MENDELIAN GENETICS

Gregor MendelAustrian Monk

1822-1884

The Father of Modern Genetics

The use of pea plants Mendel used pea plants for

his studies…but why?Many different observable

traitsReproduced very quicklyHe could control which plants

reproduced with each other

Traits that he was observing Round vs. wrinkled pea shape Tall vs. short Yellow vs. green color

Traits were easily seen from generation to generation

Allele- alternative versions of a trait or gene…such as tall vs. short or T vs. t

Homozygous vs. Heterozygous

Homozygous- The alleles in a pair are identicalTT or tt

Heterozygous- The alleles in a pair are differentTt

Genotype vs. Phenotype

Genotype Phenotype

The genetic make-up of an organism

Bb, BB, or bb

The outward appearance of an organism

Example: Brown Hair, tall, blue eyes, etc.

Mendel’s Laws

Rule of Unit Factors- each organism has 2 factors that control each of its traits

You have 2 alleles for each trait…one from each parent!

Mendel’s Laws (continued…) Rule of Dominance- Within any

characteristic one allele appears more often than the other. This may give the appearance that that allele is stronger and the other is weak.

If you have a brown hair allele from mom and a blond hair allele from dad, you would only see brown because it is dominant to blond.

Mendel’s Laws (continued…) Law of segregation-Each organism can

produce 2 different types of gametes because it has 2 different alleles.

During fertilization, male a female gametes randomly pair to form 4 combinations of alleles

Mendel’s Laws (continued…) Law of Independent Assortment- Genes

for different traits are inherited independent of each other.

Punnett Squares A chart used to solve genetic

problems

Rules for Making a Punnett Square Female gametes (eggs) go down the

side Male gametes (sperm) go across the top Capital letters = dominant Lower Case letters = recessive

Monohybrid Cross

Showing only one trait.

Probability

Dihybrid Cross