DNA
- The nucleus includes long thread structures called chromosomes, which consists of DNA wrapped around proteins called histones.
- Specific lengths of DNA in chromosomes are called genes
- individual chromosomes are not visible when cell is not dividing but the chromosomal material stains darkly and can be seen (chromatin) so DNA + hisones = chromatin.
- The human body calls have 46 chromosomes in each nucleus (diploid = 2n - because it contains two sets of chromosomes)
- In humans each of the parent contributes 23 chromosomes when the zygote is formed during sexual reproductions when the gametes fuse.
- The eggs and sperm have only one set of chromosomes
- This is called the haploid number (n)
- Chromosomes can be arranged in pairs, one of each front he parents are paired. The two members of each pair are identical in appearance.
- The chromosome pairs are therefore described as homologous and make up a homologous pair.
- Before mitosis, DNA replication takes place.
- Every chromosomes has a pair of sister chromatids which is joined together by a centromere.
- Mitosis produces two identical cells - it produces two genetically identical daughter cell that are the same as the parent cell
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