Principles of Inheritance and Variation NEET Questions

Principles of Inheritance and Variation TFQs

Principles of Inheritance and Variation is a crucial topic for NEET aspirants.

The principles of inheritance and variation are foundational concepts in genetics and are crucial for understanding how traits are passed from parents to offspring and how genetic diversity arises. Here’s a breakdown of these principles:

1. Mendelian Inheritance

Gregor Mendel’s Laws:

• Law of Segregation: Each individual has two alleles for each gene, which segregate (separate) during gamete formation. An individual inherits one allele from each parent, and these alleles recombine in the offspring.
• Law of Independent Assortment: Genes for different traits are passed independently of one another from parents to offspring. This means that the inheritance of one trait generally does not affect the inheritance of another trait, provided the genes are on different chromosomes or are far apart on the same chromosome.

Key Terms:

• Alleles: Different versions of a gene.
• Genotype: The genetic constitution of an individual (e.g., AA, Aa, aa).
• Phenotype: The observable traits or characteristics of an individual (e.g., eye color, height).

2. Non-Mendelian Inheritance

Types:

• Incomplete Dominance: Neither allele is completely dominant over the other, resulting in a phenotype that is a blend of the two alleles (e.g., red and white flowers producing pink flowers).
• Codominance: Both alleles in a heterozygous individual contribute equally and visibly to the phenotype (e.g., AB blood type where both A and B antigens are expressed).
• Multiple Alleles: More than two alleles exist for a gene, but an individual still has only two alleles. For example, the ABO blood group system has three alleles: A, B, and O.
• Polygenic Inheritance: Traits are controlled by multiple genes, each having a small additive effect (e.g., height, skin color). This leads to a continuous range of phenotypes.
• Linked Genes: Genes located close to each other on the same chromosome tend to be inherited together. This linkage can affect the patterns of inheritance observed in genetic crosses.

3. Variation

Sources of Variation:

• Mutation: Changes in the DNA sequence can introduce new genetic variations. Mutations can be beneficial, harmful, or neutral.
• Recombination: During meiosis, homologous chromosomes exchange genetic material through a process called crossing over, leading to new combinations of alleles.
• Independent Assortment: During meiosis, the random distribution of chromosomes to gametes contributes to genetic variation.
• Random Fertilization: The random combination of gametes during fertilization adds another layer of genetic diversity.

4. Sex-Linked Inheritance

Key Concepts:

• X-Linked Traits: Genes located on the X chromosome. Since males have one X chromosome (XY) and females have two (XX), X-linked traits often show different patterns of inheritance in males and females (e.g., hemophilia, color blindness).
• Y-Linked Traits: Genes located on the Y chromosome, affecting traits that are passed from father to son.

5. Epigenetics, Genetic Counseling and Other Applications

Concepts:

• Epigenetic Modifications: Changes in gene expression that do not involve changes to the DNA sequence itself, such as DNA methylation and histone modification. These modifications can influence how genes are expressed and can sometimes be inherited.

Relevance:

• Understanding these principles helps in diagnosing genetic disorders, predicting the likelihood of genetic conditions in offspring, and applying genetic knowledge in fields like medicine, agriculture, and conservation.

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