Concept of Recessiveness and Dominance

 Concept of Recessiveness and Dominance

Most people have often wondered why some people have a physical trait that they do not. Like why the eyes of one person is blue and other are deep brown. These differences are cause by genes, which all contain specific information. Everyone inherits two copies of each gene from their parents, and the copies can either be different, then one is going to mask the effects of the other. The gene that trumps over the other is usually known as the dominant gene, and the weaker gene is known as recessive. In the presence of dominant gene, a recessive gene will not show its traits. When two recessive genes are paired their traits will be visible. Dominant genes are also the ones whose traits are visible in the offspring. For recessive traits to be visible both parents have to carry that recessive gene singly or in a pair.

            Genes are usually termed dominant or recessive for a number of reasons. It is first important to note that genes are simply an instruction manual that is used to make certain protein. The protein made is what is actually responsible for the traits that are presented physically, like red hair or blue eyes. Since there are two copies of each gene(courtesy of both the parents), ‘the instruction manual’ in the mother’s gene may be slightly different from the one in the father. The combination of these two sets of instruction will cause the formation of a slightly different proteins. The reason some why some genes are dominant and other recessive all lies in the making of the proteins. When a gene makes a protein that is fundamental, then that gene is dominant. If the protein formed is broken, then the gene that has formed is recessive.

            A good example of this is the occurrence of red hair, which happens when a crucial protein in hair pigmentation fails to convert the red pigment to black, thus causing a build up of the former. If this protein is even slightly function, then the person will not have red hair. This is where the concept of dominant and recessive genes is derived.

Pedigree characteristics of autosomal recessive, autosomal dominant, x-linked recessive,  x-linked dominant and y-linked traits.  

Autosomal Recessive Traits

01.    Appears in both sexes with equal frequency.

02.    Trait tends to skip generation.

03.    Affected offspring are usually born unaffected parents.

04.   When both parents are heterozygous, approximately ¼ of the offspring will be                affected;

05.    Appear more frequently among the children of consanguine marriages

Autosomal Dominant Traits

 01.                 Appears in both sexes with equal frequently.

02.            Both sexes transmit the trait to their offspring.

03.               Does not skip generation.

04.                 Affected offspring must have an affected parent, unless they process a new                      mutation.

05.        When one parent is affected and other parent is unaffected. approximately   ½                        of the offspring will be affected.

06.             Unaffected parent do not transmit the trait.

X-linked Recessive Trait

01.            More male than female are affected.

02.            Affected some are usually born to unaffected mother; thus, the trait skips the                generations.

03.           A carrier (heterozygous) mother produces approximately ½ affected sons.

04.         Is never passed from father to son.

05.        All daughters of affected father are carriers.

  X-linked Dominant Trait

01.      Both male and female are affected; often more females than males are affected.

02.       Does not skip generations. Affected sons have must have an affected mother;               affected daughters must have either an affected mother or an affected father.

03.         Affected fathers will pass the trait on to all their daughters.

04.      Affected mothers (A heterozygous) will pass the trait on to ½ of their sons and ½         of  their daughters.

Y-linked Trait

01.                Only male are affected.

02.               Is passed to all sons from father.

03.          Does not skip generations.