Mendelian genetics

Mendelelian Genetics copyright cmassengale

Gregor Mendel (1822-1884) Responsible for the Laws governing Inheritance of Traits copyright cmassengale

Gregor Johann Mendel ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Gregor Johann Mendel ,[object Object],[object Object],[object Object],copyright cmassengale

Site of Gregor Mendel’s experimental garden in the Czech Republic copyright cmassengale

[object Object],[object Object],Particulate Inheritance copyright cmassengale

Genetic Terminology ,[object Object],[object Object],[object Object],copyright cmassengale

Types of Genetic Crosses ,[object Object],[object Object],copyright cmassengale

Punnett Square ,[object Object],copyright cmassengale

Designer “Genes” ,[object Object],[object Object],[object Object],copyright cmassengale

More Terminology ,[object Object],[object Object],copyright cmassengale

Genotype & Phenotype in Flowers Genotype of alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Genotypes RR R r rr Phenotypes RED RED YELLOW copyright cmassengale

Genotypes ,[object Object],[object Object],copyright cmassengale

Genes and Environment Determine Characteristics copyright cmassengale

Mendel’s Pea Plant Experiments copyright cmassengale

Why peas, Pisum sativum ? ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Reproduction in Flowering Plants ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Mendel’s Experimental Methods ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

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

Eight Pea Plant Traits ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Mendel’s Experimental Results copyright cmassengale

[object Object],The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The larger the sample the more nearly the results approximate to the theoretical ratio copyright cmassengale

Generation “Gap” ,[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale

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

Monohybrid Crosses copyright cmassengale

[object Object],[object Object],[object Object],[object Object],P 1 Monohybrid Cross R R r r Rr Rr Rr Rr Genotype: Rr Phenotype : Round Genotypic Ratio: All alike Phenotypic Ratio: All alike copyright cmassengale

P 1 Monohybrid Cross Review ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

[object Object],[object Object],[object Object],[object Object],F 1 Monohybrid Cross R r r R RR rr Rr Rr Genotype: RR, Rr, rr Phenotype : Round & wrinkled G.Ratio: 1:2:1 P.Ratio: 3:1 copyright cmassengale

F 1 Monohybrid Cross Review ,[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale

What Do the Peas Look Like? copyright cmassengale

… And Now the Test Cross ,[object Object],[object Object],[object Object],copyright cmassengale

[object Object],[object Object],[object Object],[object Object],F 2 Monohybrid Cross (1 st ) R R r R RR Rr RR Rr Genotype: RR, Rr Phenotype : Round Genotypic Ratio: 1:1 Phenotypic Ratio: All alike copyright cmassengale

[object Object],[object Object],[object Object],[object Object],F 2 Monohybrid Cross (2nd) r r r R Rr rr Rr rr Genotype: Rr, rr Phenotype : Round & Wrinkled G. Ratio: 1:1 P.Ratio: 1:1 copyright cmassengale

F 2 Monohybrid Cross Review ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Practice Your Crosses ,[object Object],copyright cmassengale

Mendel’s Laws copyright cmassengale

Results of Monohybrid Crosses ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Law of Dominance In a cross of parents that are pure for contrasting traits , only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds) copyright cmassengale

Law of Dominance copyright cmassengale

Law of Segregation ,[object Object],[object Object],copyright cmassengale

Applying the Law of Segregation copyright cmassengale

Law of Independent Assortment ,[object Object],[object Object],copyright cmassengale

Dihybrid Cross ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Question: How many gametes will be produced for the following allele arrangements? ,[object Object],[object Object],[object Object],[object Object],copyright cmassengale

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

Dihybrid Cross ,[object Object],[object Object],RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations copyright cmassengale

Dihybrid Cross copyright cmassengale RY Ry rY ry RY Ry rY ry

Dihybrid Cross copyright cmassengale 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 RY Ry rY ry RY Ry rY ry

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

Test Cross ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale bC b___ bc

Test Cross ,[object Object],copyright cmassengale bC b___ bc bbCc bb C c C bC b___ bc bbCc bb c c or c

Summary of Mendel’s laws copyright cmassengale 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

Incomplete Dominance and Codominance copyright cmassengale

Incomplete Dominance ,[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale R R r r

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

Incomplete Dominance copyright cmassengale

Codominance ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale

Codominance Problem ,[object Object],[object Object],copyright cmassengale I A I B I B i I A I B I B i 1/2 = I A I B 1/2 = I B i I B I A i I B

Another Codominance Problem ,[object Object],copyright cmassengale I A i I B i I A i I B i 1/2 = I A i 1/2 = I B i i I A I B i

Codominance ,[object Object],[object Object],copyright cmassengale

Codominance ,[object Object],Parents: genotypes = I A i and I B i phenotypes = A and B copyright cmassengale I A I B ii I B I A i i

Sex-linked Traits ,[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale

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

Sex-linked Trait Problem ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],copyright cmassengale X R X r X r Y

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

Female Carriers copyright cmassengale

Genetic Practice Problems copyright cmassengale

Breed the P 1 generation ,[object Object],copyright cmassengale T T t t

Solution: tall (TT) vs. dwarf (tt) pea plants copyright cmassengale T T t t Tt Tt Tt Tt All Tt = tall (heterozygous tall) produces the F 1 generation

Breed the F 1 generation ,[object Object],copyright cmassengale T t T t

Solution: tall (Tt) x tall (Tt) pea plants copyright cmassengale TT Tt Tt tt T t T t produces the F 2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype

Mendelian genetics

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