ZIMSEC O-Level Biology (4025)

Inheritance, Variation and Evolution: notes

AI-written, not yet teacher-reviewed

Not affiliated with or endorsed by ZIMSEC

Chromosome: a thread of DNA in the nucleus. A gene is a section that codes for a trait; alleles are versions of a gene.
Mitosis: makes two identical cells for growth and repair. Meiosis: makes four gametes with half the chromosomes.
Dominant allele shows in the phenotype when present. A recessive allele shows only with two copies.
Monohybrid cross: two heterozygous parents (Tt x Tt) give a 3 to 1 ratio of dominant to recessive.
Sex: XX is female, XY is male; each child has a 50% chance of either.
Mutation: a random change in a gene. Radiation and some chemicals raise its rate.
Natural selection: individuals best suited to the environment survive and pass on their alleles.
Selective breeding: farmers breed the best animals or crops, such as cattle with high milk yield.