1. Chapter 10: Sexual Reproduction and Genetics
10.1 Meiosis
10.2 Mendelian Genetics
10.3 Gene Linkage and Polyploidy

2. 10.1 Meiosis
Objectives
Explain the reduction in chromosome number that occurs during meiosis
Recognize and summarize the stages of meiosis
Analyze the importance of meiosis in providing genetic variation

3. 10.1 Meiosis Review Vocabulary New Vocabulary
Chromosome – cellular structure that contains DNA
New Vocabulary
Gene
Homologous chromosome
Gamete
Haploid
Fertilization
Diploid
Meiosis
Crossing over

4. Chromosomes and Chromosome Number
Characteristics are passed on to offspring by parents
Each characteristic is called a trait
Instructions for each trait are located on chromosomes found in the nucleus of cells
The DNA on chromosomes is arranged in segments called genes that control the production of proteins
Each chromosome consists of approximately 1500 genes, each gene playing an important role in determining the characteristics and functions of the cell.

5. Chromosomes and Chromosome Number
Human body cells have 46 chromosomes
Each parent contributes 23 chromosomes, resulting in 23 pairs of chromosomes
Homologous chromosomes – one of two paired chromosomes, one from each parent

6. Chromosomes and Chromosome Number
Homologous chromosomes
Same length
Same centromere position
Carry genes that control the same inherited traits

7. Haploid and Diploid Cells
An organism produces gametes to maintain the same number of chromosomes from generation to generation
Gametes are sex cells that have half the number of chromosomes
Human gametes contain 23 chromosomes

8. Haploid and Diploid Cells
The symbol n represents the number of chromosomes in a gamete
A cell with n chromosomes is called a haploid cell (single)
The process by which one haploid gamete combines with another haploid gamete is called fertilization
As a result of fertilization, the cell will contain a total of 2n chromosomes
A cell that contains 2n chromosomes is called a diploid cell (double)

9. Meiosis I
The sexual life cycle in animals involves meiosis, which is a type of cell division that reduces the number of chromosomes (reduction division)
Meiosis produces gametes
When gametes combine in fertilization, the number of chromosomes is restored

10. Meiosis I Stages of Meiosis I
Reduces the chromosome number by half through the separation of homologous chromosomes
Involves two consecutive cell divisions called meiosis I and meiosis II

11. Meiosis I
Interphase
Chromosomes replicate
Chromatin condenses

12. Meiosis I
Prophase I
Synapsis occurs – the physical binding of homologous chromosomes
Each chromosome consists of two chromatids
The nuclear envelope breaks down
Spindles form

13. Meiosis I
Prophase I
Crossing over produces exchange of genetic material
Crossing over – chromosomal segments are exchanged between a pair of homologous chromosomes

14. Meiosis I Metaphase I Chromosome centromeres attach to spindle fibers
Homologous chromosomes line up at the equator

15. Meiosis I
Anaphase I
Homologous chromosomes separate and move to opposite poles of the cell

16. Meiosis I Telophase I The spindles break down
Chromosomes uncoil and form two nuclei
The cell divides

17. Meiosis II
Prophase II
A second set of phases begins as the spindle apparatus forms and the chromosomes condense

18. Meiosis II Metaphase II
A haploid number of chromosomes line up at the equator

19. Meiosis II
Anaphase II
The sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell

20. Meiosis II Telophase II
The chromosomes reach the poles, and the nuclear membrane and nuclei reform

21. Meiosis II
Cytokinesis results in four haploid cells, each with n number of chromosomes

22. The Importance of Meiosis
Meiosis consists of two sets of divisions
Produces four haploid daughter cells that are not identical
Results in genetic variation

23. Mitosis v. Meiosis Mitosis Meiosis One division occurs
DNA replication occurs during interphase
Synapsis of homologous chromosomes does not occur
Two identical cells are formed per cell cycle
Mitosis occurs only in body cells
Mitosis is involved in growth and repair
See Biology Concepts 32: Mitosis v. Meiosis
Meiosis
Two sets of divisions occur during meiosis: meiosis I and meiosis II
DNA replication occurs once before meiosis I
Synapsis of homologous chromosomes occurs during prophase I
Four haploid cells (n) are formed per cell cycle
The daughter cells are not genetically identical because of crossing over
Meiosis occurs in reproductive cells
Meiosis is involved in the production of gametes and providing genetic variation in organisms

24. Meiosis Provides Variation
Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.
Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine

25. Sexual Reproduction v. Asexual Reproduction
The organism inherits all of its chromosomes from a single parent
The new individual is genetically identical to its parent
Example - Bacteria
Sexual Reproduction
Beneficial genes multiply faster over time
Example – Humans
Most protists reproduce both asexually and sexually, depending on environmental conditions
Most plants and many of the more simple animals can reproduce both asexually and sexually

26. 10.2 Mendelian Genetics Objectives
Explain the significaance of Mendel’s experiments to the study of genetics
Summarize the law of segregation and the law of independent assortment
Predict the possible offspring from a cross using a Punnett Square

27. 10.2 Mendelian Genetics Review Vocabulary New Vocabulary
Segregation – the separation of allelic genes that typically occurs during meiosis
New Vocabulary
Genetics
Allele
Dominant
Recessive
Homozygous
Heterozygous
Genotype
Phenotype
Lae of segregation
Hybrid
Law of independent assortment

28. How Genetics Began
In 1866, Gregor Mendel, an Australian monk and a plant breeder, published his findings on the method and the mathematics of inheritance in garden pea plants
Mendel is known as the father of genetics
Genetics is the science of heredity

29. How Genetics Began
The passing of traits to the next generation is called inheritance, or heredity
Mendel chose pea plants for his study
Easy to grow
Many are true breeding - they consistently produce offspring with only one form of a trait
Usually reproduce by self-fertilization - when a male gamete within a flower combines with a female gamete in the same flower
Mendel performed cross-pollination by transferring a male gamete from the flower of one pea plant to the female reproductive organ in another pea plant
Mendel followed various traits in the pea plants he bred

30. The Inheritance of Traits
The parent generation is also known as the P generation
The offspring of this P cross are called the first filial (F1) generation
The second filial (F2) generation is the offspring from the F1 cross

31. The Inheritance of Traits
Mendel studied seven different traits
Seed or pea color
Flower color
Seed pod color
Seed shape or texture
Seed pod shape
Stem length
Flower position
F1 generation plants from these crosses showed a 3:1 ratio

32. Genes in Pairs
Mendel concluded from his studies that there must be two forms of a trait, controlled by a factor, which is now called an allele
An allele is an alternative form of a single gene passed from generation to generation
Dominant - form of the trait that appeared in the F1 generation
Recessive – form of the trait that was masked in the F1 generation

33. Dominance
Dominant alleles is represented by a capital letter. Yellow-seed forms are a dominant trait (Y)
Recessive alleles are represented by a lowercase letter. Green-seed forms are a recessive trait (y)

34. Dominance
An organism with two of the same alleles for a particular trait is homozygous
YY – yellow-seed plants
yy - green-seed plants
An organism with two different alleles for a particular trait is heterozygous
Yy – dominant allele is observed, therefore, yellow-seed plants

35. Genotype and Phenotype
Genotype – genetic make-up or allelles present
YY, yy, or Yy
Phenotype – physical or observable characteristic
Yellow-seed or green-seed

36. Mendel’s Law of Segregation
Two allelles of each trait separate during meiosis
During fertilization, two alleles for that trait unite
Heterozygous organisms are called hybrids

37. Monohybrid Cross
A cross that involves hybrids for a single trait is called a monohybrid cross
Three possible genotypes YY, Yy and yy
Genotype ratio is 1:2:1
Phenotype ratio is 3:1 – yellow seeds to green seeds

38. Dihybrid Cross
The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross
Dihybrids are heterozygous for both traits

39. Law of independent Assortment
Random distribution of alleles occurs during gamete formation
Genes on separate chromosomes sort independently during meiosis
Each allele combination is equally likely to occur

40. Punnett Square-Monohybrid Cross
A tool used to predicts the possible offspring of a cross between two known genotypes

41. Punnett Square- Dihybrid Cross
Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced
The resulting phenotypic ratio is 9:3:3:1

42. 10.3 Gene Linkage and Polyploidy
Objectives
Summarize how the process of meiosis produces genetic recombination
Explain how gene linkage can be used to create chromosome maps
Analyze why polyploidy is important to the field of agriculture

43. 10.3 Gene Linkage and Polyploidy
Review Vocabulary
Protein – large, complex polymer essential to all life that provides structure for tissues and organs and helps carry out cell metabolism
New Vocabulary
Genetic recombination
polyploidy

44. Genetic Recombination
The new combination of genes produced by crossing over and independent assortment
Combinations of genes due to independent assortment can be calculated using the formula 2n, where n is the number of chromosome pairs
In humans, the possible number of combinations after fertilization would be 223 x 223, or more than 70 trillion. This number does not include the amount of genetic recombination produced by crossing over

45. Gene Linkage
The linkage of genes on a chromosome results in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently
Yet linked genes do not always travel together during meiosis due to crossing over

46. Chromosome Maps
A drawing that shows the sequence of genes on a chromosome and can be created by using cross-over data
Chromosome map percentages are not actual chromosome distances, but they represent relative positions of the genes
Genes that are further apart would have a greater frequency of crossing over.

47. Polyploidy
The occurrence of one or more extra sets of all chromosomes in an organism is polyploidy
A triploid organism, for instance, would be designated 3n, which means that it has three complete sets of chromosomes
In humans, polyploidy is always lethal
In plants, polyploidy is associated with increased vigor and size