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In this case, no further mutations would be necessary to preserve (or retain) the duplicates. However, at a later time, such mutations could still occur, leading to genes with different functions (see below). Gene dosage effects after duplication can also be harmful to a cell and the duplication might therefore be selected against.
Duplications of oncogenes are a common cause of many types of cancer. In such cases the genetic duplication occurs in a somatic cell and affects only the genome of the cancer cells themselves, not the entire organism, much less any subsequent offspring.
A gynandromorph can have bilateral symmetry—one side female and one side male. [24] Alternatively, the distribution of male and female tissue can be more haphazard. Bilateral gynandromorphy arises very early in development, typically when the organism has between 8 and 64 cells. [25] Later stages produce a more random pattern. [citation needed]
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]
During fertilization of the egg cell, a second, separate fertilization event gives rise to the endosperm, an extraembryonic structure that nourishes the embryo in a manner analogous to the mammalian placenta. Unlike the embryo, the endosperm is often formed from the fusion of two maternal cells with a male gamete. This results in a triploid ...
Repeated sequences (also known as repetitive elements, repeating units or repeats) are short or long patterns that occur in multiple copies throughout the genome.In many organisms, a significant fraction of the genomic DNA is repetitive, with over two-thirds of the sequence consisting of repetitive elements in humans. [1]
It occurs during and shortly after DNA replication, in the S and G 2 phases of the cell cycle, when sister chromatids are more easily available. [29] Compared to homologous chromosomes, which are similar to another chromosome but often have different alleles , sister chromatids are an ideal template for homologous recombination because they are ...
This is because spermatocytes go through a larger number of cell divisions throughout a male's life, resulting in more replication cycles that could result in a DNA mutation. [5] Errors in maternal ovum also occur, but at a lower rate than in paternal sperm. [5] The types of mutations that occur also tend to vary between the sexes. [7]