Mendelian Inheritance of Human Traits

Simple Recessive Heredity When a person gets two recessive alleles. Simple Recessive Genetic Disorder Cystic Fibrosis (thick accumulation of mucus in lungs and digestive tract) Tay-Sachs (disease of the central nervous system) Phenylketonuria-PKU (results in damage to central nervous system)

Simple Dominant Heredity When a person gets at least one dominant allele. Simple Dominant Traits Tongue Rolling Huntingtons Disease (results in a breakdown of certain areas of the brain)

Complex Patterns of Inheritance

Incomplete Dominance a heterozygote has a different phenotype as the two homozygotes Example-Red flowers are RR, white are WW, the heterozygous condition, RW produces pink flowers

Codominant in a heterozygote individual both phenotypes are expressed equally Example – cross a black chicken (BB) and a white chicken (WW) the heterozygote wouldn’t be grey, the chicken has both black and white feathers.

Codominant, cont. Example:  Blood type gene has three different alleles (each person has two of the three possibilities) Type A allele is dominant and produces A type protein on red blood cells Type B allele is dominant and produces B type protein on red blood cells Type O allele is recessive (defective) allele and produces no protein on red blood cells

Blood Type Genotype Phenotype AA or AO A BB or BO B AB only AB OO only

Blood Type

Polygenic Inheritance - the inheritance pattern of a trait that is controlled by two or more genes. Examples in humans include hair color (AABBCC) eye color skin color

Sex-linked Traits There are 22 pairs of chromosomes in your body that are called autosomes. The other pair are called sex chromosomes. They are called “X” and “Y”. Female genotype = XX Male genotype = XY

Sex-Linked Traits, cont. Some human traits are determined by genes carried on the sex chromosomes, most of these genes are on the X chromosome. Color blindness and hemophilia are examples of sex-linked traits.

Environmental Influences There are many, many environmental factors that affect the way our genes are expressed.

Karyotype A karyotype is a chart of chromosome pairs. This technique is used to look at the chromosomes and tell if the individual has the normal number and type.

Pedigree Charts

Pedigree Charts A Pedigree chart is a graphic representation of genetic inheritance. kind of like a family tree

Pedigree Charts, cont. When you carefully make a pedigree chart you should be able to tell which individuals are possible carriers and the probability that future offspring will express the trait shown.