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Inheritance Patterns Not all genes migrate and follow strict Medelian patterns. Because of this a spectrum of dominance was created. Complete Dominance.

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Presentation on theme: "Inheritance Patterns Not all genes migrate and follow strict Medelian patterns. Because of this a spectrum of dominance was created. Complete Dominance."— Presentation transcript:

1 Inheritance Patterns Not all genes migrate and follow strict Medelian patterns. Because of this a spectrum of dominance was created. Complete Dominance – Mendelian pattern of the F 1 (heterozygote) being indistinguishable from the dominant (homozygote) phenotype Codominance – both effect the phenotype in distinguishable ways – blood types are an example (A & B are dominant, O is recessive)

2 Inheritance Patterns Incomplete Dominance – the expression of the dominant phenotype is lessened by the existence of the recessive gene – Red & White true breeding snapdragons form pink F 1 offspring – the degree to which the dominant gene is expressed is called penetrance Tay Sachs is a disease that causes fat accumulation in the neural tissues of children leading to death in the homozygous individual. The disease is due to the loss of function of a needed enzyme. – Although the allele for the disease is dominant the heterozygote does not exhibit disease symptoms. 1/2 of the enzyme production is sufficient to eliminate symptoms. – The disease has very low penetrance on the heterozygous state.

3 Aberrations of Mendelian genetics Frequency of recessive alleles – in many instances the recessive allele is much more common than the dominant allele polydactally (6 or more digits) is a dominant trait but only expressed in ~1/400 births because the majority of the population is homozygous for the recessive gene Multiple alleles – most than 2 form of alleles exist for most human traits (unlike Mendel's 2 allele peas) – bood type I A, I B, & i (O) Pleiotropy – most genes exert more than one phenotypic effect (pick any genetic disease)

4 Aberrations of Mendelian genetics Epistasis – a gene at 1 locus alters the effect of a gene at another – hair color is effected by a gene at a different locus that is responsible for deposition of the pigment in the follicles – if the animal is homozygous for the color gene the animal is white even though it may be homozygous for the pigment (black) Polygenic Inheritance (quantitative inheritance) – describes traits that are effected by inheritance of genes on different chromosomes – the effect of the traits may be additive or pleiotrophic – skin color is additive with at least 3 genes inherited on 3 different locus and different genes – gives us a distribution of skin color instead of dark brown, tan, or white

5 Aberrations of Mendelian genetics Nature vs Nurture – the environment in which an organism lives can alter its phenotypic expression


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