Chapter 11 and 12 Notes
Chapter 11 and 12 Notes 10120
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This 5 page Class Notes was uploaded by Hannah Kennedy on Saturday March 5, 2016. The Class Notes belongs to 10120 at Kent State University taught by Professor Grampa in Spring 2016. Since its upload, it has received 33 views. For similar materials see Biological Foundations Honors in Biological Sciences at Kent State University.
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Date Created: 03/05/16
© Hannah Kennedy, Kent State University 1 Chapter 11 1. Mitosis vs. Meiosis Mitosis Meiosis Somatic cells = nonreproductive cells Gametes = sperm and eggs 1 round of cell division 2 rounds of cell division (1 S phase, provides variation) Produces 2 identical cells Produces 4 cells that aren’t identical Original cell is 2n Original cell is 2n Daughter cells are 2n Gametes are n 2. Meiosis I (first round of division of meiosis) a. Interphase occurs first, and then the 1 round of division of meiosis begins; homologous pairs behave like a unit and sister chromatids are not yet separated b. Meiosis 1 Stage of Meiosis I What’s happening Prophase I nuclear envelope disappears spindle develops homologous pairs partner up and are joined together (synapsis) by the synaptonemal complex (synaptonemal complex = a network of cohesion proteins) all 4 sister chromatids are held together homologues begin process to exchange chromosomal material = crossing over = recombination (chiasma = location where crossing over occurs); some DNA segments are exchanged between nonsister chromatids and as a result all 4 sister chromatids are unique; random process; several occurs per chromosome Metaphase I homologous pairs line up in the middle of the cell spindle microtubules attach to the kinetochore of each chromosome (not each sister chromatid) and an entire chromosome is pulled to each side of the cell random alignment occurs Anaphase I spindle microtubules shorten and pull 23 chromosomes to each side of cell cohesins of the synaptonemal complex are broken down and the sister chromatids are still attached each daughter cell contains a unique combination of maternal and paternal chromosomes = independent assortment Telophase I nuclear envelope reforms cytokinesis may or may not occur 3. Meiosis II (similar to mitosis) © Hannah Kennedy, Kent State University 2 Stage of Meiosis II What’s happening Prophase II nuclear envelope breaks down new spindle forms Metaphase II chromosomes line up in the center of each cell spindles attach to kinetochores Anaphase II spindles contract cohesins joining sister chromatids are broken down sister chromatids are pulled to opposite sides of the cell Telophase II nuclear envelope reforms in all 4 daughter cells cytokinesis occurs a. Nondisjunction = failure of chromosomes to move to opposite sides of the cell during either meiotic division a. Aneuploidy = gametes with the improper number of chromosomes © Hannah Kennedy, Kent State University1 Chapter 12 1. Monohybrid Crosses a. Monohybrid crosses = follow 2 variations of 1 trait i. the offspring represent one of the parents (they are not a blend of the parental characteristics) st b. F 1generation = first filial generation = 1 set of offspring; typically shows all dominant traits i. Dominant = trait that is more commonly observed ii. Recessive = trait that is less commonly observes and is masked by a dominant trait 1. Present but not expressed c. F 2generation = offspring produced when 2 F offs1ring reproduce; shows a 3:1 ratio of dominant:recessive traits 2. Mendel’s 5 Elements a. Parents transmit infor for traits to offspring in the forms of genes that are held within DNA i. Each individual receives 1 copy of each gene from each parent (not all copies are identical) 1. Alleles = alternate forms of a gene that can be dominant or recessive a. Homozygous = if both alleles are dominant or both are recessive b. Heterozygous = if 1 allele is dominant and the other is recessive c. Mendel’s Principle of Segregation = states that alleles are discrete, don’t blend, and are joined together at random during fertilization d. Presence of an allele doesn’t mean it’ll be expressed i. Recessive alleles are only expressed if there are no dominant ones 3. Genotype and Phenotype a. Genotype = an individual’s genetic makeup i. Homozygous dominant = 2 dominant alleles, expressed with 2 capital letters (RR) 1. Dominant trait is observed ii. Homozygous recessive = 2 recessive alleles, expressed with 2 lower case letters (rr) 1. Recessive trait observed due to absence of dominant allele iii. Heterozygous = 1 dominant allele and 1 recessive allele, expressed with 1 capital and 1 lower case letter (Rr) 1. Dominant trait is observed due to masking of the recessive trait b. Phenotype = physical expression of the genome i. Example: ability to roll the tongue is dominant 1. For homozygous dominant and heterozygous genotypes: phenotype is the ability to roll the tongue 2. For homozygous recessive genotypes: phenotype is the inability to roll the tongue ii. Example: widow’s peak is recessive 1. For homozygous dominant and heterozygous genotypes: phenotype is the absence of a widow’s peak 2. For homozygous recessive genotypes: phenotype is a widow’s peak 4. Punnett Squares © Hannah Kennedy, Kent State University2 a. Method of producing all possible offspring b. Predicts genotypes and phenotypes of certain crosses 5. Testcross a. Testcross = working backwards to figure out the genotype if the phenotype is already known (i.e. cross the unknown offspring with a homozygous recessive individual and observe the results) 6. Pedigrees a. Used to show family histories based on crosses that have already occurred, 2 types i. Genetic = coded in DNA ii. Hereditary = passed down from parent to offspring b. Symbols i. Circles = females ii. Squares = males iii. Blank shapes = unaffected individuals iv. Filledin shapes = affected individuals c. Carrier = an individual who doesn’t express a trait phenotypically but can pass it on to their offspring who may be affected in the future i. Always heterozygous 7. Dihybrid Crosses = follow the combination of 2 traits a. Mendel’s Principle of Independent Assortment = states that traits are passed on independently so the behavior of 1 trait doesn’t impact the behavior of another trait b. F 1generation contains all heterozygotes i. Just like F generations of monohybrid crosses 1 c. Example of a dihybrid cross (F 2eneration) i. Crossing of 2 heterozygotes RrYy x RrYy 1. These letters come from Mendel’s experiment on seed a. R = round b. r = wrinkled c. Y = yellow d. y = green d. has a ratio of 9:3:3:1 8. Extensions to Mendel Extension Description Polygenic inheritance = states that more than 1 follows a normal bell curve distribution gene influences the phenotype phenotypes are observed as averages with variation above and below average (i.e. the further from the average the fewer individuals in that category) Pleiotropy = states that a single gene can affect commonly observed in diseases where several more than 1 trait symptoms are produced as the result of 1 allele Multiple genes for 1 allele = states that some ex = human blood types traits are coded by more than 2 alleles Incomplete dominance = heterozygote genotype ex = if red flower petals are dominant and white produces a phenotype that is a blend of the petals are recessive, then the heterozygous dominant and recessive traits genotype will produce pink petals ex = if curly hair is dominant and straight hair is recessive then wavy hair will be the phenotype is © Hannah Kennedy, Kent State University3 made from a heterozygous genotype Environmental influences = factors such as some genes are inactivated at specific temperature temperature can influence the phenotype ex = in Siamese cates the surface of the majority of the body is above 33°C so the gene is inactivated and no melanin pigment is produced; tips of ears/nose/paws/tails are lower than 33°C so the gene is active and a dark brown melanin pigment is made
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