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 I A and I B 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-Linked Colorblindness, 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