Human Heredity Ch 14

Human Chromosomes Karyotype – picture of chromosomes grouped together in pairs 23 pairs (46 total) Two are sex chromosomes (pair #23) –Female genotype – XX –Male genotype – XY Autosomes – remaining 44 chromosomes –Pair #s 1-22 Gender of zygote is determined by male

Human Traits Pedigree – chart that shows relationship in family Used to infer genotypes of family members

Recessive alleles An abnormal gene shows up when an abnormal allele affects the phenotype Recessive – only shows up when _________

Dominant allele Expressed even if recessive allele present

Sex-linked genes Only Genes located on X and Y chromosomes X chromosome contains more genes being larger Y chromosome is small so can’t carry other traits besides the one determining the male sex characteristics Males MUST always express all of their X genes ** You can tell a trait is sex-linked if more males than females have it in the population!!**** You can tell a trait is sex-linked if more males than females have it in the population!!**

Chromosomal disorders Errors in meiosis Nondisjunction - Homologous chromosomes fail to separate Abnormal numbers of chromosomes in gametes

Sex chromosome disorders Disorders in the sex chromosomes May only have one X –Sterile, sex organs do not develop at puberty Or be a male with two X

Presence of Y chromosome produces male sexual development no matter how many X Lack of Y, the embryo develops as a female

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