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Chapter 14 (Concept 14.3:
Inheritance patterns are often more complex…
Chapter 14
Concept 14.3:
Inheritance patterns are often more complex than predicted by simple Mendelian genetics
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Nature and Nurture: The Environmental Impact on Phenotype 
~ Multifactorial: The type of hereditary pattern seen when there is more than one genetic factor involved and, sometimes, when there are also environmental factors participating in the causation of a condition.
A Mendelian View of Heredity and Variation
~ The key to make the transition from the reductionist emphasis on single genes and phenotypic characters to the emergent properties of the organisms as a whole.
Extending Mendelian Genetics for a Single Gene
~ The inheritance of characters determined by a single gene deviates from simple Mendelian patterns when alleles are not completely dominant pr recessive, when a particular gene has more than 2 alleles.
Degrees of Dominance
~ Complete Dominance: a form of dominance in heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive.~ Incomplete Dominance: a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele.
- This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.
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Co-Dominance: a relationship between two versions of a gene. Individuals receive one version of a gene, called an allele, from each parent.
- If the alleles are different, the dominant allele usually will be expressed, while the effect of the other allele, called recessive, is masked.
The Relationship Between Dominance and Phenotype
~ When a dominant allele coexists with a recessive allele in a heterozygote, they don't actually interact at all.~ Tay-Sachs Disease: A genetic metabolic disorder caused by deficiency of the enzyme hexosaminidase A (hex-A) that results in a failure to process a lipid called GM2 ganglioside that accumulates in the brain and other tissues.
- Molecular Level: Co-Dominant.
Multiple Alleles
~ Only 2 alleles exist for the pea characters that Mendel studied, but most genes exist in more than 2 allelic forms.
Pleiotropy
Definition: mutation in one gene that causes a disease with a wide range of symptoms, phenomenon in which a single gene contribution to multiple phenotypic traits.
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Drawing from the Deck of Genes
~ The explanation of heredity most widely in favor during the 1800s was the concept called "blending hypothesis".
- the idea to 2 genetic material from 2 parents.
~ Alternative - "Participate Hypothesis"
- the gene idea; a collection of genes.