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Unformatted text preview: BIOL 110: Principles of Biology
Spring 2005 Lecture 22, W 3/16/05
• ONLINE Quizzes (bi-weekly) from now on! (bi– Link TO QUIZZES: (Cañada College I.D. for login and password; (Cañ You can change it yourself with the REGISTER button) http://smcwebtest.smccd.net/accounts/staplesn/index.tpx http://smcwebtest.smccd.net/accounts/staplesn/index.tpx – Time-limited (so study well first!); Time– ~ 30 minutes to complete; once only. Posted this weekend!! • Study Guide for MT2 available. (Ch. 4-8)
– Genetics Problems: #1-7 (look at 8 & 9 too) #1• Review Session, TODAY, 12:30pm-2pm in Lab. (bring Q’s) 12:30pm(bring Q’
– Extra office hours: W, 2-3:30pm and Thurs., 1-3pm. 21- REVIEW:
• Ch. 8: Genetics: Observing Patterns of Inherited Traits.
– Mendel’s Experiments & Laws: Mendel’
• Monohybrid Cross/ Segregation (alleles of the SAME gene separate); • Dihybrid cross/ Independent Assortment (alleles of DIFFERENT genes separate – see recombinant/non-parental phenotypes). recombinant/non- – Exceptions/Beyond Mendel – Incomplete dominance…. dominance… TODAY:
• Ch. 8: Genetics: Observing Patterns of Inherited Traits.
– Exceptions/Beyond Mendel – Incomplete Dominance, Codominance, Pleiotropy, Codominance, Pleiotropy, – Environment, Continuous Variation, Sex-Determination Sex- 1 A. Flower Color in Snapdragons: Flower Incomplete Dominance
Red-flowered plant X White-flowered plant (homozygote) (homozygote) Pink-flowered F1 plants (heterozygotes) Flower Color in Snapdragons: Incomplete Dominance
Pink-flowered plant X Pink-flowered plant (heterozygote) (heterozygote) White-, pink-, and red-flowered plants in a 1:2:1 ratio (3 Phenotypes!) 1:2:1 Can see the see heterozygotes!! 2 Flower Color in Snapdragons: Incomplete Dominance (Biochemical Explanation) (Biochemical
1. Red flowers - two alleles allow them to make a red pigment 2. White flowers - two mutant alleles; can’t make red pigment 3. Pink flowers - have one normal and one mutant allele; make a smaller amount of red pigment B. Genetics of ABO Blood Types: Three Alleles (Codominance)
• Gene that controls ABO type codes for ABO enzyme that dictates structure of a glycolipid on blood cells • Two alleles (IA and IB) are codominant codominant when paired • Third allele (i) is recessive to others
– = Multiple Alleles!! 3 ABO Blood Type: Allele Combinations
• • • • Type A - IAIA or IAi Type B - IBIB or IBi Type AB - IAIB Type O - ii
or Range of genotypes: IA IA
or IA i Blood types: IA IB IB i ii A AB B O ABO Blood Type: Glycolipids on Red Cells
• Type A - Glycolipid A on cell surface • Type B - Glycolipid B on cell surface • Type AB - Both glyocolipids A & B • Type O - Neither glyocolipid A nor B 4 ABO and Transfusions
• Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface
– (attack “non-self” molecules) • Type O is universal donor, because it has universal neither type A nor type B glycolipid • Type AB is universal recipient, because universal neither A nor B are considered “non-self”. C. Pleiotropy
• Alleles at a single locus may have effects on two or more traits
– One gene, but affects multiple characteristics! • effects of the mutant allele at the beta-globin locus that gives rise to sickle-cell anemia; sickle • Cystic Fibrosis • Manx Cat • Siamese cat….. 5 III. Environmental Effects on Phenotype: eg., Temperature
• Genotype and environment interact to produce phenotype • Himalayan rabbits are Homozygous for an allele that allele specifies a heat-sensitive heat version of an enzyme in melanin-producing pathway
– Melanin is produced only in cooler areas of body • Also: plants & altitude, pH, nutrients (flamingos),….. IV. Continuous Variation
• A more or less continuous range of continuous small differences in a given trait among individuals • The greater the number of genes and greater environmental factors that affect a trait, the more continuous the more variation in versions of that trait 6 Plotting Variation
Number of individuals with some value of the trait Range of values for the trait V. Homologous Chromosomes & Sex Determination
• Homologous autosomes are identical in length, size, shape, and gene order (position)
– Homology required for proper pairing and Meiosis/Gametogenesis Meiosis/Gametogenesis • Sex chromosomes are nonidentical but still homologous
– (along portions of X & Y) • Homologous chromosomes interact, then segregate from one another during meiosis 7 Sex Determination
• Gene on X chromosome makes the “Anti-Testes Factor” Factor
– Ovaries = Female Ovaries female (XX) male (XY) eggs X X x x X X Y XX XY X XX XY sperm Y X • Another gene on Y chromosome inhibits ATF
– SRY gene – Testes = Male!!! Testes The Y Chromosome
• Fewer than two dozen genes identified • One is the master gene for male sex determination
– SRY gene (sex-determining region of Y) (sex- • SRY present (XY, XXY, XYY), testes form • SRY absent (XX, XO, XXX), ovaries form 8 The X Chromosome
• Carries more than 2,300 genes • Most genes deal with nonsexual traits • Genes on X chromosome can be expressed in both males and females
– Many recessive “X-linked” recessive alleles show up in males (no second X to mask!!) Examples of X-Linked Traits
• Color blindness
– Inability to distinguish among some or all colors • Hemophilia
– Blood-clotting disorder Blood– 1/7,000 males has allele for hemophilia A – Was common in European royal families • Cats: Calico coat color
– Orange or Black alleles? – Heterozygous females: 1 XXchromosome inactivated in early embryo; – random patches of color produced 9 X-Linked Recessive Inheritance
• Males show disorder more than females • Son cannot inherit disorder from his father • Mothers give disorder to ½ of sons Midterm 2 REVIEW:
1. 2. 3. 4. Energy & Enzymes Photosynthesis Respiration & Fermentation – both use glycolysis Reproduction – Cell Cycle, Interphase
1. Nuclear Divisions – Mitosis (constancy; 2n 2n); 2n); Meiosis (diversity; 2n n) n) 2. Gametogenesis & Fertilization 5. Genetics: Mendel & Beyond
1. Monohybrid & Dihybrid crosses – segregation; independent assortment 2. Incomplete Dominance and Codominance 3. Pleiotropy, Environment, Continuous Variation Pleiotropy, 4. Sex Determination 10 Genetic Disorder
• Inherited conditions that cause mild to severe medical problems • Why don’t they disappear?
– Mutation introduces new rare alleles – In heterozygotes, harmful allele is masked, so it can still be passed on to offspring
• Sometimes, Heterozygote has rare Advantage!
– Eg: Sickle Cell Hemoglobin Eg: Pedigree Symbols male female marriage/mating offspring in order of birth, from left to right Individual showing trait being studied sex not specified I, II, III, IV... generation 11 Pedigree for Polydactyly
I female male II 5,5 6,6 III *
6 7 6,6 5,5 5,5 6,6 5,5 6,6 5,5 6,6
12 6,6 5,5 5,6 6,7 IV 5,5 6,6 V *Gene not expressed in this carrier. 6,6 6,6 Autosomal Recessive Inheritance Patterns
• If parents are both heterozygous, child will have a 25% chance of being affected 12 ...
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This document was uploaded on 03/18/2010.
- Spring '09