Meiosis

1. Chapter 7.1 Meiosis Benagh

2. Difference Between Meiosis and Mitosis! • You need to understand the difference between mitosis and meiosis. They’re similar, but: • Mitosis: makes more body or SOMATIC cells. • Meiosis: Makes more sex cells or GAMETES. • Meiosis: a form of cell division that halves the number of chromosomes when forming specialized reproductive cells, such as gametes or spores. • There are two stages of meiosis, Meiosis I and Meiosis II • In animals, meiosis produces haploid gametes or sex cells, sperm and eggs Benagh

3. Formation of Haploid Cells • Before the process of meiosis, like mitosis, the DNA replicates. • This makes a cell with how many chromosomes? • There are 8 stages in Meiosis, and they should sound familiar: • MEIOSIS I: • Prophase I • Metaphase I • Anaphase I • Telophase I and cytokinesis • MEIOSIS II: • Prophase II • Metaphase II • Anaphase II • Telophase II and cytokinesis Benagh

4. Meiosis I • Prophase I: Chromosomes condense, nuclear envelope breaks down. Crossing-over occurs. • Crossing-Over: when portions of a chromatid on one homologous chromosome are broken and exchanged with the corresponding chromatid, increasing genetic diversity. • Metaphase I: The pairs of homologous chromosomes are moved by spindles to the equator of the cell. • Anaphase I: Homologous chromosomes separate. The chromosomes of each pair are pulled apart. • Chromatids do not separate at their centromeres—each chromosome is still composed of two chromatids • Telophase I: Individual chromosomes gather at the poles, and the cytoplasm divides. Benagh

5. Meiosis I Benagh

6. Meiosis II • Chromosomes do NOT replicate between Meiosis I and Meiosis II. • Prophase II: Chromosomes DO NOT replicate. A new spindle forms around the chromosomes. • Metaphase II: The chromosomes line up along the equator and are attached at their centromeres to spindles. • Anaphase II: The centromeres divide, and the chromatids (now chromosomes) move to opposite poles. • Telophase II: A nuclear envelope forms around each set of chromosomes. The spindle breaks down, and the cell under-goes cytokinesis, making four haploid cells. Benagh

7. Meiosis II Benagh

8. Meiosis and Genetic Variation Benagh • Meiosis allows for genetic variation. • Each gamete receives one chromosomes from each of the 23 pairs. However, each gamete can receive one of two homologous chromosomes (the one from the mother OR the father). This is random. Independent Assortment: random distribution of homologous chromosomes during meiosis.

9. Crossing-Over and Random Fertilization • DNA exchange during crossing over in Prophase I adds even more recombination to the independent assortment of chromosomes, making even MORE genetic combinations! • Crossing-Over: a type of genetic recombination that occurs when portions of a chromatid on one homologous chromosome are broken and exchanged with the corresponding chromatid, increasing genetic diversity. • Meiosis, gamete-joining, and crossing-over are essential to evolution because these processes generate genetic variation very quickly. • The pace of evolution is accelerated by genetic recombination! Benagh

10. Meiosis in Males Benagh • Remember, Meiosis is the way gametes or sex cells are made! • Spermatogenesis: the process by which sperm are produced in male animals • Occurs in the testes. • A diploid cell first undergoes meiosis I, making two cells which enter meiosis II, ultimately making four haploid cells which develop a tail and become sperm. • A typical adult male produces several hundred million sperm cells each day.

11. Meiosis in Females • Oogenesis: the process by which gametes are produced in female animals. • Occurs in the ovaries. • During Cytokinesis in Meiosis I, the cytoplasm divides unequally—one cell gets almost all of the cytoplasm. • The cell with the cytoplasm will result in the egg cell, the others are called polar bodies. The polar bodies will divide again, but the offspring cells will not survive. • The larger cell undergoes meiosis II, and makes an ovum or egg. This is a large cell, with nutrient storage. • Females are born with all of the eggs they will ever produce; about 2 million at birth. Eggs are stalled in prophase I and meiosis does not resume until puberty. Only one egg cell matures each month. Benagh

12. 11/14/12 DOL • For images 1-8 correctly identify the stage of meiosis. Identify the stage in which CROSSING-OVER OCURRS! 1. 2. 3. 4. 5. 6. 7. 8.

13. Chapter 7.2 Sexual Reproduction Benagh

14. Sexual and Asexual Reproduction • Some organisms have two parents, other only have one. • Reproduction can be sexual or asexual. • Sexual Reproduction: two parents form reproductive cells that have one-half the number (haploid) of chromosomes which combine to make a diploid individual. • Asexual Reproduction: a single parent passes copies of all its genes to each of its offspring—no fusion of haploid cells such as gametes. • Clone: an organism that is genetically identical to its parent. Benagh

15. Types of Asexual Reproduction • Fragmentation (eukaryotic organisms ): the body breaks into several pieces and the pieces develop into complete adults. • Budding: A new individual splits off from existing ones. Benagh

16. Vegetative Reproduction and Plant Propagation • Most plants can reproduce sexually and asexually. • When plants are made asexually, they are genetically the same as the parent plant. • The reproduction of plants from non-reproductive parts such as the stems, roots, and leaves is called vegetative reproduction. • People grow plants for many purposes, such as for food, decoration, or profit. • Growing new plants from seed or from vegetative parts is called plant propagation. Benagh

17. Pollination • Pollination: the transfer of pollen grains from the male reproductive structures of a plant to the female reproductive structures of a plant. Pollination Benagh

18. Genetic Diversity • Asexual reproduction is more simple and primitive. Saves energy. Little genetic variation. • Sexual reproduction provides genetic diversity, which is the raw material for evolution. • The evolution of sexual reproduction may have allowed early Protists to repair their own DNA. Benagh

19. Male Reproductive System • The role of a human male in sexual reproduction is the make haploid sex cells or gametes. Benagh

20. Female Reproductive System • Females are born with all of the egg cells (their haploid sex cells or gametes!) they will ever produce. At birth, the ovaries contain about 2 million immature egg cells that already have begun the first division of meiosis. Meiosis is not completed until a female reaches puberty and then an average of one egg cell matures each month. Benagh

21. Sexual Life Cycles in Eukaryotes • Life Cycle: The entire span in the life of an organism from one generation to the next. • Eukaryotes with sexual reproduction have one of three life cycles: • Haploid: The simplest of life cycles; most of the life is spend in the haploid stage. • Diploid: Most animals have diploid life cycle. This is the human life cycle. • Alternation of Generations: Life cycle that alternates between a haploid and diploid phase. Benagh

22. Sexual Reproduction • Sexual reproduction proceeds through three key life events: • Meiosis: the production of gametes. • Gamete Formation • Fertilization: when a sperm fertilizes an egg, producing a zygote, which is the first new cell of an individual. Benagh

23. 11/12/12 DOL For each of the examples 1-5 below, IDENTIFY as sexual or asexual reproduction. For number 6, simply answer the question. • Fertilization to form a zygote. • Budding, when a new organism breaks off an old one. • When a root from an existing plant can grow an entire new organism. • Binary Fission • Combination of a sperm and an egg. • Which method of reproduction produces GREATER genetic diversity: Sexual or Asexual.

24. 11/16/12 Journal Entry/Discussion • In the journal section of your binder, respond to the following prompts. After 5 minutes, I expect you to have 4-5 sentences written. • What is a gene? From what is a gene made? • How are genes transmitted from parent to child? • Do you get all the genes from both parents? • Can you actually see all of the traits inherited from your parents?

25. Chapter 8.1/8.2 Origins of Genetics and Mendel’s Theory Benagh

26. Mendel and the Origin of Genetics • Heredity: the passing of characters from parents to offspring. • The study of heredity began with Gregor Mendel, an Austrian monk. Mendel’s work formed the basis of genetics. • Genetics: the branch of biology that focuses on heredity. Benagh

27. Mendel’s Work • Mendel repeated the work of T.A. Knight examining crosses in garden pea plants. Mendel was scientific and recorded data on the crosses. • Mendel studied seven characters in pea plants that have clearly distinguishable forms. • Flower color • Seed color • Seed shape • Pod color • Pod shape • Flower position • Plant height Benagh

28. Traits Expressed as Simple Ratios • Mendel’s initial experiments were monohybrid crosses. • Monohybrid Cross: a cross involving one pair of contrasting traits. • Example: crossing a plant with purple flowers and a plant with white flowers • Terminology: • P Generation: Parental Generation • F1 Generation: First filial generation—first generation of offspring • F2 Generation: Second filial generation—second generation of offspring Benagh

29. Steps of Mendel’s Experiments Benagh

30. Mendel’s Results Benagh • In the F1, the offspring all looked the same. • In the F2, most offspring looked the same as before, but some looked different. • In fact, 705 were purple, 224 were white. • What is the ratio of purple vs. white plants?

31. Hypotheses for Heredity • Prior to Mendel’s work, people thought offspring were a blend of their parents. • Mendel’s work did not support the blending hypothesis. • Mendel concluded that each pea had two separate “heritable factors” for each character—one from each parent. • When sperm and eggs (gametes) form, each receives only one of the organism’s two factors for each character. • When the gametes fuse, each offspring has two factors for each character. Benagh

32. Mendel’s Hypotheses • For each inherited character, an individual has two copies of the gene—one from each parent. • There are alternative versions of genes—a pea plant can have a purple version or a white version. • Allele: the different versions of a gene Benagh

33. Mendel’s Hypotheses 3. When two different alleles occur together—one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance. • Dominant: the expressed form of the character • Recessive: the trait not expressed when the dominant form is present. Benagh

34. Mendel’s Hypotheses • 4. When gametes are formed, the alleles for each gene in an individual separate independently of one another. Thus, gametes carry only one allele for each inherited character. When gametes unite during fertilization, each gamete contributes one allele. Benagh

35. Mendel’s Findings in Modern Terms • Dominant Traits: Capital letter • Recessive Traits: lower case letter • Pea Plants: • Purple—Dominant: P (capital P) • White—Recessive: p (lowercase p) • Homozygous: if the two alleles of a particular gene are the same in an individual • Heterozygous: if the two alleles of a particular gene are different in an individual Benagh

36. Mendel’s Findings in Modern Terms • Genotype: the set of alleles that an individual has for a character. • The genes they actually have. • Phenotype: the physical appearance of a character. • How they look. Benagh

37. The Laws of Heredity • The Law of Segregation: the two alleles for a character segregate (separate) when gametes are formed. • This is the behavior of chromosomes during meiosis. • The Law of Independent Assortment: The alleles of different genes separate independently of one another during gamete formation. • The inheritance of one character does not influence the inheritance of another, as long as they’re on separate chromosomes! Benagh

38. 11/16/12 DOL • A pea plant with round seeds (R) is crossed with another pea plant with wrinkled seeds (r), as shown in the Punnett square to the right. Using this information, answer the following questions: • Which trait is dominant? • What is the genotypic ratio? • What is the phenotypic ratio? • What is the genotype of the offspring represented by the star? • What is the phenotype of the offspring represented by the star? r R r r

39. Chapter 8.3 Studying Heredity Benagh

40. Punnett Squares • Punnett Square: A diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross. Benagh

41. Contrasting Traits: One Pair • Punnett squares can predict many crosses, including a monohybrid cross, one pair of contrasting traits between two individuals. • The monohybrid cross on the left crosses two heterozygous plants. The monohybrid cross on the previous slide crossed a homozygous dominant plant and a homozygous recessive plant. Benagh

42. Contrasting Traits: Two Pairs • What are all the possible gametes? • What are the possible genotypes? • What is the genotypic ratio? • What are the possible phenotypes? • What is the phenotypic ratio? Benagh

43. Inheritance • Dominant: If the gene is autosomal dominant, every individual with the condition will have a parent with the condition. • Recessive: If the condition is recessive, an individual with the condition can have one, two, or neither parent exhibit the condition. • Heterozygous/Homozygous: If individuals with autosomal traits are homozygous dominiant or heterozygous, their phenotype will show the dominant allele. If individuals are homozygous recessive, they will show the recessive allele. Benagh

44. Test Cross • Used to determine the genotype of an individual whose phenotype is dominant, but genotype is unknown. • In other words, you know that it has ONE dominant allele—but you don’t know if the other allele is dominant or recessive. • If a plant with yellow seeds Y? and a plant with green seeds yy are crossed, how could the results tell you the genotype of the yellow-seeded parent? Benagh

45. Probability • Probability: the likelihood that a specific event will occur. • Can be expressed as words, decimals, percentages, or in fractions. Number of one kind of possible outcome Probability= ----------------------------------------------------- Total number of all possible outcomes Benagh

46. Trait Inheritance • Pedigree: a family history that shows how a trait is inherited over several generations. Benagh

47. Recessive Pedigree Versus Dominant Pedigree • The above pedigree shows an autosomal dominant trait inheritance; the trait is seen in every generation. http://www.uic.edu/classes/bms/bms655/lesson3.html http://www.uic.edu/classes/bms/bms655/lesson5.html#RECESSIVE • The above pedigree shows an autosomal recessive trait inheritance; the trait is not seen in every generation.

48. Recessive Sex-Linked Pedigree • The image above shows a sex-linked pedigree for a recessive trait on an X chromosome; females are often carriers and the affliction is more common on males. http://sparkleberrysprings.com/v-web/b2/?p=801

49. Autosomal or Sex-Linked • Autosomal: gene occurs on an autosome. • If a trait is autosomal, it will appear in both sexes equally. • Sex-Linked: gene occurs on an X or Y chromosome. • A female with a recessive trait will only show it if it occurs on both of her X chromosomes. • Thus, males are more likely to exhibit sex-linked recessive traits. Benagh

50. 11/27/12 DOL #1 1. 2. 3. 4. 5.