ch1 2 - heredity and environment are essential for...

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- heredity and environment are essential for everything you do - except for rbc, all of your cells contain a nucleus, which includes strands of hereditary material called chromosomes - each human nucleus has 23 pairs of chromosomes o except those in egg and sperm cells, which have 23 unpaired chromosomes - sections along each chromosome, known as genes, control the chemical reactions that direct development o genes are composed of chemical DNA, which controls the production of another chemical called RNA, which among other functions controls the production of proteins proteins either become part of the body’s structure or control the rates of chemical reactions in the body - dominant – a single copy of the gene is sufficient to produce its effect - recessive – its effects appear only if the dominant gene is absent o you can have 2 blue eyes if you have 2 genes for blue eyes - sex chromosomes – determine whether an individual develops as a male or female - a female has 2 X chromosomes in each cell - a male has one X chromosome and one Y chromosome - the mother contributes an X chromosome to each child o women have 2 X chromosomes, but in each cell, one of the X chromosomes is activated and the other is silenced, apparently at random - the father contributes either an X or a Y o bc men have 1 X and Y, they have unpaired genes on these chromosomes - genes located on the X chromosomes are known as sex-linked or X-linked genes o genes on Y are also sex-linked, but the Y has fewer genes - an X-linked recessive gene shows its effects more in men than in women o colorblind – a man with that gene on his X will be colorblind bc he has no other X; a woman with that gene probably has a gene for normal color vision on her other X men have color vision deficiency more often women - sex-limited gene – occurs equally in both sexes but exerts its effects mainly or entirely in one or the other o both have facial hair, but men’s hormones activate those genes o both have genes for breast development, but women’s hormones activate those genes - heritability – an estimate of the variance within a population that is due to heredity o ranges from 1 – indicating that heredity controls all the variance o 0 – indicating that it controls none of it -
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