BIO 311D 2nd Edition Exam 1 Study Guide Lectures 1 11 Lecture 1 Learning objectives 1 1 Read the syllabus state one fact about the course you learned and one new fact about biology Meiosis is the process for sperm and egg cells Mitosis can occur for haploid cells in plants 1 2 Be able to use these terms correctly DNA molecule chromosome chromatid homologous pair Homologous pair same length centromere position staining pattern and carry genes controlling the same inherited characters can have different alleles Chromosome consists of one very long DNA molecule and associated proteins Chromatid The complex of DNA and proteins that makes up eukaryotic chromosomes sister chromatids 1 3 Write out a general life cycle with arrows linking these terms haploid n diploid 2n meiosis and fertilization Are the products of meiosis haploid or are they diploid Haploid Diploid Fertilization Diploid Haploid Meiosis Products of meiosis haploid 1 4 Define sexual reproduction and asexual reproduction How do they differ in comparison of genetic traits between parent and offspring At what points are mitosis and meiosis involved Asexual reproduction a single individual is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes Through mitotic cell division DNA is copied and allocated equally to two daughter cells The genomes of the offspring are exact copies of the parent s genome Sexual reproduction two parents give rise to offspring that have unique combinations of genes inherited from the two parents Offspring of sexual reproduction vary genetically from their siblings and both parents Meiosis occurs 1 5 In animal life cycles do diploid cells undergo mitosis In life cycles of the great majority of animals do haploid cells undergo mitosis Is that the same case for plants Diploid cells do undergo mitosis In most animals haploid cells do not undergo mitosis but haploid cells in plants can 1 6 What cells in your body were formed by meiosis What cells in your body can undergo meiosis Sperm and egg cells are formed by meiosis Can only occur in the germ cells cells in the ovaries and testes 1 7 What are homologous chromosomes Is a homologous pair the same as a pair of chromatids Homologous pair same length centromere position staining pattern and carry genes controlling the same inherited characters can have different alleles Not the same as a pair of chromatids 1 8 How does Meiosis I differ from Meiosis II Do the two members of a homologous pair separate from one other at Meiosis I or Meiosis II At what point do identical chromatids separate from one another Meiosis I homologous chromosomes separate Meiosis II sister chromatids separate 1 9 If the diploid number 2n for a species is 54 what is the haploid number n for that species 27 1 10 If a cell with genome of 20 pairs of chromosomes undergoes normal meiosis how many cells result and how many chromosomes are in each of the resulting cells 4 cells 20 chromosomes 1 11 If a cell with 2n 40 chromosomes undergoes meiosis but one non disjunction event occurs in meiosis II how many chromosomes will be in each daughter cell 21 19 20 20 n 1 n 1 n n 1 12 If a diploid cell has n pairs of chromosomes how many different combinations of haploid chromosomes can be produced in meiosis of that cell ignoring any crossing over 2n 1 13 Explain how independent assortment of homologous chromosomes during meiosis I produces a large amount of genetic variation even without considering crossing over and random fertilization Because each pair of homologous chromosomes is positioned independently of the other pairs at metaphase I the first meiotic division results in each pair sorting its maternal and paternal homologs into daughter cells independently of every other pair 1 14 What is crossing over recombination Does it occur in meiosis I or meiosis II Crossing over begins in prophase I as homologous chromosomes pair loosely along their lengths Each gene on one homolog is aligned precisely with the corresponding gene on the other homolog In a single crossover event the DNA of two non sister chromatids one maternal and one paternal chromatid of a homologous pairis broken by specific proteins at precisely corresponding points and the two segments beyond the crossover point are each joined to the other chromatid 1 15 In summary what process in meiosis is the greatest source of genetic variability in offspring Independent assortment Left Fig 13 7 below Fig 13 10 Lecture 2 Mendelian Inheritance Patterns the basics Genes are distinct units of heredity that influence traits determining the structure of proteins manufactured in the cell Alternative forms of genes for a given trait at any one locus on the chromosome are known as alleles In an individual the two alleles for a particular trait may be identical and the individual is said to be homozygous for that trait or two alleles may be different and the individual is said to be heterozygous In heterozygous individuals expression of one allele may prevent expression of the other the expressed allele is dominant and the masked allele is recessive In cases of simple dominance a recessive trait shows in the phenotype ONLY in the absence of the dominant allele All the pairs of alleles constitute the individual s genotype genetic composition the alleles present The term phenotype refers to the collection of structural biochemical physiological features expressed in the individual s appearance Many examples of heritable traits do NOT involve a simple case of two alleles with simple dominance as above In the case of incomplete dominance both alleles of a heterozygous individual contribute to the phenotype so the appearance of the individual is intermediate between the two distinct forms However the alleles in the genotype are inherited distinctly Many traits have more than two possible alleles multiple alleles that can occupy that site same gene locus For example the inheritance of the human ABO blood group protein is controlled by at least three alleles for IA A IB B and i O Any diploid individual human has only two of the alleles The A and B genes are examples of co dominant alleles that is both are fully expressed in the phenotype the blood type The i O gene is recessive and individuals have type O blood only if they are homozygous recessive Learning objectives 1 16 Define and distinguish between the terms gene and allele between genotype and phenotype Gene A discrete unit of hereditary information