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Genetics

Genetics. Chapter 9. http://main.uab.edu/cord/show.asp?durki=38593. Mendelian Genetics 9.1. Genetics Alleles Dominant Recessive Homozygous Heterozygous Genotype P henotype Linked genes M onohybrid cross D ihybrid cross F1 generation F2 generation. Law of Segregation

robert-contreras
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Genetics

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  1. Genetics • Chapter 9 http://main.uab.edu/cord/show.asp?durki=38593

  2. Mendelian Genetics9.1

  3. Genetics • Alleles • Dominant • Recessive • Homozygous • Heterozygous • Genotype • Phenotype • Linked genes • Monohybrid cross • Dihybrid cross • F1 generation • F2 generation • Law of Segregation • Law of Independent Assortment • Gene linkage • Crossing over • Incomplete dominance • Codominance • Polygenic traits • Sex-linked traits • Pedigree • Genome • Clone • Gene therapy • Stem cells Vocabulary

  4. How Genetics Began • Inheritance: the passing of traits to the next generation. • Gregor Mendel: published findings on the method and mathematics of inheritance in garden pea plants. http://www.scienceclarified.com/scitech/Genetics/The-Age-of-Genetics.html

  5. Why Pea Plants? • Pea plants are easy to grow and many are true-breeding which means they consistently produce offspring with only one form of a trait. • Pea plants usually reproduce by self-fertilization (male and female gametes in same flower). • Pea plants can easily be cross-pollinated by hand (transferring a male or female gamete in one flower to another flower).

  6. Pea Plants http://www.exploringnature.org/db/detail.php?dbID=22&detID=54

  7. The Inheritance of Traits • Mendel noticed certain varieties of garden pea plants produced specific forms of a trait, generation after generation. • Mendel performed cross pollination by transferring male gametes from the flower of a true-breeding green-seed plant to the female organs of a flower from a true-breeding yellow-seed plant. • Mendel called the green-seed plants and the yellow-seed plants the parent generation or P generation.

  8. The Inheritance of Traits • When Mendel grew the seeds from the cross between the green-seed and yellow-seed plants, all of the offspring had yellow seeds. • The offspring of the P cross are called the first filial (F1) generation.

  9. The Inheritance of Traits • Mendel then planted the F1 generation of yellow seeds to determine whether the green-seed trait was no longer present or if it was being masked. • The results of the second filial (F2) generation are as follows: 6022 were yellow and 2001 were green (a nearly perfect 3:1 ratio of yellow to green seeds).

  10. Inheritance of Traits • Mendel studied seven different traits, including: seed or pea color, flower color, seed pod color, seed shape or texture, seed pod shape, stem length, and flower positions. • He found that the F1 generation plants from these crosses also showed a 3:1 ratio.

  11. F1 and F2 Generations

  12. Genes in Pairs • From his experiments, Mendel concluded that there must be two forms of the seed trait in the pea plants and that each was controlled by a factor. • Allele: an alternative form of a single gene passed from generation to generation. • The green-seed and yellow-seed are different forms of a single gene or alleles.

  13. Genes in Pairs • Mendel called the form of the trait that appeared in the F1 generation dominant and the form that was masked recessive. • The yellow-seed was dominant and the green-seed was recessive.

  14. Law of Dominance • If the allele for a trait is dominant it is represented by a capital letter. In Mendel’s case the yellow-seeds were dominant and therefore represented by a Y. • If the allele for a trait is recessive it is represented by a lowercase letter. Therefore the green-seeds in Mendel’s experiment would be represented by a y.

  15. Law of Dominance • An organism with two of the same alleles for a particular trait is homozygous. • Homozygous yellow-seed plants would be YY and homozygous green-seed plants would be yy.

  16. Law of Dominance • Heterozygous organisms have two different alleles for a trait. • In Mendel’s experiment a plant with an allele for yellow-seeds and green-seeds would be represented by Yy. • When an organism is heterozygous the dominant allele will be expressed.

  17. Genotype and Phenotype • Genotype: an organism’s allele pairs. • The genotype of a plant with yellow seeds would be YY or Yy. • Phenotype: the observable characteristics or outward expression of allele pair. • The phenotype of pea plants with the genotype yy would be green seeds.

  18. Genotype and Phenotype http://hthbio.blogspot.com/2011/02/february-7-2011-february-11-2011.html

  19. Law of Segregation • Two alleles for each trait separate during meiosis and during fertilization two alleles for that trait unite. http://www.transtutors.com/homework-help/Biology/Heredity/mendel-experiment-of-monohybrid-ratio.aspx

  20. Law of Independent Assortment • A random distribution of alleles occurs during gamete formation. • Genes on separate chromosomes separate independently during meiosis.

  21. http://bio1152.nicerweb.net/Locked/media/ch14/assortment.htmlhttp://bio1152.nicerweb.net/Locked/media/ch14/assortment.html

  22. Punnett Squares • Used to predict the possible offspring of a cross between two known genotypes.

  23. Monohybrid Cross • Examines the inheritance of one trait. • Parent generation could both be homozygous or heterozygous or one could be homozygous and the other heterozygous.

  24. Monohybrid Cross

  25. Monohybrid Practice • Plant A is heterozygous for its red flowers. Plant B is homozygous for red flowers. Set up a Punnett Square showing the results of a cross between these 2 plants.

  26. Dihybrid Cross • Examines the inheritance of two different traits.

  27. Dihybrid Cross R = dominant round, r = recessive wrinkled; Y = dominant for yellow, y = recessive green (rryy x RRYY)

  28. Dihybrid Crosses

  29. Dihybrid Crosses • List the gametes for each set of parents along the edges of the punnett square.

  30. Dihybrid Crosses

  31. Gene Linkage and Polyploidy10.3

  32. Genetic Recombination • The new combination of genes produced by crossing over and independent assortment. • The possible combination of genes due to independent assortment can be calculated by the formula 2n where n is the number of chromosomes.

  33. Gene Linkage • Linked genes are genes that are located close to each other on the same chromosomes. • These genes tend to travel together during gamete formation. • Linked genes do not segregate independently and are therefore an exception to Mendel’s Law of Independent Assortment.

  34. Chromosome Maps • Chromosome Maps: drawings that show the sequence of genes on a chromosome and represent the relative position of genes. • The higher the crossover frequency, the farther apart the two genes are because crossing over occurs more frequently between genes that are far apart. • The frequency correlates with the relative distance between the two genes.

  35. Chromosome Maps https://wikispaces.psu.edu/display/Bio110nk/Chromosome+Behavior+and+Gene+Linkage

  36. Polyploidy • Polyploidy: the occurrence of one or more extra sets of chromosomes in an organism. • Ex) 3n: 3 complete sets of chromosomes. • Rarely occur in animals but sometimes occur in earthworms and goldfish. • Approximately 1 in 3 species of flowering plants are polyploid. • Polyploidy is always lethal in humans.

  37. Polyploidy 8n

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