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Genetics

Genetics. Exam 1 September 16 nd Assignment 1 due Sept. 16 nd Sections of chapters 8, 9, 10. Chapters 8 and 9. Gregor Mendel. Was the first person to analyze patterns of inheritance Deduced the fundamental principles of genetics. Figure 9.4. Mendel’s Peas.

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Genetics

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  1. Genetics Exam 1 September 16nd Assignment 1 due Sept. 16nd Sections of chapters 8, 9, 10

  2. Chapters 8 and 9 • Gregor Mendel • Was the first person to analyze patterns of inheritance • Deduced the fundamental principles of genetics Figure 9.4

  3. Mendel’s Peas The garden of the Augustinian Convent in Brno, Moravia (Czech Republic)

  4. Mendel’s Experiments with Peas

  5. He created what he called true-breeding varieties of the plants: -All purple plants, when self-fertilized, will have purple offspring -All white plants, when self-fertilized, will have white offspring • Mendel then cross-fertilized the two different true-breeding varieties, creating hybrids

  6. P Generation (true-breeding parents) Purple flowers Whiteflowers All plants have purple flowers F1 Generation Fertilization among F1 plants (F1  F1) F2 Generation 1/4 of plants have white flowers 3/4 of plants have purpleflowers (a) Mendel’s crosses tracking one characteristic (flower color) Figure 9.8a Monohybrid Crosses • A monohybridcross is a cross between parent plants that differ in only one characteristic (in this case, flower color)

  7. Mendel’s Discoveries • Define alleles. • What are dominant and recessive alleles?

  8. Alleles • In Mendel’s peas and other examples: • For each trait there is 1 gene • Gene exists in 2 forms called alleles • Each parent can only give one allele to their offspring. • Some alleles mask others

  9. Genetic makeup (alleles) pp PP P plants All P Gametes p All F1 plants: (hybrids) All Pp P Gametes 1/2 1/2 p P P Sperm Eggs F2 plants: PP p p Phenotypic ratio 3 purple : 1 white Pp Pp pp Genotypic ratio 1 PP : 2 Pp : 1 pp (b) Explanation of the results in part (a) Figure 9.8b • An explanation of Mendel’s results, including a Punnett square

  10. An Example

  11. Some definitions • Define Homozygous. • Define Heterozygous.

  12. Homozygous • When an organism has identical alleles for a gene • Heterozygous • When an organism has different alleles for a gene • Gamete: sexual reproduction cell carrying 1 of each chromosome pair and therefore 1 allele • What do gametes have to do with the first two definitions?

  13. Mendel’s principle of segregation • Pairs of alleles (one from mom, other from dad) segregate (separate) during gamete formation • The likelihood that a gamete (sperm or egg) will receive one or the other allele from the allele pair in a gene is 50:50 (like a coin toss) • The fusion of gametes at fertilization creates allele pairs again

  14. Father’s alleles R r Mother’s alleles r r You try it • Finish the following cross: Rr x rr • What are the father’s phenotype • and genotype? • How many different genotypes could result from this cross? How many different phenotypes?

  15. Using a Testcross to Determine an Unknown Genotype • A testcross is a mating between Testcross: • An individual of unknown genotype and • A homozygous recessive individual Genotypes P_ pp Two possibilities for the purple flower: PP Pp Gametes P p P P p pp Pp Pp Offspring All purple 1 purple : 1 white Figure 9.12

  16. Now try this Alleles for flower color: P (dominant, purple flower), p (recessive, white flower)

  17. Genetics in humans • Study humans using pedigrees

  18. pedigrees Recessive Recessive or ?? Dominant

  19. What are genes? • The search was on to find where in the cell the alleles were located. • With the invention of microscopes and microscopic techniques scientists discovered the chromosomes.

  20. Chromosomes • Found in every cell (a few exceptions) • Come in pairs • Chromosomes are visible during cell division

  21. Chromosomes are visible during cell division Onion root tip

  22. Cell division in sex organs is different Sex cells (gametes) are made so they only carry half the chromosomes

  23. Early observations about Chromosomes • How do chromosomes behave like Mendel’s alleles?

  24. Human Chromosomes • 23 pairs = 46 total • 1 pair is not like the others, sex chromosomes determine your gender • XX = female • XY = male • Pairs called homologous pairs, each member of the pair carries one of the two alleles • Chromosome numbers vary in other species

  25. We can use cell division to look at our chromosomes Making a karyotype obtain sample cells culture cells burst cells and place on slides add stain photograph cut out and sort chromosomes

  26. Genetics Part 2 More from chapters 8 and 9 Not all traits are Mendelian

  27. Exceptions to Mendelian Genetics • What phenotypic ratio would you expect in the offspring of the following cross? Rr x Rr (R = red flowers, r = white flowers) • What if the offspring were ¼ red, ¼ white and ½ pink, what does that indicate?

  28. P Generation Red RR White rr r Gametes R F1 Generation Pink! Rr 1/2 1/2 r R Gametes 1/2 Sperm R R 1/2 Eggs Red RR 1/2 r r 1/2 Pink rR Pink Rr F2 Generation White rr Figure 9.18 Incomplete Dominance in Plants • In incompletedominance, F1 hybrids have an appearance in between the phenotypes of the two parents With INCOMPLETE dominance-F2Phenotypic ratio: 1 purple : 2 pink : 1 white

  29. Exceptions to Mendelian Genetics Codominance Example: human blood types Phenotypes = A, B, AB and O blood types There are 3 alleles: A and B are dominant

  30. Codominance – Multiple alleles in blood type • The ABO blood groups in humans are examples of multiple dominant alleles • Two of the human blood type alleles exhibit codominance • Both alleles are expressed in the phenotype

  31. Exceptions to Mendelian Genetics • Polygenic traits: traits determined by multiple genes. • Eye color, height, blood type including Rh factor. Ex: Human Blood types Phenotypes = A+, A-, B+, B-, AB+, AB-, O+ and O- 2 genes, • Rh factor has 2 alleles, + and – (+ is dominant) • Type has 3 alleles, A, B and O (A and B are dominant)

  32. aabbcc (very light skin) AABBCC (very dark skin) F1 Generation AaBbCc AaBbCc F2 Generation Possible Sperm Possible Eggs Figure 9.22 Polygenic Inheritance P Generation • Polygenic inheritance is the additive effects of two or more genes on a single phenotype • In the example to the right, what is the dominant phenotype? • How many genes are responsible for skin color in this example?

  33. Pleiotropy • Pleiotropy is the impact of a single gene on more than one characteristic. These characteristics are thus usually expressed together. Examples: Red hair and freckles or sickle-cell disease

  34. Human Chromosomes • 23 pairs = 46 total • 1 pair is not like the others, sex chromosomes determine your gender • XX = female • XY = male • Pairs called homologous pairs, each member of the pair carries one of the two alleles • Chromosome numbers different in other species • This is part of the reason why you can’t breed different species

  35. Genes on Chromosomes • There are many more traits than there are chromosomes • There must be more than one trait on each chromosome A b R v P S T E A b R V P s T e Chromosome pair 1 Chromosome pair 2

  36. Homologous chromosomes: Gene loci Dominant allele a P B a b P Recessive allele aa Bb PP Genotype: Homozygous for the dominant allele Heterozygous Homozygous for the recessive allele Figure 9.9

  37. Sex Determination in Humans Male Female Somatic cells 44 + XY 44 + XX • Sex chromosomes • Are designated X and Y • Determine an individual’s sex (boy or girl) 22 + X 22 + Y 22 + X Sperm Egg 44 + XY 44 + XX Female Male Figure 9.27

  38. SEX CHROMOSOMES AND SEX-LINKED GENES • Sex chromosomes • Determine gender • Influence the inheritance of certain traits

  39. Sex-Linked Genes • Are any genes located on a sex chromosome • Were discovered during studies on fruit flies • Sex-linked genes (a) (b) Figure 9.28

  40. Sex-Linked Genes • Red-green color blindness • Is characterized by a malfunction of light-sensitive cells in the eyes Figure 9.30

  41. Sex-Linked Genes • Hemophilia Queen Victoria Albert • Is a blood-clotting disease Louis Alice Czar Nicholas II of Russia Alexandra Alexis Figure 9.31

  42. DNA, Replication, and Mitosis

  43. Chapter 10 C A G T DNA Structure: the double helix

  44. DNA base pairs A – T C – G

  45. DNA is “supercoiled” around proteins called Histones to form Chromosomes

  46. This is an actual microscopic photograph of DNA super- coiled into a chromosome.

  47. Chromosomes • Chromosomes as seen with a light microscope Onion root tip

  48. Above is what is sometimes called the “central dogma” of cell biology. In the cell nucleus, DNA is involved with two major processes: (1) DNA replicates itself, making more double stranded DNA (2) One strand of DNA is: A. transcribed to make RNA B. that RNA copy leaves the nucleus, and is then translated at the ribosome to make proteins

  49. Cell Cycle Chapter 8 • Life cycle of a cell. • Cell is “born” from another cell • Cell grows • Cell gets ready to reproduce • Cell reproduces (it splits) • Or, the cell dies • When cells reproduce, they pass on their genes • Cell reproduction is called mitosis

  50. Cell Cycle • Cell Cycle • What happens at each stage? • Interphase • Mitosis

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