Biology: How Life Works - Lecture Notes PDF

 Morris Hartl Knoll Lue Michael Heitz Hens Lozovsky Merrill Phillis Pires Liu Biology: How Life Works Study unit 6 lecture 2 Chapter 14 Meiosis and Mendelian Inheritance Copyright © Macmillan Learning Session mlb153...

 Morris Hartl Knoll Lue Michael Heitz Hens Lozovsky Merrill Phillis Pires Liu Biology: How Life Works Study unit 6 lecture 2 Chapter 14 Meiosis and Mendelian Inheritance Copyright © Macmillan Learning Session mlb153 During which stage of meiosis do we observe 2n →1n? A. S phase of the cell cycle B. M phase of the cell cycle C. meiosis I phase of meiosis D. meiosis II phase of meiosis E. both M phase and meiosis II  In which stage do we find 2 sister chromatids → 1 sister chromatid? A. S phase of the cell cycle B. M phase of the cell cycle C. meiosis I phase of meiosis D. meiosis II phase of meiosis E. both M phase and meiosis II  Which of the cells in the micrographs below, 1 to 4, will undergo mitosis? Please choose the single best answer. A. 1&3 B. 2&4 C. 2&3 D. 1&4  Which of the cells in the micrographs below, 1 and 2, will undergo meiosis? Please choose the single best answer. Somatic animal cell Root tip A. 1 B. 2 C. Both D. Neither  The figure to the right represents: Please choose all the answers that you think are correct. 1.A single chromosome composed of two sister chromatids. 2.A chromosome that has undergone DNA replication. 3.A pair of homologous chromosomes. 4.A chromosome in its diploid state A. 1&2 B. 2&3 C. 3&4 D. 1&4  A cell is diploid and has a total of four chromosomes. If we pretend that the chromosomes stay condensed throughout the cell cycle, which of the diagrammes below correctly represents the chromosomes of this cell before DNA replication? Please choose the single best answer. A. 1 B. 2 C. 3 D. 4  One or more of the cells represented below is/are haploid. Which one is it / which ones are they? Please choose the single best answer. A. 1, 2 & 5 B. 3 & 4 C. All except 2 D. All except 3 Key concepts: Non-disjunction and the consequences Modern Transmission genetics One gene transmission and meiosis By the end of this lecture you should be able to do the following: Predict the possible changes in chromosome number due to nondisjunction. Explain the foundations of modern transmission genetics. Describe Mendel’s first key discovery—the principle of segregation. Nondisjunction - Errors in Meiosis Nondisjunction – failure of chromosomes to move to opposite poles during either meiotic division  First- and Second-Division Nondisjunction All of the gametes will have an incorrect number of chromosomes with first- division nondisjunction. Two of the gametes will have an incorrect number of chromosomes with second- division nondisjunction.  Trisomy 21: Down Syndrome  Trisomy 21: Translocation Down Syndrome can be caused by nondisjunction or a translocation chromosome. Which one is hereditary? A. Nondisjunction (3 copies of chromosome 21) B. Translocation chromosome (usually T 21:14)  Klinefelter and Turner Syndromes Nondisjunction in the sex- determining chromosomes can result in different syndromes. Depending on the gametes that join in fertilization, offspring can have karyotypes that show one additional X or Y chromosome or can have only one X or Y chromosome.  Modern Transmission Genetics Mendel sought to examine if patterns in progeny could be observed from crossing true-breeding plants. If patterns were observed, then he hoped to use them to predict outcomes of other crosses.  Pea Plant Traits Mendel conducted hybridization (interbreeding) studies involving two varieties of the pea plant, focusing on seven contrasting traits: color of seeds, shape of seeds, color of pods, shape of pods, color of flower, position of flowers, and plant height. Pea Plant Crossing: Step 1 Pea flowers have sperm- and egg- producing structures that allow for self- fertilization to occur. Mendel had to remove sperm-producing structures in order to ensure that only his intended cross would happen. Pea Plant Crossing: Steps 2–3 Using a paintbrush, Mendel took pollen (sperm) from one plant and placed that pollen in another plant for fertilization. To prevent any other sperm from landing on the fertilized plants, he covered them with a cloth bag. Crossing true-breeding plants In crossing two true- breeding parental strains of plants, one with yellow and the other with green seeds, all the offspring produced yellow seeds. The trait for yellow seeds is dominant over green seeds because yellow seeds is the trait that appears in the F1 generation. The trait of the pollen donor does not affect F1 appearance. Mendel explained his results by assuming there was a hereditary factor. Today, we know the following: 1. Alleles are the different forms of a gene. 2. The combination of alleles is the genotype. 3. The expression of the genotype produces the phenotype. What happens when two F1s are crossed? When the F1 generation plants were allowed to self-fertilize, an interesting pattern appeared in the phenotypes of the offspring. For all seven traits that Mendel examined, the ratio of dominant to recessive phenotypes was 3:1. The Principle of Segregation (1 of 2) One parent will only make gametes with the A allele, whereas the other parent will make gametes with the a allele. All of the offspring will be heterozygous, Aa, for the gene and show the dominant phenotype. The Principle of Segregation (2 of 2) Purpose of a Punnett square Used to predict all the possible outcomes and probabilities that can come from cross breeding  Testcrossing: Determining the Genotype of a Parent with Dominant Phenotype Segregation of Alleles in Meiosis: Separating Maternal and Paternal Chromosomes in Meiosis I Segregation of alleles corresponds to the separation of: A. genes. B. genotypes. C. chromosomes. D. phenotypes.  Mendel’s principle of segregation corresponds to what part of meiosis? A. separation of homologs in anaphase I B. condensation of chromosomes in prophase I C. alignment of homologs in metaphase I D. alignment of chromosomes in metaphase II E. separation of daughter chromatids in anaphase II Today: Nondisjunction Mendel’s monohybrid crosses Tomorrow: Examples of monohybrid crosses Exceptions to complete dominance Probabilities