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It shows 22 homologous autosomal chromosome pairs, both the female (XX) and male (XY) versions of the two sex chromosomes, as well as the mitochondrial genome (at bottom left). In genetics , a chromosomal rearrangement is a mutation that is a type of chromosome abnormality involving a change in the structure of the native chromosome . [ 1 ]
Gene duplication (or chromosomal duplication or gene amplification) is a major mechanism through which new genetic material is generated during molecular evolution.It can be defined as any duplication of a region of DNA that contains a gene.
Unequal crossing over is a type of gene duplication or deletion event that deletes a sequence in one strand and replaces it with a duplication from its sister chromatid in mitosis or from its homologous chromosome during meiosis. It is a type of chromosomal crossover between homologous sequences that are not paired precisely. Normally genes are ...
During nonfunctionalization, or degeneration/gene loss, one copy of the duplicated gene acquires mutations that render it inactive or silent. Non-functionalization is often the result of single gene duplications. [11] At this time, the gene has no function and is called a pseudogene. Pseudogenes can be lost over time due to genetic mutations.
In genetics, a maternal effect occurs when the phenotype of an organism is determined by the genotype of its mother. [1] For example, if a mutation is maternal effect recessive, then a female homozygous for the mutation may appear phenotypically normal, however her offspring will show the mutant phenotype, even if they are heterozygous for the mutation.
An example of a birth defect is cleft palate, which occurs during the fourth through seventh weeks of gestation. [14] Body tissue and special cells from each side of the head grow toward the center of the face. They join to make the face. [14] A cleft means a split or separation; the "roof" of the mouth is called the palate. [15]
CAH can occur in various forms. The clinical presentation of each form is different and depends to a large extent on the kind of the underlying 21-hydroxylase enzyme defect. [9] Classical forms appear in infancy, and nonclassical forms appear in late childhood. The presentation in patients with classical CAH can be further subdivided into two ...
Evolution by gene duplication is an event by which a gene or part of a gene can have two identical copies that can not be distinguished from each other. This phenomenon is understood to be an important source of novelty in evolution, providing for an expanded repertoire of molecular activities.