Reproduction, Heredity and Evolution
The reproduction, heredity and evolution domain of the Basque PAU Biology exam connects reproductive strategies with inheritance and population change. You should compare asexual and sexual reproduction, interpret pedigrees and explain the mechanisms that alter allele frequencies.
Reproduction
- Asexual reproduction is rapid and produces genetically identical offspring; sexual reproduction generates variation through meiosis, crossing over and random fertilisation.
- Gametogenesis produces haploid gametes; fertilisation restores the diploid number.
- Plants show alternation of generations between gametophyte and sporophyte; animals may show external or internal fertilisation and different developmental patterns.
Heredity
- Mendelian segregation and independent assortment explain inheritance patterns.
- Sex-linked traits show different frequencies in males and females because males are hemizygous for X-linked genes.
- Pedigrees distinguish dominant, recessive, autosomal and sex-linked inheritance.
Evolutionary mechanisms
- Mutation creates new alleles; gene flow moves alleles between populations; genetic drift changes allele frequencies by chance, especially in small populations; natural selection changes frequencies according to fitness.
- Hardy–Weinberg equilibrium requires no mutation, no migration, no selection, random mating and a large population.
- Speciation can be allopatric or sympatric and requires reproductive isolation.
Worked example
A recessive disorder affects 1 in 10,000 people. Under Hardy–Weinberg, q² = 0.0001, so q = 0.01 and p = 0.99. Carrier frequency is 2pq = 2 × 0.99 × 0.01 = 0.0198, about 2%. The trap is reporting q as the carrier frequency; carriers are heterozygous and are much more common than affected homozygotes.
Traps
- Evolution is a change in allele frequency, not simply an individual changing during its lifetime.
- Natural selection acts on phenotypes, not directly on genotypes.
- Dominant alleles are not necessarily more common.
- Genetic drift is stronger in small populations and can fix deleterious alleles by chance.
- Acquired characteristics are not inherited in the Darwinian sense.