Chapter 3: Genetics: The Study of Heredity

1. Chapter 3: Genetics: The Study of Heredity Pp. 78-106

2. The passing of traits from parents to offspring is called heredity.

3. Notes 3-1 • Gregor Mendel was curious about the physical characteristics, or traits of pea plants. • Mendel’s work was the foundation of genetics, the scientific study of heredity.

4. Pea plants were used because they have traits that exist in only 2 forms. • 2 pea plants with only 1 trait that differed, height, were used for the first generation, P1.

5. The parent generation used were purebreds, because they always produced offspring with the same form of the trait.

6. The first generation of offspring are called the first filial, or F1, and were all tall. The short trait seemed to have disappeared.

7. When the F1 generation was crossed again, it produced an F2 generation that was 3/4 tall and 1/4 short. • The factors that control traits are genes.

8. The different forms of a gene are called alleles. • Individual alleles control the inheritance of traits.

9. Some alleles are dominant while other alleles are recessive. • A dominant allele is one whose trait always shows up in the organism.

10. A recessive allele is masked, or covered up, when the dominant allele is present. It only shows up if 2 recessive are present.

11. The F1 generation were tall, but they were hybrids, carrying 2 different alleles, one for tall and one for short.

12. The dominant allele is represented with a capital letter, the recessive allele is represented with a lowercase version of the same letter. • Ex: TT,Tt,tt

13. Vocabulary: #1-9 • Trait, heredity, genetics, purebred, gene,allele, dominant, recessive, hybrid.

14. Notes 3-2 • Probability is the likelihood that a particular event will occur.

15. The principles of probability predict what is likely to occur, not necessarily what will occur.

16. A tool that applies the laws of probability to genetics is a Punnett Square. • Punnett Squares are charts that show all the possible combinations of alleles that can result from a genetic cross.

17. They are used to show the possible outcomes. • In the square, the possible alleles from one parent are written across the top

18. All the possible alleles from the other parent are written down the left side.

19. The combined alleles in the boxes of the punnett square represent all the possible combinations in the offspring.

20. Phenotype is the physical appearance or visible trait. • Genotype is the genetic makeup, allele combination. • When an organism has 2 identical alleles for a trait it is homozygous.

21. When an organism has 2 different alleles for a trait it is heterozygous. • Traits are not always simply dominant or recessive.

22. Codominance is when neither dominant nor recessive alleles show, both are expressed, mixing the traits.

23. Codominance is written as capital letter with superscripts to show that neither is recessive.

24. Vocabulary: #10-16 • Probability, punnett square, phenotype, genotype, homozygous, heterozygous, codominance.

25. Sect. 3-3 notes • Meiosis is the process by which the number of chromosomes is reduced by half to form sex cells-sperm and eggs.

26. Chromosome pairs are separated to form these sex cells. • Chromosomes are made up of genes joined together like beads on a string.

27. The chromosomes are separated and the pairs are separated. • During meiosis the pairs are separated and distributed to produce 2 different sex cells.

28. Each sex cell has only 1 chromosome from each pair.

29. When they combine again during reproduction, each sex cell contributes half the number of chromosomes to produce offspring with the correct number of chromosome pairs.

30. Punnett squares are used to show the results of meiosis.

31. Gregor Mendel’s work was the foundation for understanding why offspring have traits similar to those of their parents. • Vocabulary: #17 Meiosis

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33. DNA contains thousands of genes. • The order of nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced.

34. In the genetic code, a group of 3 bases codes for a specific amino acid--the building blocks of proteins.

35. During protein synthesis the cell uses information from a gene on a chromosome to produce a specific protein.

36. The protein synthesis occurs at the ribosomes in the cytoplasm of the cell. • Before it occurs, a genetic messenger RNA is made from the DNA.

37. RNA is similar to DNA, except RNA has only 1 strand and it has uracil in place of thymine.

38. In the first step of the protein synthesis the DNA molecule unzips and directs the production of the messenger RNA and it copies the coded message to the cytoplasm.

39. When messenger RNA attaches to a ribosome, transfer RNA carries amino acid and adds them to the growing protein.

40. During this process mistakes sometimes occur in the sequence of the bases and a gene is changed.

41. These changes are called mutations, which can cause a cell to produce incorrect proteins, affecting the organism’s phenotype.

42. Other mutations occur when chromosomes don’t separate correctly during meiosis.

43. If the mutation occurs in a body cell, the mutation only affects the cell that carries it.

44. But if the mutation occurs in a sex cell, the mutation can be passed on to an offspring during meiosis. • Some mutations are helpful if it helps the organism’s chances of survival.

45. Harmful mutations effect an organism’s ability to survive and reproduce. • Mutations that do not harm or help the organism depend on the organism’s environment.

46. Ex: white buffalo calf will not survive in the wild, but can do so on a farm. • Vocabulary #18-20 • uracil, RNA, mutation