Law of Segregation And Law of Dominance

Law of Segregation and Law of Dominance are the fundamental principles in genetics, formulated by George Johann Mendel, known as “father of genetics”. These are laws that explain the inheritance of traits from the parent cells. Law of Segregation demonstrates that every living organism has one pair of alleles and these alleles get separated during gamete formation thus each gamete has one allele. This results in the passing of one allele from both parents to their offspring.

The Law of Dominance stipulates that a heterozygous individual has two alleles for a single particular trait, but the dominant allele will suppress the other allele thus deciding the phenotype of an individual. For instance, father’s skin color is black and mother’s skin color is bright, but dominant allele in this is black, so the phenotype of the individual will be black.

What is Inheritance?

Inheritance is defined as the transmission of traits or characters from parents to their offspring. He studied the pattern of inheritance of contrasting characters in pea plants and proposed the principle of inheritance, known as the ‘Mendel law of inheritance‘. The law includes the Law of dominance, the law of segregation, and ​law ​of independent assortment. 

Mendel stated that the characters that are regulated by factors (genes) are found in pairs, known as alleles. The expression of the character in the offspring follows a definite pattern in the first generation (F1), second generation (F2), and so on. Based on the experiment on the monohybrid cross, he formulated the first two laws of inheritance: the law of dominance and the law of segregation.

Law of Dominance

The law of dominance states that when factors are in heterozygous conditions, dominant characters are expressed unless recessive characters are in homozygous conditions.

The law of dominance is Mendel’s first law of inheritance. It has the following features:

• Characters are regulated by distinct units called ‘factors’( later known as genes).
• These factors are present in pairs.
• In heterozygous pairs, one factor of the pair will dominate the other.

The law of dominance explains that in a monohybrid cross, there is an expression of only one of the parental characters or trait cross in F1 and an expression of both the characters in the F2 generation.

Mendel cross-pollinated two plants that differed in one specific character, that is, the height of the pea plant, one with a tall height and the other with a short height. The height of all the offspring was tall. He called this generation as F1 generation. Next, he crossed two of the F1 plants with each other and observed that the resulting offspring, the F2 generation, had a 3:1 ratio of tall to short plants. This means that the trait for tall height was dominant over the trait for short height.

The trait which expresses itself in the F1 generation is called the dominant trait, and which is suppressed is called the recessive trait. ​Therefore,

Law of Segregation

Law of Segregation states that traits for each pair of genes separate or segregate from each other during gamete formation so that each gamete carries only one trait for each gene.

The law of Segregation is Mendel’s second law of inheritance. The law is based on the following facts:

• Alleles do not show any blending, and both traits are expressed in the F1 generation.
• During gamete formation, parents contain two alleles. Pair of alleles will separate from each other, and the gamete will receive only one of the two factors.
• Heterozygous parents produce two kinds of gametes, each having ​one allele with equal proportion, and homozygous parents will have all similar gametes.

FAQs on Law of Dominance and Segregation

1. What is Mendel’s law of inheritance?

Mendel gave three laws of inheritance. The laws are:

• Law of dominance
• Law of Segregation
• Law of independent assortment

2. Define the Law of Dominance.

The law of dominance states that when factors are in heterozygous conditions, dominant characters are expressed unless recessive characters are in homozygous conditions..

3. Why did Mendel use the Pea Plant for the Experiment?

Mendel selected pea plants for their quick life cycle, distinct traits, and versatility in both self-pollination and cross-pollination, facilitating efficient observation and controlled breeding in his inheritance studies.

4. ‌Why is Mendel’s Law of Segregation Defined as the Purity Law of Gametes?

Mendel’s law of Segregation explains that alleles do not show blending, and both the characters are expressed as such in the F2 generation, that is, either it will be a dominant or recessive character, not both alleles at the same time.

5. What are the Laws of Segregation?

As per the law of segregation, each organism’s gamete (egg or sperm cell) receives only one of the two gene copies, and this distribution is random.