Write short notes on the following: (i) sickle cell anaemia, (ii) pab locus in Neurospora, (ili) ma gene in maize, (iv) Adh alleles in maize, (v) inbreeding depression, and (vi) hybrid vigour.

Sourav PanSeptember 13, 2024

Answered

Short Notes

(i) Sickle Cell Anemia

• Definition: Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene, leading to abnormal hemoglobin S (HbS).
• Cause: The mutation involves a single nucleotide change (A to T) in the β-globin gene, resulting in an amino acid substitution (valine for glutamic acid).
• Symptoms: It leads to the production of sickle-shaped red blood cells, which cause blockages in blood vessels, leading to pain, anemia, and organ damage.
• Heterozygote Advantage: Individuals with one sickle cell allele (heterozygotes) are more resistant to malaria, providing a selective advantage in malaria-endemic regions.

(ii) pab Locus in Neurospora

• Definition: The pab locus in Neurospora crassa is responsible for the synthesis of p-aminobenzoic acid (PABA), a vital component for growth.
• Gene Interaction: Heterozygotes for the pab locus produce intermediate levels of PABA, resulting in faster growth compared to homozygous mutants that produce either too little or none.
• Significance: This locus provides an example of how heterozygosity can enhance growth through intermediate gene product levels.

(iii) Ma Gene in Maize

• Definition: The Ma gene in maize (Zea mays) influences the maturity and growth of the plant.
• Gene Effect: The heterozygous Ma ma plants exhibit greater vigor and later maturity compared to the homozygous Ma Ma or ma ma plants.
• Application: This gene demonstrates how heterozygotes can show superior traits such as enhanced growth rates and longer periods of anthesis.

(iv) Adh Alleles in Maize

• Definition: The Adh (alcohol dehydrogenase) gene in maize has multiple alleles that code for different forms of the enzyme alcohol dehydrogenase.
• Enzyme Function: Different alleles produce enzymes with varying heat sensitivities.
• Heterozygote Advantage: Heterozygotes exhibit an enzyme with improved heat stability compared to the homozygotes, which contributes to better stress resistance.

(v) Inbreeding Depression

• Definition: Inbreeding depression refers to the reduced biological fitness in a population resulting from mating between closely related individuals.
• Effects: It leads to an increase in homozygosity for deleterious alleles, resulting in decreased vigor, growth, fertility, and overall fitness.
• Example: In crops, inbreeding depression can reduce yields and increase susceptibility to diseases.

(vi) Hybrid Vigour

• Definition: Hybrid vigour, or heterosis, is the enhanced growth, yield, or overall performance of hybrids compared to their parent lines.
• Cause: It results from the combination of different genetic backgrounds from the parent lines, often leading to improved traits such as higher yield, greater size, and better disease resistance.
• Application: It is widely utilized in agriculture to produce high-yielding hybrid crops and livestock. Examples include hybrid maize and hybrid vegetables, which often outperform their parent varieties in terms of productivity and resilience.