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Heredity 2012-2013 Your Physical Appearance • Heredity is the passing of traits from parents to an offspring. • Gregor Mendel was the first scientist to successfully study inheritance • He is the “Father of Genetics” Why Pea Plants? • Mendel use Garden Pea Plants for his research because: – They grow quickly – They naturally self-pollinate Mendel’s Success • Mendel was successful with his pea plant research because: – he studied one trait at a time! (independent variable) – He had studied statistics *A trait is a distinct phenotypic characteristic that may be inherited Pea Plant Traits • • • • • • • Flower Color Flower Position Seed Color Seed Shape Pod Shape Pod Color Plant Height The Experiment • Mendel began by taking pure trait plants and cross-pollinating them • He did this by hand, not with bees! The Experiment Part I (Example 1) Plant height Mendel crossed a Tall parent plant with a short parent plant: Tall TT parent 1 x short = x tt = x parent 1 = All Tall Tt First Filial (F1) The Experiment Part I (Example 2) Flower Color Mendel crossed a Purple parent plant with a white parent plant: Purple PP parent 1 x white = x pp = x parent 1 = All Purple Pp First Filial (F1) The Experiment Part II • He wondered why one trait disappeared when he crossed the two pure plants • He decided to allow the new F1 plants to naturally self-pollinate and here is what he found…….. Example 1- Plant Height F1 Tall plants self-pollinate and produce: 75% Tall Plants 25% short plants Example 2 - Flower Color F1 Purple Flower color plants self-pollinate and produce: 75% Purple flowers 25% white flowers Mendel’s Conclusion • The Principle of Dominance and Recessiveness states that one trait is more likely to occur than the other. – Dominant is a trait that is most likely to occur – Recessive is a trait that is usually hidden in the first generation, but may reappear later Probability • The chance or possibility that a certain outcome will occur. Usually written as: – Fractions – Decimals Let’s Learn a New Language.. Genotype- the genetic make-up of an organism (TT, Tt, tt) Phenotype- the physical appearance of an organim (Tall, short, Purple, white) Dominant- more likely to occur (The tall plants or the purple flowers) Recessive- less likely to occur (The short plants or the white flowers) Let’s Learn a New Language.. • Homozygous- when both alleles are the SAME – Homozygous Dominant: TT, PP, WW – Homozygous Recessive: tt, pp, ww • Heterozygous- when each allele is DIFFERENT – Tt, Pp, Ww Let’s Learn a New Language.. • An Allele is an alternate form of a gene; one part of a pair • A Gene is composed of two alleles, one from each parent Allele + T(mom) + Allele = t(dad) = Gene Tt(child) Punnett Squares • Developed by Rudolph Punnett to make genetics easier for us to understand Genetics Example 1 In garden pea plants, tall plants are dominant (T) and short plants are recessive (t). A pea plant that is homozygous dominant for height is crossed with one that is homozygous recessive for plant height. • • • • • Draw a Punnett square to represent the problem. What are the possible genotypes? What are the possible phenotypes? What is the probability of each genotype? What is the probability of each phenotype? • • • • Genotypes Phenotypes Probability of genotypes Probability of phenotypes Genetics Example 2 In garden pea plants, purple flower color (P) is dominant over white flower color (p). A pea plant that is homozygous recesive for flower color is crossed with one that is heterozygous for flower color. • • • • • Draw a Punnett square to represent the problem. What are the possible genotypes? What are the possible phenotypes? What is the probability of each genotype? What is the probability of each phenotype? • • • • Genotypes Phenotypes Probability of genotypes Probability of phenotypes Genetics Examples In garden pea plants, yellow seeds (Y) are dominant and green seeds (y) are recessive. What offspring would result if two heterozygous plants were crossed? • • • • • Draw a Punnett square to represent the problem. What are the possible genotypes? What are the possible phenotypes? What is the probability of each genotype? What is the probability of each phenotype? • • • • Genotypes Phenotypes Probability of genotypes Probability of phenotypes More Genetics Incomplete Dominance • Sometimes one trait is not completely dominant over the other – The same letter allele is used – Red x White = Pink RR x R’R’ = RR’ • This results with a combined genotype – Snap dragons Codominance • Sometimes both traits are equally dominant – Different letter alleles are used – Black x White = Checkered BB x WW = BW • This results in both traits being expressed – Checkered Chickens Alternate forms of Genetics • Gregor Mendel studied simple genetic inheritance: – Offspring were either dominant or recessive • But not all traits are simple!! Thomas Hunt Morgan • Studied Fruit Flies • Discovered – Gender inheritance – Other traits associated with gender Gender • Gender is always determined by the male QuickTime™ and a decompressor are needed to see this picture. Sex-linked Traits • Some traits are only located on the “X” chromosome • Since Males only have one “x” chromosome, they are more likely to show the trait than a female with two “x” chromosomes Sex-linked Traits • Colorblindness • Hemophilia • Muscular dystrophy Other Types of Inheritance Insert chart here Meiosis • Meiosis is the formation of gametes in sexually reproducing organisms – Sperm (male) – Egg (female) Benefits of Meiosis • Forms gametes (sex cells) • Allows for genetic variation • Reduces the number of chromosomes by half – Human body cells 46 chromosome – Human sex cells 23 chromosome • Allows the chromosome number of any organism to remain consistent Haploid vs Diploid • Haploid cells contain 1 set of chromosomes (23 total in humans) – Sperm – Egg • Diploid cells contain 2 sets of chromosomes (46 total in humans) – One set from mom – One set from dad Meiosis Male vs Female Meiosis Karyotype • A karyotype is a picture of someone’s chromosomes Male Karyotype Female Karyotype What do you think? Genetic Disorders • Genetic disorders are caused by mutations in DNA – Mutations that occur spontaneously – Congenital ( people are born with them) – Unable to cure – Can occur in children even when parents do not have them (recessive traits) Genetic Counselors • Genetic counselors are available for people who fear passing genetic disorders to their offspring – – – – – Cystic fibrosis Sickle-cell anemia Huntington’s disease Down’s syndrome Many others • They begin with making a pedigree to observe the family history of traits Pedigree • A pedigree is a map of a family genetic history Genetics in Action Selective Breeding Genetic Engineering Genetics Terminology • Purebred organisms result from crossing two organims with similar traits • Hybrids are produced when two organisms with different traits are combined Purebred • Advantages – Predictable outcome Example: Dog breeds Lab x Lab = Lab LL x LL = LL • Disadvantages – Undesirable traits are possible – A lack of genetic variation will result Hybrids • Advantages – Variety of traits may appear – Can encourage desirable traits to occur Example: kiwi x strawberry = kiwiberry • Disadvantage – Unpredictable outcomes are likely Selective Breeding • Selective breeding involves the crossing of organisms with desired traits to maximize their potential – – – – – Fruits Vegetables Flowers Livestock Insulin Genetic Engineering • A faster form of selective breeding • Genetic engineering is when genetic information is changed within the DNA of an organism