Subscribe

9th grade · Science · Unit 11 of 14

Evidence & Mechanisms of Evolution

Fossils, biogeography and homologies, rates of change, speciation, drift and gene flow.

What your child practices

Practices the evidence for common ancestry (the fossil record, biogeography, and anatomical, molecular and developmental homologies), explanations for different rates of change in the fossil record (gradualism, abrupt appearance, stasis), how natural selection can lead to speciation, and mechanisms other than selection: genetic drift, gene flow, mutation and recombination.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: B.9(A); B.9(B); B.10(C); B.10(D) · evidence of common ancestry, rates of change in the fossil record, speciation, and other mechanisms of evolution

How we explain it

Children can open this short lesson before they practice.

  1. Evidence for common ancestry: fossils, biogeography, and anatomical, molecular and developmental homologies.
  2. Gradualism is slow, steady change; punctuated equilibrium is long stability with quick bursts.
  3. Genetic drift, like a bottleneck, changes alleles by chance. Speciation forms a new species.

Example: A flood kills most of a population at random. The survivors’ alleles now dominate. What is this? The survivors were chosen by chance, not by fitness. A sudden drop in numbers is a bottleneck. Answer: the bottleneck effect

Evidence & Mechanisms of Evolution in Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 11 of 14 in 9th grade Science, after Genetic Crosses and before Systems in Animals & Plants.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Texas Education Agency (TEA)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Stasis in the fossil record means a species…

    • changes little over a long time
    • goes extinct at once
    • changes every generation
    • moves continents

  2. Question 2

    A bird wing and an insect wing do the same job but are built differently. They are…

    • vestigial
    • homologous structures
    • identical
    • analogous structures

  3. Question 3

    Deeper rock layers usually hold…

    • living animals
    • no fossils ever
    • older fossils
    • younger fossils

  4. Question 4

    A storm kills most of a beetle population at random. The survivors' alleles now dominate. This is…

    • gene flow
    • natural selection
    • homology
    • the bottleneck effect

  5. Question 5

    Genetic drift is…

    • movement of individuals
    • random change in allele frequencies
    • a change caused by diet
    • selection for helpful traits

  6. Question 6

    Crossing-over and independent assortment during meiosis add variation through…

    • gene flow
    • stasis
    • mutation only
    • genetic recombination

More 9th grade