Genetics & Evolution – Condensed Exam Notes

Page 1: Mutations

A mutation = any change in a DNA nucleotide sequence (can arise during replication or from environmental factors).
Mutations may alter protein structure/function → can influence an organism’s traits.
Categories of impact:
- Harmful: negative effect on health/survival (e.g., sickle-cell anemia, cystic fibrosis).
- Beneficial: positive effect (e.g., some variants reduce risk of Type 2 diabetes).
- Neutral: no observable effect; often involve nucleotide changes that do not alter amino-acid sequence.

Diploid organisms carry two chromosome sets arranged in homologous pairs.
Gametes (egg, sperm) are haploid → one chromosome set.
Fertilization fuses haploid gametes → restores diploid state in the zygote.
Offspring receive one chromosome set from each parent → new allele combinations create variation between parents and offspring.
Random segregation of homologous chromosomes during gamete formation generates variation among siblings.

Gene = DNA segment affecting a trait; variants are alleles.
Genotype = allele pair for a gene (one allele from each parent).
Homozygous: both alleles identical; heterozygous: alleles differ.
Phenotype = observable trait expression driven by genotype.
Dominant allele (uppercase letter) masks recessive allele (lowercase letter) in heterozygotes.
Punnett square: grid model predicting offspring genotypes/phenotypes from parental genotypes.

Evolution = heritable trait change across multiple generations in a population.
Requires genetic variation (different alleles/traits within the group).
Sexual reproduction supplies new allele combinations, fueling variation.
Over successive generations, trait frequencies shift; new traits may appear, others may diminish → population has evolved.
Accumulated changes over long periods can lead to speciation and Earth’s vast biodiversity.