1 Mendelelian Genetics copyright cmassengale

2 Gregor Johann Mendel  Studied the inheritance of traits in pea plants  Developed the laws of inheritance  Mendel's work was not recognized until the turn of the 20th century copyright cmassengale

3 Gregor Johann Mendel  He found that the plants' offspring retained traits of the parents  Called the “Father of Genetics" copyright cmassengale

4 Genetic Terminology  Gene – a segment of DNA that is located in a chromosome & codes for a specific heredity trait  Trait - any characteristic that can be passed from parent to offspring  Heredity - passing of traits from parent to offspring  Genetics - study of heredity copyright cmassengale

5 Types of Genetic Crosses  Cross – mating of two individuals  Gamete – male and female sex cells (egg & sperm)  Fertilization – the union of male and female gametes to form a zygote.  Monohybrid cross - cross involving a single trait e.g. flower color  Dihybrid cross - cross involving two traits e.g. flower color & plant height copyright cmassengale

6 Punnett Square Used to help solve genetics problems copyright cmassengale

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8 Designer “Genes”  Alleles - two forms of a gene Ex. on chromosomes that code for ht. there would be 2 alleles, short & tall)  Dominant - visible, observable trait; stronger of two genes expressed in the hybrid and masks the recessive. represented by a capital letter (R)  Recessive – hidden trait; gene that shows up less often in a cross; represented by a lowercase letter (r) copyright cmassengale

9 More Terminology  Genotype - gene combination for a trait; genetic make up of an organism (e.g. RR, Rr, rr)  Phenotype - the physical feature or visible traits of an organism (e.g. red, white) (e.g. red, white) copyright cmassengale

10 Genotypes  Homozygous genotype – both alleles are identical for a specific trait; 2 dominant or 2 recessive genes; (e.g. RR or rr); also called pure (e.g. RR or rr); also called pure  Heterozygous genotype – having 2 different alleles for a given 1 dominant & 1 recessive allele (e.g. Rr); also called hybrid (e.g. Rr); also called hybrid copyright cmassengale

Mendel’s Pea Plant Experiments copyright cmassengale11 Mendel crossed 2 plants with different characters, or forms, for the same trait. Ex. 1 tall & 1 short *The plants that grew were hybrid. Hybrid – are the offspring of crosses between parents with different traits.

12 Why peas, Pisum sativum?  Can be grown in a small area  Produce lots of offspring  Produce pure plants when allowed to self-pollinate several generations  Can be artificially cross-pollinated copyright cmassengale

13 How Mendel Began Mendel produced pure strains by allowing the plants to self- pollinate for several generations copyright cmassengale

14 Eight Pea Plant Traits Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or Green ( y ) Pod Shape --- Smooth (S) or wrinkled ( s ) Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white ( p ) copyright cmassengale

Experiment I Concluded: *Each trait is based on two genes, one from the mother and the other from the father *The hybrid plants looked like only 1 parent and the character of the other parent seemed to disappear. *Each trait is controlled by 1 gene. Alleles- controls the different forms of a gene. Genes- chemical factors that determine traits. Phenotype is based on Genotype copyright cmassengale15

16 Law of Dominance *States that some alleles are dominant & others are recessive. *Whenever a living thing inherits a dominant allele, that trait is visible. *All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds) copyright cmassengale

17 Law of Dominance copyright cmassengale

18 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. copyright cmassengale

Experiment II: Law of Segregation Mendel crossed a tall plant (dominant) with a short plant (recessive), the F1 plant inherited an allele for tallness from the tall parent & an allele for shortness from the short parent. Pg. 265 Mendel allowed his hybrid plants to self-pollinate. Some showed recessive traits, the recessive traits did not disappear. Earlier, the dominant masked the recessive, so it was not visible. Alleles for the same trait can be separated. copyright cmassengale19

Law of Segregation Segregation – When sex cells, or gametes, are formed. Each gamete carries only 1 copy of each gene. Therefore, each F1 plant produces 2 types of gametes (some with an allele for tallness & some with an allele for shortness). Ex. T, t, T, t = TT, Tt, Tt, tt copyright cmassengale20

21 Applying the Law of Segregation copyright cmassengale

22 Probability – the likelihood that a particular event will occur. Ex. Flipping a coin. The probability that it will land on tails is ½.

23 Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This helps account for genetic variations. This law can be illustrated using dihybrid crosses. Ex Pea shape & pea color copyright cmassengale

24 Generation “Gap” Parental P 1 Generation = the parental generation in a breeding experiment. F 1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) From breeding individuals from the P 1 generation F 2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) From breeding individuals from the F 1 generation From breeding individuals from the F 1 generation copyright cmassengale

25 Following the Generations Cross 2 Pure Plants TT x tt Results in all Hybrids Tt Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt copyright cmassengale

A Punnett Square shows: copyright cmassengale26 *All the possible results of a genetic cross. *The genotypes of the offspring. *The alleles in the gametes of each parent.

27 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr P 1 Monohybrid Cross R R rr Rr Genotype:Rr Genotype: Rr PhenotypeRound Phenotype: Round Genotypic Ratio:All alike Genotypic Ratio: All alike Phenotypic Ratio: All alike copyright cmassengale

28 P 1 Monohybrid Cross Review  Homozygous dominant x Homozygous recessive  Offspring all Heterozygous (hybrids)  Offspring called F 1 generation  Genotypic & Phenotypic ratio is ALL ALIKE copyright cmassengale

29 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds Rr x Rr F 1 Monohybrid Cross R r rR RR rrRr Genotype:RR, Rr, rr Genotype: RR, Rr, rr PhenotypeRound & wrinkled Phenotype: Round & wrinkled G.Ratio:1:2:1 G.Ratio: 1:2:1 P.Ratio: 3:1 copyright cmassengale

30 F 1 Monohybrid Cross Review  Heterozygous x heterozygous  Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr  Offspring called F 2 generation  Genotypic ratio is 1:2:1  Phenotypic Ratio is 3:1 copyright cmassengale

31 …And Now the Test Cross Mendel then crossed a pure & a hybrid from his F 2 generation This is known as an F 2 or test cross There are two possible testcrosses: Homozygous dominant x Hybrid Homozygous recessive x Hybrid copyright cmassengale

32 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds RR x Rr F 2 Monohybrid Cross (1 st ) R R rR RR RrRR Rr Genotype:RR, Rr Genotype: RR, Rr PhenotypeRound Phenotype: Round Genotypic Ratio:1:1 Genotypic Ratio: 1:1 Phenotypic Ratio: All alike copyright cmassengale

33 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Wrinkled seeds x Round seeds rr x Rr F 2 Monohybrid Cross (2nd) r r rR Rr rrRr rr Genotype:Rr, rr Genotype: Rr, rr PhenotypeRound & Wrinkled Phenotype: Round & Wrinkled G. Ratio:1:1 G. Ratio: 1:1 P.Ratio: 1:1 copyright cmassengale

34 F 2 Monohybrid Cross Review  Homozygous x heterozygous(hybrid)  Offspring: 50% Homozygous RR or rr 50% Heterozygous Rr  Phenotypic Ratio is 1:1  Called Test Cross because the offspring have SAME genotype as parents copyright cmassengale

35 Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2 n (n = # of heterozygotes) copyright cmassengale

36 Question: How many gametes will be produced for the following allele arrangements? Remember: 2 n (n = # of heterozygotes) 1.RrYy 2.AaBbCCDd 3.MmNnOoPPQQRrssTtQq copyright cmassengale

37 Answer: 1. RrYy: 2 n = 2 2 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2 n = 2 3 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2 n = 2 6 = 64 gametes copyright cmassengale

Experiment III *Mendel wanted to see if genes that determine 1 trait have anything to do with genes that determine another. *He followed 2 different genes as they passed from one generation to the next. *Mendel crossed true-breeding plants - round yellow peas (RRYY) with wrinkled green peas (rryy). *The F 1 offspring were all round & yellow showing that both were dominant alleles. The genotype is RrYy. Pg. 270 copyright cmassengale38

39 Dihybrid Cross Traits: Seed shape & Seed color Alleles: Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry All possible gamete combinations copyright cmassengale

40 Dihybrid Cross RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RYRyrYryRY Ry rY ry copyright cmassengale

41 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 copyright cmassengale

42 Test Cross A mating between an individual of unknown genotype and a homozygous recessive individual. Example: bbC__ x bbcc BB = brown eyes Bb = brown eyes bb = blue eyes CC = curly hair Cc = curly hair cc = straight hair bCb___bc copyright cmassengale

43 Test Cross Possible results: bCb___bcbbCc CbCb___bc bbccor c copyright cmassengale

44 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods copyright cmassengale

Pedigrees *Pedigrees – are graphic representations of a family tree, which allows for patterns of inheritance to be seen. *Each horizontal row of circles and squares represents a generation. *People that do not show the trait but are heterozygous (Tt) for the trait are called carriers. copyright cmassengale45

Pedigree on mouse color copyright cmassengale46

Different Patterns of Dominant & Recessive copyright cmassengale47 Incomplete Dominance – 1 allele is not completely dominant over another. Ex. Red flower (RR) & white flower (WW), F1 is a pink flower (RW). Pg. 272 Codominance – both alleles contribute to the phenotype. Ex. A cross of a black chicken (BB) with a white chicken (WW) will produce all speckled offspring (BBWW); colors appear separately.

Different Patterns of Dominant & Recessive Multiple Alleles – have more than 2 alleles. Ex. Coat color in rabbits. Polygenic Traits – traits controlled by 2 or more genes; “ having many genes ”. Ex. Variation in human skin color. copyright cmassengale48

49 Incomplete Dominance F1 hybrids in betweenphenotypes F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example:snapdragons (flower) Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower R R rr copyright cmassengale

50 Incomplete Dominance RrRrRrRr R Rr All Rr = pink (heterozygous pink) produces the F 1 generation r copyright cmassengale

51 Incomplete Dominance copyright cmassengale

52 Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type 1.type A= I A I A or I A i 2.type B= I B I B or I B i 3.type AB= I A I B 4.type O= ii copyright cmassengale

53 Codominance Problem Example:homozygous male Type B (I B I B ) x heterozygous female Type A (I A i) IAIBIAIB IBiIBi IAIBIAIB IBiIBi 1/2 = I A I B 1/2 = I B i IBIB IAIA i IBIB copyright cmassengale

54 Another Codominance Problem Example:Example: male Type O (ii) x female type AB (I A I B ) IAiIAiIBiIBi IAiIAiIBiIBi 1/2 = I A i 1/2 = I B i i IAIA IBIB i copyright cmassengale

55 Sex-linked Traits Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits carried on X chromosome copyright cmassengale

56 Sex-linked Traits Sex Chromosomes XX chromosome - femaleXy chromosome - male fruit fly eye color Example: Eye color in fruit flies copyright cmassengale

57 Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r X r Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed XY = male XX = female XRXR XrXr XrXr Y copyright cmassengale

58 Sex-linked Trait Solution: X R X r X r Y X R X r X r Y 50% red eyed female 50% white eyed male XRXR XrXr XrXr Y copyright cmassengale

59 Female Carriers copyright cmassengale