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AP Biology Genetics & The Work of Mendel AP Biology Gregor Mendel  Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor.

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Presentation on theme: "AP Biology Genetics & The Work of Mendel AP Biology Gregor Mendel  Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor."— Presentation transcript:

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2 AP Biology Genetics & The Work of Mendel

3 AP Biology Gregor Mendel  Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas  used experimental method  used quantitative analysis  collected data & counted them  excellent example of the scientific method

4 AP Biology Pollen transferred from white flower to stigma of purple flower anthers removed all purple flowers result Mendel’s work F1F1 P F2F2 self-pollinate  Bred pea plants  cross-pollinate true breeding parents (P)  P = parental  raised seed & then observed traits (F 1 )  F = filial  allowed offspring to self-pollinate & observed next generation (F 2 )

5 AP Biology Mendel collected data for 7 pea traits

6 AP Biology F 2 generation 3:1 75% purple-flower peas 25% white-flower peas Looking closer at Mendel’s work P 100% F 1 generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate

7 AP Biology What did Mendel’s findings mean?  Traits come in alternative versions  purple vs. white flower color  alleles  different alleles vary in the sequence of nucleotides at the specific locus of a gene  some difference in sequence of A, T, C, G purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes

8 AP Biology Traits are inherited as discrete units  For each characteristic, an organism inherits 2 alleles, 1 from each parent  diploid organism  inherits 2 sets of chromosomes, 1 from each parent  homologous chromosomes  like having 2 editions of encyclopedia  Encyclopedia Britannica  Encyclopedia Americana

9 AP Biology What did Mendel’s findings mean?  Some traits mask others  purple & white flower colors are separate traits that do not blend  purple x white ≠ light purple  purple masked white  dominant allele  functional protein  masks other alleles  recessive allele  allele makes a malfunctioning protein homologous chromosomes wild type allele producing functional protein mutant allele producing malfunctioning protein

10 AP Biology Genotype vs. phenotype  Difference between how an organism “looks” & its genetics  phenotype  description of an organism’s trait  the “physical”  genotype  description of an organism’s genetic makeup Explain Mendel’s results using …dominant & recessive …phenotype & genotype F1F1 P X purplewhite all purple

11 AP Biology Making crosses  Can represent alleles as letters  flower color alleles  P or p  true-breeding purple-flower peas  PP  true-breeding white-flower peas  pp PP x pp PpPp F1F1 P X purplewhite all purple

12 AP Biology F 2 generation 3:1 75% purple-flower peas 25% white-flower peas ???? Looking closer at Mendel’s work P X true-breeding purple-flower peas true-breeding white-flower peas PPpp 100% F 1 generation (hybrids) 100% purple-flower peas PpPpPpPpPpPpPpPp phenotype genotype self-pollinate

13 AP Biology Punnett squares Pp x Pp Pp male / sperm P p female / eggs PP 75% 25% 3:1 25% 50% 25% 1:2:1 % genotype % phenotype PPPpPp PpPppp PpPp PpPp F 1 generation (hybrids)

14 AP Biology Genotypes  Homozygous = same alleles = PP, pp  Heterozygous = different alleles = Pp homozygous dominant homozygous recessive heterozygous

15 AP Biology Phenotype vs. genotype  2 organisms can have the same phenotype but have different genotypes homozygous dominant PPpurplePpPp heterozygous purple How do you determine the genotype of an individual with with a dominant phenotype?

16 AP Biology Test cross  Breed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele pp is it PP or Pp? x

17 AP Biology PPpp How does a Test cross work? pp P P pp P p PpPppp xx PpPp PpPpPpPp PpPp 100% purple PpPp pp PpPp 50% purple:50% white or 1:1 pp

18 AP Biology Mendel’s 1 st law of heredity  Law of segregation  during meiosis, alleles segregate  homologous chromosomes separate  each allele for a trait is packaged into a separate gamete PP P P pp p p PpPp P p

19 AP Biology Law of Segregation  Which stage of meiosis creates the law of segregation? Metaphase 1

20 AP Biology Monohybrid cross  Some of Mendel’s experiments followed the inheritance of single characters  flower color  seed color  monohybrid crosses

21 AP Biology Dihybrid cross  Other of Mendel’s experiments followed the inheritance of 2 different characters  seed color and seed shape  dihybrid crosses

22 AP Biology Dihybrid cross true-breeding yellow, round peas true-breeding green, wrinkled peas x YYRRyyrr P 100% F 1 generation (hybrids) yellow, round peas Y = yellow R = round y = green r = wrinkled self-pollinate 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas F 2 generation YyRr

23 AP Biology What’s going on here?  If genes are on different chromosomes…  how do they assort in the gametes?  together or independently? YyRr YRyr YyRr YryRYRyr Is it this?Or this?

24 AP Biology Is this the way it works? Do genes sort together during gamete formation? YyRr YRyr YR yr x YyRr YRyr YYRRYyRr yyrr

25 AP Biology Or, do they sort INDEPENDENTLY? YyRr YRYryR yr YR Yr yR yr YYRR x YYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr YyRr YryRYR yr

26 AP Biology Mendel’s 2 nd law of heredity round wrinkled yellow green :11:1:1 Yr yR YR yr YyRr  Law of independent assortment  different loci (genes) separate into gametes independently  non-homologous chromosomes align independently  classes of gametes produced in equal amounts  YR = Yr = yR = yr  only true for genes on separate chromosomes or on same chromosome but so far apart that crossing over happens frequently

27 AP Biology Law of Independent Assortment  Which stage of meiosis creates the law of independent assortment? Metaphase 1 EXCEPTION  If genes are on same chromosome & close together  will usually be inherited together  rarely crossover separately  “linked”

28 AP Biology The chromosomal basis of Mendel’s laws… Trace the genetic events through meiosis, gamete formation & fertilization to offspring

29 AP Biology Review: Mendel’s laws of heredity  Law of segregation  monohybrid cross  single trait  each allele segregates into separate gametes  established by Metaphase 1  Law of independent assortment  dihybrid (or more) cross  2 or more traits  genes on separate chromosomes assort into gametes independently  established by Metaphase 1 metaphase1 EXCEPTION  linked genes

30 AP Biology Mendel chose peas wisely  Pea plants are good for genetic research  available in many varieties with distinct heritable features with different variations  flower color, seed color, seed shape, etc.  Mendel had strict control over which plants mated with which  each pea plant has male & female structures  pea plants can self-fertilize  Mendel could also cross-pollinate plants: moving pollen from one plant to another

31 AP Biology Mendel chose peas luckily  Pea plants are good for genetic research  relatively simple genetically  most characters are controlled by a single gene with each gene having only 2 alleles,  one completely dominant over the other

32 AP Biology Probability & Genetics

33 AP Biology Genetics & Probability  Mendel’s laws:  segregation  independent assortment reflect same laws of probability that apply to tossing coins or rolling dice

34 AP Biology Probability & genetics  Calculating probability of making a specific gamete is just like calculating the probability in flipping a coin  probability of tossing heads?  probability making a B gamete? 50% 100% BB B B Bb B b

35 AP Biology Probability & genetics  Outcome of 1 toss has no impact on the outcome of the next toss  probability of tossing heads each time?  probability making a B gamete each time? 50% Bb B b

36 AP Biology Calculating probability spermegg 1/2 offspring =x1/4 PPPP PpPpPp 1/2 =x1/4 pppp pP Pp x Pp Pp male / sperm P p female / eggs PPPpPp PpPppp 1/2 =x1/4 1/2 =x 1/4 1/2 +

37 AP Biology  Chance that 2 or more independent events will occur together  probability that 2 coins tossed at the same time will land heads up  probability of Pp x Pp  pp Rule of multiplication 1/2 x 1/2 = 1/4 PpPp P p

38 AP Biology Calculating probability in crosses Use rule of multiplication to predict crosses YyRr x yyrr ?% Yy x Rr x 1/4 1/16 yyrr x

39 AP Biology Apply the Rule of Multiplication AABbccDdEEFfAaBbccDdeeFfx AabbccDdEeFF Bb x Bb  bb cc x cc  cc Dd x Dd  Dd EE x ee  Ee Ff x Ff  FF AA x Aa  Aa 1/2 1/4 1 1/2 1 1/4 1/64

40 AP Biology Rule of addition  Chance that an event can occur 2 or more different ways  sum of the separate probabilities  probability of Bb x Bb  Bb spermeggoffspring 1/2 =x1/4 BbBb 1/2 =x1/4 bBBb 1/4 + 1/2

41 AP Biology Chi-square test  Test to see if your data supports your hypothesis  Compare “observed” vs. “expected” data  is variance from expected due to “random chance”?  or is there another factor influencing data?  null hypothesis  degrees of freedom  statistical significance

42 AP Biology


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