Mendel’s Laws of Heredity

Important Terms

1. Traits – characteristics that are inherited2. Heredity – passing on of characteristics

from parents to offspring3. Genetics – branch of biology that

studies heredity4. Genes- sections of DNA that code for a

trait5. 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 letters9. 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 SAME2 tall =TT (homozygous dominant)

or2 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 19th 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. F1 generation – crossed two purebred parents (ex: tall plant and short plant) to create hybrids. TT x tt= Tt (tall)

3. F2 generation – allowed F1 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