BIOL 111 1st EditionExam 3 Study Guide- Before Mendel (<1860s)—ideas about inheritanceo- Gregor Mendel (1822-1884): the Revolutionary monko Training in mathematicso Simple system-Pea plants: True breeding plants- Very prolific (get lots of offspring), grow very quickly, have lots of characteristics that are easy to follow- If you let the plant self-fertilize, the characteristics of the plant stay true Study one characteristic at a time- Mendel didn’t try to study everything at once and used different experimentsto study different characteristics Use quantitative analysis, determine patterns- Counting, measuring to get data- Experiment #1o Monohybrid cross: two true-breeding plants What traits appear in F1?- Purple and white flowers, the dominant trait is purple and the recessive is white Review:- P-the parents- F1-the offspring- True-breed- Hybrid- one of each of the traits from the true-breeding parents- Dominant-the trait that appears - Recessive –the trait that is covered up by the dominant traito Mendel’s simple system True breeding pea plants Study one characteristic at a time Count and determine patterns- Experiment #2 o What traits appear in F2?o Repeat with different characteristicso Notice ratio~3:1—Why? Realized that the blending hypothesis did not work anymore and decided to make a different modelo What is an allele (or heritable factor)? Like sister chromatids except that alleles are different from one another because one is from mom and one is from dad while sister chromatids are exactly identical to each other o Review F2-second generation of species Allele-heritable factors that can be passed down form generation to generation - Meiosis oo Where are alleles during gamete formation? An individual trait has only one allele in gamete formation - How to geneticists represent alleles?o Dominant trait-CAPITAL lettero Recessive trait-lower case lettero Use letters to show all possible alleles present in gameteso Punnent square: used to predict possible offspring allele combos from parents with known genetic makeup - Law of segregation o Following one trait o Allele pairs separate (segregate) suring gametogenesis and re-pair at fertilizationo Review: Homozygous-same alleles (AA, aa) Heterozygous-different alleles (Aa) Phenotype-the outward appearance of an individual (flower color purple) Genotype-the actual genetic make up of the individual (the alleles, AA)o F2 ratios: - Experiment #3: Test Crosso Determine unknown genotype of a dominant phenotype by crossing with recessive homozygote—why? If you did not cross with the homozygote, you would not know whether the unknown was homozygous or heterozygouso- Experiment #4: Dihybrid cross follow two traits for two generationso Now following two traits, start out with true breeding individuals and wants to find out if two traits are inherited independently/dependentlyo How to alleles segregate? Independently or dependently?- Law of independent assortmento Determine possible gamete alleles for P generation RRYY, rryyo Predict genotype and phenotype of F1 Dependent assortment you would get YYRR, YyRr, YyRr yyrr and would get a phenotypic ratio of 3:1 Independent assortment you would get YYRR, YYRr, YyRR, YyRr, YYRr, YYrr, YyRr, Yyrr, YyRR, YyRr, yyRR, yyRr, YyRr, Yyrr, yyRr, yyrr and the phenotypic ratio is 9:3:3:1o Following two traits at a time=dihybrid crosso Each allele pair segregates independently of other pairs of alleles during gamete formation - Sex determination in mammals o Sex chromosomes—XY systemo Sex linked genes Examples in mammals- SRY gene-sex determining region of Y chromosomes- DAX gene-dosage sensitive gene on X chromosome- Sex-linked traits/disorderso Due to gene on a sex chromosome (X or Y)o Often recessive Female (XX)—carrier if heterozygous or affected by homozygous Male (XY)—hemizygous, affected if have gene- Ex. Color blindness, hemophiliao Sex-linked traits were one of the original pieces of evidence for genes associating with chromosomes- Discovery timelineo 1860s—Mendel’s laws of inheritanceo 1870-1890s—physical process of mitosis and meiosis discoveredo 1902—Sutton and Boveri propose chromosomal theory of inheritance (Medelian genes have specific loci/positions on chromosomes)- Thomas Hunt Morgan (early 1900’s)o Provided physical evidence for genes associating with chromosomeo Used Drosophilia melanogaster (Fig 15.3)o Studied sex-linked traits o Morgan’s correlation: a trait (eye-color) correlates with an individual’s sex lends support to chromosomal theory of inheritance- Genetic variation recombination of geneso Independent assortment recombines unlinked genes Examine figure 15.2—do all of the offspring look like the parents?o Independent assortment recombines unlinked genes Use TESTCROSS to study (figure 15.UN2 Pg. 294)o Crossing over recombines linked genes Figure 15.9—Morgan’s experiment #3 TESTCROSSo If TESTCROSS results in: Parental type—greater than 50% offspring phenotypes Recombinant type—much less than 50% offspring phenotypes new combos- THEN Linked genes: genes located on the same chromosome, “tend” to be inherited together but not always du to crossing over- Abnormal chromosome number o Nondisjunction-when homologous chromosomes or sister chromatids do NOT separate Aneuploidy-offspring with abnormal number of a particular chromosome (monosomy, trisomy)- Ex. Down syndrome—trisomy 21, klinefelter syndrome (XXYY), turner syndrome (XO) Polyploidy-offspring with more than 2 complete chromosome sets- Triploidy (3N), tetraploid (4N), etc.- Testing for Genetic Disorderso Identify carriers-use in vitro fertilization and screen embryoso Fetal testing (Fig. 14-18)-amniocentesis, chorionic villus sampling, ultrasoundo Newborn screening-PKU (phenylketonuria)-treat with special
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