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An inversion is a chromosome rearrangement in which a segment of a chromosome becomes inverted within its original position. An inversion occurs when a chromosome undergoes a two breaks within the chromosomal arm, and the segment between the two breaks inserts itself in the opposite direction in the same chromosome arm.
1. Values for heterozygote inversions of the third chromosome were often much higher than they should be under the null assumption: if no advantage for any form the number of heterozygotes should conform to N s (number in sample) = p 2 +2pq+q 2 where 2pq is the number of heterozygotes (see Hardy–Weinberg equilibrium). 2.
There are two popular and overlapping theories that explain the origins of crossing-over, coming from the different theories on the origin of meiosis.The first theory rests upon the idea that meiosis evolved as another method of DNA repair, and thus crossing-over is a novel way to replace possibly damaged sections of DNA. [9]
Other mutations, which inactivate the enzyme (= null alleles) are lethal when inherited homozygously (two defective copies of the TPI gene), but have no obvious effect in heterozygotes (one defective and one normal copy). However, the frequency of heterozygous null alleles is much higher than expected, indicating a heterozygous advantage for ...
Schematic karyogram, with annotated bands and sub-bands as used in the International System for Human Cytogenomic Nomenclature of chromosomal rearrangements. 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).
Because of the unusual cruciform pairing configuration in translocation heterozygotes, nondisjunction of homologous centromeres occurs at a measurable but low rate. This nondisjunction produces an adjacent-2 segregation pattern in which the homologous centromeres N1 and T1 go to the same spindle pole while the homologous centromeres N2 and T2 ...
Compound heterozygotes are often observed only through subclinical symptoms such as excess iron. Disease is rarely observed in such compound heterozygotes unless other causal factors (such as alcoholism) are present. As a result, compound heterozygosity for hemochromatosis may be more common than diagnosis based on pathology would suggest.
In the seaweed fly, Coelopa frigida, heterozygotes at the locus alcohol dehydrogenase (Adh) have been shown to express better fitness by having higher larval density and relative viability. [12] Females displayed disassortative mating in respect to the Adh locus because they would only mate with males of the opposite Adh genotype. [13]