BIO 111, Week 3 Notes
BIO 111, Week 3 Notes BIOL 11100 - Fundamentals of Biology II
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BIOL 11100 - Fundamentals of Biology II
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This 5 page Class Notes was uploaded by Phoebe Notetaker on Friday January 29, 2016. The Class Notes belongs to BIOL 11100 - Fundamentals of Biology II at Purdue University taught by Dr. Athena Anderson in Winter 2016. Since its upload, it has received 44 views. For similar materials see Biology in Science at Purdue University.
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Date Created: 01/29/16
1/26/16 Genetics Gregor Mendel: The Austrian/monk/biologist who figured out a large part of how genetics works with the garden pea model. Mendelian Genetics ● Before Mendel, the idea about inheritance was not quantitative ● Blending inheritance was the idea before Mendel’s work: offspring would have intermediate characteristics compared to their parents. ○ Ex: Child grows to a height that is in b/w the heights of his parents. ○ The problem is that each generation would be more alike than the previous one, eventually leading to a clonelike population. ● Mendel showed the importance of quantifying experiments to discover the goings on of genetics. ● He coined these terms: ○ Genotype: Alleles carried by an individual/gene makeup. ○ Phenotype: Physical appearance of the individual. ○ Hybrid: Offspring of truebreeding parents w/ different traits for same character. ○ Cross: Sexual reproduction b/w different individuals. ○ Character: A feature, like hair color or plant height. ○ Trait: The genotype or phenotype of an individual for a given character (red hair). ● Familiarize yourself with meiosis to understand genetics. ● Consider: ○ What kinds of gametes can parents make? ○ Sex = combining gametes from parents ○ As chromosomes go, so go genes ● Eventually we will be able to map genes and figure out where they are located on chromosomes. ● Truebreeding: Individuals always produce offspring that resemble themselves when selffertilized (only applies to plants). ● Mendel crossed pea plants that were truebreeding for round seeds with pea plants that were truebreeding for wrinkled seeds. ● P0: Parental generation ● F1: First filial/offspring generation ● F2: Offspring of a cross b/w two F1 individuals ● Wrinkled trait disappeared in the first generation. ● Cross of F1 individuals will create a second generation of offspring. What does F2 look like? ● Wrinkled reappears in the second generation. ● Mendel counted many seeds and discovered: ○ Proportions of ¾ round, ¼ wrinkled. ○ Phenotypic ratio: 3 round: 1 wrinkled ● Recessive trait: Masked by dominant trait; in this case, the wrinkled phenotype [r] ● Dominant trait: Masks recessive traits; in this case, the round phenotype [R] ● Offspring get one set of chromosomes from each parentone allele for a character from each parent. ● What happens when you cross: RR x rr ? ● The first parent can produce only gametes w/ ‘R’ ● The second parent can produce only gametes with ‘r’ ● F1 generation: all ‘Rr’ ● F2 generation: 3 round: 1 wrinkled phenotypic ratio ● Law of Segregation: Two alleles for a heritable character separate from each other during gamete formation, ending up in different gametes. ● Genotype determines phenotype: ○ RR dominant phenotype (homozygous) ○ Rr dominant phenotype (heterozygous) ○ rr recessive phenotype (homozygous) ● Different genotypes can have the same phenotypes ○ Ex: A yellow rose (phenotype) could be homozygous (YY) or heterozygous (Yy). ● Punnett Squares are used to show possible genotypes and phenotypes of offspring ● Gametic types are equally likely ● They combine randomly and the outcome in each square is equally probable ● Monohybrid cross: Only examining one trait in a cross ○ Ex: Pea size or color but not both ● Dihybrid cross: Examine two traits ○ Ex: Pea size and color ● Coss homozygous dominant for both w/ homozygous recessive for both: RRYY x rryy ○ RRYY make only RY gametes ○ rryy make only ry gametes ● RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy Law of Independent Assortment: Two or more genes are sorted into gametes independently of each other. ● If independent assortment is occurring, laws of probability can be used, which allows us to predict outcomes probabilistically. ● Product Rule: The probability of two independent events occurring equals the product of individual probabilities. ● Many independently segregating loci exist ○ Consider each individual probability and multiply individual probabilities. ● Consider: AaBbCc x AaBbCc ○ Probability of certain genotypes or phenotypes? ○ To solve, consider each locus individually. ○ The overall probability is the product of individual probabilities (events must be independent) ● Product Rule 1/28/16 ● Incomplete Dominance: Dominant allele doesn’t completely mask the recessive allele. ● The degree of dominance is the result of biochemistry caused by gene expression. ○ Ex: The plumage in chickens (blue, black, splash, white). ● Black (bl) is wild type and recessive; blue is dominant (Bl) and inhibits eumelanin. ○ Chickens bl/bl are black (no inhibition). ○ Chickens Bl/Bl are splash (lots of inhibition). ○ Chickens are blue (Bl/bl are blue (intermediate inhibition). ● Codominance: Two alleles have equal contribution to offspring phenotype; when both traits from the parents are expressed in the offspring. ○ Heterozygotes have traits of both homozygous parents; offspring is red and blue ○ Incomplete dominance in this example would make the offspring purple (blue + red). ● An example of codominance in people is Sickle Cell Disease ○ Sickle shaped red blood cells can’t c2as well as normal red blood cells. ○ SS genotype → All RBCs are sickle cells; severe health issues. ○ AA genotype → No sickle cells. ○ AS genotype → Normal and sickle cells. ■ They carry the sickle allele, but they do not express the sickle cell disease. ● 1/10 african americans have the AS genotype. ● Why hasn’t this detrimental allele been eliminated via natural selection if it is so harmful to humans? ● It conferadaptive advantage on heterozygotes (AS) in areas with high malaria risk. ● Heterozygotes have enough normal red blood cells to be relatively healthy, but not enough for malarial parasite to take over their body and make them sick. ● Multiple alleles: One gene controls a character, but has more than twoslide 8 . → ○ Coat color in rabbits: C, c, ch, and h alleles. ■ Four alleles influence coat color in rabbits. ○ Human blood type: A, B, and O alleles. ● Pleiotropy: One gene has multiple phenotypic effects. ○ Ex: Frizzled chickens: One gene causes curled (defective) feathers, higher metabolism and blood flow rates, and higher digestive capacity. ○ Not so cute examples: Cystic fibrosis, Marfan syndrome ● Epistasis: Phenotypic expression of one gene affects that of another gene at different locus (genes can be bossy to each other). ○ Ex: Horse coat color ■ Extension gene codes for production of coat pigmentation (E [black] or e [yellow/redish]). ■ Agouti gene controls [where these genes are expressed] location of eumelanin deposition on body (A or a). ○ Coat color in horses: ■ EE produces black/brown coat pigment eumelanin (cannot make phaeomelanin). ■ ee produces chestnut coat pigment phaeomelanin (cannot make eumelanin). ■ Ee is intermediate brown/red color (incomplete dominance). ■ A_ produces eumelanin only on “points” ■ aa produces uniform eumelanin deposition ○ EEA_ produces a brown bay ○ EeA_ produces a red bay ■ [know phenotypes these genotypes produce for the exam] ○ ee__ produces a chestnut/sorrel ○ E_aa produces a black ● Modifiers are genes that affect the degree to which another gene is expressed. ○ Champagne gene is dominant and dilutes eumelanin and phaeomelanin. ○ Cream gene dilutes red to yellow in heterozygotes. ***No need to know the names of the horse colors, but you do need to know how the genes work! ● Polygenic inheritance: Two or more genes affect the same phenotypic character (converse of pleiotropy). ○ Ex: Human skin color and eye color. REVIEW (very likely to appear on the exam): Be able to distinguish these and know examples: 1. Dominance: dominant allele prevents expression of recessive allele in offspring 2. Codominance: both alleles expressed equally in offspring 3. Incomplete dominance: offspring have intermediate traits 4. Multiple alleles: one gene has more than 2 alleles 5. Pleiotropy: one gene has many phenotypic effects 6. Epistasis: one gene masks the expression of another 7. Polygenic inheritance: more than one gene affects phenotype of one character (Human eye and skin color). NonMendelian Genetics ● Examples in which the genes do not behave the way that Mendel described: Sexlinked genes, linkage, abnormal chromosome numbers. ● Sexlinked genes: Genes located on sex chromosomes. ○ Ylinked genes are generally harmless, because the Y chromosome is so tiny that it doesn’t cause many problems. ○ Xlinked genes are responsible for several conditions: ■ Color blindness in men: Cannot distinguish red from green. ■ Duchenne muscular dystrophy in men: Progressive weakness in muscles. ■ Hemophilia: Decreases blood’s ability to clot, risk of bleeding to death. ● Some cat coat colors are the result of xlinked genes ○ The genes for orange and black coat color are both on the X chromosome ○ Males (Xy) express the color that’s on their one X ○ Females (XX) express both colors, causing tortoiseshell and calico patterns if black and orange. ○ ONLY males w/ XXy genotype can be tortoiseshell or calico. ● Linkage: Autosomal genes are frequently inherited together during meiosis if their loci are in close proximity. ○ As distance b/w genes increases, the more likely recombination increases. ● Abnormal chromosome numbers: Nondisjunction during meiosis results in gametes that are diploid for some genes. ● Polyploid: Individual has more than diploid chromosome sets; many commercial fruits are polyploid. ● Pedigree analysis: Graphical method that summarizes family data. ○ Suggests models of inheritance for diseases ○ Can be used for genetic mapping ○ Ex: A pedigree could be used to determine whether a couple is at high risk for passing on a genetic disorder to a child Human Genome Project ● Initiated in 1990 ● Existing genetic and physical maps were used as foundation ● In 2001 partial maps were reported w/ ~25,000 genes ● Gaps are currently still being filled in ● New techniques are now being used to fill gaps: Identifying single nucleotide differences
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