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Genetics

Genetics. Chapter 7. What we thought before Mendel?. Aristotle (sometime in the 400’s) Thought we were composed of “vapors” & “fluids” “Fluids”- male ejaculate “purified blood” b/c it wasn’t red This first led to the thought that heredity was related to blood

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Genetics

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  1. Genetics Chapter 7

  2. What we thought before Mendel? Aristotle (sometime in the 400’s) • Thought we were composed of “vapors” & “fluids” • “Fluids”- male ejaculate “purified blood” b/c it wasn’t red • This first led to the thought that heredity was related to blood • “Vapors”- female “invisible particles” • During intercourse these, fluids and vapors combine, thus creating offspring similar to parents.

  3. We can see everything with Microscopes • Theory of Preformation (1600-1700)- Thought they could see “little people” in sperm when viewed under a microscope.

  4. Epigenetics • Schools in 1800’s taught acquired characteristics- that you can alter yourself to affect your offspring. • Ex: playing music, building muscles, smarts • We now call this Epigenetics or changes in gene expression by mechanisms other than changes in DNA.

  5. Epigenetics Continued… • It was first rejected but now recent evidence has shown might have been right all along. • This idea was discovered in mice by the work of Randy Jirtle • He discovered that what a mother mouse ate during pregnancy can have a effect on gene expression in the next generation of mice. • This food was high in methyl groups, a substance that can turn on and off gene expression.

  6. Those poor Rats • August Weismann(1883)- experiment on rats by cutting off their tails • Rats with cut tails produced rats with tails (~20x) • Cast doubt on Aristotle’s theory • Also proposed the idea of Somatic and Germ tissue.

  7. Gregor Mendel (1822-1884) • THE Father of Genetics • Worked on Pea Plants (Pisumsativum) • In 1866, his papers were 1st published but weren’t found until the 1900’s.

  8. Why Pea Plants? • They reproduced quick and with a large amount of offspring • They contained a wide variety of variation (to which he studied and composed 7 traits) • Both male and female parts were on one flower • Very convenient to work with.

  9. 3 Steps that led to his Discovery • Had plants self-pollinate until he was sure that it was a true-bred trait. • Called this the Parental(P) Generation • He then mated the two opposite traits via cross-pollination. • Called this the Filial (F1) Generation • He let those offspring then self-pollinate. • F2 Generation. Counted the number of each trait that was produced.

  10. Terms and How they relate to genetics • Gene- a segment of DNA that transmits information from parent to offspring. • Allele- Alternative forms of a gene for a trait. • Ex: T, t • Dominant- An allele that has a higher potency.

  11. More Terms • Recessive- a copy of an allele that is not readily expressed unless it contains another recessive allele. • Homozygote- 2 alleles are similar. Purebred. • Ex: RR, rr • Heterozygote- alleles are different. Hybrid/mutt. • Ex: Rr • Phenotype- Physical expression of a gene. • Ex: Tall, short • Genotype- Actual genetic construction. • Ex: AA, aa, Aa

  12. Mendel’s Genetic Laws • Law of Dominance • Law of Segregation • Law of Independent Assortment

  13. Law of Dominance • Only the dominant allele in a heterozygote is expressed. • Dominant is always put first and capitalized when written out. • Ex: SS= Smooth Ss= Smooth ss= Wrinkled

  14. Law of Segregation • 2 alleles of a parent separate during Sexual Reproduction and only one is randomly chosen to be passed to offspring. • Mendel created this law by saying that his “factors” split during meiosis. • Walter Sutton- found that chromosomes also split during meiosis and that Mendel’s “factors” were on these chromosomes. We call this the chromosomal theory of inheritance.

  15. TT Example tt

  16. How Segregation relates back to Meiosis Genes Chromosomes Parental: Parental Gametes: Generation 1: RR rr Only R only r Rr

  17. Law of Independent Assortment • The segregation of 1 pair of alleles occurs independently of the segregation of any other pair. • We inherit one and then the other.

  18. Using Probability and Ratios • Mendel was a mathematician so he used math to predict genetic outcomes. • Probability uses rules that can predict how genes will be distributed among the offspring of two parents. Probability = # of one outcome # of total outcomes • Ex: Rolling dice or Flipping a coin.

  19. Monohybrid Cross and Punnett Squares • Only using one trait and determining the outcome.

  20. Dihybrid Cross and Law of IA • Using two pairs of contrasting traits.

  21. Punnett square Problems

  22. How many Different Gametes? • When given Allele combinations, we can use math to figure out how many possible gametes could be produced. • We know that there are only 2 possibilities that the gamete can have for one trait. • Its either going to have a Dominant or a Recessive Allele • Ex: AA Aaaa 1 2 1

  23. How many DIFFERENT Gametes Can you have Out of the following Combinations? • AABb 1 x 2 = 2 possible different gametes (AB or Ab) • CcDdEe 2 x 2 x 2 = 8 possible different gametes (CDE, CDe, CdE, Cde, cDE, cDe, cdE, cde) • ffGgHhIiJJ 1x2x2x2x1 = 8 possible different gametes (fGHIJ, fGHiJ, fGhiJ, fGhIJ, fgHIJ, fgHiJ, fghIJ, fghiJ)

  24. One last problem. • AaBbCCDDeeFFGGhhIIjjKkLlMmNNooPP 2x 2 x1 x1x1x1x1 x1x1x1x2x2 x2 x1 x1x1 = ? =32 possible different gametes • Now Imagine how our genes work and in each gamete we have 23,000 different genes. • That would be 2^23,000 = error • That is a whole lot of different gametes.

  25. How many Phenotypes/Genotypes? • The secret to this is the mastery of the F.O.I.L. • First, Outside, Inside, Last For example: lets look at a monohybrid cross Aa x Aa (A a)x(A a) Four pairs of alleles: AA, Aa, Aa, aa

  26. How Many Phenotypes/Genotypes How many Phenotypes are possible in the following Combination? Aabb x AaBb Aa x Aa bb x Bb AA, Aa, Aa, aa Bb, bb, Bb, bb 2 x 2= 4 phenotypes Genotypes? Aa x Aa bb x Bb AA, Aa, Aa, aa Bb, bb, Bb, bb 3 x 2 = 6

  27. Ratio Problems and Quiz • The handout for today contains the ratio problems. They will be due on • Also, a quiz over the previous material and the 4 exceptions to Mendel on: FRIDAY

  28. Exceptions to Mendel • Multiple Alleles • Incomplete Dominance • Co-dominance • Lethality

  29. Multiple Alleles • More than 2 alleles exist for some gene • Means more phenotypes and genotypes to deal with. • Ex: Coat color in rabbits • C+- agouti • Cch- chinchilla • Ch- Himalayan • C- albino • C+ > Cch > Ch > C

  30. Incomplete Dominance • Heterozygote has a phenotype intermediate to the two homozygote types. • Ex: Snapdragon color • RR= Red • Rr= Pink • rr= White • Phenotype ratio is similar to genotype • 1:2:1

  31. Co-Dominance • Both alleles of a Heterozygote are expressed • Ex: Blood Types • IA – A Antigen IB- B Antigen i= no Antigen • Antigen- Proteins that mark you as being you. Phenotypes Genotypes A IAIA, IAi B IBIB, IBi AB IAIB O ii

  32. Lethality • Some offspring have a reduce chance to live because of their gamete. • Ex: Corn • G- Green color- produces chlorophyll • g- Yellow Color- no chlorophyll • GG and Gg- Green= live • gg= Yellow = die b/c no chlorophyll • Genotype ratio- 1:2

  33. Role of the X and Y Chromosomes • Females – XX • Males – XY • Sperm determines sex • Only true of Fruit flies and Humans • Region on Y chromosome that determines sex= SRY • Heterogametic Sex- can make two dif. Gametes • Homogametic Sex- can only make one Gamete

  34. Other Sex are determined differently • Fish, bird, reptiles • Homogametic- Males Heterogametic- Females • Bees and other select insects • They don’t have sex chromosomes but rather male or female determined by polyploidy. • Males- n Females- 2n • Marine worm • Females release pheromones • No adult females- females adult females- males

  35. Sex- Linked Genes • First studied by Thomas Morgan Hunt • Used Red and white eyed Fruit flies P: red females and white males F1: Red females and males F2: Red females and males and White males Sex-linked because the gene is located on X chromosome

  36. Sex- Linked Female Male WW- Red WY- Red Ww- Red wY- White ww – White • Hemizygous- only one allele of a gene is present.

  37. Why do we use Fruit flies for Genetics? • Long time between generations for humans • About 2 weeks from generation to next for fruit flies. • Humans produce small # of offspring/ generation • Fruit flies produce ~ 100-200 • Humans have a large # of chromosomes • Fruit flies have 8 • Ethical problems when messing with humans • No one cares that much about flies.

  38. Genetic Disorders • Sex-linked • Sex-Modified • Chromosomal • Sex Chromosome • Recessive disorders • Dominant disorders

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