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Chapter 11 Introduction to Genetics

Chapter 11 Introduction to Genetics. Gregor Mendel and his work (Section 11-1) Peas and Genetics Genes and Dominance Probability and Punnett Squares ( Section 11-2) Exploring Mendelian Genetics (Section 11-3) Independent Assortment Mendel’s principles Beyond Mendelian Genetics. X.

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Chapter 11 Introduction to Genetics

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  1. Chapter 11Introduction to Genetics • Gregor Mendel and his work(Section 11-1) • Peas and Genetics • Genes and Dominance • Probability and Punnett Squares(Section 11-2) • Exploring Mendelian Genetics(Section 11-3) • Independent Assortment • Mendel’s principles • Beyond Mendelian Genetics

  2. X First Generation (F1) X 100% pink!!! Second Generation (F2) How did this happen? 3 pink, 1 blue - ¾ pink(75%), ¼ blue (25%)

  3. Genetics!!! Section 11-1 • Patterns of Inheritance • You inherit traits(physical characteristics)from your parents- Heredity! • Heredity is what makes you unique • Examples of Traits: • Blue, Green, Brown, Black, Hazel Eye color • Red, Brown, Black, Blonde hair color • Pale, Olive, Dark skin color • Tall, short, average heights • Or, pink and blue fur! • Genetics = the scientific study of heredityand its importance in biology Box 1 Box 2 Box 1 Box 3

  4. Gregor Mendel Am I in heaven? • Gregor Mendel (1822), an Austrian monk who studied inheritance patterns in pea plants, his work is now considered the foundation of modern genetics • He worked with ordinary garden peas, planted in the garden at his monastery. • His love of plants and science allowed him to spend a lifetime devoted to both. • In 1866, he published a groundbreaking work that later became known as Mendel’s Laws on Heredity, but NO ONE BELIEVED HIM!!! • Years later, his work was rediscovered, and modern genetics was born Box 4 Yet another lovely flower! I am truly in heaven! Ah! What a lovely flower!

  5. What Mendel Did Let’s cross you with the white flower. • Background: • Fertilization = when the female’s egg and the male’s sperm (flower sperm = pollen) unite to produce an embryo • Plants, animals, and most living things, sexually reproduce • Sexual reproduction = combination of egg and sperm to create a new cell, or embryo • Mendel’s peas were True-Breeding, meaning if they were allowed to self-pollinate, they would produce baby pea plants (offspring) identical to themselves • Mendel knew what to expect from his pea plants- they should look exactly like their parent plant! • He Cross-pollinated his pea plants, mixed up the parents, to see what the resulting plants would look like Box 5 Box 6 Box 7 Box 7 Hmm, what have we here?

  6. What Mendel Found P x P F1 X F1 Box 11 F2 Box 8 • Mendel studied 7 different pea plant traits that varied from one individual plant to the next (like human traits!) • These traits had 2 forms, such as either green seeds or yellow seeds, smooth pods or wrinkled pods • He crossed plants with each of the 7 contrasting characteristics and studied their offspring • P = represents the parent generation • F (from the Latin word fillius and filia- son and daughter) • F1 = first generation • F2 = second generation • Hybrids =offspring of crosses between parents with different traits Box 9 Are you an F1 or F2? Box 9 Box 10

  7. Mendel’s Experiment P generation tall short

  8. Mendel’s Experiment F1 generation P generation tall short tall tall

  9. Mendel’s Results Box 12 All the F1 plants expressed only the dominant trait! Seed Shape Seed Color Seed Coat Color PodShape PodColor FlowerPosition FlowerHeight wrinkled green white constricted yellow terminal short Yellow dominant Smooth dominant Axial dominant Tall dominant round yellow gray smooth green tall axial Round dominant Gray dominant Green dominant Ha! Those are MY peas!

  10. Mendel’s Principles of Heredity Hello! • Mendel learned 2 principles from these experiments: • Biological inheritance is determined by factors (we call them genes) that are passed from one generation to the next, Genes = chemical factors that determine traits – each trait is controlled by 1 genethat occurs in 2 contrasting forms or alleles Box 13 Box 14 Allele = a different form of a gene Box 15 • 2. Principle of Dominance: some alleles are dominant and others are recessive Box 13

  11. Principle of Dominance Brown eyes = BB or Bb Blue eyes = bb Box 16 • An organism with a dominant allele for a particular form of a trait will always exhibit that form of the trait • In other words, if you have the dominant allele, you will express that dominant trait • An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele is not present • In other words, you must have 2 recessive alleles to express the recessive trait I’m Dominant!! Tall = TT or Tt Short = tt Box 17 I’m so proud! Eeek!

  12. Where did the recessive traits go? • Mendel wanted to know why all his F1 plants expressed only dominant traits ????? • He wondered, “Had all the recessive traits disappeared? Or were they still present in the F1 plants?” • To answer this question, he allowed his F1 plants to self- • pollinate Box 18 Naughty! Naughty! F1 XF1 F2

  13. Mendel’s Experiment Tall, short, tall, tall F1 generation P generation tall short tall tall

  14. Mendel’s Experiment Tall, short, tall, tall, tall, tall, tall, tall, SHORT! Ha! F1 generation F2 generation P generation tall short tall tall tall tall tall short

  15. F1 Cross Man of the Year All in Box 18 • Mendel thought the results for his F1 cross were amazing! • All the recessive traits re-appeared in the F2 offspring! • This was due to segregation (separation) of alleles • Segregation of the alleles happens when gametes (sexcells) are formed • One trait comes from the father, one trait comes from the mother I’m good!

  16. Segregation Tt Tt F1 X Tall Tall Segregation T t T t Gametes Gametes TT Tt Tt tt Hmmm…. F2 Tall Tall Tall Short 3 :1 Ratio 3 Tall, 1 Short

  17. Genetics and Probability Section 11-2 • Probability = the likelihood that a particular event will occur • For example, tossing a coin • Probability of heads = ½ or 50% • Probability of tails = ½ or 50% • If you flip a coin 3 times in a row, what is the probability of heads each time? • Each coin toss is independent of the previous toss, so ½ x ½ x ½ = 1/8 or 13% chance of all heads • The way alleles segregate is completely random, like a coin toss (50% chance for each allele) • We can use the principles of probability to PREDICT the outcome of genetic crosses Box 19 Yeah, I look good. Box 20 Box 20

  18. Punnett Squares Box 21 Punnett Squares = tool used to predict and compare the genetic variations that may result from a cross Box 22 Genotype = genetic makeup(Geno = genes) Box 23 Phenotype = physical characteristics(Pheno = physical) Box 24 Heterozygous = 2 different alleles for the same trait Homozygous = 2 identical alleles for the same trait Box 25 • Punnett Squares X T t T TT Tt Tall = Tt Tall = Tt Tt tt t Fill in the Punnet Square Genotype = TT, Tt, tt Phenotype = Tall, short Tt = Heterozygous Why didn’t I think of that? TT or tt = Homozygous

  19. Punnett Squares X Phenotype = Brown eyes Phenotype = Blue eyes Genotype = BB or Bb Genotype = bb B B B B b b b b B BB Bb Bb Bb Bb bb b b b Bb bb Bb Bb Bb bb Genotype offspring = 50% Bb, 50% bb Genotype offspring = 100% Bb Genotype offspring = 25% BB, 50% Bb, 25% bb Phenotype offspring = 100% brown eyes Phenotype offspring = 50% brown, 50% blue eyes Phenotype offspring = 75% brown, 25% blue eyes

  20. Mendelian Genetics Section 11-3 100% RrYy, RoundYellow peas Box 26 • Mendel wondered if the traits segregated independently, or were they somehow linked together • His experiment = 2 factor Test Cross for F1 and F2 RoundYellow peas Genotype: RRYY Wrinkled Green peas Genotype: rryy X ‘Tis my peas against yours! I won!

  21. 2 Factor Cross: F2 • Mendel’s F1 plants were RrYy, or all heterozygous for seed shape and color genes • Mendel asked himself, “Would these alleles segregate independently? Or would they stay together?” • To find out, Mendel crossed his F1 plants to create the F2 generation: RrYy x RrYy To segregate or not to segregate, that ‘tis question. Box 27 X

  22. 2 Factor Cross: F2 Box 27 F2 plants : 556 seeds 315 round and yellow (parental) 32 wrinkled and green (parental) 209 combination of phenotypes (combo of alleles) Alleles for seed shape and colorsegregated independently Ah, my beautiful peas!

  23. Mendel’s Principles Therefore, thou must write all my Principles! Box 28 • Genes, passed from parents to offspring, determine the inheritance of biological characteristics. • When 2 or more forms (alleles) of a gene exist, some forms may be dominant and some recessive. • In sexual reproduction, each adult has 2 copies of each gene (one from each parent), and these genes segregate from each other when gametes are formed. • The alleles for different genes usually segregate independently of one another. Thou must remember my Principles! And, stop whining- start writing!!!

  24. Principle of Independent Assortment Box 29 • Principle of Independent Assortment: genes for different traits can segregate independently during the formation of gametes • This helps to account for the many genetic variations observed in plants, animals and other organisms • Seed color isn’t tied to seed shape or plant height • Just like having red hair doesn’t mean you have blue eyes, or being tall doesn’t mean you have a big nose • Genes for different traits are independently assorted into the sex cells (eggs and sperm) Did you know pollen is flower sperm?

  25. Exceptions to Mendel’s Rules Section 11-4 • Some alleles are neither dominant or recessive – what???? • Some traits are controlled by multiple alleles or multiple genes • Incomplete Dominance = cases when one allele is not completely dominant over another Box 30 What??? Say it ‘tisn’t so

  26. Incomplete Dominance Box 31 When you cross Red and White Four O’clock Flowers, you get PINK flowers!!!! Red should be dominant over white, or vise versa, but neither is completely dominant, thus, incomplete dominance. Four o’clock plants Pink Flowers!

  27. Codominance Box 33 Roan cow Neither white or red Red fur and white fur Box 32 • Codominance = both alleles contribute equally to the phenotype • The offspring is a mixture of both alleles Le Moo. Red cow White cow X A pink cow? I don’t think so.

  28. Multiple Alleles Box 35 Blood type A = AA or AO Box 34 • Multiple Alleles = when a gene has more than two alleles • Does NOT mean a person can have more than two alleles for a single trait (still 1 gene from mom, 1 from dad) • The trait itself has more than 2 forms (alleles) • Ex. Blood types, A, B, AB, O • All are a type of human blood • But, humans can be either blood type Blood? I don’t do blood. Where are my peas? Blood type B = BB or BO Blood type AB = AB Blood type O = OO

  29. Polygenic Traits If you see a graph like this on my test, or the TAKS test, then you know one gene can’t control the trait! Polygenic! Box 37 This range of heights and skin colors tells us more than2 genes control both traits.If 2 genes controlled height and 2 genes controlled skin color, we would see either tall or short people, light or dark skin, and nothing in between. Is that what we see? Poly = many, Genic = genes Box 36 • Polygenic traits = traits controlled by more than one gene I’m tall.

  30. Drosophila melanogaster Box 38 So, Mendel’s principles apply to all organisms, not just plants! Box 38 • Thomas Hunt Morgan (1900s)- worked with Drosophila melanogaster(fruit fly) to study Mendel’s principles • Why study fruit flies? • Produce lots of offspring (don’t we know it) • Short life span (can do lots of tests) • Has variations we can cross I prefer flowers. Especially peas.

  31. Genes and the Environment • Genetics is only part of what determines the physical characteristics of an organism • Our environment also plays a big role • Your behavior is partially determined by genes inherited from your parents, but also by the environment in which you were/are raised • Twin studies • Plants are dependent on weather • Domesticated animals vs. wild animals Box 39 So, don’t blame your genes totally for your behavior - that’s mostly learned at home! Wonder twin powers, Activate! Form of.. A pea plant! Form of.. Pea soup?

  32. Linkage and Gene Maps Section 11-5 • Genes are found on chromosomes, and we inherit whole chromosomes from our parents • Therefore, it’s actually chromosomes that assort independently, not individual genes • So, some genes are “linked” together by virtue of being on the same chromosome Box 40 Box 40 I have curly hair, and I’m tall. Gene for curly hair Gene for hair length

  33. Genetic Diversity • Even if 2 genes are found on the same chromosome, they may not be linked forever • Crossing Overduring Prophase I of Meiosis leads to a genetic “mixing” up • This generates Genetic Diversity Box 41 Stop that. It’s wrong! Or is it? Crossing over

  34. Gene Maps Chromosome 19 Box 42 Gene Map = shows the location of a variety of genes on a chromosome and how far apart the genes are • The further apart two genes are on a chromosome, the more likely they are to be separated during meiosis • The rate at which genes were separated and recombined is used to make Gene Maps That doesn’t look like a pea plant.

  35. End of Ch. 11 I wonder if anyone will miss me? Will they forget about me and my research? I hope thou hast enjoyed learning about my work! Go plant some peas! Save the peas! Hmm…pea soup sounds good, I wonder if I have any peas left over?

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