Chickens vary in color Black and white color variation can b

Chickens vary in color. Black and white color variation can be traced to a single co-dominant gene in which black chickens and white chickens are each homozygous for the black (BB) and white (bb) allele, respectively, while speckled hens are heterozygous (Bb) Cause of Variation If one of the alleles was ancestral, what is the most likely event that caused the other allele encoding a color variant to arise in chickens? During which cellular process did this most event most likely occur? Name one enzyme that was involved in this cellular process. Selection and the maintenance of variation Generate a hypothesis for why this variation in chicken color may be present today (do not consider the hypothetical situation in Q2b) Hypothetically, say that speckled hens lay twice as many eggs, and thus produce twice as many offspring as either white or black hens. If this were the case, briefly explain one possible reason that black and white chickens are still produced.

Solution

Codominance is observed when two different alleles of a specific single-gene trait are both expressed simultaneously. It follows non-Mendelian inheritance patterns. Both the dominant alleles coexist and work together to express both phenotypes in equal measures. This would lead to the phenotype having characteristics of both alleles.

For example, feather colour in hens may be white, black or speckled (it has both white feathers and black feathers). The alleles can be shown as W for white and B for black.

There are three possible genotypes: WW, BB and BW.

There are also three possible phenotypes: WW = white, BB = black, and BW = speckled.

The event which may have caused the allele ecoding a color varient could be that, When genes are far apart on the chromosome they can segregate independantly. This is due to crossing over. this event occurs during meiotic division.Mutations are caused due to this and give rise to variations.

In birds and mammals, unpigmented pigment cell precursors known as melanoblasts migrate from the neural crest to the epidermis and into developing feather or hair follicles. Mature pigment cells known as melanocytes synthesize melanin pigment, package it into melanosomes and then transfer those melanosomes to keratinocytes for deposition into developing feathers and hairs.Though mammals and birds have only one pigment cell type, the melanocyte, these cells can produce either eumelanin (black/brown) or pheomelanin (yellow/red) and can switch rapidly between the synthesis of these two pigment types

Increased production of eumelanin and a corresponding reduction in pheomelanin synthesis generates a melanic phenotype, which may be dark brown or entirely black. This switch is primarily controlled by the interaction of two genes: the melanocortin receptor 1 (Mc1r) and agouti.

which are affected by mutations and polymorphisms.

Melanism is the pattern,

Mc1r is the gene in

chicken (Gallus gallus)