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? Meiosis
Vocabulary Review chromosome New gene homologous chromosome gamete haploid fertilization diploid meiosis crossing over Meiosis
Chromosomes and Chromosome Number Characteristics such as hair color, eye color, etc., are called traits. 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. Meiosis
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. Meiosis
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. Meiosis
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 Meiosis
Meiosis I Interphase Chromosomes replicate. Chromatin condenses. Meiosis
Meiosis I Prophase I Pairing of homologous chromosomes occurs. Each chromosome consists of two sister chromatids. Meiosis
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. Meiosis
Meiosis I Metaphase I Chromosome centromeres attach to spindle fibers. Homologous chromosomes line up as a pair at the equator. Meiosis
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. Meiosis
Meiosis I Telophase I Chromosomes reach the cell s opposite poles. Cytokinesis occurs. Meiosis
Meiosis II Prophase II A second set of phases begins as the spindle apparatus forms and the chromosomes condense. Meiosis
Meiosis II Metaphase II Chromosomes are positioned at the equator. Meiosis II involves a haploid number of chromosomes. Meiosis
Meiosis II Anaphase II Sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell. Meiosis
Meiosis II Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform. Meiosis
Meiosis II Cytokinesis results in four haploid cells, each with n number of chromosomes. Meiosis
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. Meiosis
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. Meiosis
Sexual Reproduction v. Asexual Reproduction 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. Meiosis
Review 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? Vocabulary gene homologous chromosome gamete haploid fertilization diploid meiosis crossing over Meiosis
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? Mendelian Genetics
Vocabulary Review segregation New genetics allele dominant recessive homozygous heterozygous genotype phenotype law of segregation hybrid law of independent assortment Mendelian Genetics
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. Mendelian Genetics
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. Mendelian Genetics
The Inheritance of Traits F 1 and F 2 generations The offspring of this P cross are called the first filial (F 1 ) generation. The second filial (F 2 ) generation is the offspring from the F 1 cross. In Mendel s peas, the green-seed trait disappeared in the F 1 generation, but reappeared in the F 2 generation. The F 2 generation showed a 3:1 ratio of yellow: green seeds Mendelian Genetics
The Inheritance of Traits F 1 and F 2 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 F 2 generation plants showed a 3:1 ratio of traits. Mendelian Genetics
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 F 1 generation. Recessive alleles were masked in the F 1 generation. Mendelian Genetics
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. Mendelian Genetics
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. Mendelian Genetics
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. Mendelian Genetics
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. Mendelian Genetics
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. Mendelian Genetics
Punnett Squares Punnett squares predict the possible offspring of a cross between two known genotypes. Mendelian Genetics
Punnett Squares Punnett square monohybrid cross The number of squares is determined by the number of different types of alleles produced by each parent. Mendelian Genetics
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. Mendelian Genetics
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. Mendelian Genetics
Review 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? Vocabulary genetics allele dominant recessive homozygous heterozygous genotype phenotype law of segregation hybrid law of independent assortment Mendelian Genetics
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? Gene Linkage and Polyploidy
Vocabulary Review protein New genetic recombination polyploidy Gene Linkage and Polyploidy
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 2 n, 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 2 n X 2 n. Gene Linkage and Polyploidy
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. Gene Linkage and Polyploidy
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. Gene Linkage and Polyploidy
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 Gene Linkage and Polyploidy
Review 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? Vocabulary genetic recombination polyploidy Gene Linkage and Polyploidy