Mendelian Genetics

What is Heredity? Female normal wing The passing on of traits from one generation to the next X P- generation Male double wing F1 – normal wing

Early Ideas about Heredity Chapter 9, Section 1: Pre-Mendel Early Ideas about Heredity Blending Theory (19th 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.

Gregor Mendel (1822 – 1884) Augustinian monk who studied pea plants Chapter 9, Section 1: 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 (data) His work remained undiscovered until 1903.

Why did he research pea plants? Character Dominant Trait Recessive Trait Mendel’s Research Flower Color Why did he research pea plants? Purple White They are normally self-pollinated, but can be cross-pollinated. They have several qualitative traits that are easy to distinguish i.e.,Tall vs. Short Self Pollination Flower Position Side Top Seed Color Yellow Green Seed Shape Round Wrinkled Pod Shape Inflated Constricted Pod Color Green Yellow Cross Pollination Stem Length Tall Dwarf

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

Mendel’s Conclusions Law of Segregation Factors (genes) for a particular trait occur in pairs For each trait, an organism inherits two genes, one from each parent. Dominant alleles mask recessive ones Exception 1: Incomplete Dominance Exception 2: Co-dominance Two alleles for each trait segregate (separate) during gamete production

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

Each individual is diploid Each gamete is haploid W w or or w w W = widow’s peak w = no widow’s peak Ww ww 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) Law of Segregation: One version of each gene is inherited from each parent Back to Mendel’s Conclusions

P (Parent) Generation True-breeding parents Dominant alleles mask recessive ones P (Parent) Generation True-breeding parents (PP x pp) F1 (1st Filial) Generation Hybrid Offspring (Pp) What happened to the recessive traits? 705 plants had purple flowers F2 (2nd Filial) Generation 224 plants had white flowers What is the F2 ratio? 705:224  3:1

P Generation F1 Generation F2 Generation PP:Pp:pp  1:2:1 3: 1 Dominant alleles mask recessive ones P Generation Phenotype (Appearance) Purple Flowers White Flowers Genotype (Genetic Makeup) PP pp Gametes P p F1 Generation Phenotype (Appearance) Purple Flowers Genotype (Genetic Makeup) Pp Gametes P p Punnett Square F2 Generation P P What is the Genotypic Ratio of the F2 Generation? PP p p PP:Pp:pp  1:2:1 Pp Pp pp What is the Phenotypic Ratio of the F2 Generation? 3: 1

Genotype Phenotype PP Purple 1 (homozygous) Pp Purple 3 (heterozygous) Dominant alleles mask recessive ones Genotype Phenotype PP Homozygous: same alleles Heterozygous: different alleles Purple 1 (homozygous) Pp Purple 3 (heterozygous) 2 Pp Purple (heterozygous) pp 1 1 (homozygous) White Ratio = 1:2:1 Ratio = 3:1

Vocabulary Practice We will now play “Got Gametes?” in order to practice understanding the following new terms: alleles, genotype, phenotype, homozygous, heterozygous

Vocabulary Practice Each of you are haploid gametes carrying single alleles – for a trait. Your single letter can be combined with another single letter (i.e., Hh) to form a genotype in a diploid organism. You will observe a series of faces. Come to the front of the classroom if you think you have the right genotype to match the phenotype shown. Make sure to find the corresponding allele for the trait you represent!

How do you set up a Punnett square? Now you try! Example 1: Heterozygous short hair (____) X heterozygous short hair (____) Hh Hh Hh Hh H H HH h h Hh Hh Genotypic Ratio HH:Hh:hh 1:2:1 Phenotypic Ratio Short hair:long hair 3:1 hh

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

P Generation F1 Generation F2 Generation Phenotype(s): Red and White Genotype(s): CRCR and CWCW Gamete of Red flower: CR Gamete of White flower: CW CR CW F1 Generation Phenotype: Pink Genotype: CRCW Gametes: CR and CW CR CW F2 Generation Exception to Dominant Alleles Masking Recessive Alleles Incomplete Dominance: Pink Snapdragons Use Root Letter “C” to designate incomplete dominance interaction CR CR CRCR CW CW CRCW CRCW CWCW Back to Mendel’s Conclusions

Back to Mendel’s Conclusions Exception to Dominant Alleles Masking Recessive Alleles: Co-dominance: Blood Types (video) Use root letter “I” for dominant alleles of equal strength and “i” for recessive Back to Mendel’s Conclusions

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

Mendel’s Conclusions The law of segregation followed one single trait at a time, such as seed color. What if two traits were followed, such as seed color and seed shape? Are these genes somehow connected (linked) and inherited together?

Following two traits: Seed shape and seed color Gametes YR yr 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 matched sets in the gametes. F1 YyRr Ova Sperm YR YR yr yr F2 For the traits of seed shape and color, this hypothesis is NOT supported by experimental evidence

What did the data support instead?

YyRr Now try to do it on your own! What are the phenotypic ratios? What are the genotypes of the P Generation? YYRR yyrr Law of Independent Assortment What does the P Generation pass on to F1? YR yr Gametes F1 Phenotype? YyRr F1 Genotype? What does the F1 Generation pass on to F2? Ova Sperm YR YR Yr Combine the sperm and ova to produce the offspring in F2 Yr YYRR yR yR YYRr YYRr yr yr What do you expect the phenotype will be when YR and YR are combined? YyRR YYrr YyRR Phenotypic Ratios YyRr YyRr YyRr YyRr 9/16 Yellow & Round What will the Genotype be when YR and YR are combined? Yyrr yyRR Yyrr 3/16 Green & Round yyRr yyRr 3/16 Yellow & Wrinkled Now try to do it on your own! yyrr 1/16 Green & Wrinkled What are the phenotypic ratios?

Mendel’s Conclusion! FOIL Law of Independent Assortment: If the genes are not connected, then they should segregate independently. The alleles are randomly packaged into different gametes during meiosis (For example, genes for seed shape and color were not inherited together.) YyRr  FOIL YR Yr yR yr

Significance of Mendel’s Research Punnett Square was introduced as a tool to predict or determine the probability of an event Now, let’s practice dihybrid crosses!

White board exercises 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 In a population of Wisconsin fast plants, purple color is created by the pigment anthocyan. The gene that codes for this pigment is dominant (A), and without this pigment, the plant is green recessive (a). Predict the offspring from the cross of a purple homozygous plant and a green plant. What if the purple plant was heterozygous? How would the offspring be different? Purple plant: AA Green plant: aa Purple plant: Aa Green plant: aa A a A a a A Aa a a Aa Aa Aa 50% Purple 50% Green 100% Purple aa Aa Aa aa Green Purple

Punnett Square Exercise One-trait cross In 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. Brown hampster: Bb White hampster: bb B b Offspring 50% brown mice 50% white mice b b Bb bb Bb bb

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. Go to Test Crosses

White-board exercises 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)