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[3] Fur color in domestic cats: the gene that causes orange pigment is on the X chromosome; thus a Calico or tortoiseshell cat, with both black (or gray) and orange pigment, is nearly always female. The first sex-linked gene ever discovered was the "lacticolor" X-linked recessive gene in the moth Abraxas grossulariata by Leonard Doncaster. [4]
Crossing two members of the F1 generation produces the second filial (F2) generation. Probability theory predicts that three quarters of the F2 generation will have the dominant allele's phenotype. And the remaining quarter of the F2s will have the recessive allele's phenotype. This predicted 3:1 phenotypic ratio assumes Mendelian inheritance.
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]
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.
According to the model of Mendelian inheritance, alleles may be dominant or recessive, one allele is inherited from each parent, and only those who inherit a recessive allele from each parent exhibit the recessive phenotype. Offspring with either one or two copies of the dominant allele will display the dominant phenotype.
An individual that is homozygous-recessive for a particular trait carries two copies of the allele that codes for the recessive trait. This allele, often called the "recessive allele", is usually represented by the lowercase form of the letter used for the corresponding dominant trait (such as, with reference to the example above, "p" for the ...
Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction.Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart.
A hereditary carrier (genetic carrier or just carrier), is a person or other organism that has inherited a recessive allele for a genetic trait or mutation but usually does not display that trait or show symptoms of the disease. Carriers are, however, able to pass the allele onto their offspring, who may then express the genetic trait.