Molecular Genetics

Homozygous – Definition, Characteristics, and Examples

Homozygous refers to a cell that has two identical alleles for a single trait form both the father and mother cell. The topic of this cell is very important in molecular biology. Students can learn more information about homozygous cells and their characteristics here.

homozygous

 

Definition and Meaning of Homozygous

Homozygous means having identical alleles for a single trait only. Furthermore, an allele refers to one particular specific form of a gene. Moreover, the alleles are known to exist in various different forms. Also, diploid organisms contain two alleles for a particular trait.

The unification of the alleles randomly happens upon fertilization. Furthermore, this unification takes place as the homologous chromosomes pair up.

One must consider for example a human cell, which contains 23 pairs of chromosomes for a total of 46 chromosomes. The donation of one chromosome in each pair is from the mother and other from the father. Moreover, the alleles which exist on these chromosomes determine traits or the characteristics in the organisms.

One from Each

An organism’s genes consist of molecules of the chemical DNA. Moreover, the arrangement of such genes is in structures called chromosomes. Above all, these chromosomes contain all the genetic instructions which an organism’s life processes require.

Each parent passes along one gene for each and every trait which is inherited. Moreover, two or more variations or “alleles” are possible in genes. A good example is a pea plant that certainly has two alleles for height: tall and short.

The human blood type has three possible alleles which are A, B, and O. Although the environment plays a part, an individual’s phenotype depends a great deal upon one’s parent’s contribution to alleles.

Same or Different

Sometimes both the parents may pass along the same allele for a gene, a homozygous trait is a result. In case the alleles are different, then the heterozygous trait is the result.

A homozygous trait will most probably appear in the organism. If a pea plant receives two alleles related to tallness, then certainly it will have a long stem. In contrast, if it gets two “short” alleles, then the growth will not be significant. A person whose parents both gave B blood type alleles has that kind of blood. For a specific trait, the genotype is either homozygous or heterozygous, however, the phenotype is identified by the way it is expressed. Example of this can be a tall stem or B blood type.

Spell It Out

When discussions of genotype take place, the identification of alleles is typically by letters. The use of capitals takes place for alleles that are dominant. The expression of a dominant allele mostly takes place even if the other allele is different.

Lowercase letters certainly give an indication of recessive alleles. These most probably will not show up unless both alleles are the same. For example, one homozygous genotype for pea plant height can certainly be TT, what this means is that it will have the phenotype “tall.” Genotype can very well be homozygous for recessive genes as well.

Playing It Out

Homozygous genotypes are certainly visible in the phenotypes of many types of organisms. However, there are some genes that are dominant. Therefore one can know for sure that a trait is homozygous in case it is recessive.

An appropriate example can be of some members of a cattle species which have the presence of black coats: BB or Bb. The red ones are certainly bb. Most noteworthy, not all inherited traits are of a harmless nature.

Solved Question For You

Q1 Which of the following statements is not true with regards to Homozygous?

A. The allele refers to one particular specific form of a secretion

  1. It refers to a cell that has two identical alleles for a single trait from both the father and mother cell
  2. Homozygous genotypes are certainly visible in the phenotypes of many types of organisms
  3. The unification of the alleles randomly happens upon fertilization

A1 The correct option is option A., which is “the allele refers to one particular specific form of a secretion.” This is because the correct statement is “the allele refers to one particular specific form of a gene.”

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