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-** You can tell a trait is sex-linked if more males than linked if more males than females have it in the females have it in the population!!**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

• http://www.zerobio.com/drag_gr11/sexlink.htm