologous chromosome pairs - 23 in humans so 8,388,608 possible combos
independent assortment by itself is a significant source of genetic variation
Random combination of gametes
haploid gametes undergo random fusion with gametes from another organism (of the same species) at fertilisation the resulting zygote will therefore contain genetic material from 2 unrelated induvial, introducing further genetic variation
Mutations
chromosomal mutations
non-disjunction failure
= failure of homologous chromosomes to separate properly during anaphase
whole chromosone level, e.g. non-disjunction
point mutations
DNA level, e.g. insertion/deletion of nucleotides
