Meiosis and genetic variation. IB Biology HL E. McIntyre . Genome. Genome : Complete complement of an organism’s DNA. Includes genes (control traits) and non-coding DNA organized in chromosomes . Genes. Eukaryotic DNA is organized in chromosomes.
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IB Biology HL E. McIntyre
Exception: Sex chromosomes (X, Y).
Other chromosomes are known as autosomes, they have homologues.
All are even numbers – diploid (2n) sets of homologous chromosomes!
Ploidy = number of copies of each chromosome.Diploidy
First division of meiosis
Second division of meiosis: Gamete formation
No daughter cells formed during meiosis are genetically identical to either mother or father
During sexual reproduction, fusion of the unique haploid gametes produces truly unique offspring.
Wait no more…..
Number of combinations: 2n
e.g. 2 chromosomes in haploid
2n = 4; n = 2
2n = 22 = 4 possible combinations
e.g. 23 chromosomes in haploid
2n = 46; n = 23
2n = 223 = ~ 8 million possible combinations!
Chiasmata – sites of crossing over, occur in synapsis. Exchange of genetic material between non-sister chromatids.
Crossing over produces recombinantchromosomes.
At least 8 million combinations from Mom, and another 8 million from Dad …
>64 trillion combinations for a diploid zygote!!! Ykes……that’s a lot of sex…ual reproduction
Generalized animal life cycle
Remember, YOU contribute only half the genetic material to your offspring.
So when you are choosing a mate for reproduction remember Indiana Jones
& the Temple of Doom.
-” Choose, but choose wisely.”