From Genes to Phenotypes Part I: Gene structure and RNA replication From Chapter 10, Human Genetics Concepts and Applications, 6 th edition by Ricki Lewis

Who was Mendel? - Austrian monk - Background in agriculture (grew up on a farm) - Failed his teacher’s exam - University of Vienna: math, causes of variation in plants - Teaching at the Brünn Modern School

What did he do? Pea breeding Testing mechanisms of inheritance Used many different characters Published results in 1865

Mendel’s pea plants

Mendel`s Traits; These have controlled by two genes Genes located on autosomes chromosomes. It have shown by two form allelels; dominance & resecive. Monohybridism Testing

To create hybrid plants, Mendel snipped off the male stamens from the reproductive organs to prevent self-fertilization. He then used a paintbrush to transfer pollen from another plant for fertilization.

Why did his experiments succeed? Control over fertilization Multiple generations: P, F 1, F 2 True breedin g parents “Either/or” characters

ParentalPP ×pp Parental:PP ×pp Purple White GametesP onlyp only Gametes:P onlyp only Fusion of Gametes ? Can we make a Punnett square?

F2 Parental:P p×P p Gametes: P p P p Gives us:P p Pp Now let’s allow the F1 generation to self- fertilize to get an F2 generation. The F1 products of meiosis assort independently *We’ll use these gamete types to make a Punnett square

PPPp Pppp Pp P p 3:1 Phenotypic ratio 1:2:1 Genotypic ratio F2 Sperm Eggs

When hybrid plants produce gametes, the two parental factors segregate: half the gametes get one type, half get the other type. 3. Law of segregation All possible combinations, random combinations

DNA Functions 1. Storage of genetic information 2. Self-duplication & inheritance. 3. Expression of the genetic message. DNA’s major function is to code for proteins. Information is encoded in the order of the nitrogenous bases.

Nucleotide structure of DNA Each nucleotide of DNA contains: –Deoxyribose –Phosphate –Nitrogen base (either A, G, C, T)

What is DNA? DNA = deoxyribonucleic acid –composed of phosphate, deoxyribose sugar and four different nitrogenous bases (A, T, C, G) RNA = ribonucleic acid –Composed of phosphate, ribose sugar, and four different nitrogenous bases (A, U, C, G) DNA and RNA very similar, though RNA is generally single stranded

DNA is a double helix P A P C P G P T P C P G P A P C P T G P P C P A sugar and phosphate “backbone” connects nucleotides in a chain. P G P Two nucleotide chains together wind into a helix. DNA strands are antiparallel. DNA has directionality. 5’ 3’ 5’ Hydrogen bonds between paired bases hold the two DNA strands together.

A brief history of DNA… Edward Chargaff Showed that DNA from several species contains equal amounts of A and T, and equal amounts of G and C (1950s) Chargaff’s rules: %A=%T %G=%C 1 purine: 1 pyrimidine

Chargaff

II. What did Mendel find? A. Law of segregation (of alleles) B. Law of independent assortment (of traits)

What is a testcross? We use a testcross to determine the genotype of an organism that displays an ambiguous phenotype; That is, a purple-flowered pea plant can have either the PP genotype or the Pp genotype We can cross the purple-flowered plant with a homozygous recessive plant—a white one with a genotype that is known