Introduction to Genetics

1. Introduction to Genetics To be used with guided genetics guided outline.

2. Basic Genetics -- Mendel (1866) • Gregor Mendel was an Austrian monk who experimented with pea plants and laid the foundation of modern genetics. Mendel studied science and mathematics at the University of Vienna.

3. Basic Genetics -- Mendel (1866) • ** Mendel developed some basic principles of heredity without any knowledge of genes or chromosomes. • ** Mendel observed contrasting characters in pea plants in his work.

4. Basic Genetics -- Mendel (1866) • Why was Mendel successful with the pea? • 1. Used pure breeding, contrasting varieties. • 2. Studied characteristics one at a time for many generations. • 3. Used statistics in analyzing his results. • 4. Obtained large numbers of offspring. • 5. Chose pea plants which normally self-fertilize.

5. Genes • ** Mendel had no knowledge of genes or chromosomes. • Genes: factors that control the traits of an organism -- the part of the DNA molecule containing the genetic code.

6. -Every organism requires a set of coded instructions for specifying its traits.  For offspring to resemble their parents, their must be a reliable way to transfer hereditary information from one generation to the next.

7. Alleles • Alleles: different forms of a gene associated with a particular characteristic            (ex. height -- tallness -- shortness) • -Each gene may have one or more forms called alleles. The alleles determine how each gene is expressed.

8. Chromosomes • Chromosomes: hereditary units of an organism • Locus: particular point where a certain gene is found on a chromosome

9. Homologous Chromosomes • Homologous chromosomes: pair of associated chromosomes • -- each chromosome in the pair is called a homologue • ** Alleles are located in the same position or locus on homologous chromosomes.

10. Homozygous (pure) -- an individual with two identical alleles for a trait. • Heterozygous: (hybrid) -- an individual with two different alleles for a trait.

11. Parental generation (P) -- the two original organisms being crossed • F1 generation -- the first generation of offspring from the parents • F2 generation -- generation of offspring arising from the F1 generation

12. Some Major Genetic Concepts • 1.Law of Dominance (Mendel) • -- A pattern of heredity in which only one gene of a pair is expressed (has both dominate and recessive alleles). • --The dominate trait will show more often than the recessive trait.

13. Law of Dominance (Mendel) • Ex. red flowering X white flowering-->red flowering peas

14. Traits • Dominant trait: the trait or allele that is expressed • Recessive trait: the trait or allele that is present but that is not expressed

15. Punnett squares • Punnett square: used to represent genetic crosses

16. Traits • Genotype: the genetic makeup of an organism • Phenotype: the appearance of an organism

17. Segregation and Recombination Principle of Segregation and Recombination (Mendel) • -- When gametes are formed during meiosis there is a random separation of homologous chromosomes.

18. Segregation and Recombination • As a result of fertilization, alleles recombine. As a result, new gene combinations are likely to be produced.

19. Segregation and Recombination • ** Ex: Heterozygous individual punnett square • What's wrong with this punnett Square?

20. Law of Independent Assortment (Mendel) • 3. Law of Independent Assortment (Mendel) • --If the genes for two different traits are located on different chromosomes, they separate randomly during meiosis and may be inherited independently of each other.

21. The cross of two organisms heterozygous for a trait is known as a hybrid cross.

22. Intermediate Inheritance • Intermediate Inheritance • 2 examples – • Incomplete dominance • Codominance

23. Incomplete Dominance • (a.) Incomplete Dominance • -- No allele is dominate. The phenotype of the offspring is somewhere in between the two parents. The two traits mix!!!

24. Incomplete Dominance • Ex: Cross a red and white flower (Mirabilis) you will get pink flowers

25. Incomplete Dominance • ** A cross between long and round squash produces oval squash

26. Codominance • (b.) Codominance: a case of contrasting alleles in which neither allele is dominant over the other (alleles have equal power)

27. Codominance • Ex. cross between red and white short horned cattle gives roan cattle which have a combination of red and white hairs.

28. Gene linkage • Gene linkage: when genes for two different traits are located on the same chromosome pair. • Linked genes are usually inherited together.

29. Crossing over • Crossing over: during the first meiotic division, the chromatids in a homologous pair of chromosomes often twist around each other, break, exchange segments and rejoin • ** Crossing over results in the rearrangement of linked genes and increases the variability of offspring.

30. Crossing over

31. Karyotype: an enlarged photograph of the chromosomes in an organism • Above is a karyotype of a normal human male.

32. What’s wrong with this person?

33. Chromosomes • Human diploid cells contain 23 pairs of chromosomes. • Autosomes: body chromosomes (22 pr. in humans) • Homo sapiens have only one pair of sex chromosomes.

34. Sex Determination • ** The sex of a human is genetically determined at fertilization when a sperm cell containing either an X or a Y chromosome unites with an egg cell containing an X chromosome. • Male =X, Y Female= X, X

35. Fertilization

36. Types of Chromosomal Alterations • Nondisjunction: homologous chromosomes fail to separate during meiosis, producing offspring with one chromosome more or less than is normal

37. Types of Chromosomal Alterations • Disjunction -- the separation of homologous chromosomes during meiosis • ** If disjunction fails to occur, gametes with an addition or a missing chromosome will be produced.

38. Types of Chromosomal Alterations • Polyploidy • -- The presence of one or more entire additional sets of chromosomes in an organism (3n,4n number, etc.)

39. Types of Chromosomal Alterations • Mutation: a random change in the chemical nature of the genetic material (DNA) • ** Most mutations are harmful and recessive. • http://www.pbs.org/wgbh/evolution/library/01/2/l_012_02.html

40. Causes of Mutations • 1. Radiation -- X-rays, ultraviolet, radioactive substances, and cosmic rays • 2. Chemicals -- formaldehyde, benzene, asbestos fibers, THC, nicotine

41. Types of Selective Breeding • 1. Artificial Selection --Individuals with desirable traits are mated to produce offspring with those traits

42. Types of Selective Breeding • 2. Inbreeding • -- Offspring produced by artificial selection are mated with one another to reinforce those desirable traits

43. Types of Selective Breeding • Hybridization:crossing two individuals with different desirable traits to produce offspring with a combination of both desirable traits • English shorthorn cattle(good beef) X Brahman cattle (heat resistant)  Santa Gertrudis cattle(good beef and heatresistance)

44. Types of Selective Breeding • Mutations may be preserved by vegetative propagation • Example: seedless oranges and bananas