patterns of inheritance i n humans
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Patterns of Inheritance i n 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?. - PowerPoint PPT PresentationTRANSCRIPT
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.