Human genetics
From an evolutionary perspective, a recessive disease or trait can remain hidden for several generations before displaying the phenotype.
One example of an X-linked trait is Coffin–Lowry syndrome, which is caused by a mutation in ribosomal protein gene.
This mutation results in skeletal, craniofacial abnormalities, mental retardation, and short stature.
It is important that this process occurs otherwise a woman would produce twice the amount of normal X chromosome proteins.
A pedigree is a diagram showing the ancestral relationships and transmission of genetic traits over several generations in a family.
Penetrance is the percentage expressed frequency with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait.
Genetic counselors commonly use pedigrees to help couples determine if the parents will be able to produce healthy children.
A karyotype is picture of all the chromosomes in the metaphase stage arranged according to length and centromere position.
[1] Giemsa banding, g-banding, of the karyotype can be used to detect deletions, insertions, duplications, inversions, and translocations.
A FISH, fluorescent in situ hybridization, can be used to observe deletions, insertions, and translocations.
Medical genetics is the branch of medicine that involves the diagnosis and management of hereditary disorders.
[3] Four different forces can influence the frequencies: natural selection, mutation, gene flow (migration), and genetic drift.
Mitochondria are inherited from one's mother, and their DNA is frequently used to trace maternal lines of descent (see mitochondrial Eve).
However, females carry two or more copies of the X chromosome, resulting in a potentially toxic dose of X-linked genes.
[4] To correct this imbalance, mammalian females have evolved a unique mechanism of dosage compensation.
In particular, by way of the process called X-chromosome inactivation (XCI), female mammals transcriptionally silence one of their two Xs in a complex and highly coordinated manner.
