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Whilst XY sex determination is the most familiar, since it is the system that humans use, there are a range of alternative systems found in nature. The inverse of the XY system (called ZW to distinguish it) is used in birds and many insects, in which it is the females that are heterogametic (ZW), while males are homogametic (ZZ). [18]
For example, there are moths and butterflies that are ZW, but some have been found female with ZO, as well as female with ZZW. [22] Also, while mammals deactivate one of their extra X chromosomes when female, it appears that in the case of Lepidoptera , the males produce double the normal amount of enzymes, due to having two Z's. [ 22 ]
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 full) form of the condition due to a phenomenon known as skewed X-inactivation, in which the normal ...
The first 22 pairs are called autosomes. Autosomes are homologous chromosomes i.e. chromosomes which contain the same genes (regions of DNA) in the same order along their chromosomal arms. The 23rd pair of chromosomes are called allosomes. These consist of two X chromosomes in females, and an X chromosome and a Y chromosome in males. Females ...
The words homozygous, heterozygous, and hemizygous are used to describe the genotype of a diploid organism at a single locus on the DNA. Homozygous describes a genotype consisting of two identical alleles at a given locus, heterozygous describes a genotype consisting of two different alleles at a locus, hemizygous describes a genotype consisting of only a single copy of a particular gene in an ...
The human genome consists of two copies of each of 23 chromosomes (a total of 46). [1] One set of 23 comes from the mother and one set comes from the father. [1] Of these 23 pairs of chromosomes, 22 are autosomes, and one is a sex chromosome. [1]
A total of 120 subjects (women who had never had sons) were investigated, and it was found that 21% of them had male DNA in their peripheral blood. The subjects were categorised into four groups based on their case histories: [97] Group A (8%) had had only female progeny. Patients in Group B (22%) had a history of one or more miscarriages.
Let us assume an estimated babies are born with cystic fibrosis, this is about the frequency of homozygous individuals observed in Northern European populations. We can use the Hardy–Weinberg equations to estimate the carrier frequency, the frequency of heterozygous individuals, 2 p q {\displaystyle \textstyle 2pq} .