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Length of p, q corresponds to allele frequencies (here p = 0.6, q = 0.4). Then area of rectangle represents genotype frequencies (thus AA : Aa : aa = 0.36 : 0.48 : 0.16 ). The different ways to form genotypes for the next generation can be shown in a Punnett square , where the proportion of each genotype is equal to the product of the row and ...
The phenotypic ratio of a cross between two heterozygotes is 9:3:3:1, where 9/16 of the individuals possess the dominant phenotype for both traits, 3/16 of the individuals possess the dominant phenotype for one trait, 3/16 of the individuals possess the dominant phenotype for the other trait, and 1/16 are recessive for both traits. [1]
To perform a test cross with C. elegans, place worms with a known recessive genotype with worms of an unknown genotype on an agar plate. Allow the male and hermaphrodite worms time to mate and produce offspring. Using a microscope, the ratio of recessive versus dominant phenotype will elucidate the genotype of the dominant parent. [9]
Thus, allele R is dominant over allele r, and allele r is recessive to allele R. [4] Dominance is not inherent to an allele or its traits . It is a strictly relative effect between two alleles of a given gene of any function; one allele can be dominant over a second allele of the same gene, recessive to a third, and co-dominant with a fourth.
if the allele A frequency is denoted by the symbol p and the allele a frequency denoted by q, then p+q=1. For example, if p=0.7, then q must be 0.3. In other words, if the allele frequency of A equals 70%, the remaining 30% of the alleles must be a, because together they equal 100%. [5]
The following example illustrates a dihybrid cross between two double-heterozygote pea plants. R represents the dominant allele for shape (round), while r represents the recessive allele (wrinkled). A represents the dominant allele for color (yellow), while a represents the recessive allele (green).
X-linked recessive inheritance. X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be always expressed in males (who are necessarily hemizygous for the gene mutation because they have one X and one Y chromosome) and in females who are homozygous for the gene mutation, see zygosity.
Since each parent must have a copy of the recessive allele in order to have an affected offspring, the parents are referred to as carriers of the condition. [ 11 ] [ 12 ] [ 13 ] In autosomal conditions, the sex of the offspring does not play a role in their risk of being affected.