BIO 311D 1st Edition Exam 1 Study Guide Lectures 1 9 Lecture 1 The Stages of Meiosis 1 Interphase Chromosomes duplicate 2 Meiosis I Homologous chromosomes separate a Prophase I Chromosomes condense homologous chromosomes pair up synapsis and crossing over occurs b Metaphase I Tetrads line at metaphase plate microtubules attach to kinetochores c Anaphase I Pairs of homologous chromosomes separate and move toward pole by spindle apparatus 3 Telophase I Cytokinesis Cleavage furrow divides the cell into two Meiosis II Sister chromatids separate a Prophase II Spindle apparatus forms b Metaphase II Sister chromatids due to crossing over sister chromatids are no longer identical align at the metaphase plate and microtubules attach to kinetochores c Anaphase II Sister chromatids separate and move towards opposite poles d Telophase II Cytokinesis Nuclei form and chromosomes decondense Each daughter cell is genetically different from the others Comparing Mitosis and Meiosis Property DNA Replication Number of Divisions Synapsis of Chromosomes Number of Daughter Cells Role in the Animal Body Mitosis Interphase One None Two Identical Growth Repair Meiosis Interphase Two Prophase I Four Unique Produces Gametes Characteristics Unique to Meiosis all occur in Meiosis I 1 Prophase I Synapsis and crossing over occurs 2 Metaphase I Tetrads paired homologous chromosomes line up at the metaphase plate 3 Anaphase I Homologous chromosomes separate instead of sister chromatids Mendel and the Gene Idea Lectures 2 3 Advantages of pea plants 1 2 3 4 Many varieties with distinct heritable features Mating can be controlled Each flower has sperm producing organs stamens and egg producing organs carpel Cross pollination fertilization between different plants involves dusting one plant with pollen from another The Law of Segregation Two alleles for a heritable character segregate during gamete formation and end up in different gametes Discovered by using monohybrids crosses between one character The white color trait did not disappear but rather it was recessive Mendel called the purple flower the dominant trait The white colored flower became the recessive trait The Law of Independent Assortment Dihybrid cross determines whether two characters are transmitted to offspring as a package or independently Dihybrid cross was used to discover the law of independent assortment Found that each pair of alleles segregates independently of each other during gamete formation However genes located near each other on the same chromosome tend to be inherited together Why are humans not good subjects for genetic research Generation time is too long Parents produce relatively few offspring Breeding experiments are unacceptable Multiple Alleles Example is the four phenotypes of the ABO blood group are determined by three alleles for the enzyme I that attaches A or B carbohydrates to red blood cells Pleiotropy Most genes have multiple phenotypic effects known as Pleiotropy This is responsible for multiple symptoms of certain hereditary diseases Examples include cystic fibrosis and sickle cell disease Epistasis Some traits may be determined by two or more genes One gene at a locus alters the phenotypic expression of a gene at a second locus In other words one gene determines whether or not that trait is shown Example Labrador Retrievers and their coat color o One gene determines the pigment color either black or brown o The other gene determines if the color is shown Polygenic Inheritance Quantitative characters are those that vary in population Quantitative variation indicates polygenic inheritance Example Skin color Chromosomal Basis of Inheritance Lectures 4 5 Morgan s Experimental Evidence Thomas Hunt Morgan an embryologist found evidence associating a specific gene with a specific chromosome He performed an experiment with fruit flies which provided evidence that chromosomes are the location of Mendel s heritable factors Advantages of breeding fruit flies o Fruit flies produce many offspring o A generation can be bred every two weeks o They only have four pairs of chromosomes X Inactivation in Female Mammals Because females have XX one X becomes inactive Inactive x condenses into a barr body One of the two x chromosomes in each cell is randomly inactivated Example Female cats can have certain spots where she is brown and other spots where she is orange This is due to the inactivation of random X chromosomes Mapping the Distance Between Genes Using Recombination Data Alfred Sturterant Morgan s Student constructed a genetic map Genetic map is an ordered list of genetic loci along a particular chromosome He predicted that the farther apart two genes are the higher probability that a crossover will occur between them therefore a higher recombination frequency Linkage map Genetic map of a chromosome based on recombination frequencies Map Units Distances between genes o One centimorgan represents a 1 recombination frequency o Map units indicate relative distance order NOT the precise location of genes Cytogenetic maps indicate the positions of genes with respect to chromosomal features Exceptions to Mendelian Genetics Two normal exceptions are 1 Genes located in the nucleus 2 Genes located outside the nucleus In both cases the sex of the parent contributing an allele is a factor in the pattern of inheritance Genomic Imprinting The phenotype depends on which parent passed along the alleles for those traits Involves the silencing of certain genes that are stamped with imprint during gamete production It appears that imprinting is the result of the methylation addition of CH3 of cysteine nucleotides Thought to affect a small fraction of mammalian genes Most imprinted genes are critical for embryotic development The Evolution of Populations Lectures 6 7 The Hardy Weinberg equation Can be used to test whether a population has evolved The frequency of an allele in a population can be calculated o For diploid organisms the total number of alleles at a locus is the total number of individuals times 2 By convention if there are 2 alleles at a locus p and q are used to represent their frequencies o P is in reference to dominance o Q is used in reference to the recessive allele o P Q will always equal 1 For example consider a population of wildflowers that is incompletely dominant for color o 320 red flowers CRCR o 160 pink flowers CRCW o 20 white flowers CWCW Calculate the number of copies of each allele o CR 320 2 160 800 o CW 20 2 160