1. Ch. 11 Introduction to Genetics
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 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)