Genetics Course Module Introduction

Study Notes

Traits are passed down from generation to generation, displaying heredity.
Heredity maintains consistent properties and functions during reproduction, with variations called genotypical variations.
Genetics is the study of heredity and genotypical variations.

Genotype: Internal structure of an individual.
Phenotype: External appearance of a character.
Homozygous: Two identical alleles for a character (pure race).
Heterozygous: Two different alleles for a character (hybrid).
Allele: Variant of a gene, occupying the same locus on homologous chromosomes.
Dominant Allele: An allele expressed even when present on only one homologous chromosome.
Recessive Allele: An allele requiring presence on both homologous chromosomes to be expressed.
Gene: A unit of genetic information, part of a DNA sequence, responsible for character expression.
Allele: A particular form or version of a gene.
Locus: Location of a gene on a chromosome.
Genome: The complete set of DNA and chromosomes, constituting an individual's genetic material.
Chromosome: Linear or circular arrangement of genes, DNA, protein, and RNA.
DNA: Deoxyribonucleic acid, a double-stranded chain of nucleotides, forming the fundamental substance of genes.

Monohybridism: Crossing two individuals of the same species that differ in only one character.
Dihybridism: Crossing of two individuals of the same species with two differing characters.
Polyhybridism: Crossing between individuals exhibiting several differing characters.
Mendel's Experiment (1st step): Crossing peas with differing seed appearance, leading to an F1 generation of 100% smooth hybrids.
Conclusion: All F1 hybrids are uniform in appearance.
1st Mendel's Law (Uniformity of F1): All offspring from a cross between parent plants having distinct traits are similar.
Phenotypic disappearance of a trait (2nd step): Crossing F1 plants demonstrates reappearance of the wrinkled trait, revealing the presence of recessive alleles.

2nd Cross: Crossing F1 hybrids to yield an F2 generation, showing different ratios of smooth or wrinkled seeds - revealing recessive and dominant traits. Proportion of smooth traits is 3:1.
Conclusion: Recessive trait is hidden within the dominant trait in the F1 generation but reappears in the F2 generation.
Gamete Purity (2nd Mendel's Law): During gamete formation, the two alleles of a gene separate.
Allele notation: Dominant alleles are capitalized (e.g., S) and recessive alleles are lowercase (e.g, s).
Genotype ratios for F2: Observed ratios reflect the predictable outcomes of allele combinations during parental gamete formation and subsequent fertilization (e.g., 1/4 smooth breed, 1/2 hybrids, ¼ wrinkled breed).