Background Info
Gregor Mendel
– Austrian Monk (1822-1884)
– Father of Genetics
– Genetics – study of heredity
– Heredity – passing of
characteristics from parent
to offspring.
Background Info
Gregor Mendel
– Identified that all traits
are controlled by a “factor”
– This “factor” is a gene
– GENE – section of a
chromosome/DNA that
codes for a trait.
– TRAIT– characteristic
passed from parent to
offspring
Genome
• ALL of an organism’s genetic
material
Background Info
Gregor Mendel
• Studied Pea Plants to show
how traits are passed from
one generation to the next
• He applied math to his
observations
• Studied pea plants because
they came in 2 distinct forms
Why did he choose
the Pea Plant?
• 1. The Structure of the
Pea Flower
• 2. The seven distinct
traits (2 distinct forms)
• 3. Rapid reproduction
(Most pea plants reproduce in
90 days)
Pea
Plant
Traits
(Each
trait only
has 2
distinct
forms)
Genes & Alleles
• Genes – chemical factors that determine
traits
(Flower color)
• Alleles – different forms of genes that
code for traits
(Purple flowers or White flowers)
Mendel found
Dominant and Recessive Traits
• An Allele is a distinct form of a
gene
• A dominant allele is the form that
is visibly seen.
• A recessive allele is the form that
is there but not seen (unless there
are 2 recessive alleles together).
Symbols
• Dominant
Alleles
– Capital
Letters
• Recessive
Alleles
– Lower Case
Letters
Genotypes
• Genotype
– Genetic makeup represented
by symbols
– AA, Aa, aa, TT, Bb, dd
Phenotypes
• Phenotype
– Physical appearance expressed
in words
– Brown hair, Green eyes,
Freckles
Heterozygous
• Heterozygous (different)
– Gene pairs that carry one
dominant and one recessive
allele
– Aa, Bb, Cc, Dd
Homozygous
• Homozygous (same)
– Gene pairs that carry 2
dominant OR 2 recessive
alleles
– AA, aa, BB, bb
Probability
• Determining the likelihood of
an event to occur
• Can be shown in 3 ways
– Fraction 1/2
– Percent 50%
– Ratio
1:2
Hybrids & Purebreds
• Hybrids receive different
alleles from each parent (Hh,
Bb, Zz)
• Purebreds receive the same
alleles from each parent (HH,
bb, ZZ)
Laws of Genetics
• Law of Dominance: Dominant traits will
always show over recessive traits
• Law of Segregation: Alleles separate
during meiosis
• Law of Independent Assortment: gene
pairs separate randomly and independently
of each other
Mendel’s Crosses
• He started with 2 groups of purebred
plants, called the P1 generation.
1. He crossed the purebreds by hand.
2. The P1’s offspring was called the F1
generation. The F1s then self-fertilized.
3. The F1’s offspring was known as the
F2 generation.
Monohybrid Crosses
A genetic cross that looks at 1 trait
• Cross a homozygous
tongue roller with a nontongue roller
• Genotype of parents
– TT x tt
t
• Phenotypes of parents
– Tongue roller, non-tongue
roller
• Possible Outcomes
– Genotypic ratio
•
100%Tt
– Phenotypic ratio
• 4 Tongue rollers:0 non-tongue
rollers
t
T
T
Tt
Tt
Tt
Tt
Monohybrid Crosses
• Cross 2 Heterozygous
tongue rollers
• Genotype of parents
– Tt x Tt
T
T
• Phenotypes of parents
t
TT
Tt
Tt
tt
– Tongue roller, Tongue
roller
• Possible Outcomes
– Genotypic ratio
• 1TT:2Tt:1tt
– Phenotypic ratio
• 3 tongue rollers: 1 nontongue roller
t
Monohybrid Crosses
• Cross a heterozygous
Tongue roller with a
Non-Tongue roller
• Genotype of parents
T
t
– Tt x tt
t
Tt
tt
Tt
tt
• Phenotypes of parents
– Tongue roller, non-tongue
roller
• Possible Outcomes
– Genotypic ratio
• 2Tt:2tt
– Phenotypic ratio
• 2 tongue rollers:2 nontongue rollers
t
Dihybrid Crosses
• A genetic cross that looks at 2 traits
• Cross 2 heterozygous green, round peas
GgRr x GgRr
G= green
R= Round
• Genotypic Ratio
– 1:2:1:2:4:2:1:2:1
• Phenotypic Ratio
– 9:3:3:1
g = yellow
r = wrinkled
Dihybrid Crosses
GR
Gr
gR
gr
GR
GGRR
GG Rr
Gg RR
Gg Rr
Gr
GG Rr
GG rr
Gg Rr
Gg rr
gR
Gg RR
Gg Rr
gg RR
gg Rr
gr
Gg Rr
Gg rr
gg Rr
gg rr