1 Genetics, the oldest branch of Biology

2 Genetics = Information Flow Transmission Genetics = information flow between generations Molecular Genetics = information flow within cells/organisms DNA  RNA  Protein

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pea plant from green seed Data of Goss (1824) X pea plant from yellow seed All seeds yellow – grow and self fertilize Some pods with all yellow seeds – grow into plants and self fertilize Some pods with all seeds yellow, some with green and yellow seeds Some pods with all green seeds Many pods with both yellow and green seeds Self fertilization of plants grown from green All progeny plants Have pods with green seeds only

5 Data of Mendel (1866) pea plant from green seed X pea plant from yellow seed All seeds yellow - Grow into plants and self fertilize (F1) First filial generation Count # of green and yellow seeds: total seeds yellow green – grown into plants: self fertilization yields all green seeds (F2)second filial generation Take 519 yellow seeds – grown into plants: self fertilization Of these 519 plants, 166 bred true (all yellow seeds), 353 did not (mixed yellow and green seeds)

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9 Mendel ’ s model True breeding yellow AA True breeding green aa egg cells pollen cells x fertilize Aa (yellow seeds) – grow into plants and self fertilize F1 F2 AAAa aAaa (pollen) (eggs) A A a a 3:1 yellow:green __________________ ¼ true breeding yellow ½ “ impure ” yellow ¼ true breeding green a A

10 Mendel ’ s First Law Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cell Formation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization). Testing the law: - the test cross (Aa x aa) predicts new ratios - other traits tested *Introduce modern terms: dominant, recessive, alleles, phenotype, genotype, heterozygote, homozygote

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12 Results of all Mendel's crosses in which parents differed for one character Parental phenotype F1 F2 F2 ratio 1. Round X wrinkled seeds All round 5474 round; 1850 wrinkled2.96:1 2. Yellow X green seeds All yellow 6022 yellow; 2001 green 3.01:1 3. Purple X white petals All purple 705 purple; 224 white3.15:1 4. Inflated X pinched pods All inflated 882 inflated; 299 pinched2.95:1 5. Green X yellow pods All green 428 green; 152 yellow2.82:1 6. Axial X terminal flowers All axial 651 axial; 207 terminal3.14: 1 7. Long X short stems All long 787 long; 277 short2.84: 1 What happens if two character traits are followed simultaneously?

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15 Mendel ’ s Second Law Second Law=The Law of Independent Assortment: During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.

16 Genes ’ eye view of meiosis and mitosis

17 Mendel’s Second Law The Law of Independent Assortment: During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other. Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cell Formation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization). Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cell Formation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization). Mendel’s First Law A Gene's (allele) Eye View of Mitosis and Meiosis

18 Figure 10.5 Meiosis Accounts for the Segregation of Alleles (Part 1)

19 Figure 10.5 Meiosis Accounts for the Segregation of Alleles (Part 2)

20 Figure 10.8 Meiosis Accounts for Independent Assortment of Alleles

A a A a A a A a A a mitotic metaphase anaphase, telophase, cytokinesis

A a A a A a b b B B B b a a b b A A B B genotype: Aa; Bb Meiosis I metaphase Meiosis I product cells replication Meiosis I anaphase, telophase, cytokinesis

a a b b A AB B Meiosis I product cells A B A B a b a b Meiosis II product cells Meiosis II anaphase, telophase, cytokinesis Meiosis II metaphase AB ab

a a b b A A B B Meiosis I product cells A B A a a b Meiosis II products cells Meiosis II anaphase, telophase, cytokinesis Meiosis II metaphase b Ab aB B

25 Eye Color Is a Sex-Linked Trait in Drosophila

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28 Probability – Predicting Results Rule of addition: the probability of 2 mutually exclusive events occurring simultaneously is the sum of their individual probabilities. When crossing Pp x Pp, the probability of producing Pp offspring is probability of obtaining Pp (1/4), PLUS probability of obtaining pP (1/4) ¼ + ¼ = ½

29 Probability – Predicting Results Rule of multiplication: the probability of 2 independent events occurring simultaneously is the PRODUCT of their individual probabilities. When crossing Rr Yy x RrYy, the probability of obtaining rr yy offspring is: probability of obtaiing rr = ¼ probability of obtaining yy = ¼ probability of rr yy = ¼ x ¼ = 1/16

30 Testcross Testcross: a cross used to determine the genotype of an individual with dominant phenotype -cross the individual with unknown genotype (e.g. P_) with a homozygous recessive (pp) -the phenotypic ratios among offspring are different, depending on the genotype of the unknown parent

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33 Genes Phenotypes polygenic inheritance pleiotropy

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35 Figure Inheritance of Coat Color in Rabbits “ continuous ” variation: multiple alleles of one gene

36 Gene Interaction (alleles of same gene) - dominance - incomplete dominance - co-dominance - lethal alleles Gene Interaction (alleles of different genes): - in different pathways (Drosophila eye pigmentation) - in same pathway - recessive epistasis

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38 codominance

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wild-type (+/+) Antennapedia mutant (Antp/+) fly heads +/+ x Antp/+ ½ “ Antp ” (Antp/+) ½ “ + ” (+/+) Antp/+ x Antp/+ 2/3 “ Antp ” (Antp/+) 1/3 “ + ” (+/+) ? ¼ +/+ ( “ + ” ) ½ Antp/+ ( “ Antp ” ) ¼ Antp/Antp (lethal)

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44 Extensions to Mendel

45 Eye Color Is a Sex-Linked Trait in Drosophila

46 white-eyed, normal-winged female x red-eyed, miniature winged male (wild type) w + mw m + w + m wild type females w m + white-eyed, normal-winged males x w m + ½ red-eyed, miniature winged for male progeny, EXPECT: w + m ½ white-eyed, normal-winged 64% of males fell into above classes, but 36% were either wild type Or doubly mutant !!!!!!!

47 w m + w + m wild type females genetic recombination = chromosomal crossing over 36% of chromosomes in meiosis I: w m + white-eyed, normal-winged males x w + m + w m 36% of males are either doubly mutant or wild type :

48 Chiasmata visible in Locusta migratoria spermatogenesis A synaptonemal complex

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54 Genetic Mapping Mapping genes in humans involves determining the recombination frequency between a gene and an anonymous marker Anonymous markers such as single nucleotide polymorphisms (SNPs) can be detected by molecular techniques.

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Testis Determining Factor (SRY) Channel Flipping (FLP) Catching and Throwing (BLZ-1) Self Confidence (BLZ-2) - (note: unlinked to ability) Addiction to Death and Destruction Films (T2) Preadolescent fascination with Arachinida and Reptilia (MOM-4U) Sitting on John Reading (SIT) Selective Hearing Loss (HUH?) Lack of Recall for Important Dates (OOPS) Inability to Express Affection Over the Phone (ME-2) Spitting (P2E) New Genes Identified on the Human Y Chromosome

57 effects of recombination on chromosomes within a family siblings inherit different chromosome regions from their parents grandson inherits chromosome regions from all four of his grandparents’ chromosomes

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59 Early Ideas of Heredity Before the 20 th century, 2 concepts were the basis for ideas about heredity: -heredity occurs within species -traits are transmitted directly from parent to offspring This led to the belief that inheritance is a matter of blending traits from the parents.

60 Early Ideas of Heredity Botanists in the 18 th and 19 th centuries produced hybrid plants. When the hybrids were crossed with each other, some of the offspring resembled the original strains, rather than the hybrid strains. This evidence contradicted the idea that traits are directly passed from parent to offspring.

61 Early Ideas of Heredity Gregor Mendel -chose to study pea plants because: 1. other research showed that pea hybrids could be produced 2. many pea varieties were available 3. peas are small plants and easy to grow 4. peas can self-fertilize or be cross- fertilized

62 Early Ideas of Heredity Mendel’s experimental method: 1. produce true-breeding strains for each trait he was studying 2. cross-fertilize true-breeding strains having alternate forms of a trait -perform reciprocal crosses as well 3. allow the hybrid offspring to self-fertilize and count the number of offspring showing each form of the trait

63 Monohybrid Crosses Monohybrid cross: a cross to study only 2 variations of a single trait Mendel produced true-breeding pea strains for 7 different traits -each trait had 2 alternate forms (variations) -Mendel cross-fertilized the 2 true-breeding strains for each trait

64 Monohybrid Crosses F 1 generation (1 st filial generation): offspring produced by crossing 2 true- breeding strains For every trait Mendel studied, all F 1 plants resembled only 1 parent -no plants with characteristics intermediate between the 2 parents were produced

65 Monohybrid Crosses F 1 generation: offspring resulting from a cross of true-breeding parents F 2 generation: offspring resulting from the self-fertilization of F 1 plants dominant: the form of each trait expressed in the F 1 plants recessive: the form of the trait not seen in the F 1 plants

66 Monohybrid Crosses F 2 plants exhibited both forms of the trait in a very specific pattern: ¾ plants with the dominant form ¼ plant with the recessive form The dominant to recessive ratio was 3 : 1. Mendel discovered the ratio is actually: 1 true-breeding dominant plant 2 not-true-breeding dominant plants 1 true-breeding recessive plant

67 Monohybrid Crosses gene: information for a trait passed from parent to offspring alleles: alternate forms of a gene homozygous: having 2 of the same allele heterozygous: having 2 different alleles

68 Monohybrid Crosses genotype: total set of alleles of an individual PP = homozygous dominant Pp = heterozygous pp = homozygous recessive phenotype: outward appearance of an individual

69 Monohybrid Crosses Principle of Segregation Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent, during fertilization.

70 Monohybrid Crosses Some human traits are controlled by a single gene. -some of these exhibit dominant inheritance -some of these exhibit recessive inheritance Pedigree analysis is used to track inheritance patterns in families.

71 Dihybrid Crosses Dihybrid cross: examination of 2 separate traits in a single cross -for example: RR YY x rryy The F 1 generation of a dihybrid cross (RrYy) shows only the dominant phenotypes for each trait.

72 Dihybrid Crosses The F 2 generation is produced by crossing members of the F 1 generation with each other or allowing self-fertilization of the F 1. -for example RrYy x RrYy The F 2 generation shows all four possible phenotypes in a set ratio: 9 : 3 : 3 : 1

73 Dihybrid Crosses Principle of Independent Assortment In a dihybrid cross, the alleles of each gene assort independently.

74 Extensions to Mendel Mendel’s model of inheritance assumes that: -each trait is controlled by a single gene -each gene has only 2 alleles -there is a clear dominant-recessive relationship between the alleles Most genes do not meet these criteria.

75 Extensions to Mendel Polygenic inheritance occurs when multiple genes are involved in controlling the phenotype of a trait. The phenotype is an accumulation of contributions by multiple genes. These traits show continuous variation and are referred to as quantitative traits. For example – human height

76 Extensions to Mendel Pleiotropy refers to an allele which has more than one effect on the phenotype. This can be seen in human diseases such as cystic fibrosis or sickle cell anemia. In these diseases, multiple symptoms can be traced back to one defective allele.

77 Extensions to Mendel Incomplete dominance: the heterozygote is intermediate in phenotype between the 2 homozygotes. Codominance: the heterozygote shows some aspect of the phenotypes of both homozygotes.

78 Extensions to Mendel The human ABO blood group system demonstrates: -multiple alleles: there are 3 alleles of the I gene (I A, I B, and i) -codominance: I A and I B are dominant to i but codominant to each other

79 Extensions to Mendel The expression of some genes can be influenced by the environment. for example: coat color in Himalayan rabbits and Siamese cats -an allele produces an enzyme that allows pigment production only at temperatures below 30 o C

80 Extensions to Mendel The products of some genes interact with each other and influence the phenotype of the individual. Epistasis: one gene can interfere with the expression of another gene