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The LOD score (logarithm (base 10) of odds), developed by Newton Morton, [8] is a statistical test often used for linkage analysis in human, animal, and plant populations. The LOD score compares the likelihood of obtaining the test data if the two loci are indeed linked, to the likelihood of observing the same data purely by chance.
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 ...
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]
The alleles of genes can either be dominant or recessive. A dominant allele needs only one copy to be expressed while a recessive allele needs two copies (homozygous) in a diploid organism to be expressed. Dominant and recessive alleles help to determine the offspring's genotypes, and therefore phenotypes. [citation needed]
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.
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]
Sample (k = 2) happens to be an "extreme" case, with p k = 0.9 and q k = 0.1; while the remaining sample (k = 4) is "middle of the range" in its allele frequencies. All of these results have arisen only by "chance", through binomial sampling.
It is relatively common in adult females; around 35% of women have a skewed ratio over 70:30, and 7% of women have an extreme skewed ratio of over 90:10. [3] This is of medical significance, due to the potential for the expression of disease genes present on the X chromosome that are normally not expressed due to random X-inactivation.