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

Sex-influenced traits

They are traits that their genes are carried on autosomes and the sex of individual acts to modify their dominance where the act of these genes is influenced by the hormones secreted from gonads of adult males and females , Sometimes, the sex of living organism 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 .

Baldness

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

In Males

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

In Female

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

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

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 the females, because they have certain hormones 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 trait is limited to females only such as birds and some 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 as hepatitis and AIDS and genetic diseases as thalassaemia .
• Giving the medical councel 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 healthy children .
• Limiting the spreading out of genetic diseases , congenital deformities and mental retardation .
• Avoiding the financial , psychic , 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 a research 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 the identical twins only, He named them the human DNA fingerprint ( or DNA typing).

DNA fingerprint

It is sequences of genetic material ( DNA ) 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 tissues implantation .
• In forensic medicine : Identifying deformed corpses , tracing missing children , judging tissues of ancestries and exoneration and condemntation 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 human genome appeared and number of genes identical by scientists was about 450 genes , At the middle of 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 human genome by other ones of other living organisms.
• Breed improving through identifying genes of diseases in the fetus before its delivery and act to improve them.
• Manufacturing drugs without side effects .