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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.
Researchers have investigated the relationship between race and genetics as part of efforts to understand how biology may or may not contribute to human racial categorization. Today, the consensus among scientists is that race is a social construct, and that using it as a proxy for genetic differences among populations is misleading. [1] [2]
In genetics, complete (or absolute) linkage [1] is defined as the state in which two loci are so close together that alleles of these loci are virtually never separated by crossing over. The closer the physical location of two genes on the DNA, the less likely they are to be separated by a crossing-over event.
Since humans have many more genes on the X than the Y, there are many more X-linked traits than Y-linked traits. However, females carry two or more copies of the X chromosome, resulting in a potentially toxic dose of X-linked genes. [4] To correct this imbalance, mammalian females have evolved a unique mechanism of dosage compensation.
A disease or trait determined by a gene on the X chromosome demonstrates X-linked inheritance, which can be divided into dominant and recessive patterns.. In X-linked recessive inheritance, a son born to a carrier mother and an unaffected father has a 50% chance of being affected, while a daughter has a 50% chance of being a carrier, however a fraction of carriers may display a milder (or even ...
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 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.
Sex-limited genes are also distinguished from sex-influenced genes, where the same gene will show differential expression in each sex. Sex-influenced genes commonly show a dominant/recessive relationship, where the same gene will have a dominant effect in one sex and a recessive effect in the other (for example, male pattern baldness).