1 Chapter 8- Mendel And Heredity

2 I. The origins of Genetics A. The passing of traits from parents to offspring is called heredity. 1. Mendel was a mathematician and looked at genetics differently than anyone in the past ever did.

3 2. Genetics is the branch of biology that focuses on heredity. 3. Mendel counted the number of each kind of offspring and analyzed the data. 4. Quantitative approaches to science-those that include measuring and counting.

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5 B. Useful features in peas 1. The garden pea is a good subject for studying heredity for several reasons.

6 a. The garden pea has many traits that have two clearly different forms that are easy to tell apart. b. The mating of the garden pea flowers can be easily controlled. c. The garden pea is small, grows easily, matures quickly and produces many offspring.

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8 C. Mendel observed that traits are expressed as simple ratios 1. Mendel ’ s initial experiments were monohybrid crosses. A cross with ONE pair of contrasting traits. 2. Mendel allowed true breeding or self- pollination to occur.

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10 3. These true-breeding plants served as the parental generation in Mendel ’ s experiments. 4. The parental generation, or P generation are the first two individuals that are crossed.

11 5. Mendel crossed the P generation to get the F1 generation. First generation. He then examined each F1 plant and recorded the number of F1 plants and their traits. 6. Mendel then mated the F1 generation to get a F2 generation. The second generation and then again examined each of their traits.

12 D. Mendel’s results. 1. See page 162 figure 8.4

13 II. Mendel’s theory A. Mendel ’ s work became a theory of heredity. 1. The four hypotheses Mendel developed were based directly on the result of his experiments.

14 a. For each inherited trait, an individual has two copies of genes- one from each parent. b. There are alternative versions of genes. These are called alleles.

15 c. When two different alleles occur together, one of them bay be completely expressed, while the other may have no affect on the appearance. Mendel explained these to be dominant and recessive. d. When gametes are formed, the alleles for each gene in an individual separate independently of one another.

16 B. Mendel ’ s findings in modern terms 1. If two traits are the same they are called homozygous. 2. If two traits are different they are called heterozygous.

17 3. Dominant genes are expressed with capital letters. 4. Recessive genes are expressed with lower caps. 5. Example Brown is dominant= B, blue is recessive =b. 6. A set of alleles that an individual has is called the genotype.

18 7. What the individual expresses is called the phenotype. 8. Example: BB, Bb and bb are genotypes. 9. BB, and Bb would have brown eyes, and bb would have blue eyes. The colors are the phenotypes.

19 B. Mendel ’ s Ideas gave rise to the laws of heredity. 1. The first law, the law of segregation, states that the two alleles for a trait segregate or separate when gametes are formed.

20 2. The law of independent assortment states that the alleles of different genes separate independently of one another during gamete formation.

21 II. Studying heredity A. Punnet squares- see board.

22 B. Probability on the board.

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24 C. Pedigrees on the board.

25 D. Sex linked traits on board.

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29 III. Patterns of Heredity can be complex A. Traits influenced by several genes 1. When several genes influence a trait, the trait is said to be polygenetic.

30 2. In some traits there is neither dominant nor recessive genes. These are called incomplete dominance. Example: Red flower RR and a White WW flower both with incomplete dominance will have pink flowers.

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32 3. When two dominant alleles are expressed at the same time, both forms of the trait are displayed this is called co dominance. Example: Coat colors in a horse. 4. Genes with three or more alleles are said to have multiple alleles. Example blood groups ABO.

33 1. GenotypesPhenotypes I A I A A I A I o A I B I B B I B I o BI A I B AB I o I o O

34 5. An individual ’ s phenotype often depends on conditions in the environment. 6. Some traits are affected by the temperature, sunlight or seasons. 7. In humans the environment influences height. Height is influenced by nutrition, an internal environment conditions.

35 B. Some traits are caused by mutations 1. Sickle cell anemia is a recessive genetic disorder caused by a mutated allele that produces a defected form of the protein hemoglobin. 2. Hemophilia is a recessive genetic disorder that impairs the blood ’ s body to clot.

36 3. Huntington ’ s disease is a genetic disorder caused by a DOMINANT allele. The symptoms do not appear until the victim is in their 30 ’ s or 40 ’ s. This disease caused severe mental illness and eventually death. 4. Most genetic disorders cannot be cured, but progress is being made

37 5. There is genetic testing to detect any bad genes. 6. Gene technology may soon by replacing defected genes with copies of healthy ones this is called gene therapy.