NEET'22 Crash Course

Heterozygous Meaning

Heterozygous means that an organism inherits different variants of the specific gene from both parents. Furthermore, a heterozygous genotype differs from a homozygous genotype. This is because a person with a homozygous genotype inherits identical copies of a gene from both parents.


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A heterozygote is represented by a capital letter as well as a lower case letter. As a result, Rr or Ss are used to represent it. Experts also consider that a heterozygote for gene R is Rr. The uppercase letter takes precedence in this case.

Heterozygote advantage is a circumstance in which the heterozygous genotype has a distinct benefit. The heterozygous genotype has greater relative fitness than the homozygous dominant or homozygous recessive genotypes in this case. Furthermore, heterozygote advantage is limited to a single gene in this scenario. Furthermore, this is a case of overdominance.


Heterozygous Example 

The two different alleles in a heterozygous genotype interact with one another. This affects how their characteristics are expressed.

This encounter is frequently based on dominance. "Dominant" refers to the allele that is expressed more strongly, whereas "recessive" refers to the other. The dominant allele covers the recessive allele.  Depending on how the dominant and recessive genes interact, a heterozygous genotype may include:


Complete Dominance

The heterozygous dominant allele entirely covers the recessive one in total dominance. The recessive allele does not have any effect.

Eye colour, for example, is influenced by a number of genes. The brown eye allele is more common than the blue eye gene. Brown eyes are the result of having one of each. You do, however, carry the recessive mutation for blue eyes. It's probable that your child will have blue eyes if you reproduce with someone who shares the same allele.


Incomplete Dominance

When the dominant allele doesn't overcome the recessive one, it's called incomplete dominance. Instead, they integrate together, resulting in a third characteristic.

Hair texture is a good example of this type of dominance. You'll have wavy hair if you have one allele for curly hair and one for straight hair. Curly and straight hair combine to create waviness.


Codominance

When both alleles are present at the same time, codominance occurs. They don't, however, blend in. Both features are present in equal measure.

Codominance is illustrated by the blood type AB. In this scenario, you have one allele for type A blood and one for type B blood. Both alleles produce both types of blood, rather than combining to form a third type. Type AB blood is the result of this.


Differences Between Heterozygous and Homozygous 

Basis for Comparison

Homozygous

Heterozygous

Definition

Homozygous is a genetic situation in which a person inherits similar alleles from both parents for a gene.

Heterozygous is a genetic situation in which a person inherits different alleles of the same gene from both parents.

Genotype representation

Homozygous genotypes are indicated as AA or aa, respectively, for homozygous-dominant or homozygous-recessive situations.

Heterozygous genotypes are denoted by the letter Aa.

Phenotypes

With dominant or recessive homozygous circumstances, two alternative phenotypes are available.

In the heterozygous state, the dominant allele is primarily responsible for the phenotype.

Gametes

A single type of gamete is produced by homozygous genotypes.

Two types of gametes originate from heterozygous genotypes.

Traits

Over generations, homozygous genotypes create the same properties.

Over generations, heterozygous genotypes develop diverse phenotypes.

Hybrid vigour

The homozygous state seems to be free from hybrid vigour.

Heterozygous condition has  hybrid vigour.

Types

The two forms of homozygous circumstances are homozygous-dominant and homozygous-recessive.

Co-dominance, incomplete dominance and total dominance are three alternative ways to display the heterozygous situation.

Also called

Homozygotes are organisms or cells that have a homozygous state.

Heterozygotes are organisms or cells that have a heterozygous state.

Observed in

Homozygous genotypes have been observed in asexually reproducing animals.

Heterozygous genotypes are most commonly found in animals that reproduce sexually.

Diseases

Fibrosis, sickle cell anaemia, and phenylketonuria are all disorders linked to the homozygous state.

Huntington's disease, Marfan's syndrome, and familial hypercholesterolemia are all disorders linked to the heterozygous condition.


Heterozygous Genes and Disease

A mutant allele can result in genetic disorders. Because the mutation changes the way DNA is expressed, this is the case. The mutant allele may be dominant or recessive, depending on the situation. If it's dominant, it suggests that sickness can be caused by just one mutant copy. A "dominant sickness" or "dominant disorder" is what this is referred to as.

You're more likely to get a dominant condition if you're heterozygous for it. If you're heterozygous for a recessive mutation, on the other hand, you won't acquire it. You become a carrier when the typical allele takes over. As a result, it's possible that your children will contract it.


The Following are Some Examples of Dominating Diseases:

Huntington’s Disease

Huntingtin, a protein associated with nerve cells in the brain, is produced by the HTT gene. Huntington's disease is a neurological condition caused by a mutation in this gene. An individual with just one copy of the mutant gene will develop Huntington's disease because the defective gene is dominant. This degenerative brain disease, which most usually manifests in adults, can lead to:

  • uncontrollable motions

  • emotional problems

  • low mental abilities

  • Having difficulty walking, speaking, or swallowing


Marfan’s Syndrome

Marfan's syndrome affects the connective tissue, which gives the body's structures strength and shape. Symptoms of a genetic disease include:

  • Scoliosis is an abnormally curved spine.

  • expansion of some bones in the arms and legs

  • nearsightedness

  • difficulties with the aorta, the artery that transports blood from your heart to your body

  • the rest of your body to your heart

A mutation in the FBN1 gene is linked to Marfan's syndrome. To cause the disease, only one mutant variation is required.


Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is caused by a mutant copy of the APOB, LDLR, or PCSK9 gene in heterozygous genotypes. It's quite prevalent, affecting 1 in 200 to 250 people, according to Trusted Source. FH raises LDL cholesterol levels to dangerously high levels, increasing the risk of coronary heart disease at a young age.

Assume that being heterozygous for a gene means that you have two different versions of that gene. The dominant form can totally obscure the recessive one, or they can merge. Both versions may display at the same time in some circumstances. The two genes can interact in a variety of ways. Their relationship is what determines your physical characteristics, blood type, and other characteristics that define who you are.


Do you know? 

What is the probability of the heterozygous offspring?  The following are the probabilities of the outcome: 50 % dominant allele x 50 % recessive allele = 25% chance that both offspring's alleles are dominant. Both of the offspring's alleles have a 50 % x 50 % = 25 % chance of becoming recessive. The probability of the kids being heterozygous is 50 % x 50 % + 50 % x 50 % = 25 % + 25 % = 50 %.

FAQs (Frequently Asked Questions)

1. What is the example of heterozygous genotype?


Ans: Heterozygous genotype is exemplified by sickle-cell anaemia.

  • Sickle-cell anaemia is caused by a recessive disease that affects the development of blood cells.

  • As a result, people with heterozygous genes display the dominant phenotype, preventing sickle-cell anaemia.

  • The structure of red blood cells transforms to a sickle shape in sickle-cell anaemia, making them small and unable to carry adequate oxygen.

  • As a result, such persons profit from the heterozygous genotype of the gene that causes sickle-cell anaemia.

2. What is a heterozygous female?


Ans: After going through heterozygous meaning it is very simple that a person has two copies of a gene (one inherited from one parent, and the other from the other parent). The X and Y chromosomes, which play a role in gender differentiation, are known as sex chromosomes. One from each parent, women inherit two X chromosomes. As a result, a female can be homozygous or heterozygous for a given X chromosomal characteristic.

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