Biology Secondary Exam — Chromosomes, Mendel and Mutations
Learn the fundamentals of genetics: DNA structure, what a gene and chromosome are, Mendel's laws (dominant vs. recessive), genotype vs. phenotype, mutations and their causes, genetic engineering and cloning — all explained with curriculum examples.
Biology & Geology · Secondary
Double helix with 4 bases: A-T and C-G always pair together. Watson and Crick, 1953. 20,000-25,000 genes in the human genome, packaged into 46 chromosomes.
Dominant (A) masks recessive (a). AA or Aa → dominant phenotype; aa → recessive phenotype. Use Punnett squares to calculate inheritance probabilities.
Mutations: spontaneous or caused by mutagens (UV, tobacco). Source of genetic variability → evolution. Genetic engineering: insulin, CRISPR, transgenic plants, gene therapy.
"A Year 10 student thought blue eyes were dominant. After the question "blue eyes only appear in homozygous recessive (aa) individuals", he understood the difference between genotype and phenotype."
Tricks and techniques to master this topic faster:
Human somatic cells have 46 chromosomes (23 pairs). Gametes (egg, sperm) have 23.
A recessive allele is only expressed when the individual is homozygous recessive (aa).
The father determines the biological sex: he contributes X (girl) or Y (boy).
If you are studying Genetics — DNA, Genes and Heredity, these curriculum topics complement each other:
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