Extensions of Mendelian Inheritance

• The term Mendelian inheritance refers to inhertitance patterns that obey two lawa, the law of segreagtion and the law of independence assortment. 

Recessive Alleles oftern cause a reduction in the anount or function of the encoded proteins 

• Throught the range of species in Europe, both yellow and red flowered individuals are prevalent.
• Both colours are considered wild type. 
• Molecular level, a wild type allel typically encoded a protein that made in the proper amount and functions normally. 

Dominant mutant alleles usually exert their effects in one of three ways 

• Gain of function mutations change the gene or the protein encoded by a gene so that it gains a new or abnormal function, For example, a mutant gene may be overexpresses, producing too much of the encoded protein.

Traits mat skip a generation due to imcomplete penetrace and vary in their expressivity 

• Phenomenon called incompleye penetrance is a situation in which an allele that is expected to cause a particular phenotype does not. 
• A human pedigree for a dominant trait known as polydactyly. 
• Trait causes the affcted individual to have additional finger or toes 
• Polydactyly is due to an autosomal dominant allele, allele occurs in a gene located on an autosome, and a single copy of this allele is sufficient to cause this condition.
• Individuals carry the dominant allele but do not echibit the trait. 
• Individual III2 has inherited the poludactyly allele from his mother and passed the allele to a daughter and son. 
• Individual III 2 does not actually exhibit the trait himself, even though he is a heterzygote. 
• Polydactyly, dominant allele does not always penetrate into the phenotype of the individual. 
• Recessive traits, incomplete penetrance occurs if a homozygote carrying the recessive allele does not exhibit the recessive trait. 

Environmental effects on gene expressions 

• Example the artic fox goes through two colour phases.
• During the cold winter, the artic fox is white, but in the warmer summer, it is mostly brown. 
• Fox has temperature sensative alleles affecting fur colour, found amoung many species of mammals.

Incomplete dominance occur when two alleles produce an intermediate phenotype

• Incomplete dominance is a condition in which the phenotype of a heterozygote is intermediate between the corresponding homozygous undividuals. 
• 1905, German Carl Correns first observed this phenomenon in the colors of the flowers of the four o clock plant. 

Overdominance occurs when Heterozygotes have greater reproductive success 

• Phenomenon in which a heterozygote has freater reproductive success compared with either rge corresponding homozygote is called overdominance or heterozygote advantage. 
• Homozygous Hbs, individual usually has a shortened life…