Patterns of Inheritance i n Humans

Patterns of Inheritancein Humans

Pedigree• Geneticists study the inheritance of certain traits

by using a Pedigree

• A pedigree is a visual representation of a family and shows inheritance patterns over several generations.

• Can be used to determine genotype

• Why do we need pedigrees?

Autosomal Inheritance

• Most traits and genetic disorders are coded on autosomal chromosomes.

• Traits and disorders can be autosomal dominant or autosomal recessive.

Huntington’s Disease

• Autosomal Dominant• Causes Brain to deteriorate over 15 years

Cystic Fibrosis

• Autosomal Recessive• Mucus buildup causes breathing and digestive

problems.

Moving Beyond Mendel

• Mendel’s experiments only considered traits to be dominant or recessive

• Sometimes both traits are expressed and sometimes the trait is an intermediate of the parental traits

Incomplete Dominance

• A situation when neither allele for a trait can completely mask the other.

• Heterozygote's have a phenotype in-between that of their parents

Codominance

• Both alleles are fully expressed

Codominance in Humans

• Ex: Sickle Cell Anemia

• Homozygous recessive individuals have all sickle cells while Heterozygotes have sickle cells and normal cells.

• Heterozygotes have resistance to malaria.

Heterozygous Advantage

• This is a situation where Heterozygotes have an advantage over homozygous dominant and homozygous recessive.

• Why would having the Sickle Cell trait be an advantage?

Multiple Alleles

• Many traits in Humans and other species are a result of interactions between more than 2 alleles on a specific gene.

• That is, there are more than just two possible phenotypes and genotypes.

ABO Blood type

• In Humans, Blood Type is determined by the interaction of 3 blood type alleles.

• IA IB and i

Polygenic Inheritance

• Some traits show continuous variation and will vary gradually from one extreme to another

• Traits like these are usually controlled by more than one gene and are called Polygenic Traits

• The group of genes that all contribute to the phenotype are called polygenes.

Skin Colour

• Only the dominant forms of the gene will contribute to the phenotype.