[Biology Class Notes] on Co Dominance and Multiple Alleles Pdf

Dominance may be a relationship between two alleles of 1 gene that affect the phenotype of 1 allele and masks the contribution of another allele.The trait which is expressed in a phenotype is called the dominant trait and the suppressed one is called a recessive trait. Incomplete dominance may be a sort of dominance where a trait incompletely dominates over the opposite and leads to an intermediate progeny.

Codominance

Co-dominance is the sort of dominance where the offspring show similarity to both the oldsters and it’s thanks to the blending of alleles. When the F1 generation exhibits both the parental characters, this is often called codominance. The offspring will be a combination of both the parents. The ABO blood type system is one among the simplest samples of codominance. There are differing types of red blood cells like A, B, AB and O with or without the rhesus factor . The difference is within the antigen present on the red blood corpuscle surface which determines the precise blood type in an organism. For example: If an individual is blood type A, it means the RBC surface consists of antigen-A.But this is often decided by the gene I. The gene I even have three sorts of alleles namely, IA, IB and i. The alleles IA and IB produce two different antigens while the allele-i don’t produce any antigen. Hence, allele i has dominance of alleles IA and IB over them. 

As we know, two pairs of alleles have a diploid organism. Hence, in humans, there are two sorts of alleles of any combination. Depending on the mixture and dominance of the allele blood group of a private might be determined. The different combinations of alleles and their type of blood groups are given below.

Multiple Alleles

Mendel’s work suggested that just two alleles existed for every gene. Today, we all know that’s not always, or maybe usually, the case. However,individual human beings (and all diploid organisms) can only have two alleles for a given gene. Although, multiple alleles generally exist during a population level, and different individuals within the population may have different pairs of these alleles. 

As an example, let’s consider a gene that specifies coat color rabbits, called the c gene. The C gene hasin total of four common alleles, namely, C, Cch, ch and C:

• A CC rabbit has black and brown fur

• A chh chh rabbit has chinchilla coloration

• A ch ch rabbit has has Himalayan (color-point) patterning, with a white body and dark ears, face, feet, and tail

• A cc rabbit is albino, along with a pure white coat.

Multiple alleles makes for many possible dominance relationships. In this case, the black C allele is completely dominant to all the others; the chinchilla c^{ch} allele is incompletely dominant to the Himalayan c^h and albino C alleles; and the Himalayan c^h allele is totally dominant to the albino C allele. Rabbit breeders found out these relationships by crossing different rabbits of various genotypes and observing the phenotypes of the heterozygous kits (baby bunnies).