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What is
Genetics?
• Genetics: Field of
biology devoted to
understanding how
characteristics are
transmitted from
parent to offspring
• Traits are inherited
from previous
generations
• Heredity: passing of
traits from parent to
child
• “Father of Genetics”
• Famous for pea plant
studies
• Mendel studied seven
pea traits such as:
– 1) Seed Color (yellow
or green)
– 2) Flower Color
(purple or white)
– 3) Seed texture
(smooth or wrinkled)
• More common traits are called Dominant
• Less common traits are called Recessive
• Example: Pea Height
– 75% of peas were tall (Dominant)
– 25% of peas were short (Recessive)
• Test 1:
– Mendel crossed pure
purple with pure white
plants
– F1 generation: 100%
Purple
• Test 2:
– F1 purple crossed with
another F1 purple
– F2 generation: 75%
purple, 25% white
• Conclusion: 1 form of a trait
prevents the expression of
another
•
•
•
•
Gene: Segment of DNA that controls a trait
Every trait has two genes (from mom and dad)
Allele: Alternative forms of a gene
Letters used to abbreviate alleles
– Dominant Allele = Capital letters
– Recessive Allele = Lowercase letters
• Dominant alleles hide recessive alleles
• Phenotype: Actual
appearance of an
organism
• Phenotype = Purple
flowers
• Genotype: Genetic
makeup of an
organism
• Ex: 2 dominant alleles
• Genotype = PP
• Genotype determines
phenotype
• Homozygous:
Combination of two
same alleles
• Ex: PP (homozygous
dominant)
• Ex: pp (homozygous
recessive)
• Heterozygous:
Combination of 2
different alleles
• Ex: Pp (heterozygous
dominant)
Mendel’s First Test
• P generation: pure purple (PP)
x pure white (pp)
• All F1 possibilities are purple
(but carry the white allele)
Mendel’s Second Test
• F1 generation: Purple (Pp) x
Purple (Pp)
• F2 possibilities are:
– ¾ purple
– ¼ white
Quick Review
• Mendel started work in genetics by
studying peas
• Each trait is determined by two alleles
(one from each parent)
• Dominant alleles hide recessive alleles