Lab 10 Mitosis Meiosis and Human Genetics Terms to know A Mitosis cell division which results in the production of two daughter cells from a single parent cell The daughter cells are genetically identical to one another and to the original parent cell B Meiosis cell division that results in four daughter cells with half the original genetic material of the parent cell C Chromatin loosely tangled DNA strands in the nucleus of a eukaryotic cell during periods of the cell cycle when the DNA has not been duplicated D Chromosomes condensed DNA strands Before separation during anaphase duplicated identical chromosomes are held together at the centromere E Sister chromatids one of the two identical chromosomes F Homologous chromosomes chromosomes that contain the same genes but not necessarily the same alleles G Gene specific segments of DNA that control cell structure and function the functional units of inheritance H Allele alternate forms of a gene If an individual has two identical alleles on their homologous chromosomes they are homozygous for that gene If the alleles are different they are heterozygous for that gene Five differences between mitosis and meiosis Mitosis 1 Two identical daughter cells with a full set of genetic material Meiosis 1 Four different daughter cells with half of the genetic material of the parent cell 2 One cycle of cell division 2 Two cycles of cell division 3 Sister chromatids line up during metaphase 3 Homologous chromosomes line up during metaphase I 4 Occurs in somatic cells 4 Occurs in sex cells 5 Crossover does not occur 5 Crossover occurs Mitosis 1 Interphase DNA in chromatin form a G1 Centriole duplication typically begins Cell growth b S DNA is replicated c G2 Cell growth Cells prepare for division 2 Prophase a DNA condenses to form chromosomes b Mitotic spindles form c Nucleoli disappear d Centrioles begin to migrate 3 Prometaphase a Centrioles arrive at the poles b Nuclear membrane fragments c Microtubules attach to chromosomes at their kinetochores within the centromere region and begin to move them toward the midline 4 Metaphase a Chromosomes are lined up at the metaphase plate 5 Anaphase a Centromeres split and sister chromosomes migrate to opposite poles 6 Telophase a Nuclear envelopes appear around the chromosomes at the poles b DNA begins to uncoil c Cytokinesis begins i Cleavage furrow in animal cells ii Cell plate in plant cells TODAY IN LAB YOU WILL 1 Watch a DVD about mitosis and meiosis 2 Examine slides under the microscope and identify the different stages of the cell cycle Be able to visually tell the different mitosis stages apart 3 Record your personal phenotypic traits on from the human genetic trait section of your labbook 4 Conduct a blood type paternity test to determine the parents of the children that were mixed up at birth 5 learn how to complete a Punnett square and a dihybrid cross pgs 235 237 Crosses Complete Dominance One Trait with different alleles The same genes located at the same position on two homologous chromosomes code for the different alleles One allele is dominant always expressed symbolized in this case by the capitol letter D The other allele lower case d is recessive not expressed unless both alleles are the recessive copy Let s examine a simple cross between two individuals and only examine this one trait Parent One Homozygous Dominant They both have two homologous chromosomes each with a copy of the gene containing this trait 2n What gametes n with a single copy of each of their chromosomes are possible Parent Two Homozygous Recessive dd DD Each parent can only contribute a single type of allele These two gametes combine into a new individual with the genotype Dd This individual will express the dominant trait but will carry a copy of the recessive trait on one of its homologous chromosomes D d Offspring Heterozygous Let s try a different match Both parents will be heterozygous for this trait Parent One Heterozygous Parent Two Heterozygous What are the possible gametes of each parent Dd Dd D d Each parent can donate a D or a d allele on one of their chromosomes How do we calculate the possible genotypes in the offspring We can use a Punnett Square D d PUNNETT SQUARE A tool used to determine potential genotypes or phenotypes offspring The gametes of one parent are arranged down the side or top of the square The gametes of each parent are matched up inside the square and the results are analyzed D d D DD Dd d Dd dd It s very similar to a multiplication table Inside the square are the genotypes that potential offspring could carry One of the three genotypes is homozygous dominant DD Another is heterozygous Dd The last one is homozygous recessive dd The ratio of genotypes in this monohybrid cross would be 1 2 1 1 DD 2 Dd 1 dd What about phenotypes Obviously there are two phenotypes The individual would either express the trait or not DD and Dd would express the dominant form of the trait Whenever one of the homologous chromosomes contains the dominant code that allele will express The individual with the dd set of alleles would show the recessive form of the trait The ratio of phenotypes in this monohybrid cross would be 3 1 3 D 1 dd A Punnett square can be constructed for any set of gametes It can work for multiple traits if set up correctly Dihybrid Cross Complete Dominance Two unrelated traits with different alleles for each In this case D will be the dominant allele for one trait and R will be the dominant allele for the other trait The lower case d and r will represent the recessive alleles for each of their traits A Punnett square becomes an invaluable tool to determine the possible genotypes from a dihybrid match D d Dr If an individual has the genotype DdRr what are the possible gametes that he could produce Each gamete would have one of the two chromosomes in a homologous pair R r DR dr dR Convince yourself that these are the only possible combinations of these alleles Let s cross a DdRr against a DdRr Dd Rr X DdRr Using a Punnett square line up all the possible gametes of each parent down or across one edge of the square DR Dr dR DDRR DDRr DdRR DdRr Dr DDRr DDrr DdRr Ddrr dR DdRR DdRr ddRR ddRr DR dr DdRr Ddrr ddRr dr ddrr How many different genotypes are there There are 9 DDRR 1 DDRr 2 DDrr 1 DdRR 2 DdRr 4 Ddrr 2 ddRR 1 ddRr 2 ddrr 1 How many different phenotypes are there There are 4 D R 9 D rr 3 ddR 3 ddrr 1 The phenotypic ratio from this dihybrid cross between two heterozygous individuals 9