Sex-influenced traits, Sex-limited traits and Medical examination before the marriage

Sex-influenced traits are traits that their genes are carried on autosomes and the sex of individuals acts to modify their dominance where the act of these genes is influenced by the hormones secreted from the gonads of adult males and females, Sometimes, the sex of living organisms acts to modify the dominance of some traits that are called sex-influenced traits, such as the presence of horns in cattle trait and genetic baldness trait in humans.

Sex-influenced traits

Sex-influenced traits are genetic traits where the expression of a particular gene is influenced by the sex of the individual, even though the gene is not located on the sex chromosomes (X or Y). These traits are typically autosomal, meaning the genes for them are found on non-sex chromosomes, but they are expressed differently in males and females due to hormonal differences, particularly related to androgens (like testosterone) and estrogens.

Baldness

Baldness spreads among males of some families more than the females, Its appearance is controlled by a dominant gene that is carried on autosomes and influenced by the masculinity hormones only.

In Males

• Pure genotype (B⁺ B⁺), Male suffers from baldness due to the presence of two dominant genes and Masculinity hormones.
  
• Hybrid genotype (B⁺ B), Male suffers from baldness due to the presence of one dominant gene and Masculinity hormones.
• Pure genotype (B B) has normal hair.
  

In Female

• Pure genotype (B⁺ B⁺), The Female suffers from hair falling due to the presence of two dominant genes.
• Hybrid genotype ( B⁺ B), Normal hair although the presence of one dominant gene but it does not express its effect due to the absence of masculinity hormones.
• Pure genotype ( B B ) has normal hair.

Therefore, the phenotype of the hybrid genotype  (B⁺ B) is different in males and females.

Sex-limited traits

They are traits constricted (limited) to one sex only due to differences in sex hormones of each sex.

Examples

1. Milk production is limited only to females because they have certain hormones that help the gene to express its effect.
2. The appearance of beard trait is limited to males only and it is one of the secondary sex characteristics in human males.
3. Egg laying is limited to females only, such as birds and other animals.

Medical examination before the marriage

Medical examination before marriage is a series of medical examinations carried out for the person who will get married.

Causes of medical examination of persons who will get married:

• To be sure that they are free from Infectious diseases such as hepatitis and AIDS and genetic diseases such as thalassaemia.
• Giving the medical council about the possibility of the transmission of the previous disease to the partner or offspring in the future.
• Providing the choices or alternatives to who will get married in planning for a healthy family.

Importance of medical examination before marriage:

• Giving birth to healthy children.
• Limiting the spreading out of genetic diseases, congenital deformities, and mental retardation.
• Avoiding the financial, psychic, and social loads when caring the children infected with genetic diseases.

Genetic fingerprint (DNA fingerprint)

Discovering genetic fingerprint: In 1984, Sir Alec Jeffreys at Leicester University in London published research that showed that the genetic material (DNA) may repeat several times inside the living organism.

In 1985, he stated that these repetitive sequences are unique and characteristic for each individual and they are impossible to be similar in two individuals except in identical twins only, He named them the human DNA fingerprint (or DNA typing).

DNA fingerprint

It is sequences of genetic material (DNA) that repeat several times in the living organism, It is a mean used to identify individuals through comparing DNA sections (fragments).

Uses of genetic fingerprint

• In medicine: Studying the genetic diseases and operations of tissue implantation.
• In forensic medicine: Identifying deformed corpses, tracing missing children, judging tissues of ancestries, and exoneration and condemnation of persons from killing and ravishment crimes.

Human genome

It is all genes found in the nucleus of each somatic cell.

Discovering the human genome:

In 1953, Watson and Crick proved that the gene is a double helix of the nucleus acid DNA, In 1980, the idea of the human genome appeared and several genes identical to scientists were about 450 genes, At the middle of the eighties, scientists identified about 1500 genes.

Uses of human genome:

• Identifying the genes causing genetic diseases through drawing a good genetic map that identifies the location of genes on chromosomes accurately.
• Studying the evolution of living organisms by comparing the human genome to other ones of other living organisms.
• Breed improves through identifying genes of diseases in the fetus before its delivery and acting to improve them.
• Manufacturing drugs without side effects.

Examples of Sex-Influenced Traits

• Pattern baldness: This trait is more common in males than in females. While both men and women can carry the gene for baldness, it is often expressed more prominently in men due to the influence of testosterone.
• Beard growth: The ability to grow a thick beard is a sex-influenced trait that is expressed more in men due to higher levels of testosterone.
• Voice pitch: Genes related to voice pitch can be expressed differently in men and women, where men tend to have deeper voices due to the effect of testosterone on the vocal cords.

Autosomal inheritance: These traits are not tied to the sex chromosomes (X or Y), so both males and females can carry the genes.

Hormonal influence: Sex-influenced traits depend on the hormonal environment, so they may be expressed differently in males and females despite having the same genotype.

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