a) Hardy-Weinberg Law
The Hardy-Weinberg Law is a fundamental principle in population genetics. It states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences. These conditions include no mutation, no migration, no natural selection, random mating, and a large population size.
Equation:
p² + 2pq + q² = 1
- p² = frequency of homozygous dominant genotype
- 2pq = frequency of heterozygous genotype
- q² = frequency of homozygous recessive genotype
This law helps in studying genetic variation and predicting the distribution of traits in a population.
b) Polymorphism
Polymorphism refers to the occurrence of two or more genetically determined variants or alleles in a population at a frequency greater than 1%. These differences can be in the form of morphological traits, blood types, or molecular variations like DNA sequences.
Types:
- Single Nucleotide Polymorphisms (SNPs)
- Insertion/Deletion polymorphisms
- Blood group polymorphism (e.g., ABO)
Polymorphisms are useful in genetic research, forensic science, disease studies, and evolution tracking.
c) FISH (Fluorescence In Situ Hybridization)
FISH is a powerful molecular cytogenetic technique used to detect and locate specific DNA sequences on chromosomes. It uses fluorescent probes that bind to only those parts of the chromosome that have a high degree of sequence complementarity.
Applications:
- Identifying chromosomal abnormalities
- Detecting genetic disorders like Down syndrome
- Cancer diagnostics
FISH provides rapid and accurate results and is widely used in clinical and research genetics.
d) Y-linked Inheritance
Y-linked inheritance, also known as holandric inheritance, refers to the transmission of genes located on the Y chromosome. Since only males have a Y chromosome, Y-linked traits are passed from father to son and never to daughters.
Characteristics:
- Only males are affected
- Trait appears in every generation
- Example: Hypertrichosis (excessive hair growth on ears)
Y-linked inheritance is rare because the Y chromosome has relatively few genes compared to the X chromosome.