crossed the gene for coat color in rabbits (the C gene) which comes in four color
Multiple Alleles
Mendel studied just two alleles of his pea genes, but real populations of
ten have multiple alleles of a given gene. In this activity you will learn how to
alleles (C, Cch, C,
below.
c) as shown by the figure
Gancryps
energ
CHEVRA
Using the given genotypes, find the Fland F2 generation of the crossed between
black rabbit and chinchilla, the crossed of himalayan and albino. Use the Punnet
squares below to guide you.
A. Black (CC) x Chinchilla (Ceh Cch)
F1 Offspring with corresponding %
F2 Offspring with corresponding %
Guide Question
1. Based on the results of the genetic crosses you have shown, how do you
think the red and white flower alleles can interact with one another? Explain
both the Fland F2 generations.
2. How are the results of the crosses differ if the red allele was dominant over the
white allele? Explain both the Fi and F2 generations.
A
Answers
Answer:
Mendel implied that only two alleles, one dominant and one recessive, could exist for a given gene. We now know that this is an oversimplification. Although individual humans (and all diploid organisms) can only have two alleles for a given gene, multiple alleles may exist at the population level such that many combinations of two alleles are observed. Note that when many alleles exist for the same gene, the convention is to denote the most common phenotype or genotype among wild animals as the wild type (often abbreviated “+”); this is considered the standard or norm. All other phenotypes or genotypes are considered variants of this standard, meaning that they deviate from the wild type. The variant may be recessive or dominant to the wild-type allele.
An example of multiple alleles is coat color in rabbits (Figure 1). Here, four alleles exist for the c gene. The wild-type version, C+C+, is expressed as brown fur. The chinchilla phenotype, cchcch, is expressed as black-tipped white fur. The Himalayan phenotype, chch, has black fur on the extremities and white fur elsewhere. Finally, the albino, or “colorless” phenotype, cc, is expressed as white fur. In cases of multiple alleles, dominance hierarchies can exist. In this case, the wild-type allele is dominant over all the others, chinchilla is incompletely dominant over Himalayan and albino, and Himalayan is dominant over albino. This hierarchy, or allelic series, was revealed by observing the phenotypes of each possible heterozygote offspring.
This illustration shows the four different variants for coat color in rabbits at the c allele. The genotype CC produces the wild type phenotype, which is brown. The genotype c^{ch}c^{ch} produces the chinchilla phenotype, which is black-tipped white fur. The genotype c^{h}c^{h} produces the Himalayan phenotype, which is white on the body and black on the extremities. The genotype cc produces the recessive phenotype, which is white
Figure 1. Four different alleles exist for the rabbit coat color (C) gene.
This photo shows Drosophila that has normal antennae on its head, and a mutant that has legs on its head.
Figure 2. As seen in comparing the wild-type Drosophila (left) and the Antennapedia mutant (right), the Antennapedia mutant has legs on its head in place of antennae.
The complete dominance of a wild-type phenotype over all other mutants often occurs as an effect of “dosage” of a specific gene product, such that the wild-type allele supplies the correct amount of gene product whereas the mutant alleles cannot. For the allelic series in rabbits, the wild-type allele may supply a given dosage of fur pigment, whereas the mutants supply a lesser dosage or none at all. Interestingly, the Himalayan phenotype is the result of an allele that produces a temperature-sensitive gene product that only produces pigment in the cooler extremities of the rabbit’s body.
Explanation:
hope it helps!!!
According to Mendel, a gene may have just two alleles, one dominant and the other recessive.
Explanation:
We now see that this is a gross exaggeration. Although humans (and other diploid organisms) can only have two alleles for each gene, multiple alleles may exist at the population level, resulting in a variety of two-allele combinations. When there are many alleles for a gene, the wild type (often abbreviated "+") is used to indicate the most frequent phenotype or genotype among wild animals; this is considered the standard or norm. All other phenotypes or genotypes are variants of this standard, which means they are not identical to the wild type. The variation might be recessive or dominant in the wild-type allele.
Coat colour in rabbits is an example of many alleles (Figure 1). The c gene has four alleles in this region. Brown fur is expressed in the wild-type form, C+C+. Cchcch is a chinchilla phenotype that has black-tipped white fur. chch is a Himalayan genotype with black hair on the extremities and white fur everywhere else. Finally, the albino or "colourless" trait usually manifests itself as white fur. Dominance hierarchies can arise when numerous alleles are present. The wild-type allele is dominant over all others in this case, chinchilla is somewhat dominant over Himalayan and albino, and Himalayan is dominant over albino. Observing the traits of each conceivable heterozygote offspring showed this hierarchy, or allelic series.