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An individual that is homozygous-dominant for a particular trait carries two copies of the allele that codes for the dominant trait. This allele, often called the "dominant allele", is normally represented by the uppercase form of the letter used for the corresponding recessive trait (such as "P" for the dominant allele producing purple flowers ...
where p is the frequency of one allele and q is the frequency of the alternative allele, which necessarily sum to unity. Then, p 2 is the fraction of the population homozygous for the first allele, 2pq is the fraction of heterozygotes, and q 2 is the fraction homozygous for the alternative allele.
Genes may possess multiple variants known as alleles, and an allele may also be said to reside at a particular locus. Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygous with respect to that locus, while those that have different alleles at a given locus are called heterozygous. [3]
In the example on the right, both parents are heterozygous, with a genotype of Bb. The offspring can inherit a dominant allele from each parent, making them homozygous with a genotype of BB. The offspring can inherit a dominant allele from one parent and a recessive allele from the other parent, making them heterozygous with a genotype of Bb.
An organism's genotype may not define its haplotype uniquely. For example, consider a diploid organism and two bi-allelic loci (such as SNPs) on the same chromosome.Assume the first locus has alleles A or T and the second locus G or C.
Females acquire one X-chromosome from their father and one from their mother, and this means they can either be heterozygous for the mutated allele or homozygous. If heterozygous, she is a carrier of the mutated allele because the disease is recessive. If homozygous, she has the disease.
All the peas of this F1 generation have an Rr genotype. All the haploid sperm and eggs produced by meiosis received one chromosome. All the zygotes received one R allele (from the round seed parent) and one r allele (from the wrinkled seed parent). Because the R allele is dominant to the r allele, the phenotype of all the seeds was round.
In population genetics, a fixed allele is an allele that is the only variant that exists for that gene in a population. A fixed allele is homozygous for all members of the population. [1] The process by which alleles become fixed is called fixation. For this hypothetical species, the population in the topmost frame exhibits no fixed allele for ...