Gregor Mendel Brno, Austria One of the first people to examine the inheritance of traits across generations by: One of the first people to examine the inheritance of traits across generations by: Carrying out many experiments - breeding of pea plants Carrying out many experiments - breeding of pea plants Examining the traits of the offspring and parentsExamining the traits of the offspring and parents Proposing a model of inheritanceProposing a model of inheritance 8 years ( )8 years ( )

Why Pea plants? There were many pea plants in the monastery garden There were many pea plants in the monastery garden Many offspring produced in just one cross Many offspring produced in just one cross Fairly quick to reproduce- don’t take too long to mature Fairly quick to reproduce- don’t take too long to mature

How he did it Although not a professional scientist, his methods were very scientific: Although not a professional scientist, his methods were very scientific: Investigated one or two traits at a time by deliberately breeding selected plantsInvestigated one or two traits at a time by deliberately breeding selected plants Always started with pure- breeds for the traits he was investigatingAlways started with pure- breeds for the traits he was investigating Careful records of parents in crossesCareful records of parents in crosses Used statistics to analyse resultsUsed statistics to analyse results

Traits Although he examined one at a time, there were 7 different traits that Mendel examined over the 8 years of his scientific work Although he examined one at a time, there were 7 different traits that Mendel examined over the 8 years of his scientific work

Cross-breeding Transferred pollen from one pure- breed plant to another Transferred pollen from one pure- breed plant to another Observed offspring traits before Observed offspring traits before Interbred the first generation offspring Interbred the first generation offspring

For Example Mendel crossed: pure-bred yellow seed plant x pure-bred green seed plant and obtained all yellow seed offspring Mendel crossed: pure-bred yellow seed plant x pure-bred green seed plant and obtained all yellow seed offspring So the factor that caused the yellow colour was more powerful than the factor for green colour So the factor that caused the yellow colour was more powerful than the factor for green colour Mendel said that the yellow factor "dominated" the green factor Mendel said that the yellow factor "dominated" the green factor We now recognise that these factors are alleles of genes with slightly different instructions on homologous chromosomes and that one allele is dominant to the other We now recognise that these factors are alleles of genes with slightly different instructions on homologous chromosomes and that one allele is dominant to the other

The experiment continues Mendel then allowed the first generation to self pollinate: Mendel then allowed the first generation to self pollinate: GametesYy YYYYy y yy Phenotypic ratio: 3/4 yellow : 1/4 green or 3 yellow : 1 green

The Findings Gregor observed the following: 1.Each trait is controlled by a pair of inherited factors (alleles) 2.For each trait individual plants had two factors which could be identical or different (homo or heterozygous). Gregor called these pure-bred and hybrid. 3.Each factor was a discrete particle that retained its identify across generations (didn’t get diluted or blended)

The Findings 4.The trait shown in the 1 st generation hybrid plants were assumed to be dominant while the hidden trait was recessive 5.During gamete formation, each pair of factors separated to different gametes – one factor per gamete 6.In separating, the factors within the pair behaved independently of each other

The findings 7.Results of crosses that were repeated revealed the same results, regardless of which plant was used as the male parent and which was used as the female parent

Mendel’s Laws From these findings, Gregor devised two laws of inheritance: From these findings, Gregor devised two laws of inheritance: The principle of segregation of alleles:The principle of segregation of alleles: That alleles of parents are separated into different gametes That alleles of parents are separated into different gametes The principle of independent assortment:The principle of independent assortment: That alleles behave independently of one another when separating into alleles That alleles behave independently of one another when separating into alleles

Rejected & Rediscovered When Mendel presented his findings to the scientific community in Brno in they were largely ignored When Mendel presented his findings to the scientific community in Brno in they were largely ignored It was not until the early 1900s that they were rediscovered by 3 geneticists working independently of one another It was not until the early 1900s that they were rediscovered by 3 geneticists working independently of one another

Not so simple… It was found that Mendel’s laws of inheritance were largely correct and seemed to apply to many traits across many different species It was found that Mendel’s laws of inheritance were largely correct and seemed to apply to many traits across many different species However, in the early 1900s two geneticists discovered that some traits can be inherited together, going against Mendel’s laws of independent assortment (linkage) However, in the early 1900s two geneticists discovered that some traits can be inherited together, going against Mendel’s laws of independent assortment (linkage)

Chromosomes In 1902, the structure of chromosomes were first discovered by an American scientist In 1902, the structure of chromosomes were first discovered by an American scientist He assumed that these chromosomes housed the genetic factors proposed by Mendel He assumed that these chromosomes housed the genetic factors proposed by Mendel

DNA structure The 3D structure of DNA was proposed by Watson and Crick in 1953 The 3D structure of DNA was proposed by Watson and Crick in 1953

What does DNA stand for? Deoxy-riboseNucleic Acid Type of monosaccharide Found in the nucleus (eukaryote) or nucleoid (prokaryote) of cells As in acids and bases DNA can also be written as Deoxyribonucleic Acid

Building blocks A single unit of DNA is called a nucleotide it is made up of: A single unit of DNA is called a nucleotide it is made up of: A Sugar Molecule (Deoxy-ribose)A Sugar Molecule (Deoxy-ribose) A Phosphate moleculeA Phosphate molecule A Nitrogenous BaseA Nitrogenous Base P

Building blocks PPPPP The nucleotides are bound together via covalent bonds between the phosphate groups, forming a strand of DNA The nucleotides are bound together via covalent bonds between the phosphate groups, forming a strand of DNA These covalent bonds are very strong and difficult to break These covalent bonds are very strong and difficult to break The phosphate and sugar ‘backbone’ are on the outer part of the double helix The phosphate and sugar ‘backbone’ are on the outer part of the double helix

DNA DNA is made up of 2 strands. The strands are held together by weak bonds between the nitrogen bases which face inwards The bonding between the strands is made up of hydrogen bonds which are so weak that the two strands will easily separate at 100˚C There are four types of nitrogen bases: Cytosine (C), Guanine (G), Adenine (A) and Thymine (T) What pairs with C? What pairs with A?

Complementary Base Pairs There are four types of nitrogen bases: Cytosine (C), Guanine (G), Adenine (A) and Thymine (T) Cytosine pairs with Guanine These are called Adenine pairs with thymine complementary base pairs

DNA The two strands of DNA run in opposite directions to one another and are said to be ‘anti-parallel’ Once the 2 strands of DNA are bound together, the strands coil to form a helical shape This is why DNA is often called a double helix In this diagram, the 2 DNA strands have backbones that are shown in blue and red The nitrogen bases are shown in yellow

The significance of complementary base pairing Complementary base pairing means that DNA can act as a template for its own replication Complementary base pairing means that DNA can act as a template for its own replication If you know the sequence of one chain, you can infer the sequence of the otherIf you know the sequence of one chain, you can infer the sequence of the other Contains genetic instructions for protein production Contains genetic instructions for protein production DNA strands can dissociate and then reassociate when heated and cooled respectively DNA strands can dissociate and then reassociate when heated and cooled respectively

The Gene Code The order of the nitrogenous bases A, T, G & C is very important. The order of the nitrogenous bases A, T, G & C is very important. The sequence provides cells with templates for the production of every protein in the body The sequence provides cells with templates for the production of every protein in the body These proteins play many different roles in the body These proteins play many different roles in the body Each segment of DNA which determines the structure of one protein is called a gene Each segment of DNA which determines the structure of one protein is called a gene