Extending Mendelian Genetics Complex Patterns of Inheritance CoDominance

Extending Mendelian Genetics Complex Patterns of Inheritance

Co-Dominance with multiple alleles n Both alleles affect the phenotype in separate distinguishable ways. n Example: blood types with multiple alleles. n The genes affect the enzyme I, which attaches the A or B carbohydrate to the surface of red blood cells.

Incomplete Dominance n Heterozygotes have a phenotype in between the phenotype of the parents. n Blending of characteristics in the heterozygote. n Blending of flower colors, where each heterozygote has less pigment from each parent.

What is dominance? n Genes make proteins and the dominance is expressed when a number of critical proteins are being made. n Alleles do not interact, but it is there protein products, which determine the phenotype. n Example Tay-Sachs Disease.

Deficit in Hex-A enzyme of the lysosome

Pleiotropy n Genes have multiple phenotypic effects n Alleles are responsible for multiple symptoms. n As genes code for enzymes, an enzyme can be involved in a variety of pathways, which lead to complex symptoms.

Epistasis n One gene alters the expression of another gene.

Polygenic Inheritance n Skin color is a quantitative character with variations of shades. n Skin color is controlled by at least three separated genes.

Sex-Linkage n Genes located on the X or Y chromosomes n Not all species determine their gender with X and Y chromosomes. n Sex-linkage happens when a gene is expressed and passed on the sex chromosomes.

SRY on Y chromosome n Determines the gender in humans

Color Blindness

X inactivation in females mammals n One of the X chromosomes in females become n n n inactivated during embryonic development except in reproductive cells in the ovary. Only one set of genes is expressed. This inactivation occurs randomly in each cell, resulting in a genetic mosaic. The inactive X chromosome condenses into a Barr Body Inactivation comes from CH 3 groups on the genes. The XIST (X-Inactive Specific Transcript) gene on the X chromosome is expressed only in the inactivated chromosome.

Epigenome n Influences of the environment on gene expression n Modification of genes over a life time, turns them on or off n These modifications can be transmitted to the offspring n The epigenic tags are CH 3 groups on the DNA.

Mosaicism n Two fertilized eggs fused into one during embryonic development. n The resulting individual has two sets of cells with different DNA. n This condition is extremely rare. n Blaschko Lines