Unit 4 Genetics

1. Unit 4 Genetics Ch. 11 Introduction to Genetics

2. The Work of Gregor Mendel • Genetics - the scientific study of heredity • Mendel is considered the “Father” of genetics

3. Gregor Mendel’s Peas • Mendel was an Austrian monk, that worked on pea plants • His experiments with pea plants laid the foundation of the science of genetics

4. Gregor Mendel’s Peas • Fertilization - when male & female sex cells join together • Pea flowers are normally self-pollinating, meaning the sperm cells in the pollen fertilize the egg cells in the same flower

5. Gregor Mendel’s Peas • Seeds produced by self-pollination inherit all of their characteristics from the single plant that bore them • True-breeding - if plants were allowed to self-pollinate, they would produce offspring identical to themselves

6. Gregor Mendel’s Peas • Mendel wanted to produce seeds by joining male & female sex cells from 2 different plants • He cut off the pollen (male) parts of a plant, & dusted pollen from another plant onto the flower (female)

7. Gregor Mendel’s Peas • Cross-pollination - produces seeds that had 2 different parent plants

8. Genes & Dominance • P - parent generation • F1 - First generation (first generation of offspring) • F2 - Second generation (offspring from the F1 generation)

9. Genes & Dominance • Trait - a specific characteristic • Ex.) seed color, plant height • Hybrids - offspring of crosses between parents with different traits • Ex.) cross between plant with yellow seed color & plant with green seed color

10. Genes & Dominance • Mendel concluded that biological inheritance is determined by factors that are passed from 1 generation to the next • Genes - chemical factors that determine traits

11. Genes & Dominance • Alleles - different forms of a gene • Ex.) gene for plant height occurs in 1 form that produces tall plants & in another form that produces short plants • Mendel’s 2nd conclusion is the principle of dominance

12. Genes & Dominance • The principle of dominance states that some alleles are dominant & others are recessive • Dominant allele for a trait will always be exhibited (expressed or shown) • Recessive allele will only be expressed when a dominant allele is not present

13. Mendel’s Seven F1 Crosses on Pea Plants

14. Segregation • Gametes - sex cells (sperm or egg) • Segregation - during gamete formation, alleles segregate (separate) from each other so each gamete only carries a single copy of each gene

15. Segregation • Therefore, each F1 plant produces 2 types of gametes, those with the allele for tallness & those with the allele for shortness

16. Punnett Squares • Punnett square - a diagram that might result from a genetic cross • Punnett squares can be used to predict & compare the genetic variations that will result from a cross

17. Punnett Squares • Homozygous - organisms that have 2 identical alleles for a particular trait • Ex.) TT or tt • Heterozygous - organism that has 2 different alleles for the same trait • Ex.) Tt

18. Punnett Squares • Phenotype - physical characteristics • Ex.) Tall plants • Genotype - genetic makeup • Ex.) TT

19. Independent Assortment • Independent assortment - genes for different traits can segregate (separate) independently during gamete formation • Independent assortment increases genetic variation (genetic diversity, helps create genetically different organisms)

20. A Summary of Mendel’s Principles 1. The inheritance of biological characteristics is determined by individual units - genes • Genes are passed from parents to their offspring

21. A Summary of Mendel’s Principles 2. In cases where 2 or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant & others may be recessive

22. A Summary of Mendel’s Principles • 3. In most sexually producing organisms, each adult has 2 copies of each gene (1 from each parent) • These genes are segregated (separated) from each other when gametes are formed

23. A Summary of Mendel’s Principles • 4. The alleles for different genes usually segregate (separate) independently of 1 another

24. Beyond Dominant & Recessive Alleles • Some alleles are neither dominant nor recessive, & many traits are controlled by multiple alleles or multiple genes

25. Beyond Dominant & Recessive Alleles • Incomplete dominance - when 1 allele is not completely dominant over another • The heterozygous phenotype is somewhere in between the 2 homozygous phenotypes

26. Beyond Dominant & Recessive Alleles • Codominance - where both alleles contribute to the phenotype • Flowers would not be pink, (a blend of red & white), but both red & white speckled

27. Beyond Dominant & Recessive Alleles • Multiple alleles - when genes have more than 2 alleles • It does not mean that an individual can have more than 2 alleles • It only means that more than 2 possible alleles exist in a population

28. Multiple Alleles

29. Beyond Dominant & Recessive Alleles • Polygenic traits - traits controlled by 2 or more genes • Ex.) at least 3 genes are responsible for making the reddish-brown pigment in the eyes of fruit flies

30. Genetics & the Environment • The characteristics of any organism are not determined solely by the genes it inherits • Characteristics are determined by interaction between genes & the environment

31. Genetics & the Environment • Ex.) genes may affect a sunflower plant’s height & the color of its flowers • However, these conditions are also influenced by climate, soil conditions, & the availability of water • Ex.) Rabbit fur color in winter & summer

32. Chromosome Number • All cells of an organism (except for sex cells, gametes) have the same # of chromosomes • Each body cell has 2 sets of chromosomes • Homologous chromosomes - the same chromosomes, 1 set from each parent

33. Homologous Chromosomes

34. Chromosome Number • Diploid - (2n) - a cell that has both sets of homologous chromosomes • Haploid - (n) - a cell that has half the normal set of chromosomes, or 1 set (only sex cells are haploid)

35. Phases of Meiosis • Meiosis - process of reduction division, where the # of chromosomes per cell is cut in 1/2, through the separation of homologous chromosomes in a diploid cell

36. Phases of Meiosis • During meiosis 1, crossing-over may occur • Crossing-over - when chromosomes exchange portions of their chromatids

37. Phases of Meiosis • Crossing-over results in the exchange of alleles between homologous chromosomes & produces new combinations of alleles • Crossing-over increases genetic variation (genetic diversity, helps create genetically different organisms)

38. Phases of Meiosis • Meiosis II, begins with 2 genetically different haploid (n) cells, & results in 4 (n) genetically different haploid cells • Therefore, Meiosis II is a mitotic division

39. Meiosis I

40. Meiosis II

41. Gamete Formation • In males, the haploid gametes are sperm • In females, the haploid gametes are eggs

42. Comparing Mitosis & Meiosis • Mitosis results in the production of 2 genetically identical diploid (2n) cells • Mitosis produces all cells of the body, except sex cells • Meiosis produces 4 (n) genetically different haploid cells • Meiosis produces ONLY sex cells (gametes)

43. Gene Linkage • Each chromosome is a group of linked genes • It is the chromosomes, however, that line up independently, not individual genes (Principle of Independent Assortment)