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Key Idea: Genetic variation results from mutations and allele shuffling during reproduction, which leads to variation in proteins and, finally, to variation in traits.

Students are expected to know that:

  1. During reproduction, genetic information (DNA) passes from parent to offspring.
  2. Heritable traits pass by way of genes (made of DNA) from parent to offspring.
  3. Variation in DNA sequences leads to variation in proteins, which leads to variation in traits.
  4. Heritability can be determined by comparing traits in parents and offspring. If a trait is heritable, offspring tend to resemble parents.
  5. During sexual reproduction, individuals inherit two copies of each gene, one from each parent. Each copy is called an allele.
  6. Alleles of the same gene have some nucleotide sequences in common and some that are different.
  7. Alleles are shuffled during sexual reproduction (recombination, independent assortment, and fertilization), which produces new allele combinations.
  8. Allele shuffling during reproduction contributes to genetic variation in a population.
  9. Mutation is a natural process that generates variation in DNA sequences, i.e., new alleles.
  10. DNA variations that arise through mutation can be beneficial, harmful, or neutral (to the organism). DNA variations that decrease viability or reproduction are not propagated, so they are eliminated from the population. Most DNA variations have no effect on viability or reproduction, and through random chance many are maintained in the population.
  11. Only when it happens in sex cells can mutation generate new alleles that can be passed to offspring. Mutations that occur in body cells cannot be passed on to offspring.
  12. Mutations can occur in sex cells at any time.
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If a mutation occurs to a DNA molecule in an organism's skin cell before the organism reproduces, none of the organism's offspring will have the mutation.