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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