Genetics

1. Genetics • The scientific study of heredity • Traits are the characteristics that are passed from parent to offspring • What are some traits that you inherited from one of your parents?

2. Inheritance • What is the relationship between chromosomes and how or what traits are passed on? • Gregor Mendel (The Father of Genetics) was the first scientist to answer this question in the 1850’s • Statistics (why would this be important?) • He self fertilized pea plants (why peas?)

3. Mendel’s Studies • Self-fertilization • Purebred: offspring that receives the same genetic traits from both parents • Hybrid: an organism that receives different forms of a trait from each parent

4. Mendel’s Crosses • The first cross Mendel made he called the P1 generation (parent) • Their offspring is the F1 (“filial”) • When two F1’s are crossed the next generation is the F2 generation

5. Mendel’s Observations

6. Mendel’s Conclusions • Disproved the “blending” hypothesis • Each trait is controlled by a distinct “factor” (allele) and there must be at least two forms of each factor • Offspring must receive one allele from each parent

7. Genes are sections of a chromosome that code for a trait • An allele is the distinct form of a gene (only one allele may be expressed • Dominant allele: a form of a gene that is fully expressed when two different alleles are present (represented by a capital letter) • Recessive allele: a form of a gene that is not expressed if paired with a dominant allele (represented by a lower case letter)

8. Genes Affect Traits • Genotype: the genetic makeup of a person (YY, Yy, or yy) • Homozygous: two of the same alleles (YY, yy) • Heterozygous: two different alleles (Yy) • Phenotype: the outward expression of a trait

9. Law of Independent Assortment • Gene pairs segregate into gametes randomly and independently of each other

10. The Law of Segregation • Each pair of genes segregates (separates) during meiosis, so half of an organism’s gametes contain one gene from a homologous pair and half the other gene

11. Law of Dominance • Dominant allele is expressed and the recessive allele is hidden and only expressed when no copy of the corresponding dominant allele is present

12. For pea plants, based on the genotype, describe the phenotype: • Flower color Pp • Pea shape ii • Height TT

13. Probability • The likelihood that something will occur • Used to predict genotypes and phenotypes • Punnett squares are used to help make these predictions • Shows probabilities, not actual results

14. Monohybrid Cross • The study of inheritance of only one trait at a time • Alleles for one parent are written across the top and the other down the side • The combination of alleles in the box are the possible genotypes

15. Dihybrid Cross • The study of the inheritance of two traits • Alleles will sort into all possible combinations • Ex: Alleles for two traits are RrYy, what possible combinations of alleles can there be. • RY, Ry, rY, ry • Setting up a Punnett Square • Set up a four by four square • Write the possible combinations of alleles for one parent across the top and the other down the side

17. Test Cross • Used to distinguish between homozygous dominant and heterozygous organisms • Geneticists breed the organism whose genotype is unknown with a homozygous recessive organism • Heterozygous will result in about ½ showing recessive phenotype • Homozygous dominant will result in all dominant phenotypes

18. Why are human populations more difficult to study? • Fewer offspring • Mature slowly • Pedigrees can show how a trait and the genes that control it are inherited in a family

19. Types of Inheritance

20. 1. Dominant Inheritance • Trait is expressed when only one copy of the dominant allele is present (homozygous dominant and heterozygous individuals) • Hitchhikers thumb • Freckles • Widow’s peak • Polydactyly • Huntington’s Disease

21. 2. Recessive Inheritance • Traits that are inherited only when you have two copies of a recessive allele • Tay Sachs • Cystic Fibrosis • Albinism

22. Carriers have a recessive allele, but do not express the recessive trait. • The recessive allele can be passed on to the offspring

23. Dominant Every affected individual has at least one affected parent Two affected individuals may have unaffected offspring Trait normally appears in every generation Recessive Affected individuals may have unaffected parents All the children of two affected individuals are affected Trait is sometimes seen to skip generations Comparing Dominant and Recessive Pedigrees

26. Genetic Counselors • Can determine the likelihood that a genetic disorder can be passed on to the offspring of parents who have a family history of the disease • Tracing family history and making pedigrees • Molecular techniques (genes, proteins) • Prenatal screenings (PKU)

27. Intermediate Inheritance • Not all genes have purely dominant and recessive alleles • A third phenotype can result

28. 3. Incomplete Dominance • Heterozygous offspring show a phenotype between the phenotypes of the two homozygous parents • Neither allele is fully expressed • Hypercholesterolemia

29. 4. Codominance • Both alleles of a heterozygous are expressed fully

31. 5. Polygenic Traits • A trait that is controlled by two or more genes • Skin color • Height • AABBCC x aabbcc  AaBbCc

32. Three or more alleles for one trait Blood type (IA, IB, i) Phenotype Genotype A IA IA or IAi B IB IB or IBi AB IA IB O ii Multiple Alleles

33. Pleiotropy • A single gene affects more than one trait • Sickle cell disease can have many phenotypic affects on the body

34. Sex Determination • Autosomes: your 22 pairs of homologous chromosomes • Sex Chromosomes: the two chromosomes that determine sex • Males XY • Females XX

35. 6. Sex-linked Traits • Traits that are inherited on your sex chromosomes • Written as superscripts of the X or Y • Color blindness, hemophilia

36. Environmental Effects • Factors that influence the expression of a gene • External: temperature, nutrition, light, chemicals, and infectious agents • Internal: social environment; shyness, age,