mutation

Here’s a summary of the key points on mutations:

Chromosomes, Genes, and Mutations

• DNA consists of two strands of nucleotides forming a genetic code in triplets (codons).

• Genes are segments of DNA that code for specific proteins.

• Each gene is located at a specific position on a chromosome.

• Organisms inherit chromosomes in pairs, carrying genes in different versions (alleles), which contribute to genetic variation.

What Are Mutations?

• Mutations are changes in DNA due to errors in replication or external factors (mutagens).

• If a mutation occurs in germ cells, it can be passed to offspring; if in somatic cells, it is not inherited.

• Base substitution mutation: A single nucleotide change, which can be beneficial, neutral, or harmful.

Examples of Beneficial Mutations

1. HIV immunity: A mutation in a receptor protein prevents HIV binding.

2. Type II diabetes resistance: A mutation in the SLC30A8 gene provides protection.

3. Color vision: A historical mutation allowed primates to see three colors.

Types of Mutations

• Substitution: One nucleotide is replaced (can be silent due to genetic code degeneracy).

• Insertion: Extra nucleotides added, potentially disrupting protein function.

• Deletion: Removal of nucleotides, often causing severe effects.

• Inversion: A section of DNA is reversed.

Degeneracy in the Genetic Code

• Some amino acids are coded by multiple codons, making DNA more resistant to mutation effects.

• Silent mutations: Base changes that do not alter the final protein.

Sickle-Cell Anemia: A Harmful Mutation

• Caused by a base substitution (GAG → GTG), leading to valine replacing glutamic acid in hemoglobin.

• Red blood cells become sickle-shaped, reducing oxygen transport.

• Carriers (heterozygous individuals) have malaria resistance, explaining the mutation’s persistence in malaria-prone regions.

Insertion & Deletion Mutations

• Huntington’s Disease: Caused by excessive CAG trinucleotide repeats in the HTT gene, leading to brain cell degeneration.

• HIV resistance (CCR5-Δ32 mutation): A deletion in the CCR5 gene prevents HIV from entering immune cells.

Genetic Engineering and CRISPR

• CRISPR-Cas9 is a gene-editing tool that can modify or deactivate specific DNA sequences.

• Used to treat conditions like HPV-related cancers, hepatitis B, and cataracts.

Why Are Some Genes Conserved?

• Conserved sequences remain unchanged through evolution due to their crucial roles (e.g., ribosomal RNA and homeobox genes).

Let me know if you need further clarification or a more focused summary!