Human Genome

Karyotype – a picture of a cell’s chromosomes group in homologous pairs

•Humans have 46 chromosomes

•Two of these are sex chromosomes (XX in females and XY in males)

•The other 44 are autosomes

• Eggs carry X chromosomes (23,X)• Sperm can carry either an X or a Y chromosome

(23,X or 23,Y)• Zygote would result as either 46, XX or 46, XY• This is why about 50% offspring are male and

50% are female

Pedigree Charts

• Used to study human inheritance• Shows how a trait is transmitted through a

family, one generation to the next• Helps make inferences (guess) about

genotypes or whether certain alleles are dominant or recessive.

• In pedigrees, circles represent females and squares represent males

• Symbols that are shaded indicates the individual expresses the trait

• No shading means the trait is not exhibited• Important to understand that most traits are

polygenic and also can be influenced by environment

Human Blood Groups

• Rh factor – Rh positive is dominant which means Rh negative is recessive

• ABO blood grouping are multiple alleles• IA and IB are codominant while i is recessive

Genetic Disorders-Autosomal• PKU (Phenylketonuria) – Caused by a recessive

allele: Causes severe mental retardation unless diagnosed early

• Huntington’s Disease – Caused by a dominant allele: Causes neurological/muscular problems and death in 40’s

• Sickle-cell Disease – Caused by a codominant allele• Cystic Fibrosis• ALS (Lou Gehrig’s Disease)

Genetic Disorders - Sex-Linked

• Inheritance patterns on sex chromosomes will be found on X chromosome (Y is too small with little genetic information)

• Disorders called Sex-LinkedColorblindness, Hemophilia,

Duchenne Muscular Dystrophy

Chromosomal Disorders

Nondisjunction - Caused during meiosis when homologous chromosomes fail to separate.

• Leads to abnormal numbers of chromosomes in the gametes

• Results in various disorders: Down’s Syndrome and various sex chromosome disorders

Down’s Syndrome• Trisomy (three copies) of chromosome 21• Produces mild to severe mental retardation

Turner’s Syndrome• Female disorder where the person has only

one X chromosome (45,X)• Sterile, which means unable to reproduce• Sex organs never develop

Klinefelter’s Syndrome• Male disorder where the person has an extra

X chromosome (47,XXY)• Typically individual is sterile