Mendel’s Laws of Heredity

Important Terms 1. Traits – characteristics that are inherited 2. Heredity – passing on of characteristics from parents to offspring 3. Genetics – branch of biology that studies heredity 4. Genes- sections of DNA that code for a trait 5. Gametes- sex cells

6. Alleles – alternative forms of genes (plant could have alleles for tall or short) 7. Dominant Trait – trait that is seen more frequently. Upper case letters. 8. Recessive Trait – trait that is “hidden”. Lowercase letters 9. Phenotype – way an organism looks (ex. Tall or short) 10. Genotype – gene combination. Written using letters (ex: TT, Tt, tt )

11. Homozygous/Purebreds – both alleles are the SAME 2 tall =TT (homozygous dominant) or 2 short = tt (homozygous recessive) 12. Heterozygous/Hybrid – alleles are DIFFERENT 1 tall and 1 short =Tt

Gregor Mendel Monk that began to breed pea plants to study the inheritance of their characteristics in the 19 th century He was the first to succeed in predicting how characteristics are transferred from one generation to the next

Mendel’s Pea Plants He picked pea plants because they reproduce sexually – they produce gametes Male gamete – pollen (produced by anther) Female gamete –eggs located at bottom of pistil anther

Mendel’s Experiment Peas normally self-pollinate (both gametes come from same flower) Mendel took pollen from 1 flower and put it onto another. Cross-pollinated He created hybrids – offspring that have different forms of one trait (ex. green peas, yellow peas)

Punnett Squares Tool used to predict outcomes of genetic crosses. Gives us the EXPECTED number. Monohybrid cross: cross involving 1 trait Dihybrid: cross involving two traits

Mendel’s Monohybrid Crosses 1.P Generation: Purebred parents created TT (tall) and tt (short) 2. F 1 generation – crossed two purebred parents (ex: tall plant and short plant) to create hybrids. TT x tt= Tt (tall) 3. F 2 generation – allowed F 1 generation to self- pollinate. Tt x Tt = ¾ of offspring were tall and ¼ were short

Gregor Mendel’s Laws 1. Law of Dominance- When dominant alleles occur with recessive, dominant alleles will be expressed. 2. Law of Segregation – during gamete formation, pairs of alleles are separated so that each gamete contains only one member of the pair. 3. Law of Independent Assortment- as gametes form, the genes for various traits are not tied together and separate independently of one another.

Traits Studied in Mendel’s Pea Plants 1. flower color is purple or white 2.flower position is axial or terminal 3.stem length is long or short 4.seed shape is round or wrinkled 5. seed color is yellow or green 6.pod shape is inflated or constricted 7.pod color is yellow or green