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Lecture # 6 Date _________

Lecture # 6 Date _________. Chapter 14~ Mendel & The Gene Idea. VOCAB. P (parental) generation – true-breeding parents in a genetic cross F1 (1 st filial) generation – offspring of P F2 (2 nd filial) generation – offspring of F1. Mendel’s Model.

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Lecture # 6 Date _________

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  1. Lecture # 6 Date _________ • Chapter 14~ Mendel & The Gene Idea

  2. VOCAB • P (parental) generation – true-breeding parents in a genetic cross • F1 (1st filial) generation – offspring of P • F2 (2nd filial) generation – offspring of F1

  3. Mendel’s Model • Alternative versions of genes cause variations in inherited characgteristics among offspring - ie. Gene for flower color comes in 2 versions - the alternatives are called alleles, which are slightly different DNA sequences • For each character, every organism inherits 1 allels from each parent

  4. If the 2 alleles are different, then the dominant allele will be fully expressed in the offspring, whereas recessive allele will have no noticable effect on the offspring • The 2 alleles for each character separate during gamete production (meiosis) - LAW of SEGREGATION – if parent has the same 2 alleles the offspring will get it. If the parent has one of each, then they have a 50% chance of making it to offspring

  5. These 4 ideas led to Mendel’s Model in explaining traits in pea plants HOW HE DID IT! - observed two different P’s - all F1’s were purple -but F2 had a 3:1 ratio

  6. What We KnowNow

  7. Law of Independent Assortment • Mendel’s 2nd law • States: each pair of alleles will segregate (separate) independently during gamete formation (meiosis)

  8. More Vocabulary • Homozygous – organism has two of the same alleles (both dominant or both recessive) • Heterozygous – organism has two different alleles • Phenotype – refers to the expressed traits (what you see) • Genotype – refers to the genetic makeup (cannot see)

  9. Monohybrid cross – cross involving the study of only 1 trait (ie. Flower color) • Dihybrid cross – cross involving the study of 2 characteristics (ie. Flower color AND seed shape)

  10. Dominance • Complete Dominance – form of dominance where the Heterozygous (Rr) and Homozygous Dominant (RR) both express the same phenotype (red) • Co-Dominance – occurs when two alleles are dominant and can have 3 different phenotypes: (ie. Red, white, r&w polka dot) • Incomplete dominance – occurs when two alleles are dominant and the result is a phenotype between the two parents (ie. red, white, pink)

  11. Multiple alleles – gene has more than two alleles! • Blood types alleles: IA, IB and i • IA IA, IA i : TYPE A (anti-B) • IB IB, IB i : TYPE B (anti-A) • IA IB : TYPE AB (anti-none…universal donor) • i i : TYPE O (anti-A, anti-B)

  12. Pleiotrophy – occurs when a gene has multiple phenotypic effects. - Sickle-cell disease has multiple symptoms due to one single defective gene • Epistasis – gene in one loci affects the gene at another loci - person has gene for heavy skin pigmentation but a separate gene which produces the gen may be defective leading to the pigment not being made….ALBINO (albinism)

  13. Polygenic Inheritance – two or more genes have affect the expression of a phenotype - height and skin color is an expression of multiple genes - the result in a population is usually a bell-shaped curve to show that individuals with the “average” trait will be the most numerous and the “extreme” phenotypes are few

  14. Pedigree • A diagram that shows the relationship between parents and offspring • Circle = female • Square = male • White = phenotype 1 • Black = phenotype 2

  15. Recessively inherited disorders - diseases that require two recessive alleles to be expressed

  16. Cystic Fibrosis • Mutation in an allele that codes for protein to transport chloride ions into and out of cell • High levels of chloride lead to thick sticky mucus • Organ malfunction & bacterial infections • Life expectancy 37 years

  17. Tay-Sachs • Allele that codes for a dysfunctional enzyme • Cannot break down lipids in brain • Blindness, seizures, degeneration of brain function, death • Life expectancy 3-4 years

  18. Sickle-Cell • Allele codes for mutant hemoglobin and forms “sickle” shaped blood cells when oxygen is low • Clogged blood vessels, pain, organ damage, and paralysis • Life expectancy 50 years

  19. Lethal Dominant alleles • Requires only 1 copy of the allele to be expressed (duh! It’s dominant) • Dead • Only passed on if it’s a “late-acting” lethal dominant allele • Huntington’s disease is lethal dominant • Degeneration of nervous system • No effect until 40 years old (so the affected person can pass it on to kids!!!)

  20. Testing for disorders • Amniocentesis – doctor removes amniotic fluid around fetus. The fluid has cells that can be cultured to detect some disorders • Chorionic Villus Sampling – inserting narrow tube to suction small sample of placenta that contians fetal cells

  21. Human disorders • The family pedigree • Recessive disorders: •Cystic fibrosis •Tay-Sachs •Sickle-cell • Dominant disorders: •Huntington’s • Testing: •amniocentesis •chorionic villus sampling (CVS)

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