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Non-Disjunction Review • http://www.sumanasinc.com/webcon tent/animations/content/mistakesmei osis/mistakesmeiosis.html Lesson# 1.6Genetic Diversity and Heredity Gregor Mendel (1822-1884) • Pioneer of genetics • Austrian monk • Explained the mechanism of gene Inheritance • Basis for understanding heredity What is heredity? • The passing on of characteristics (traits) from parents to offspring • Genetics is the study of heredity Mendel’s Research • Used pea plants • They reproduce sexually • They have two distinct, male and female, sex cells called gametes • Their traits are easy to isolate Mendel… • Cross-pollinated plants to see the outcomes and later to manipulate desired combinations Mendel’s Research • Fertilization - the uniting of male and female gametes • Cross - combining gametes from parents with different traits = Cross-Fertilization OR Cross-Pollination Cross-Pollination stigma anther style filament ovary ovule petal sepal peduncle receptacle Mendel’s Observations • Results were ALWAYS the SAME • Example: He crossed – TALL pea plant x SHORT pea plant • Result: TALL pea plants, ~100% of the time – ROUND pea plant x WRINKLED pea plant • Result: ROUND pea plants, ~100% of the time Mendel’s Observations What Did Mendel Find? • Each organism has two alleles for each trait • Alleles - different forms of the same gene • Genes - located on chromosomes, they control how an organism develops What does this mean…? • Mendel concluded that there had to be factors that controlled the traits expressed in plants – Genes • He realized that genes control what traits are passed on to offspring • Different variation/version of a gene: alleles gene: plant height, alleles: tall, short Gene for flower colour GENETIC WHEEL Activity Dominant or Recessive? • Dominant: alleles of this type determine the expression of the genetic trait in offspring • Recessive: alleles of this type are overruled by dominant alleles The Symbol System • Used letters of the alphabet to show what traits were passed on to offspring • UPPERCASE letters = Dominant • lowercase letters = recessive Y = yellow pea plant y = green pea plant The Crossing of 2… • A yellow pea plant might inherit the alleles Yy (one from each parent) • Since there is a dominant allele (Y) the expressed colour is YELLOW • YY = Yellow (dominant) • Yy = Yellow (dominant) • yy = green (recessive) Example: YY Parents yy x Meiosis (segregation of homologs) Y y Y y gametes Cross-fertilization F1 gen. 100% Tall Yy Yy Yy Meiosis (segregation of homologs) Y YY y Y Yy y Yy gametes Cross-fertilization Yy yy F2 gen. 75% Tall 25% Short What Did Mendel Find? • Mendel discovered different laws and rules that explain factors affecting heredity… Mendel’s Laws of Heredity 1. Law of Segregation 2. Law of Independent Assortment 3. Law of Dominance 1. Law of Segregation • The two alleles for a trait must separate when gametes are formed 2. Law of Independent Assortment • The genes for different traits are inherited independently of each other. • A parent randomly passes only one allele for each trait to each offspring 3. Law of Dominance • The trait that is observed in the offspring is the dominant trait –(UPPERCASE) • The trait that disappears in the offspring is the recessive trait –(lowercase) Single –Trait Inheritance • Genotype: the alleles an organism contains – Tall plant can have the genotype TT or Tt, short plant only one tt • Phenotype: the traits you can SEE – A plant can either be TALL or SHORT – A pea can be yellow or green • Homozygous: genotype that has 2 alleles that are the same (TT or tt) • Heterozygous: genotype that has two different alleles (Tt) Single –Trait Inheritance • Monohybrid Cross: a cross that includes only one trait – Ex. Height or colour • Punnett Square: a chart used to show the possible combinations of alleles in offspring Punnett Square Let’s look at the possible crosses Plant height: • TT x TT = all TT • TT x Tt = 2 TT, 2 Tt • TT x tt = all Tt • Tt x Tt = TT, 2 Tt, tt • Tt x tt = 2 Tt. 2 tt • tt x tt = all tt T T TT T TT t TT Tt Tt T Tt TT Tt tt Tt Tt TT tt Tt Tt tt t Tt T TT T Tt TT Tt t TT tt Tt Tt Tt tt tt Activity: • Simple Genetics Practice Problems #s 1-3 Monohybrid Crosses Cross a pea plant that is heterozygous for round seeds and a pea plant that has wrinkled seeds. The allele for round seeds is dominant. Use the symbols R=round and r=wrinkled *Determine the phenotypes and genotypes of the offspring in the F1 generation Monohybrid Crosses TRAIT: seed shape • Parent phenotypes: round x wrinkled • Parent genotypes: Rr x rr • Parent gametes: R, r, x r, r R r Rr r rr F1 Phenotypes: r Rr rr 50% Rr, 50% rr 50% round, 50% wrinkled F1 Genotypes: Reverse Monohybrid Cross • PURPOSE: to determine the genotypes/phenotypes of the parents if the offspring phenotypic ratio is known • Question: Determine the genotypes of the parents given the information Offspring Genotype Numbers Round seed 5472 Wrinkled seed 1850 Activity: • Simple Genetics Practice Problems #s 4-15 • Practice Quiz • In-Class Assignment Test Cross • An organism showing a dominant phenotype can have two possible genotypes: – Homozygous dominant (TT) – Heterozygous dominant (Tt) • Therefore, a test cross is performed to determine the genotype of the unknown parent Test Cross • A test cross is always performed by crossing the unknown genotype with a homozygous recessive (T? x tt) • The genotype of the unknown parent can be deduced from the appearance of the offspring: – IF half the offspring show the recessive trait unknown parent = heterozygous – IF all the offspring show the dominant trait unknown parent = homozygous Activity Let’s say you decide to make your living as a mink farmer. In mink, black fur is dominant over white fur. Since the market for black mink coats is higher than white mink, you (being the entrepreneur that you are) decide to only raise black mink. Everything is going well but the guy you bought your mink from seemed a little sketchy! You want to make sure they are pure breeds so you run a test-cross. #1 Give the phenotypes of the mink in your test-cross: white black ____________x___________ #2 In your fist test-cross, 30 out of 60 offspring are black and the rest are white! No wonder you got such a good deal! What are the genotypes of the mink used in your testcross? (Use “B” and “b”) Bb bb ___________X__________ B B B b b Bb Bb b Bb bb b Bb Bb b Bb bb #3 Was the black-furred mink you chose for your test-cross a pure breed? Bb What is his genotype? ______________ Try it! In fruit flies, red eyes are dominant over sepia (brownish) eyes. Being the great genetic student that you are, you happen to have a culture of pure red eye and pure sepia eye flies in your laboratory. While working in your lab late one night, a cute, fuzzy, and fantastically friendly, red eyed fruit fly came in for a crash landing on your banana. Wanting (naturally) to know more about your new friend, you decide to run a test-cross on your little, buzzing buddy. …answer these.. 1.Give the phenotypes of the flies in your test-cross: ___________X___________ Red eyes Sepia eyes 2. If all of the offspring turn out to be redeyed (all 347 of them!!!) what are the genotypes of the flies used in your testcross? (Use “R” and “r”) ___________X__________ RR rr …but what about…. If instead, 179 of the 347 show up with sepia eyes, what was the actual genotype of your new found friend? Rr _______________ Genetic diversity is due to… • “Crossing over” during Meiosis I – Prophase I • Independent assortment during Meiosis I and II – Metaphase I and II • Random fertilization of gametes • Certain reproductive technologies • Mutations Types of Reproductive Technologies • • • • Selective Breeding Inbreeding Hybridization Mutations Selective Breeding • Humans take advantage of naturally occurring variation in organisms and choose advantageous traits to pass down to the next generation – Example: domestic animals and desirable crops Types of Reproductive Technologies • • • • Selective Breeding Inbreeding Hybridization Mutations Inbreeding • Continued breeding of individuals with similar characteristics to maintain the desired characteristics of a line – Example: Pure breeds • Increases breed’s susceptibility to diseases and deformations Types of Reproductive Technologies • • • • Selective Breeding Inbreeding Hybridization Mutations Hybridization • Crossing dissimilar individuals to bring together the best (most desirable) traits of both • Produces “hybrids” • New varieties of plants and animals are developed Types of Reproductive Technologies • • • • Selective Breeding Inbreeding Hybridization Mutations Mutations • Definition: the changing of one or more genes • Breeders can increase variation in a population by causing mutations in the DNA – Example: oil-eating bacteria, new species of flowers, etc. • Mutations can either occur spontaneously or can be induced by radiation and chemicals