1. Meiosis produces haploid gametes.
Section 1: Meiosis
Meiosis produces haploid gametes.

2. Essential Questions
How does the reduction in chromosome number occur during meiosis?
What are the stages of meiosis?
What is the importance of meiosis in providing genetic variation?
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Meiosis

3. Vocabulary Review New chromosome gene homologous chromosome gamete
haploid
fertilization
diploid
meiosis
crossing over
Meiosis
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4. Chromosomes and Chromosome Number
Characteristics such as hair color, eye color, etc., are called traits
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Meiosis

5. Each chromosome contains hundreds of genes.
VOCAB: Genes
The instructions for each trait are located on chromosomes, in the nucleus of cells.
DNA is organized in segments called genes that control the production of a protein.
Each chromosome contains hundreds of genes.
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Meiosis

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Meiosis

7. Where does Transcription/Translation Fit in?
Genes direct the production of proteins .
Proteins dictate virtually every reaction in the cell
They are directly responsible for observable characteristics.

8. Where does Transcription/Translation Fit in?
Slight variation in the activity of an enzyme for pigment synthesis in a plant may result in white flowers rather than red.

9. Where does Transcription/Translation Fit in?
Slight difference in a protein responsible for cell communication during the development of leaf tissue might result in variation of leaf shape

10. Chromosomes and Chromosome Number
Homologous chromosomes
Human cells have 46 chromosomes, or 23 pairs (one contributed by each parent).
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Meiosis

11. Chromosomes and Chromosome Number
Homologous chromosomes
Human cells have 46 chromosomes, or 23 pairs (one contributed by each parent).
The chromosomes that make up the pairs are called homologous chromosomes.
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Meiosis

12. Chromosomes and Chromosome Number
Homologous chromosomes
Human cells have 46 chromosomes, or 23 pairs (one contributed by each parent).
The chromosomes that make up the pairs are called homologous chromosomes.
Homologous chromosomes are the same length, same centromere position, and carry genes for the same traits.
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Meiosis

13. Chromosomes and Chromosome Number
Haploid and diploid cells
To maintain the same number of chromosomes from generation to generation, organisms produce gametes – sex cells with half the number of chromosomes.
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Meiosis

14. Chromosomes and Chromosome Number
Haploid and diploid cells
To maintain the same number of chromosomes from generation to generation, organisms produce gametes – sex cells with half the number of chromosomes.
The symbol n can be used to represent the number of chromosomes in a gamete.
A cell with n chromosomes is called a haploid cell.
A cell that contains 2n chromosomes is called a diploid cell.
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Meiosis

15. Meiosis I
Meiosis is a type of cell division that reduces the number of chromosomes in a cell and produces gametes.
Involves two consecutive cell divisions, meiosis I and meiosis II
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Meiosis

16. Meiosis I Interphase Chromosomes replicate. Chromatin condenses.
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Meiosis

17. Meiosis I Prophase I Pairing of homologous chromosomes occurs.
Each chromosome consists of two sister chromatids.
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Meiosis

18. Meiosis I
Prophase I
As homologous chromosomes condense, they are bound together in a process called synapsis, which allows for crossing over.
Crossing over – chromosomal segments are exchanged between a pair of homologous chromosomes.
Crossing over produces exchange of genetic information.
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Meiosis

19. Meiosis I Metaphase I Chromosome centromeres attach to spindle fibers.
Homologous chromosomes line up as a pair at the equator.
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Meiosis

20. Meiosis I
Anaphase I
Homologous chromosomes separate and move to opposite poles of the cell.
The chromosome number is reduced from 2n to n when the homologous chromosomes separate.
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Meiosis

21. Meiosis I Telophase I Chromosomes reach the cell’s opposite poles.
Cytokinesis occurs.
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Meiosis

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

23. Meiosis II Metaphase II Chromosomes are positioned at the equator.
Meiosis II involves a haploid number of chromosomes.
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Meiosis

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

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

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

27. The Importance of Meiosis
Mitosis consists of one cell division that produces identical cells.
Meiosis consists of two cell divisions that produce haploid daughter cells that are not genetically identical.
Meiosis results in genetic variation.
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Meiosis

28. The Importance of Meiosis
Meiosis provides variation
During prophase I, the chromosomes line up randomly at the equator.
Gametes end up with different combinations of chromosomes.
Genetic variation also is produces during crossing over and during fertilization, when games randomly combine.
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Meiosis

29. 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.
Sexual reproduction
Rate of beneficial mutations is faster.
Beneficial genes multiply faster over times than they do for asexual organisms.
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Meiosis

30. Review Essential Questions Vocabulary
How does the reduction in chromosome number occur during meiosis?
What are the stages of meiosis?
What is the importance of meiosis in providing genetic variation?
Vocabulary
gene
homologous chromosome
gamete
haploid
fertilization
diploid
meiosis
crossing over
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Meiosis

31. Section 2: Mendelian Genetics
Mendel explained how a dominant allele can mask the presence of a recessive allele.

32. Essential Questions
What is the significance of Mendel’s experiments to the study of genetics?
What is the law of segregation and the law of independent assortment?
What are the possible offspring from a cross using a Punnett square?
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Mendelian Genetics

33. Vocabulary Review New segregation genetics allele dominant recessive
homozygous
heterozygous
genotype
phenotype
law of segregation
hybrid
law of independent assortment
Mendelian Genetics
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34. How Genetics Began
The passing of traits to the next generation is called inheritance, or heredity.
Gregor Mendel published his findings on the method of inheritance in garden pea plants:
Cross-pollinated pea plants, which normally self-fertilize
Rigorously followed various traits in the pea plants he bred
Began the study of genetics, the science of heredity.
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Mendelian Genetics

35. The Inheritance of Traits
One trait Mendel noticed was seed color – some plants always produced green seeds, others always produced yellow seeds.
Mendel cross-bred the green and yellow seed plants.
Mendel called the green-seed and yellow-seed plants the parent, or P, generation.
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Mendelian Genetics

36. The Inheritance of Traits
F1 and F2 generations
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.
In Mendel’s peas, the green-seed trait disappeared in the F1 generation, but reappeared in the F2 generation.
The F2 generation showed a 3:1 ratio of yellow: green seeds
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Mendelian Genetics

37. The Inheritance of Traits
F1 and F2 generations
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
In all cases, Mendel found the F2 generation plants showed a 3:1 ratio of traits.
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Mendelian Genetics

38. The Inheritance of Traits
Genes in Pairs
Mendel concluded that there must be two forms of the seed trait in the pea plants, and that each was controlled by a factor.
An allele is an alternative form of a single gene.
The gene for yellow seeds and the gene for green seeds are different alleles for the same gene.
Dominant alleles controlled the traits that appeared in the F1 generation.
Recessive alleles were masked in the F1 generation.
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Mendelian Genetics

39. The Inheritance of Traits
Genes in Pairs
Mendel concluded that there must be two forms of the seed trait in the pea plants, and that each was controlled by a factor.
An allele is an alternative form of a single gene.
The gene for yellow seeds and the gene for green seeds are different alleles for the same gene.
Allele
The alternative form of a single gene
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Mendelian Genetics

40. The Inheritance of Traits
Alleles
Dominant alleles controlled the traits that appeared in the F1 generation.
Recessive alleles were masked in the F1 generation.
Dominant vs Recessive
The Recessive allele is recedes to the dominant
The dominant allele dominates over the recessive
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Mendelian Genetics

41. The Inheritance of Traits
Dominance
When modeling inheritance, the dominant allele is represented by a capital letter (Y), and a recessive allele is represented with a lower case letter (y).
An organism with two of the same alleles for a particular trait is homozygous for that trait (YY or yy).
An organism with two different alleles for a particular trait is heterozygous for that trait (Yy).
In heterozygous individuals, the dominant trait will be observed.
Homozygous
YY or yy
Homo means the same!
Heterozygous Yy
The dominant Y wins
Mendelian Genetics
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42. The Inheritance of Traits
Genotype and phenotype
The appearance of an organism does not always indicate which pair of alleles it possesses.
An organism’s allele pairs are called its genotype.
The observable characteristic or outward expression of an allele pair is called the phenotype.
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Mendelian Genetics

43. The Inheritance of Traits
Genotype and phenotype
An organism’s allele pairs are called its genotype.
The observable characteristic or outward expression of an allele pair is called the phenotype.
Phenotype
The outward expression or characteristic
Genotype
The allele pairs
Mendelian Genetics
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44. The Inheritance of Traits
Mendel’s law of segregation
The law of segregation states that the two alleles for each trait separate during meiosis.
During fertilization, two alleles for that trait unite.
Heterozygous organisms are called hybrids.
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Mendelian Genetics

45. The Inheritance of Traits
Monohybrid cross
A cross that involves hybrids for a single trait is called a monohybrid cross.
Dihybrid cross
The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross.
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Mendelian Genetics

46. The Inheritance of Traits
Law of independent assortment
The law of independent assortment states that random distribution of alleles occurs during gamete formation.
Genes on separate chromosomes sort independently during meiosis.
Each allele combination is equally likely to occur.
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Mendelian Genetics

47. Punnett Squares
Punnett squares predict the possible offspring of a cross between two known genotypes.
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Mendelian Genetics

48. Punnett Squares Punnett square—monohybrid cross
The number of squares is determined by the number of different types of alleles produced by each parent.
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Mendelian Genetics

49. Punnett Squares 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.
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Mendelian Genetics

50. Probability
The inheritance of genes can be compared to the probability of flipping a coin.
Actual data might not perfectly match the predicted ratios.
Mendel’s results were not exactly a 9:3:3:1 ratio, but the larger the number of offspring involved, the more likely it will match the results predicted by Punnett squares.
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Mendelian Genetics

51. Review Essential Questions Vocabulary
What is the significance of Mendel’s experiments to the study of genetics?
What is the law of segregation and the law of independent assortment?
What are the possible offspring from a cross using a Punnett square?
Vocabulary
genetics
allele
dominant
recessive
homozygous
heterozygous
genotype
phenotype
law of segregation
hybrid
law of independent assortment
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Mendelian Genetics

52. Section 3: Gene Linkage and Polyploidy
The crossing over of linked genes is a source of genetic variation.

53. Essential Questions
How does the process of meiosis produce genetic recombination?
How can gene linkage be used to create chromosome maps?
Why is polyploidy important to the field of agriculture?
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Gene Linkage and Polyploidy

54. Vocabulary Review New protein genetic recombination Polyploidy
Gene Linkage and Polyploidy
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55. Genetic Recombination
The new combination of genes produced by crossing over and independent assortment is called genetic recombination.
Combinations of genes due to independent assortment can be calculated using the formula 2n, where n is the number of chromosome pairs.
Any possible male gamete can fertilize any possible female gamete, so the possible combinations after fertilization are 2n X 2n.
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Gene Linkage and Polyploidy

56. Gene Linkage
Genes located close to each other on the same chromosome are said to be linked.
They usually travel together during gamete formation.
Gene linkage results in an exception to Mendel’s law of independent assortment.
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Gene Linkage and Polyploidy

57. Gene Linkage Chromosome maps
Crossing over occurs more frequently between genes that are farther apart.
Cross over data can be used to create chromosome maps, depictions of how genes are arranged on a chromosome.
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Gene Linkage and Polyploidy

58. Polyploidy
Polyploidy is the occurrence of one or more extra sets of all chromosomes in an organism.
A triploid organism is designated 3n, which means that it has three complete sets of chromosomes.
Many agricultural crops are polyploid.
Wheat (6n), oats (6n), and sugar cane (8n)
Polyploid plants often have increased vigor and size
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Gene Linkage and Polyploidy

59. Review Essential Questions Vocabulary
How does the process of meiosis produce genetic recombination?
How can gene linkage be used to create chromosome maps?
Why is polyploidy important to the field of agriculture?
Vocabulary
genetic recombination
polyploidy
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Gene Linkage and Polyploidy