Chapter 10 Section 2 Mendelian Genetics

How Genetics Began In 1866, Mendel published the paper "Experiments in Plant Hybridization" studied seven basic characteristics of the pea pod plants chose pea pod plants because they are true breeders- they consistently produce offspring with one trait Figured out he could cross pollinate a normal self fertilizing plant Developed Mendel’s Laws

Inheritance of Traits The offspring of crosses between parents with different traits are called Hybrids When Mendel crossed plants with different traits he expected them to blend, but that’s not what happened at all. All of the offspring had the character of only one of the parents

F 1 and F 2 Generations -Cross bred a yellow and green pea and produced all yellow offspring (F1) -All offspring were grown and allowed to self fertilize and offspring were in a ratio of 3:1 -Mendel further investigated what happened to the green trait

Pea Plant Traits

Conclusion 1. Inheritance: determined by factors that are passed from generation to generation – today we call these factors genes –Allele: different forms of a gene

Conclusion 2. The Principal of Dominance: some alleles are dominant and some are recessive –Dominant covers up recessive (T) –Recessive gets covered up in the presences of a dominant allele (t) (3:1 ratio because alleles are paired in each of the plants. F1 yellow was dominant and green was recessive)

Conclusion Mendel concluded there are two forms of the seed trait (allele pairs or genotype) in each seed that can be observed (phenotype) – They can either be dominant or recessive Dominant (Y) Recessive (y) Homozygous- 2 of the same alleles – Yellow: YY Green: yy Heterozygous- 2 different alleles – Yellow: Yy

Conclusion Law of Segregation- the two alleles for each character separate during gamete production – Mendel used homozygous yellow and green seeds (YY and yy) Chromosomes divide in half in meiosis

Conclusion Hybrids- Heterozygous organisms – Mendel pollinated one dominate and one recessive gamete and it produced a hybrid that will also produce all hybrid offspring Fertilized sex cell

Conclusion Monohybrid Cross After creating hybrids, Mendel did some more investigating and allowed these heterozygous plants to self fertilize Called it a monohybrid cross: a breeding experiment between P generation (parental generation) organisms that differ in one trait. The random fertilization of male and female gametes produced a 3:1 phenotypic ratio.

Thus…Punnett Squares Developed in the early 1900’s by Dr. Reginald Punnett – predict the possible offspring of a cross between 2 known genotypes Genotypic ratio is 1:2:1 Phenotypic ratio 3:1

– # of squares depends on # of alleles – Female vertical side, Male horizontal PARENT 1 PARENT 2

Punnett Square RULES A. Divide the parent genotype in half (meiosis) B. Put the genotype of each HAPLOID cell along top and left edge of square C. Combine sperm and egg in each box of square D. Capital Letters first, same letters together

2 parents heterozygous genotypes

DAD MOM Genotype of each haploid

B= dominant (purple) b= recessive (white)

Now…your turn to practice simple dihybrid crosses on the white boards! (R = red r = white) A) Cross: Homozygous dominant mom Heterozygous dad B) Cross: Heterozygous red mom Homozygous recessive dad C) Cross : Purebred red mom White dad D)Cross: Red mom White dad

BUT…. Is there anyway to cross more than one allele in a Punnet Square?

Why, yes there is! Dihybrid Cross After the development of monohybrid crosses, Mendel took it even another step further Called it a dihybrid cross: a breeding experiment between P generation (parental generation) organisms that differ in two traits. R: round r: wrinkled Y: yellow y: green Homozygous round yellow Homozygous Wrinkled green

Law of Independent Assortment After the development of dihybrid crosses, Mendel took it even another step further Called it a law of independent assortment: Determined there was a random assortment of alleles that occurs during gamete formation, each with the same likelihood to occur – Combinations crossed: YR, Yr, yR, yr

Dihybrid Cross -4 types of alleles present -Phenotypic ratio 9:3:3:1 9 yellow round 3 green round 3 yellow wrinkled 1 green wrinkled 9 different genotypes: YYRR, YYRr, Yyrr, YyRR, YyRR, Yyrr, yyRR, yyRr, yyrr 4 different phenotypes: yellow round, green round, yellow wrinkled, green wrinkled

S= white s= brown B= long tail b= short tail

Chapter 10 Section 3 Gene Linkage and Polyploidy

Genetic Recombination The new combination of genes after crossing over (prophase I) and independent assortment (metaphase I) occur in meiosis Independent assortment calculated by 2n n= # of pairs of chromosomes Humans n= 23, so 2n= 46 for male and female 2 n = 2 46 = ~ 70 trillion different recombinations

Gene Linkage One exception of Mendel’s Law of Independent Assortment – Chromosomes have multiple genes that code for proteins, said to be linked to one another on the same chromosome and thus usually travel together during meiosis – Drosophila melanogaster- fruit fly study confirmed this Chromosome maps show the sequence of genes on chromosomes using data

Polyploidy Occurrence of one or more extra sets of all chromosomes in an organism (most are diploid organisms) Triploid= 3n (3 complete sets of chromosomes) – Earthworms, goldfish, flowering plants Others – Bread Wheat (6n) Oats (6n) Sugar Cane (8n)