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Heredity

Heredity. Genetics is the branch of biology that studies heredity characteristics that are inherited are traits What is heredity? The passing on of characteristics from parents to offspring

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Heredity

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  1. Heredity • Genetics is the branch of biology that studies heredity • characteristics that are inherited are traits • What is heredity? • The passing on of characteristics from parents to offspring • Mendel was the first to succeed in predicting how traits would be transferred from one generation to the next

  2. Genetics Notes Who is Gregor Mendel? worked on plant breeding experiments using pea plants Principle of Independent Assortment – Inheritance of one trait has no effect on the inheritance of another trait “Father of Genetics”

  3. Mendel’s Work • Used pea plant • He collected data for 10 years • Large sample sizes; • Results from 28,000 pea plants • Published work but was dismissed • Found later

  4. Mendel’s Experiment • P Generation – parent generation • F1 generation – first filial generation, offspring of parents • F2 generation – second filial generation, offspring of F1 generation

  5. Collected 6022 yellow and 2001 green 3:1 ratio

  6. Mendel’s Results 3:1 ratio

  7. Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers Conclusions 1. Inheritance of traits are determined by "units" or "factors" that are passed on to offspring • called genes • Different forms of a gene are alleles 2. For each trait, an individual inherits one gene from each parent 3. A trait may not show up in an individual but can still be passed on

  8. Mendel’s Laws • Law of Segregation • The two alleles for a trait must separate when gametes are formed • A parent randomly passes only one allele for each trait to each offspring • The principle of independent assortment • Genes for different traits assort independently of one another in the formation of gametes.

  9. Dominant and Recessive Genes • Gene that prevents the other gene from “showing” – dominant • Gene that does NOT “show” even though it is present – recessive • Symbol – Dominant gene – upper case letter – T • Recessive gene – lower case letter – t Recessive color Dominant color

  10. Example: Straight thumb is dominant to hitchhiker thumb T= straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles— No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * Must have 2 recessive allelesfor a recessive trait to “show”

  11. Homozygous (pure bred) Organism with two of the same allele HH hh Homozygous dominant Homozygous recessive

  12. Heterozygous (hybrid) Organism with two different alleles Hh Rr Dominant trait observed (notice the dominant allele)

  13. Genotype and Phenotype • Combination of genes an organism has (actual gene makeup) – genotype • Ex: TT, Tt, tt • Physical appearance resulting from gene make-up – phenotype • Ex: hitchhiker’s thumb or straight thumb

  14. Phenotype Observable characteristics of an individual

  15. Punnett Square and Probability • Used to predict the possible gene makeup of offspring – Punnett Square • Example:Black fur (B) is dominant to white fur (b) in mice • Cross a heterozygous male with a homozygous recessive female. Black fur (B) White fur (b) Heterozygous male Homozygous recessive female White fur (b) White fur (b)

  16. Predicting traits • Monohybrid Crosses Provide information about one pair of contrasting traits. Parent’s Genotype Parent’s Genotype

  17. Ratios Genotypes: Homozygous dominant:Hetergozygous:Homozygous recessive AA:Aa:aa Phenotypes: Dominant:recessive Tall:short

  18. Types of genetic crosses • Monohybrid • Mono = 1 • Cross looking at 1 trait • Dihybrid • Di = 2 • Cross looking at 2 traits • Traits are not linked (do not affect each other) • For example: round vs. wrinkled seeds and yellow vs. green seeds

  19. Dihybrid Cross Making gametes • Independent assortment – each allele distributes randomly with the other **more combinations than with a monohybrid RrYy

  20. Round (R) is dominant to wrinkled Yellow (Y) is dominant to green Cross a RRYy with a Rryy

  21. Polyploidy • Most cells are Diploid (2n) • Some are polyploid • One or more extra sets of chromosomes • Triploid – 3n • Rarely occurs in animals • Mostly plants • Roughly 1 in 3 plants are polyploidy • Increased vigor and size

  22. Practice A Tt (tall) plant is crossed with a Tt (tall plant). 1. What is the genotypic ratio?

  23. A green pea seed (gg) is crossed with a hybrid yellow seed (Gg). What will be the genotypic and phenotypic ratios of the offspring?

  24. A heterozygous plant (Tt) is crossed with short (tt) plant. What percentage of the offspring will be tall? What percentage of the offspring will be short?

  25. The punnett square shows the offspring of two parents. What are the genotypes of the parents?

  26. Whiteboard Questions • Who was the “father of genetics”? • What is the allele make-up of an organism called? • What is the physical characteristic of an organism called? • If an organism has two dominant alleles what are they? • If an organism has two recessive alleles what are they?

  27. 6. Different forms of a gene are called what? A heterozygous plant (Tt) is crossed with a short (tt) plant. 7. What is the dominant trait? 8. What is the genotypic ratio? 9. What is the phenotypic ratio? A Tt (tall) plant is crossed with a Tt (tall plant). 10. What percentage of the offspring will be tall? 11. What percentage of the offspring will be short?

  28. 11. The punnett square shows the offspring of two parents. What are the genotypes of the parents?

  29. Genetic Recombination • New combination of genes produced by crossing over and independent assortment Why is genetic recombination important?

  30. Gene Linkage • Genes on same chromosomes are said to be linked • Travel together during Meiosis • Not always true – crossing over occurs • Genes further apart cross over more frequently • Make chromosome maps based on that info.

  31. Chromosome Map • Map genes A, B, C, D • AB=3 AC=1 • AD=4 BC=2 • BD=7 CD=5 • Map genes A, B, C, D • AD = 25 AB = 30 • CD = 15 BD = 5 • BC = 20

  32. In guinea pigs, rough coats are dominant over smooth coats. An Rr guinea pig is crossed with an Rr guinea pig. 1. What are the chances of each genotype and phenotype? 2. What are the genotypic and phenotypic ratios? Agenda for Tuesday May 3rd • QUIZ • Dihybrid crosses

  33. What would the gametes look like for a parent with a RrYy genotype? Agenda for Friday May 6th • Quiz • Baby Lab

  34. What is the point of meiosis and sexual reproduction? Agenda for Wednesday April 27th • Genetics and Punnett Squares Test tomorrow

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