Biology Chapter 7.2

Page 1

  • Title: Human Genetic Disorders

  • Photo Credit: Science Source

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Page 2

Objectives

  • Analyze the effects of errors in meiosis.

  • Evaluate how small changes in DNA affect human traits.

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Page 3

Chromosomal Disorders: Nondisjunction

  • Nondisjunction: Error in meiosis where homologous chromosomes do not separate correctly.

  • Results in gametes that may have an abnormal number of chromosomes.

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Page 4

Chromosomal Disorders - Trisomy

  • Most common trisomy: Down syndrome occurs with three copies of chromosome 21.

  • Nondisjunction of the X chromosomes can lead to Turner’s syndrome.

  • In males, nondisjunction may cause Klinefelter’s syndrome.

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Page 5

From Molecule to Phenotype

  • Changes in the DNA sequence of a gene can lead to changes in proteins:

    • Altering amino acid sequences

    • Affecting the phenotype

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Page 6

Cystic Fibrosis

  • Most cases result from a deletion of three bases in the DNA of a single gene.

  • This results in the body not producing normal CFTR protein.

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Page 7

Genetic Advantages

  • Some alleles associated with disease may also provide benefits, such as:

    • Carrying one copy of the sickle cell allele provides protection from malaria.

    • Carrying one copy of the CF allele provides protection from typhoid bacterium.

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Page 8

TEKS Checkpoint

  • Question: How does a change in DNA lead to a human genetic disorder? Provide a specific example to explain your answer.