Genetics for Medical Aspirants

Pleiotropy is a genetic inheritance pattern in which a single gene causes or affects an entire series of traits.

Regulator genes control the timing and duration of production of a variety of substances such as proteins in our bodies.

The example of an incompletely penetrant genetic inheritance is multiple sclerosis. It apparently develops when an individual who carries the gene or genes for this disease is attacked by a virus that causes a flu-like illness.

Polygenic traits are determined by multiple pairs of alleles. Simple Mendelian rules of dominance do not readily apply. Human stature is an example. It results from all of the genes that determine the size of all body parts from head to foot.

This hypothetical example would be an example of the intermediate expression of a trait. Apparently, this is rare. For most genes, it is expected that individuals with heterozygous genotypes will have phenotypes like homozygous dominant individuals.

Codominant traits are the ones in which both alleles are expressed when the phenotype is heterozygous. In the case of the ABO blood type system, A and B are codominant. They are also completely dominant over O.

Only one gender actually has sex-limited genes expressed in the phenotype, while both inherit them. The typical heavy male facial beard is an example of a trait whose inheritance follows this pattern.

When genes have a different effect depending on the gender of the parent from whom they are inherited, it is referred to as genome imprinting. Diabetes, psoriasis, and Prader-Willi syndrome are other examples of this phenomenon.

Modifying genes alter the effect of companion genes in the phenotype of an individual. A real life example is a gene that modifies the effect of a dominant cataract allele.

An example of a sex-controlled genetic trait is gout. While both men and women can get it, men generally have more severe symptoms.

While monozygotic twins are identical in genetic makeup, but the individuals after conception and birth can alter their phenotypes.

It is described as the interaction between genes. It can be contrasted with dominance, which is an interaction between alleles at the same gene locus.

Stuttering or unstable alleles structurally change from generation to generation. Segments of these rare genes are doubled with each generation, resulting in an intensification of a trait. One form of muscular dystrophy apparently can follow this pattern.

When the family history or age of the mother indicates a high risk of gross chromosomal abnormalities, embryonic or fetal tissue samples are often collected and cultured so that a karyotype of the chromosomes can be analyzed.

A karyotype of the embryonic or foetal cells extracted from within a mother's uterus may show chromosome irregularities that are associated with specific kinds of major genetic problems.

There is a far greater probability of males expressing recessive alleles in their phenotypes if they are carried on X chromosomes. For females to have such traits, they would have to inherit the recessive allele for them on both of their X chromosomes.

A foetus and the surrounding amniotic fluid are within the amniotic sac. Amniotic fluid mostly contains fetal urine but also has millions of fetal skin cells that can be cultured to produce a karyotype. As a result, this is what actually sampled.

These are standard diagnostic tools to determine whether or not an unborn child is at risk for a small range of very serious genetic disorders.

People with Turner syndrome are females who inherit only one X chromosome.Their genotype is usually written X0.

Cells in blood, hair, finger nails, and any other tissues in our body can be cultured to create a karyotype of the chromosomes. Since all of your somatic cells will have the same chromosomes, it generally doesn't matter which ones are used.

They have a much greater chance than average of having epilepsy, hypothyroidism, crossed eyes, cataracts, heart defects, hernias, a marked susceptibility to respiratory infections such as pneumonia, and childhood leukemia.

Women with Turner syndrome are essentially postmenopausal from early childhood and are sterile because their ovaries do not develop normally and they do not ovulate.

Because sex chromosome abnormalities rarely result in an early death and their symptoms are not often severe, comparatively large number of people with these abnormalities survive to old age.

The feminising effects of Klinefelter syndrome can be diminished if boys are treated regularly with testosterone injections from the age of puberty. As a result of this treatment, most become sufficiently ordinary in appearance to live in society without notice.

In most Down syndrome cases, there is an extra chromosome 21 (i.e. trisomy-21). More rarely, there is a structural modification in one or both of the chromosomes in this homologous pair.