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Paper 2
Inheritance, Variation, and Evolution
Both
Remember: genes are sections of DNA that code for proteins.
Key Facts
- Genotype is the genetic makeup; phenotype is the expressed characteristic.
- A dominant allele is expressed even with one copy.
- Homozygous means two identical alleles; heterozygous means two different alleles.
- Sex is determined by XX and XY chromosomes.
Topics Covered
DNA and Genes
What you need to know
- •DNA is made of two strands coiled in a double helix.
- •Genes are sections of DNA that code for proteins.
Exam Tips
- Use the word "allele" for versions of a gene.
Inheritance and Punnett Squares
What you need to know
- •Use Punnett squares to predict ratios.
- •Dominant alleles are shown with capital letters.
Exam Tips
- State the genotype and phenotype ratios separately.
Natural Selection
What you need to know
- •Variation within a species can give survival advantages.
- •Those with advantageous traits reproduce and pass on alleles.
Exam Tips
- State variation, selection, reproduction in that order.
Selective Breeding
What you need to know
- •Select parents with desired traits and breed repeatedly.
- •May reduce genetic diversity and increase inherited problems.
Exam Tips
- Give one benefit and one risk to secure full marks.
Key Terms
Allele
Different versions of the same gene.
Phenotype
Observable characteristics caused by genes and environment.
Genotype
The alleles an organism has.
Homozygous
Two identical alleles for a gene.
Heterozygous
Two different alleles for a gene.
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Common Exam Questions
Explain how antibiotic resistance develops in bacteria.
5 markshardPaper 2
Model Answer
Random mutations create resistant bacteria. Antibiotics kill non-resistant bacteria, leaving resistant ones to survive, reproduce, and pass on resistance.
What examiners want to see
- ✓Mention mutation and selection.
- ✓Link to survival and reproduction.
A heterozygous brown eye parent (Bb) and blue eye parent (bb) have children. Give the ratio of brown to blue.
2 marksmediumPaper 2
Model Answer
1:1
What examiners want to see
- ✓Use a Punnett square.
- ✓State the ratio clearly.
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