ORIGIN OF GENETICS

1. The passing on of characteristics from parents to offspring is called heredity. The characteristics that are passed on are called genes- located on chromosomes. ORIGIN OF GENETICS

2. Gene- chemical factor that determines a trait • EX: seed color, plant height, seed shape, seed coat color, pod shape, pod color, flower position. • Allele- different forms of genes • EX: green & yellow seed color, tall & short plant height, etc.

3. GREGOR MENDEL • Australian monk- 1800’s • One of the first to study heredity using pea plants • “Father of genetics”

4. WHY DID MENDEL USE PEA PLANTS? • Seeds readily available • Grew quickly • Produced large number of offspring that could be analyzed. • Self pollinate- creating genetically identical offspring. • Pea plants have distinct traits- tall or short plant never a medium size.

5. MENDEL’S EXPERIMENTS • Knew that yellow seed plants always produced yellow seed offspring. • Cross-bred two purebred plants- one plant that produces yellow seed and one that produces green seeds. • He called this the parental or P-generation.

6. MENDEL’S EXPERIMENTS • Crossed pollen (sperm) from yellow seed pea plant with egg of green seed pea plant. • Resulting offspring are called the F1 generation- first filial generation. All were yellow. Green trait seemed to disappear. • When offspring from F1 are crossed- resulting offspring are ¾ yellow seeds and ¼ green seeds. This second generation of offspring is called the F2-2nd filial generation. • Why did green trait disappear then reappear?

7. RULE OF DOMINANCE • One allele in a gene pair may prevent the other allele in the gene pair from being expressed. • RECESSIVE GENE • Gene that is hidden if a dominant gene is present. • Represented by a lowercase letter • EX: green is recessive- y • DOMINANT GENE • Gene that is shown • Represented by capital letter of dominant trait. • EX: Yellow is dominant- Y

8. Law of Segregation • Explains the disappearance of a trait in the F1 generation and its reappearance in the F2 generation. • Each pair of genes separates when gametes are formed during meiosis.

9. The way in which alleles segregate is random. • A sperm with a yellow seed allele may meet with an egg with a green seed allele- this is totally random also. • You can predict the outcomes of genetic crosses based on probability- the likelihood that a particular event will occur.

10. PUNNETT SQUARES • Used to predict the outcome of offspring when crossing two parent organisms. Parent #1- yellow Y Y Parent plant #1- YY- yellow Parent plant #2- yy- green Offspring- Yy- yellow but carry recessive green allele. y Y y Y y Yellow Yellow Parent #2- green Y Y y y y Yellow Yellow

11. y Y Predict what offspring would look like if you crossed two of the Yy offspring. Y Y Y Y y Yellow Yellow ¼ of offspring- YY- yellow ½ of offspring- Yy- yellow ¼ of offspring- yy- green Y y y y y Yellow green

12. HOMOZYGOUS • When two genes in a pair are the same. • Also called purebred. • Can be either: • Homozygous dominant • Two dominant traits • YY- yellow • Homozygous recessive • Two recessive traits • yy- green

13. HETEROZYGOUS • Individuals that have one dominant and one recessive gene. • Dominant gene is always expressed. • Person who has this gene pair is a carrier for the recessive trait. • Also called hybrids • EX: Yy- looks yellow but carries a green trait

14. Genotype- gene combination that organisms have for each trait. Represented by two letters EX: yellow seed plant has two alleles (one from mother, one from father) for yellow so its genotype is YY Phenotype- The trait that is shown by genotype. Represented by a descriptive word. EX: YY seed will look yellow GENOTYPE VS. PHENOTYPE