Bios 208 1st EditionExam #7 Study GuideI. Autosomes Sex ChromosomesA. Any chromosome, which is not a sex chromosome, is an autosome. B. There are 22 pairs of autosomes in humans. C. Each autosome contains a large number of genes arranges in a definite sequence. In these homologous pairs, the 2 chromosomes are of the same length.II. Genetic crossesA. Crossing pea plants Self-cross:B. Peas are self-fertile.C. Pollen (which carries sperm) can fertilize carpels (which contain eggs) from the same flowerD. True-breeding plants produce one kind of offspring (purple or white)E. Out-cross or hybridization: transfer of pollen to another plantF. Seeds are the offspring. They grow into plants with the same genes.G. Parents: Cross true-breeding purple and white parentsH. F1 generation: all offspring have purple flowersI. F2 generation: mostly purple, some whiteJ. Mendel counted: 705 purple,K. 224 white, ~ 3:1 ratioL. Every gene occurs on a specific chromosome and a specific location or locus (pl. loci).M. Alleles are alternative forms of a gene.III. Heterozygous and Homozygous A. An organism with two identical alleles for a character is said to be homozygous for the gene controlling that characterB. An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that characterC. Unlike homozygotes, heterozygotes are not true-breedingIV. Allelesa) Most genes exist in populations in more than two allelic formsb) For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i.c) The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neitherV. Mendel’s work and lawsA. Agrarian upbringingB. Studied math, chemistry and physics inC. Vienna – mathematical descriptions of nature D. Augustinian monk in Brnö. Teacher; later became abbot.E. Pea breeding experiments, ca. 1855-1865.F. Published results in 1866. Sent papers to European scientists … no response!G. His notes were burned after he died.H. Discoveries: mitosis, 1875; meiosis, 1890I. Results and laws rediscovered in 1900 (Correns, Tschermak, DeVries).J. Genes that influence different traits are inherited independently.K. Recombinants (non-parental combinations of traits) appear in the F2 generationL. Inheritance patterns are often more complex than predicted by simple Mendelian geneticsM. The relationship between genotype and phenotype is rarely as simple as in the pea plantcharacters Mendel studiedN. However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritanceVI. Monohybrid and Dihybrid Crosses Ratios of offspringA. A dihybrid cross (e.g., seed shape and seed color).B. What is the fate of traits that began together in the parents?C. Here, P1 is yellow/round, YYRR; P2 is green/wrinkled, yyrr:D. Remain together? 2) Assort independently?a) YYRR x yyrr 100% YyRrb) P1 P2 F1c) YyRr x YyRr produce F2d) F1 F1e) 9/16 Yellow, Round YYRR Parentalf) 3/16 Yellow, wrinkled YY rr non parentalg) 3/16 green, Round yy RR non parentalh) 1/16 green, wrinkled yy rr ParentalE. phenotype genotypeF. Mendel identified his second law of inheritance by following two characters at the same timeG. Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both charactersH. A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independentlyI. Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations:a) When alleles are not completely dominant or recessiveb) When a gene has more than two allelesc) When a gene produces multiple phenotypesJ. Beyond Mendel:a) incomplete dominanceb) epistasisc) multiple alleles (ABO blood groups)d) co-dominance (ABO blood groups)e) pleiotropyf) polygenic traitsg) environmental influencesVII. Sources of variation during meiosis and sexual reproductionA. Independent assortment of homologues in meiosis produces many types of gametes (eggs and sperm)B. Random fertilization. Any egg (1n) might be fertilized by any sperm (1n) to produce a zygote (2n).C. Crossing-over during Prophase I In humans, average of 2-3 cross-overs per tetrad.D. The locations of cross-overs are random.E. This generates much additional variation (but it is hard to quantify precisely).VIII. Phenotype and Genotype, environment effectsA. Each parent carries 2 factors for each trait, PP or pp (we call factors genes)B. Gametes (eggs and sperm) contain one copy of each factor (P or p).C. Offspring get one factor from each parent. In the F1 (Pp), the recessive factor is present but masked by the dominant factor.D. F1 plants make gametes containing either P or p. Fertilization produces zygotes (F2 generation) that are PP, Pp or ppE. EpisA. In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locusF. For example, in Labrador retrievers and many other mammals, coat color depends on two genesG. One gene determines the pigment color (with alleles B for black and b for brown)H. The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hairI. Epistasis: A single trait is influenced by the interaction of 2 or more genes; Coat color in animal fur; Golden retriever dogs.a) BbCc x BbCc >b) 9 black 9/16 B- C-c) 3 chocolate 3/16 bb C-d) 4 yellow 3/16 B- cce) 1/16 bb ccf) What’s going on?g) Need C- to get any colorh) Also need B- (i.e., B-C-) to get blackJ. B and C encode enzymes that are part of a pigment synthesis pathway IX. Morgan’s Fruit Fly ExperimentsA. The first solid evidence associating a specific gene with a specific chromosome came fromB. Thomas Hunt Morgan, an embryologistC. Morgan’s experiments with fruit flies provided convincing evidence that chromosomes are the location of Mendel’s heritable factorsD. Several characteristics make fruit flies a convenient organism for genetic studiesa) They produce many offspringb) A generation can be bred every two weeksc) They have only four pairs of chromosomesE. Morgan noted wild type, or normal, phenotypes that were common in the fly populationsF. Traits alternative to the wild type are called