Section 11.3: Genetic Changes

1. Any change in the DNA sequence is called a mutation.

2. Name four things that cause mutations 2. Name four things that cause mutations. 1) Errors in replication 2) Errors in transcription 3) Errors in cell division 4) External agents

3. Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides within a gene in a sperm or an egg cell.

4. If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the offspring.

5. The mutation may produce a new trait or it may result in a protein that does not work correctly.

6. Sometimes, the mutation results in a protein that is nonfunctional, and the embryo may not survive. 7. In some rare cases, a gene mutation may have positive effects.

8. If the DNA of a nonreproductive cell is changed, the mutation would not be passed on to offspring. 9. However, the mutation may cause problems for the individual.

10. Damage to a gene may impair the function of the cell. 11 10. Damage to a gene may impair the function of the cell. 11. When that cell divides, the new cells will also have the same mutation.

12. Some mutations of DNA in body cells affects genes that control cell division. 13. This can result in the cells growing and dividing rapidly, producing cancer.

14. A point mutation is a change in a single base pair in DNA.

15. A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein.

16. A mutation in which a single base is added to or deleted from DNA is called a frameshift mutation because it shifts the reading of codons by one base.

17. This mutation would cause nearly every amino acid in the protein after it to be changed.

18. In general, point mutations are less harmful to an organism because they disrupt only a single codon.

19. Changes may occur in chromosomes as well as in genes.

20. Sometimes parts of chromosomes are broken off and lost during mitosis or meiosis. 21. Often, chromosomes break and then rejoin incorrectly.

22. These structural changes in chromosomes are called chromosomal mutations.

23. Homologous chromosomes do not pair correctly when one chromosome has extra or missing parts, so separation of the homologous chromosomes does not occur normally.

24. Gametes that should have a complete set of genes may end up with extra copies or a complete lack of some genes.

25. Few chromosomal mutations are passed on to the next generation because the zygote usually dies.

26. In cases where the zygote lives and develops, the mature organism is often sterile and thus incapable of producing offspring.

27. Some mutations just seem to happen, perhaps as a mistake in base pairing during DNA replication.

28. However, many mutations are caused by factors in the environment 28. However, many mutations are caused by factors in the environment. 29. Any agent that can cause a change in DNA is called a mutagen.

30. Name three different mutagens 30. Name three different mutagens. 1) Radiation 2) Chemicals 3) High temperatures

31. Name three kinds of radiation mutagens 31. Name three kinds of radiation mutagens. 1) X rays 2) Cosmic rays 3) ultraviolet light 4) Nuclear radiation

32. Name three chemical mutagens 32. Name three chemical mutagens. 1) Dioxins 2) Asbestos 3) Benzene 4) formaldehyde

33. Repair mechanisms that fix mutagens in cells have evolved.

34. Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides. 35. These repair mechanisms work extremely well, but they are not perfect.

36.