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Why is meiosis necessary?
· Meiosis produces four daughter nuclei, each with half the number of
chromosomes as the parent cell.
· Every diploid cell of an organism has two sets of chromosomes.
· During meiosis, the chromosome pairs separate, so that only one
chromosome from each pair enters each gamete. This is known as the
haploid number of chromosomes.
· When two haploid gametes fuse, the diploid number is restored.
· If each gamete has a diploid number of chromosomes, then the cells that
they produce has double this number.
· This doubling of the number of chromosomes would continue at each
· In order to maintain a constant number of chromosomes in the adults of
a species, this number must be halved and it occurs as a result of
meiosis.…read more

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Process of Meiosis
Meiosis involves two nuclear divisions
· First division (meiosis 1)
- homologous chromosomes pair up
- their chromatids wrap around each other
- equivalent portions of chromatids get exchanged (crossing over)
- by the end of this stage, homologous pairs separate
- one chromosome from each homologous pair goes into one of
the two daughter cells
· Second division (meiosis 2)
- the chromatids move apart
- at the end of meiosis 2, four cells are formed
- in humans, each of these cells contain 23 chromatids…read more

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Genetic Variation by Meiosis
· Meiosis also produces genetic variation among the offspring, allowing
an organism to adapt and survive in a changing world.
· Genetic variation by meiosis occurs in two ways
- independent segregation of homologous chromosomes
- recombination of homologous chromosomes by crossing over
· Refreshing some basic terms
- Gene: a section of DNA that codes for a polypeptide
- Locus: the position of a gene on a chromosome/ DNA molecule
- Allele: one of the different forms of a particular gene…read more

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Summary of Meiosis…read more

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Independent Segregation
· During meiosis 1, each chromosome lines up alongside its homologous
· In humans, this means that there will be 23 homologous pairs lying
side by side.
· They arrange themselves in this line randomly.
· One of each pair will pass to each daughter cell.
· Which one of the pair goes into the daughter cell, and with which one
of any of the other pairs, depends on how the pairs are lined up in the
parent cell.
· Since the pairs are lined up at random, the combination of
chromosomes that goes into the daughter cell at meiosis 1 is also
random. This is called independent segregation of chromosomes.…read more

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