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Chapter 11. Introduction to Genetics. 11- 1 The Work of Gregor Mendel. Every living thing – plant or animal, microbe or human being – has a set of characteristics inherited from its parents
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Chapter 11 Introduction to Genetics
11- 1 The Work of Gregor Mendel • Every living thing – plant or animal, microbe or human being – has a set of characteristics inherited from its parents • Since the beginning of recorded history, people have wanted to understand how that inheritance is passed from generation to generation
Genetics • The scientific study of heredity • Heredity- the passing on of characteristics from parents to offspring
Gregor Mendel • Austrian Monk • Born 1822 in Czech Republic • Worked at monastery and taught high school • Tended the monastery garden in Austria • Grew peas and became interested in the traits that were expressed in different generations of peas
Why the pea plant? • Reproduce sexually (use gametes) • Easy to cross pollinate ensuring control of the parental generation • Easy to study one trait at a time • Very distinguishable traits
Mendel was the first person to succeed in predicting how traits are transferred from one generation to the next.
True breeding • If allowed to self pollinate they would produce offspring identical to themselves • He was also able to cross breed peas for different traits
Genes and Dominance • Mendel studied seven different pea plant traits • Each trait he studied had a contrasting form
Genes and Dominance • The offspring of crosses between parents with different traits are called Hybrids • When Mendel crossed plants with different traits he expected them to blend, but that’s not what happened at all. • All of the offspring had the character of only one of the parents
Mendel’s generations • Parents: (P) trait of height. Tall x Short • First generation: (F1) All tall • Second generation: (F2) allowed first generation tall plants to self pollinate. ¾ were tall and ¼ were short • * “F” stands for filial- son or daughter
Mendel drew two conclusions • “Rule of Unit Factors” Inheritance is determined by factors that are passed from generation to generation – today we call these factors genes
Alleles • Different forms of a gene • Examples: Gene of plant height: alleles for tallness, alleles for shortness
Mendel’s 2nd conclusion 2. The Rule of Dominance • Some alleles are dominant and some are recessive
dominant • Covers up the recessive form Ex.) T = tall • “observed trait of an organism that masks the recessive form of a trait”
recessive • Gets covered up in the presence of a dominant allele Ex.) t = short • “trait of an organism that can be masked by the dominant form of a trait”
Expression of Alleles • Upper case letter represent dominant alleles and lower case letters represent recessive alleles. • Examples: for plant height • T= tall t=short • TT= tall • tt= short • Tt= tall
Law of Segregation • Mendel wanted to answer another question Q: Had the recessive alleles disappeared? Or where they still present in the F1 plants? • To answer this he allowed the F1 plants to produce an F2 generation by self pollination
P1 Parental F1 F2 Tall Short All Tall 3 tall : 1 short 75% tall 25% short
The F1 Cross • The recessive traits reappeared! • Roughly 1/4 of the F2 plants showed a recessive trait
Explanation of the F1 Cross • The reappearance indicated that at some point the allele for shortness had been separated from the allele for tallness • Mendel suggested that the alleles for tallness and shortness in the F1 plants were segregated from each other during the formation of sex cells or gametes • When each F1 plant flowers, the two alleles segregate from each other so that each gamete carries only a single copy of each gene. Therefore, each F1 plant produces two types of gametes – those with the allele for tallness and those with the allele for shortness
30 minute video • http://www.youtube.com/watch?v=6OPJnO9W_rQ • Watch this at home if you need more help
Probability and Punnett Squares • Mendel kept obtaining similar results, he soon realized that the principals of probability could be used to explain the results of genetic crosses
Probability • The likelihood that a particular event will occur • The way in which alleles segregate is random like a coin flip
Punnett Square Vocab • Phenotype • Genotype • Homozygous • heterozygous
Punnett Square • Diagram used to determine genetic crosses
Homozygous • Organisms that have 2 identicle alleles for a trait Ex.) TT , tt
Heterozygous • Have two different alleles for a trait Ex.) Tt
Phenotype • Physical characteristics – (words) Ex.) tall
Genotype • Genetic make-up - (letters) Ex.) Tt, TT, tt
Bozeman biology video • http://www.youtube.com/watch?v=NWqgZUnJdAY&feature=related
Mendel wondered if alleles segregate during the formation of gametes independently • Does the segregation of one pair of alleles affect the segregation of another pair of alleles? • For example, does the gene that determines whether round or wrinkled in shape have anything to do with the gene for color? • Must a round seed also be yellow?
All heterozygous 9:3:3:1 Ratio
Independent Assortment • Genes that segregate independently do not influence each others inheritance
A Summary of Mendel’s Principles • The inheritance of biological characteristics is determined by individual units known as _______________. In organisms that reproduce sexually, _______________ are passed from parents to offspring Genes Genes
A Summary of Mendel’s Principles • In cases in which 2 or more forms of a gene are present, some forms of the gene may be _______________________ or ___________________________ • In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed • The alleles for different genes usually segregate independently of one another dominant recessive
Incomplete Dominance • When one allele is not dominant over another • Four o’clock flowers • The heterozygous phenotype is somewhat in-between the two homozygous phenotypes
Codominance • When both alleles contribute to the phenotype of an organism Ex.) Speckled Chickens
Multiple Alleles • When more than two possible alleles exist in a population Ex.) blood type • IA • IB • i Dominant Recessive
Polygenic Traits • Traits controlled by two or more genes Ex.) eye color, skin color
Genetics and the Environment • The characteristics of any organism, is not only determined by the genes it inherits • Characteristics are determined by interactions between genes and the environment • Ex.) genes may affect a plants height but the same characteristic is influenced by climate, soil conditions and availability of water
Do Now • Human hair is inherited by incomplete dominance. Human hair may be curly (CC) or straight (cc). The heterozygous genotype (Cc) produces wavy hair. Show a cross between two parents with wavy hair
Do Now • A man is suing his wife on grounds of infidelity. The man claims that the child is blood type O and therefore must be fathered by someone else. Can he use this evidence in court if he and his wife both have heterozygous B genotypes? • Show the cross of the two parents
