Mendelian Inheritance of Human Traits

Pedigree A PEDIGREE is a graphic representation of family inheritance Similar to a family tree Follows the inheritance a single trait E.g. color blindness Generations are marked with Roman numerals I, II, III, IV, V

Pedigree Symbols Male Mating Siblings Affected Female Carrier (Heterozygous) Consanguineous Mating Death Dizygotic Twins Monozygotic Twins

Pedigree How many generations? How many females? How many males? How many great grandchildren? Who has the disease?

Simple Recessive Heredity Most genetic disorders are caused by recessive alleles You must have TWO copies of the recessive allele to be affected Examples: Cystic Fibrosis – build up of thick mucous in the lungs and digestive tract Tay-Sachs disease – a lipid that the body can’t break down accumulates in the nervous system; death by age 5 Phenylketonuria (PKU) – body can’t break down the amino acid phenylalinine; brain damage can occur without a special diet

Simple Dominant Heredity Some traits are caused by dominant alleles Only one dominant allele must be inherited for the trait to be present Examples: Cleft chin Widow’s peak Free/Attached earlobes Hitchhiker’s Thumb Huntington’s disease – degeneration of brain and nervous system; death between 30-50 yrs old

Karyotype Karyotype – a picture of a person’s pairs of chromosomes Can be used to identify an abnormal number of chromosomes or sex determination (XX or XY)

Down Syndrome – Trisomy 21

Ex. Turner Syndrome 1 in 5000 Usually sterile

Turner Syndrome

Ex. Edwards Syndrome (Trisomy 18) Most fetuses abort. If survives, 50% do not survive past 1 week. 90% do not survive past 1 yr.

Tri-18

Huntington’s neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and psychiatric problems

PKU and Fragile X PKU-unable to break down proteins Fragile X- mutation in the X chromosome causing mild retardation and autism

TaySach –destroys the nervous system neurons/brain and is life threatening Destroys brain function

Codominance in Humans Sickle-cell anemia A = normal allele a = sickle cell allele AA = normal Aa = both normal and sickle cell blood cells Heterozygous individuals have unique resistance to Malaria aa = sickle-cell anemia

Sickle Cell Anemia: genetic disorder where blood cells are oval shaped causing pain

aa AA Aa Normal and Sickle Red Blood Cells Sickle Red Blood Cells Normal Red Blood Cells aa AA Aa

Blood Types Human blood types exhibit both MULTIPLE ALLELES and CODOMINANCE IA or IB or i IA and IB are codominant to each other i is recessive to both IA and IB

Blood Types Blood Type Phenotypes IAIA or IAi= A blood IBIB or IBi = B blood IAIB = AB blood ii = O blood Blood Type Genotypes IA IA = A blood IA i = A blood IBIB = B blood IBi = B blood ii = O blood IAIB = AB blood

Codominance

IA IA i i IB IB i i IA IB IA i IB i i i x x IA = A blood IB = B blood i = O blood IA IA i i IB IB i i x x A blood B blood IA IB IA i AB blood A blood IB i i i B blood O blood

Blood Types: Donors/Recipients