1. GENETICS Gregor Mendel’s Discoveries Complex Inheritance Patterns of Inheritance

2. Gregor Mendel: 1843 - Augustinian monastery. University of Vienna - 1851 to 1853 Experimentation in causes of variation in plants. 1857 - breeding garden peas to study inheritance. Many varieties, distinct heritable features (characters) with different variants (traits). Mendel brought an experimental and quantitative approach to genetics. Gregor Mendel Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

3. Hybrids The true-breeding parents - P generation hybrid offspring - F 1 generation. Pollinate F 1 hybrids - F 2 generation. law of segregation law of independent assortment.

4. Law of segregation - the two alleles for a characteristics are packaged into separate gametes Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 705 purple-flowered F 2 plants 224 white-flowered F 2 3-1 ratio Dominant Recessive

5. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Table 14.1

6. Mendel’s hypothesis to explain the results. 1. Alternative version of genes (different alleles) account for variations in inherited characters. Different alleles vary somewhat in the sequence of nucleotides at the specific locus of a gene. The purple-flower allele and white-flower allele are two DNA variations at the flower-color locus. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 14.3

7. 2. For each character, an organism inherits two alleles, one from each parent. A diploid organism inherits one set of chromosomes from each parent. - Each diploid organism has a pair of homologous chromosomes (two copies of each). These homologous loci may be identical, homozygous for that character (PP or pp) Alternatively, the two alleles may differ, heterozygous for that character (Pp). Ex. - a plant can inherit a purple-flower allele from one parent and a white-flower allele from the other. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8. 3. If two alleles differ, The dominant allele, is fully expressed in the the organism’s appearance. The other, the recessive allele, has no noticeable effect on the organism’s appearance. 4. The two alleles for each character segregate (separate) during gamete production. (law of segregation) Distribution of homologous chromosomes to gametes in meiosis. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

9. Review Questions Define P, F 1, F 2 generation. What does Mendel’s law of segregation state? What are the four parts of Mendel’s law of segregation? Define Homozygous and Heterozygous. What is another way to say homozygous? Define Dominant and Recessive

10. Punnett square Fig. 14.4 Predicts the outcome of a cross between two organisms. law of segregation - 3:1 ratio in F 2 generation. F 1 - two gametes: 1/2 purple-flower allele 1/2 white-flower allele gametes unite randomly four combinations

11. Some vocab: description of traits - phenotype. The words that describe the character (Purple or White) genetic makeup - genotype. The letters we assign to the character (PP or Pp or pp) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

12. For flower color in peas, both PP and Pp plants have the same phenotype (purple) but different genotypes (homozygous and heterozygous). The only way to produce a white phenotype is to be homozygous recessive (pp) for the flower- color gene. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 14.5

13. Test Cross It is not possible to predict the genotype of an organism with a dominant phenotype. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

14. Dominance does not mean more common in a population. Polydactyly is due to an allele dominant to the recessive allele for five digits per appendage. The recessive allele is far more prevalent than the dominant allele in the population. 399 individuals out of 400 have five digits per appendage. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

15. Single character cross - monohybrid cross. Two different characters - dihybrid cross. Mendel crossed true-breeding plants that had yellow, round seeds (YYRR) with true-breeding plants that has green, wrinkled seeds (yyrr). The allele for yellow seeds (Y) is dominant to the allele for green seeds (y). The allele for round seeds (R) is dominant to the allele for wrinkled seeds (r). Law of independent assortment Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

16. two characters are not transmitted from parents to offspring as a package. The Y and R alleles and y and r alleles do not stay together. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

17. Two pairs of alleles segregate independently of each other. The presence of one specific allele for one trait has no impact on the presence of a specific allele for the second trait. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Four distinct phenotypes in a 9:3:3:1 ratio. law of independent assortment - alleles must be on different chromosomes

18. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 15.1

19. Mendel used traits that were classified as complete dominance. Each character (but one) is controlled by a single gene. Each gene has only two alleles, one of which is completely dominant to the other. Complete Dominance (recap) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

20. Check in? Define Genotype and Phenotype What do we use a Punnett square for? Define Mendel’s Law of Independent Assortment

21. Beyond Mendel We know that the relationship between genotype and phenotype is rarely as simple as dominant and recessive. Mendel was never able to prove these… Incomplete dominance Codominance Multiple Alleles Polygenic inheritance Sex-linked traits

22. Heterozygotes show a distinct phenotype, not seen in homozygotes. The dominant trait is not completely dominant over the recessive. Result is a mixed phenotype. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Incomplete Dominance

23. Codominance Two alleles affect the phenotype in separate, distinguishable ways. There are two dominant alleles that both contribute to phenotype. MN blood groups - due to the presence of two specific molecules on the surface of red blood cells. (genotype MM) have one type of molecule on their red blood cells, (genotype NN) have the other type, MN (genotype MN) have both molecules. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

24. Multiple Alleles (and codominance) There are more than 2 alleles that contribute to genotype. The ABO blood groups in humans are determined by three alleles, I A, I B, and i. Both the I A and I B alleles are DOMINANT to the i allele The I A and I B alleles are codominant to each other. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

25. Because each individual carries two alleles, there are six possible genotypes and four possible blood types.

26. RBC Surface Antigens Antigens are proteins found on the surface of a cell

27. Rh Factor with blood typing What about the + and – blood types? Rh factor is what determines the + or – blood typing. Alleles= Rh+ and Rh-

28. Stop and Review A woman with type A+, whose dad was O-, has a child with a man who is AB-. What are the potential blood types of their child A cat with a long tail is crossed with a cat who has a short tail. All of their offspring have medium length tails. Why? What alleles would you use?

29. Polygenic Inheritance Additive effects of two or more genes on a single phenotypic character. skin color in humans. An AABBCC individual is dark and aabbcc is light. AaBbCc X AaBbCc (intermediate skin shades) produce offspring with a range of shades. Fig. 14.12

30. In addition to their role in determining sex, the sex chromosomes, especially the X chromosome, have genes for many characters. These traits typically follow the complete dominance principles discussed previously, but are linked to the X chromosome, as shown below. Men are affected more often by a sex linked trait. Sex-linked traits Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

31. Duchenne muscular dystrophy Absence of normal X-linked gene for a key muscle protein, called dystrophin. Progressive weakening of the muscles and loss of coordination. Hemophilia - absence of one or more clotting factors. Normal proteins slow and stop bleeding. Individuals with hemophilia have prolonged bleeding because a firm clot forms slowly. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

32. Pedigree analysis reveals Mendelian patterns in human inheritance Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings heterozygotes are carriers - may transmit a recessive allele to their offspring, but do not suffer from the disease.

33. Recap and review? Distinguish between Incomplete dominance and Codominance. What are the three different alleles for human blood typing. How many geneotypes can be made with these alleles? Define Polygenic Inheritance. Why are men more susceptible to a sex- linked disease? What is a pedigree used for?