KMarsh

Vocabulary dominant gene: dominant gene: F 1 generation: F 1 generation: F 2 generation: F 2 generation: gene: gene: genetic trait: genetic trait: genotype: genotype: monohybrid cross: monohybrid cross:

KMarsh Hybrid: Hybrid: phenotype: phenotype: principle of independent assortment: principle of independent assortment: principle of segregation: principle of segregation: Punnett square: Punnett square: Recessive gene: Recessive gene:

KMarsh Study Questions 1. List and explain the four principles of genetics established by Mendel. 1. List and explain the four principles of genetics established by Mendel. 2. Complete a monohybrid cross between a pure breeding tall plant (TT) and a pure breeding dwarf plant (tt). Carry the cross through to the second generation (F2 generation) by letting the plants of the first cross (Tt) self-fertilize. Describe the phenotypes and genotypes of both generations. 2. Complete a monohybrid cross between a pure breeding tall plant (TT) and a pure breeding dwarf plant (tt). Carry the cross through to the second generation (F2 generation) by letting the plants of the first cross (Tt) self-fertilize. Describe the phenotypes and genotypes of both generations.

KMarsh 3. Show how your knowledge of meiosis provides tangible evidence concerning Mendel’s Principles of Segregation and Independent Assortment. 3. Show how your knowledge of meiosis provides tangible evidence concerning Mendel’s Principles of Segregation and Independent Assortment. 4. Complete a monohybrid cross between (Tt X tt). List all the potential types of gametes produced by each parent and then combine them into all possible combinations in the offspring. List the various phenotypes and ratios from this cross. 4. Complete a monohybrid cross between (Tt X tt). List all the potential types of gametes produced by each parent and then combine them into all possible combinations in the offspring. List the various phenotypes and ratios from this cross. 5. List and discuss several of the approaches which made Mendel’s work successful. 5. List and discuss several of the approaches which made Mendel’s work successful.

KMarsh Review Meiosis

KMarsh Mendel’s Work with Pea Plants Mendel’s Work with Pea Plants First Steps to Genetics First Steps to Genetics

KMarsh

Mendel’s Studies of the Pea Plant A. Characteristics studied by Mendel (7 traits) A. Characteristics studied by Mendel (7 traits)

KMarsh

Dominant vs Recessive 1.Form of ripe seed2.Color of seed coat 1.Form of ripe seed2.Color of seed coat SmoothYellow WrinkledGreen 3.Flower Color 4.Form of ripe pods 3.Flower Color 4.Form of ripe pods Purple Inflated Purple Inflated White Constricted White Constricted 5.Color of unripe pods 6.Position of flowers 5.Color of unripe pods 6.Position of flowers Green Axial Green Axial YellowTerminal YellowTerminal 7.Length of stem Tall & Dwarf 7.Length of stem Tall & Dwarf

KMarsh Dominant and Recessive Defining alleles: Defining alleles: R = the round allele (dominant). R = the round allele (dominant). r = the wrinkled allele (recessive). r = the wrinkled allele (recessive).

KMarsh Why Pea Plants? 1- Many true breeding varieties available 1- Many true breeding varieties available 2- The flower is self-fertile 2- The flower is self-fertile 3- Generation time is very short 3- Generation time is very short

KMarsh Some wise (educated guesses) decisions made by Mendel 1- Selection of well-defined, contrasting traits 1- Selection of well-defined, contrasting traits 2- Extensive groundwork completed prior to establishment of final experimental design 2- Extensive groundwork completed prior to establishment of final experimental design 3- Extensive replication of crosses 3- Extensive replication of crosses

KMarsh Mendel’sProblems Mendel’sProblems 1- No concept of DNA or chromosomes 1- No concept of DNA or chromosomes 2- No concept of meiosis 2- No concept of meiosis

KMarsh Mendel’s Test Evaluating the Inheritance of Seed Shape in Pea Plants Recognized two different traits for the seed shape character in pea plants: round versus wrinkled seeds. Recognized two different traits for the seed shape character in pea plants: round versus wrinkled seeds.

KMarsh Testing continued Established true-breeding varieties for each of these traits. Established true-breeding varieties for each of these traits. RR and rr RR and rr Offspring (F 1 generation) are called “hybrids”. Rr

KMarsh True vs Hybrid In true- breeding individuals, both alleles are the same. In true- breeding individuals, both alleles are the same. Homozygous Homozygous –RR or rr Hybrids, on the other hand, one of each kind of allele. Heterozygous – Rr

100% of these hybrids produced round seeds. Why?

KMarsh The Next Step Crossed these F 1 generation hybrids among each other (individual crosses being selected at random). Crossed these F 1 generation hybrids among each other (individual crosses being selected at random). Rr X Rr Rr X Rr Results for their offspring (F 2 generation): 5474 (74.7%) were plants that produced round seeds.1850 (25.3%) were plants that produced wrinkled seeds.Ratio of round:wrinkled = approx. 3:1

KMarsh The Explaination For every character (e.g., seed shape) an individual possess two instruction sets (alleles). For every character (e.g., seed shape) an individual possess two instruction sets (alleles). One of these alleles was originally derived from the individual’s mother, the other allele being originally derived from the individual’s father. One of these alleles was originally derived from the individual’s mother, the other allele being originally derived from the individual’s father.

KMarsh Mendel’s Further Explanation Mendel believed that only two alleles were possible for a given genetic character, and that one of the alleles (the dominant one) masked the expression of the other (the recessive one) in the hybrid. Mendel believed that only two alleles were possible for a given genetic character, and that one of the alleles (the dominant one) masked the expression of the other (the recessive one) in the hybrid. When the hybrid formed gametes, only one of the two possible alleles would end up in a gamete. When the hybrid formed gametes, only one of the two possible alleles would end up in a gamete.

KMarsh Law of Segregation con’t In the formation of gametes, two members of a gene pair (alleles) segregate into different haploid gametes with equal probability. In the formation of gametes, two members of a gene pair (alleles) segregate into different haploid gametes with equal probability.

KMarsh P Generation and F 1 Generation Parental (P) Cross Round X Wrinkled Round X Wrinkled RR rr RR rr Gametes: Gametes: R r R r F 1 (first felial) Generation Hybrids 100% Round phenotype 100% Rr genotype

KMarsh Punnett Square Diagram

KMarsh F 1 and F 2 Generations Mendel’s Explanation for his Results Mendel’s Explanation for his Results F 1 Generation Cross Round X Round Rr Rr Gametes: R r R r F 2 Generation Outcome Round Wrinkled RR Rr Rr rr Note: 3:1 ratio of round:wrinkled F 1 Generation Cross Round X Round Rr Rr Gametes: R r R r F 2 Generation Outcome Round Wrinkled RR Rr Rr rr Note: 3:1 ratio of round:wrinkled

KMarsh

Law of Segregation

KMarsh Phenotype & Genotype genotypes –allele combination phenotypes –outward appearance genotypes –allele combination phenotypes –outward appearance RR genotype (homozygous dominant) = round phenotype. RR genotype (homozygous dominant) = round phenotype. rr genotype (homozygous recessive) = wrinkled phenotype. rr genotype (homozygous recessive) = wrinkled phenotype. Rr genotype (heterozygous) = round phenotype Rr genotype (heterozygous) = round phenotype

KMarsh

Genotype Vs. Phenotype

Test Crosses When you cross an individual whose genetics you are not sure about with an individual who is homozygous recessive for the trait(s) in question.

KMarsh Test Cross Pea Plants

KMarsh Mendel’s Law of Independent Assortment Whenever two or more pairs of different genes are brought together in a hybrid, the alleles of the different genes segregate independently of one another during gamete formation. Whenever two or more pairs of different genes are brought together in a hybrid, the alleles of the different genes segregate independently of one another during gamete formation.

KMarsh Dihybrid Crosses Defined: two trait crosses Seed Shape Character- gene 1 Defined: two trait crosses Seed Shape Character- gene 1 R = round seed trait (dominant) r = wrinkle seed trait (recessive) Seed Color Character- gene 2 Y = yellow seed trait (dominant) y = green seed trait (recessive

KMarsh First Cross (Dihybrid) Parental (P) cross: crossed true- breeding plants that produce round- yellow (RRYY) seeds with true- breeding plants that produce wrinkled-green seeds (rryy). Parental (P) cross: crossed true- breeding plants that produce round- yellow (RRYY) seeds with true- breeding plants that produce wrinkled-green seeds (rryy). F 1 Genereation: hybrids for both characters (Rr & Yy; or RrYy) were100% round-yellow. F 1 Genereation: hybrids for both characters (Rr & Yy; or RrYy) were100% round-yellow.

KMarsh With Independent Assortment

KMarsh Comparing Observed to Expected Results Observed Round-Yellow 315 Round-Green 108 Wrinkled-Yellow 101 Wrinkled-Green 32 Observed Round-Yellow 315 Round-Green 108 Wrinkled-Yellow 101 Wrinkled-Green 32 Expected Round- Yellow Round-Green Wrinkled-Yellow Wrinkled-Green 34.75

KMarsh

Results of Mendel’s Work A. The principle of unit characters (elementum or genes) A. The principle of unit characters (elementum or genes) B. The phenomenon of dominant and recessive genes B. The phenomenon of dominant and recessive genes C. The principle of segregation: C. The principle of segregation: D. The principle of independent assortment D. The principle of independent assortment