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Errors in meiosis resulting in aneuploidy (an abnormal number of chromosomes) are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities. [ 4 ] In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the ...
The leptotene stage, also known as leptonema, is the first of five substages of prophase I during meiosis, the specialized cell division that reduces the chromosome number by half to produce haploid gametes in sexually reproducing organisms.
Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum; the process is known as meiosis Main article: Oogenesis The formation of an oocyte is called oocytogenesis, which is a part of oogenesis. [ 1 ]
This is typical in animals, though the number of chromosome sets and how that number changes in sexual reproduction varies, especially among plants, fungi, and other eukaryotes. [ 2 ] [ 3 ] In placental mammals , sperm cells exit the penis through the male urethra and enter the vagina during copulation , [ 4 ] [ 5 ] while egg cells enter the ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 21 December 2024. Procreative biological processes of humanity Part of a series on Sex Biological terms Sexual dimorphism Sexual differentiation Feminization Virilization Sex-determination system XY XO ZW ZO Temperature-dependent Haplodiploidy Heterogametic sex Homogametic sex Sex chromosome X chromosome ...
A karyotype of an individual with trisomy 21, showing three copies of chromosome 21. An abnormal number of chromosomes is known as aneuploidy, and occurs when an individual is either missing a chromosome from a pair (resulting in monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.).
Otherwise, the offspring will have twice the normal number of chromosomes, and serious abnormalities may result. In humans, chromosomal abnormalities arising from incorrect spermatogenesis results in congenital defects and abnormal birth defects (Down syndrome, Klinefelter syndrome) and in most cases, spontaneous abortion of the developing foetus.
Organisms in which a particular chromosome, or chromosome segment, is under- or over-represented are said to be aneuploid (from the Greek words meaning "not", "good", and "fold"). Aneuploidy refers to a numerical change in part of the chromosome set, whereas polyploidy refers to a numerical change in the whole set of chromosomes. [44]