Mendel and the Gene Idea

The passing on of characteristics from parents to offspring Trait physical characteristic Genetics is the study of heredity

 Gene – segments of DNA that code for the basic units of heredity and are transmitted from one generation to the next  Allele – genes that reside at the same locus on homologous chromosomes  Alleles are the result of mutation!!!!!!

 At each locus (except for sex chromosomes) there are 2 genes. These constitute the individual’s genotype at the locus. The alleles that are present.  The expression of a genotype is termed a phenotype. For example, hair color, weight, or the presence or absence of a disease.

Genotype Gene(s) responsible for the trait The alleles that are present on each homologous chromosome that code for the trait

Phenotype Expression of the characteristic The trait The way we “look” Red hair or Brown hair The expression of the gene

 Gregor Mendel  ( ) is the called the “Father of Genetics”  Researched with garden peas  Developed the ideas that are the basis of genetics

Characters (inherited characteristic) are in two distinct forms (such as white and purple color) called traits. Not many traits Easy to keep track The male and female gametes are enclosed within the same flower – He could control the fertilization process Self-fertilization Cross-pollination The garden pea is small, grows easily, matures quickly and produces many offspring.

Mendel studied a number of characteristics in pea plants including: TALLHeight - short or TALL YELLOWSeed color - green or YELLOW ROUNDSeed shape - wrinkled or ROUND GRAYSeed coat color - white or GRAY SMOOTHPod shape - constricted or SMOOTH GREENPod color - yellow or GREEN AXIALFlower position - terminal or AXIAL

 Carefully controlled experiments  Studied one trait at a time  Kept detailed data  Cross - combining gametes from parents with different traits  The offspring are called hybrids  offspring of parents with different traits  A monohybrid cross is one that looks at only one trait (let’s look at plant height – tall or short)  Cross fertilization  Pollen from one plant to fertilize another plant

MENDEL’S MONOHYBRID CROSSES  Step One: self-pollinate  Mendel allowed the peas to self-pollinate for several generations. What Did Mendel Find?

MENDEL’S MONOHYBRID CROSSES Step One: true-breeding Each variety was true-breeding for a particular character. tall plants only produced tall plants parental generation These plants served as the parental generation. P generation The P generation is the first two individuals that are crossed in a breeding experiment

MENDEL’S MONOHYBRID CROSSES  Step Two: cross-pollinatedP generation traits  Mendel cross-pollinated two P generation plants with different traits first filial F1 generation  The offspring were the first filial generation or F1 generation  Mendel recorded the traits of the offspring What Did Mendel Find?

MENDEL’S MONOHYBRID CROSSES  Tall plant crossed with short plants produced all tall offspring  Purple flowers crossed with white flowers produced all purple offspring

MENDEL’S MONOHYBRID CROSSES Step Three: F1 generation self- pollinate. Finally, Mendel allowed the F1 generation to self- pollinate. F1 generation F2 generation He called the offspring of the F1 generation, the second filial generation, or F2 generation Again, Mendel recorded the traits of the offspring What Did Mendel Find?

MENDEL’S MONOHYBRID CROSSES  The short plants reappeared!!!!!! 3 out of 4 (¾) 1 out of 4 (¼)  Mendel found that 3 out of 4 (¾) of the offspring were tall & 1 out of 4 (¼) were short

MENDEL’S MONOHYBRID CROSSES  Mendel found the same 1:3 ratio (1 out of 4) in the other traits as well!

MENDEL’S RESULTS laws rules heredity  He discovered different laws and rules that explain factors affecting heredity

THEORY OF HEREDITY  Before Mendel, people thought offspring were a blend of traits  Tall x short = medium  Mendel’s experiments did not support this theory  Mendel’s work led him to the understanding that traits are carried in pairs (one from each parent)

What did Mendel cross? What are traits? What are gametes? What is fertilization? What is heredity? What is genetics?

MENDEL AND HEREDITY Why we look the way we look...