Lecture 6: Non-Mendelian inheritance

pleiotropy

occurs when one gene influences multiple phenotypic traits

Pleiotropy in Mendelian inheritance

Mendel treated traits as independent, but pleiotropy shows that a single Mendelian gene can affect many traits at once

example of pleiotropy in Mendelian inheritance

Sickle-cell allele (HbS):

• Affects red blood cell shape

• Causes anemia

• Influences resistance to malaria

• One gene → multiple effects

Pleiotropy in chromosome theory

A gene encodes a protein used in multiple tissues or pathways. Because the gene occupies one locus on a chromosome, all its effects are inherited together.

linkage

when different genes located close together on the same chromosome tend to be inherited together

linkage in Mendelian inheritance

Linked genes violate independent assortment leading to non-Mendelian ratios

linkage in chromosome theory

The closer the genes are, the less likely crossing over will separate them

genetic linkage map

uses recombination frequencies from meiosis to estimate the order and relative distances of genes on a chromosome

complementation test

determine whether two recessive mutations that produce the same phenotype are in the same gene or in different genes

Epistasis

occurs when one gene masks or modifies the expression of another gene at a different locus

epistatis usually occurs when…

modified dihybrid ratio instead of 9:3:3:1.