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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]
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.
The distance between two alleles on a chromosome can be determined by calculating the percentage or recombination between two loci. These probabilities of recombination can be used to construct a linkage map, or a graphical representation of the location of genes and gene in respect to one another. If linkage is complete, there should be no ...
The linked frequency of crossing over between two gene loci is the crossing-over value. For fixed set of genetic and environmental conditions, recombination in a particular region of a linkage structure ( chromosome ) tends to be constant and the same is then true for the crossing-over value which is used in the production of genetic maps .
The SHOX gene in the PAR1 region is the gene most commonly associated with and well understood with regards to disorders in humans, [17] but all pseudoautosomal genes escape X-inactivation and are therefore candidates for having gene dosage effects in sex chromosome aneuploidy conditions (45,X, 47,XXX, 47,XXY, 47,XYY, etc.).
Linkage disequilibrium refers to the association of genes in a population. Linkage, on the other hand, tells us whether genes are on the same chromosome in an individual. There is no necessary relationship between the two. Genes that are closely linked may or may not be associated in populations.
The Y-chromosome has been entirely mapped, [7] revealing many Y-linked traits. [8] Y linkage is similar to, but different from X linkage; although, both are forms of sex linkage. X linkage can be genetically linked and sex-linked, while Y linkage can only be genetically linked. This is because males' cells have only one copy of the Y-chromosome.
Dihybrid cross is a cross between two individuals with two observed traits that are controlled by two distinct genes.The idea of a dihybrid cross came from Gregor Mendel when he observed pea plants that were either yellow or green and either round or wrinkled.