Early Ideas about Heredity The Blending Theory: –Main theory of inheritance until the late 19 th century –Each parent contributed “factors” that were blended in the offspring What was the problem with this theory? –All individuals of a population would eventually look the same. –Once blended, traits would never separate and show up in later generations. Chapter 9, Section 1: Pre-Mendel

Gregor Mendel (1822 – 1884) Augustinian monk who studied pea plants Established the particulate theory of heredity Significance: –Developed pure lines –Counted results and kept statistical notes His work remained undiscovered until Chapter 9, Section 1: Mendel

CharacterDominant TraitRecessive Trait Flower Color Flower Position Seed Color Seed Shape Pod Shape Pod Color Stem Length PurpleWhite SideTop YellowGreen RoundWrinkled InflatedConstricted GreenYellow TallDwarf Mendel’s Research Why did he research pea plants? 1.They are normally self-pollinated, but can be cross-pollinated. 2.They have several qualitative traits that are easy to distinguish i.e.,Tall vs. Short

Mendel’s Research 1.Removed stamens from purple flower. 2.Transferred pollen from stamens of white flower to pistil of purple flower. 3.Pollinated flower matured into a pod. 4.Planted seeds from pod. All purple flowers 5.Examined offspring: All purple flowers… Watch this video clip, and see if you can explain why…video clip

Mendel’s Conclusions 1.Law of Segregation a.Factors (genes) for a particular trait occur in pairs pairs b.For each trait, an organism inherits two genes, one from each parent.each parent c.Dominant alleles mask recessive onesmask i.Exception 1: Incomplete DominanceIncomplete Dominance ii.Exception 2: Co-dominanceCo-dominance d.Two alleles for each trait segregate during gamete productionsegregate

Homologous pair of Chromosomes Locus for Flower Color Gene Allele for White Flowers Allele for Purple Flowers Law of Segregation: Factors for a particular trait occur in pairs Back to Mendel’s Conclusions Genes: The “factors” that control traits. Alleles: Different forms of a gene.

Each individual is diploid –Diploid: Containing a double-set of chromosomes (2n) Each gamete is haploid –Gamete: Reproductive cell (egg or sperm) –Haploid: Containing a single-set of chromosomes (n) Back to Mendel’s Conclusions Law of Segregation: One version of each gene is inherited from each parent Wwww W w or w w

P (Parent) Generation True-breeding parents F 1 (1 st Filial) Generation Hybrid Offspring F 2 (2 nd Filial) Generation What is the F 2 ratio? 705 plants had purple flowers 224 plants had white flowers 705:224  3:1 What happened to the recessive traits? Dominant alleles mask recessive ones

Pp PP pp P p Pp PP Pp pp PP pp P Generation F 1 Generation F 2 Generation Phenotype (Appearance) Purple FlowersWhite Flowers Genotype (Genetic Makeup) Gametes Phenotype (Appearance) Gametes Purple Flowers Genotype (Genetic Makeup) 3:1 What is the Genotypic Ratio of the F2 Generation? PP:Pp:pp  1:2:1 What is the Phenotypic Ratio of the F2 Generation? Dominant alleles mask recessive ones Punnett Square

GenotypePhenotype Purple White PP Pp pp (homozygous) (heterozygous) (homozygous) Ratio = 1:2:1Ratio = 3:1 Dominant alleles mask recessive ones

Dominate alleles mask recessive ones Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp If PP, then all offspring purple: If Pp, then ½ offspring purple and ½ offspring white: What would your hypothesis be if the genotype was PP? P p Ppp P p p Pp pp What would your hypothesis be if the genotype was Pp? This is called a test cross If you have a dominant phenotype (like purple flowers) how would you design an experiment to determine if it was homozygous (PP) or heterozygous (Pp)? Back to Mendel’s Conclusions

Exception to Dominant Alleles Masking Recessive Alleles: Incomplete Dominance: Pink Snapdragons CRCRCRCR CRCRCRCR CWCWCWCW CWCWCWCW CWCWCWCW CWCWCWCW CRCRCRCR CRCRCRCR CRCWCRCWCRCWCRCW CRCWCRCWCRCWCRCW CRCRCRCRCRCRCRCR CWCWCWCWCWCWCWCW P Generation F 1 Generation F 2 Generation Phenotype(s): Red and White Phenotype: Pink Genotype(s): C R C R and C W C W Genotype: C R C W ½ ½ Gametes: C R and C W ½ ½ ½ ½

Exception to Dominant Alleles Masking Recessive Alleles: Co-dominance: Blood TypesBlood Types Back to Mendel’s Conclusions

This is a process called meiosis: Specifically it is “crossing over,” which occurs very early during Prophase I of Meiosis Law of Segregation: Two alleles for each trait segregate during gamete production Back to Mendel’s Conclusions

Mendel’s Conclusions 2.Law of Independent Assortment The law of segregation followed one single trait at a time, such as flower color. What if two traits were followed? Two hypotheses were written and experimented on to determine if traits were: –Dependent (linked), orDependent –Independent (not linked) If the genes are not connected, then they should segregate independently.

Following two traits: Seed shape and seed color Hypothesis: If the genes for seed shape and color are connected in some way, then the dominant R and Y alleles and the recessive r and y alleles will be segregated as matched sets in the gametes. YR yr YyRr P Gametes F1F1 F2F2 YR yr OvaSperm

YYRRyyrr YR yr What are the genotypes of the P Generation? What does the P Generation pass on to F 1 ? F 1 Phenotype? YyRr F 1 Genotype? Gametes What does the F 1 Generation pass on to F 2 ? YR Yr yR yr SpermOva YYRR Combine the sperm and ova to produce the offspring in F 2 What do you expect the phenotype will be when YR and YR are combined? What will the Genotype be when YR and YR are combined? Now try to do it on your own! YYRr YyRR YyRr yyRr yyRRYyrr YYrr Yyrr yyrr Phenotypic Ratios Yellow & Round Green & Round Yellow & Wrinkled Green & Wrinkled 9/16 3/16 1/16 What are the phenotypic ratios? Law of Independent Assortment

Significance of Mendel’s Research 1.Probability was introduced as a biological concept:Probability The number of times an event occurs The number of trials 2.Punnett Square was introduced as a toolPunnett Square

Probability: The number of times an event occurs The number of trials Back to Mendel’s Principles Segregation of alleles into ova Segregation of alleles into sperm PP pp ½ ½ ½ ½ ½ x ½ = ¼ PP Pp x Pp ¼ Pp ¼ Pp ¼ pp How do you get a genotypic ratio of 1:2:1 from these numbers?

Punnett Square Exercise One-trait cross The allele for the hairy trait is “H,” while the allele for the hairless trait is “h.” Make a cross between two homozygotes for each of these traits.

Punnett Square Exercise One-trait cross Henry VIII divorced six of his wives (two of whom were executed) for not bearing him any sons. Use Mendelian Genetics to prove to King Henry that it wasn’t his wives’ fault. Remember: Females are XX and Males are XY.

Punnett Square Exercise One-trait cross In a populations of hamsters, brown fur is dominant (B), and white fur is recessive (b). Predict the offspring from the cross of a white hamster and a brown hamster if the brown hamster's mother was white.

Punnett Square Exercise Two-trait cross Following two traits: Kernel shape: Plump vs. withered (P and p) and Kernel color Red vs. yellow (R and r) Predict the cross between a homozygous recessive corn plant and a homozygous dominant corn plant.

Punnett Square Exercise Two-trait cross Now take the offspring from that cross, and self-pollinate that plant. What is the phenotypic ratio of this cross?

Punnett Square Exercise Two-trait cross My pet guinea pigs (Joni and Chachi) are going to have little guinea pigs. What is the possibility that their offspring will have long hair, if I know that Joni and Chachi are heterozygous for the following traits? Black fur (B)White fur (b) Long hair (L)Short hair (l)