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Diploids and Haploids
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Almost all organisms alive on earth have life cycles in which the genetic content of their cells (number of chromosomes) alternates between a higher number and a lower number. In almost all animals, for example, the cells of the adult, multicellular body have the higher number, which the sex gametes have the lower number.
Key concepts:
- In most of the somatic ("body") cells of a human there are 46 chromosomes.
- These are found in homologous pairs; autosomal pairs and a pair of sex chromosomes.
- This number is called the diploid number of chromosomes and very often represented by the number/letter "2n".
- Some cells, in the heart for example, have multiples of this number (i.e. 4n, 6n, 8n, etc.) this is called being polyploid.
- Many plants are polyploid in all their somatic cells.
- In reproductive sex gametes, the sperm and the eggs, the number of chromosomes is reduced. In humans it is reduced from 46 down to 23.
- This is the haploid number of chromosomes and consists of one each of the homologues. It is often represented by the letter "n".
- In humans, 2n = 46, and n = 23.
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Science@a Distance
© 2001, Professor John Blamire |
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