Intro to Life Processes - Chapter 21.4 to end

Polygenic traits

traits that are controlled by several allelic pairs, which produces a continuous range of phenotypic variation, with each dominant allele having an additive effect

• skin color

• eye color

• height

• etc.

polygenic inheritance

Skin color

• results from pigmentation produced in specialized cells in the skin called melanocytes

• over 100 genes control skin color

• polygenic inheritance

Environmental Influence

many genetic disorders including clef lip, clubfoot, schizophrenia, diabetes, phenylketonuria, and even allergies and cancers are likely controlled by polygenic traits that are subject to environmental influences

Multifactorial trait

• a condition that is caused by the interaction of multiple genes and environmental conditions

• environmental influence

Codominance

occurs when alleles are equally expressed in a heterozygote

• a common example occurs within human blood types

• ^ AB blood type exists when one allele is for A and the other is for B

• Unlike incomplete dominance, the heterozygote does not express a condition at a midpoint between two alleles, but instead expresses both alleles equally

Multiple alleles

occurs when a gene exists with more than two allelic forms; however, one person can still only have two of the possible alleles

• ex: human blood types - phenotypes (A, B, AB, O), possible genotypes (IAIA IAi, IBIB IBi, IAIB, ii)

Sex-linked

traits controlled by genes on the sex chromosomes (X or Y)

• most sex-linked genes are X-linked (the Y chromosome is much smaller than a typical chromosome)

• most genes on the X-chromosome have nothing to do with an individual’s gender

• ^for example, our ability to perceive color is coded on the X-chromosome

X-linked

alleles on the X chromosome

Y-linked

alleles on the Y chromosome

Genotypes and Phenotypes for perception of color

• Genotypes: XBXB, XBXb, XbXb, XBY, XbY

• Phenotype: Female with normal vision, carrier female who has normal vision, female who is color blind, male who has normal vision, male who is color blind

Most notable X-linked disorders

• Color blindness

• Duchenne muscular dystrophy

• Fragile X syndrome

• Hemophilia