Genetics and evolution flashcards

Genetics and evolution covers how characteristics are inherited from parents to offspring through genes carried on chromosomes. Students must understand the difference between DNA, genes and chromosomes, and how alleles can be dominant or recessive. Monohybrid crosses using Punnett squares show how traits are passed on, and students need to distinguish between genotype and phenotype, and homozygous and heterozygous individuals. Variation within a species can be genetic, environmental or both. Natural selection explains how organisms with advantageous traits are more likely to survive and reproduce, passing on those traits over generations. Over long periods, this can lead to the formation of new species through speciation. Evidence for evolution comes from the fossil record, antibiotic resistance in bacteria and comparative anatomy.

1. Card 1

   What is a gene?

   A gene is a section of DNA that codes for a specific protein, which determines a particular characteristic of an organism.

2. Card 2

   What is the difference between a genotype and a phenotype?

   Genotype is the combination of alleles an organism carries, while phenotype is the observable characteristic those alleles produce.

3. Card 3

   What is an allele?

   An allele is an alternative version of a gene. Most organisms carry two alleles for each gene, one inherited from each parent.

4. Card 4

   What does homozygous mean?

   Homozygous means an organism carries two identical alleles for a gene, for example BB or bb.

5. Card 5

   What does heterozygous mean?

   Heterozygous means an organism carries two different alleles for a gene, for example Bb.

6. Card 6

   What is the difference between a dominant and a recessive allele?

   A dominant allele is always expressed in the phenotype, whereas a recessive allele is only expressed when two copies are present.

7. Card 7

   What is a Punnett square used for?

   A Punnett square is a diagram used to predict the possible genotypes and phenotypes of offspring from a genetic cross.

8. Card 8

   What is natural selection?

   Natural selection is the process by which organisms with advantageous traits survive, reproduce and pass those traits to offspring more than others.

9. Card 9

   How does antibiotic resistance in bacteria demonstrate natural selection?

   Random mutations produce antibiotic resistance in some bacteria. These survive treatment, reproduce and pass on resistance, so the resistant strain spreads.

10. Card 10

    What is speciation?

    Speciation is the formation of a new species when populations become reproductively isolated and evolve differently over many generations.

11. Card 11

    What are the two main sources of genetic variation in a species?

    Mutation produces new alleles, and sexual reproduction shuffles existing alleles through meiosis and random fertilisation, creating variation.

12. Card 12

    What does the fossil record provide evidence for?

    The fossil record shows how organisms have changed over millions of years, providing evidence that evolution has occurred over geological time.

• Many students confuse genotype with phenotype, forgetting that two organisms can look identical (same phenotype) but carry different alleles (different genotypes), such as BB and Bb both appearing tall.
• A common error is thinking that organisms deliberately change or adapt during their lifetime in response to the environment, when in fact natural selection acts on random variation that already exists in a population.
• Students often incorrectly state that a recessive allele is never expressed, when it is expressed in the phenotype whenever an organism is homozygous recessive, carrying two copies of that allele.

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