Law of Segregation
The law of segregation had been put forth by Mendel while experimenting on pea plants to elaborate the inheritance pattern.
His two experiments lead to the development of Mendel’s laws which is also known as the laws of inheritance.
The elementary principles of this law are postulated as follows:
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
Mendel’s law of segregation states that the two alleles of a gene which were already instituted on the chromosome pair separates, with the descendant acquiring one allele from the paternal end while other from the maternal end.
Moreover, he states that these two alleles are segregated from each other during meiosis while formation of gametes.
To be more specific, it is more evident in the F2 generation or in the second of the two cell divisions of meiosis, leading the two distinct alleles separate from one another.
According to Mendel’s law, these two alleles act in a separated fashion and do not mingle or dominate each other.
This law is also referred to as law of purity of gametes since a gamete fetch either a recessive or a dominant allele but not both the alleles at the same time.
The other laws Mendel had postulated are as follows:
Law of Dominance
This is also called Mendel’s first law of inheritance. According to this, hybrid descendant will only transmit the dominant trait in the phenotype. In the heterozygous trait, the alleles that are suppressed are denoted by as recessive trait while those determining the trait are called as the dormant or dominant trait.
Law of Independent Assortment
Also called as Mendel’s second law of inheritance, it states that a pair of trait segregates independently of another pair during gamete formation.
As the individual heredity factors assort independently, totally different traits get equal chance to occur together.
Law of Segregation
The law of segregation states that during the production of gametes, two copies of each hereditary factor separate so that descendant receive one factor from each parent.
In other words, pairs of allele segregate during the formation of gamete which re-join randomly during fertilization. This is also called as Mendel’s third law of inheritance.
One can found more than one type of allele for a single gene.
The segregation is evident during the formation of gametes at the time of meiosis.
To consider the Mendelian trait, two alleles are involved — one is recessive and the other is dominant.
Another most important feature of this law, none of the allele influence each other and they continue to be in their pure form.
The alleles do not mix or blend, as it was truly believed before the Mendel’s postulation of the law of inheritance.
Thus, the law of segregation is also known as the law of purity of gametes.
Law of Segregation Principle
It was principally stated that every individual has two set of alleles for each particular phenotypic trait but during the gametogenesis, these alleles gets parted away, leading to creation of one allele per gamete.
The significance of this law is by describing the production of genotypic ratio in the haploid gametes.
Where Does the Law of Segregation Occur in Meiosis?
The physiological evidence of the Mendel’s segregation law lies in anaphase (I and II) of meiosis.
In the first meiotic division phase the homologous chromosomes are divided into two daughter nuclei with different variety of each gene.
During meiosis, the behaviour of homologous chromosomes can contribute to the partition of the alleles into distinct gametes for each genetic locus.
During the meiosis, the chromosomes separate into two equal portion to form two different gametes, similarly the two distinct alleles for a single gene often separate resulting in two separate alleles present on each gametes.
For example, in gametogenesis of humans, female gamete carries only X chromosome, thus, human eggs contain only X chromosome.
While human sperm contain either X or Y chromosome where the sex of the descendant will determine.
Thus, considering the law of segregation, for any characteristic, including the dominant or recessive trait, a gamete will receive one of the two alleles.
Another example taken into consideration is the color of flower, where the type of allele inherited by the descendant will decide the color trait of the flower.
The result of uniting of two different gametes (Red from paternal and white from maternal) at fertilization will depend on the transfer of alleles to the offspring from each parent.
Why is the Law of Segregation Universally Accepted?
Since there is no exception to this law, it is one of the universally accepted law of inheritance. Though, others have some sort of exception, they are also well accepted.
It states that during gametogenesis, each gene consisting of two different allele gets segregated, but the combined during fertilization.
Equal Segregation of Alleles
The law of segregation states that every person that is a diploid has a set of alleles for a specific attribute.
Every parent passes associated factor randomly to their descendant leading to a diploid organism.
The following 3 possible combinations of genotypes could result: homozygous dominant, heterozygous, or homozygous recessive for the F2 generation of a crossbreeding.
As a result of allele heterozygotes may appear from two totally different pathways and because heterozygotes and homozygous dominant people are phenotypically similar, the law supports Mendel’s determinant of 3:1 phenotypic ratio.
The equal segregation of alleles is that the reason we will apply the Punnett square to accurately predict the offspring of oldsters with renowned genotypes.
The physical basis of Mendel’s law of segregation is in the initial division of meiosis during which the homologous chromosomes with their totally different versions of every gene are separated into daughter nuclei.
The behavior of homologous chromosomes throughout meiosis can account for the segregation of the alleles at each genetic locus to totally different gametes.
Law of Segregation Summary
Mendel’s observation of 3:1 phenotypic ratio has been supported by the Law of Segregation.
Each gamete acquires one of the two alleles as chromosomes separate into different gametes during meiosis.
While heterozygotes, which have one dominant and one recessive allele, can receive each allele from either parent and will look identical to homozygous dominant individuals.
Law of Segregation Citations
- Cheaters sometimes prosper: distortion of mendelian segregation by meiotic drive. Trends Genet . 1993 Jun;9(6):205-10.
- Genetics, Autosomal Dominant.
- Statistics of Mendelian segregation-A mixture model. J Anim Breed Genet . 2019 Sep;136(5):341-350.