Chapter 5 - Nature Nuture Development

Chapter 5 - Nature Nuture Development - Chapter 5.1...

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Chapter 5.1 Genetics and Evolution of Behaviours Chromosomes – strands of hereditary material. Each human have 23 pairs of chromosomes (23 chromosomes from sperm and 23 chromosomes from egg combine to form 23 pairs) Genes – sections along each chromosomes, control the chemical reactions that direct development. (E.g. height or hair colour) The Law of segregation Dominant – a single copy of the gene is sufficient to produce its effect. Recessive – its effects appear only of the dominant gene is absent. (E.g. if you have either one or two genes for brown eyes, you will have brown eyes because the brown eye genes is dominant. The gene for blue eyes is recessive; you have blue eyes only if you have two genes for blue eyes.) Almost every aspect of behaviour depends on the combined influence of many genes and environmental influences. Also the exact borders of gene are ambiguous. Portions of the chromosome that do not code for any proteins of their own can modify the effectiveness of a portion that does. Sex chromosomes – it determines whether an individual develops as a male or female. A female has two X chromosomes. One of the X chromosomes is activated and the other is silenced, apparently at random. A male has one X chromosomes and one Y chromosomes. A mother contributes an X chromosome while the father contributes either an X or Y chromosome to the child. Sex linked/X linked genes – genes located on the X chromosomes. Genes on the Y chromosomes are also sex linked but it has fewer genes. An X linked recessive genes shows its effect more in men than in women. E.g. Red green deficiency depends on an X linked recessive gene. A man with that gene on his X chromosomes will be red green deficient because he has no other X chromosome to carry a gene that would overrule the recessive red green colour deficiency. Whereas for woman, they have 2 X chromosomes, one which has the red green colour deficiency gene and the other X chromosomes might have the dominant colour vision. She will have normal colour vision but may pass on the red colour deficiency to her offspring. Sex limited gene – occurs equally in both sexes but exerts its effect mainly or entirely in one or other. (E.g. both men and women have the genes for facial hair, but men’s hormones activate those genes, both men and women have the genes for breast development, but women’s hormones activate the genes) Heritability – an estimate of the variance within a population that is due to heredity. Heredity ranges from 1, indicating that heredity controls all of the variance, to 0 which indicates that it controls none of it. Researchers study twins and adopted children to estimate the heritability of various traits.
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