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Mendel and
Meiosis
Learning Goal:predict possible outcomes of various genetic combinations such as monohybrid crosses
Gregor Mendel HeredityHeredity is the passing of
characteristics from parents to offspring.
GeneticsGenetics is the study of heredity or how those traits are inherited.
Gregor Mendel was the first person to succeed in predicting how traits were inherited thus he became known as the Father of Genetics.Father of Genetics.
Gregor Mendel Gregor Mendel is best known for
his study of pea plantspea plants. He used pea plants because they
have 2 distinct sex cells called gametesgametes.
Mendel pollinated the flowers himself by transferring the male pollen to the stigmastigma of the flower (pollination).(pollination).
Pollen
Uniting of the male and female gametes is called fertilizationfertilization.
Mendel cross-pollinatedcross-pollinated pea plants in order to study the various traits:
DominaDominantnt: the trait that was
observed
RecessiveRecessive: the trait
that disappear
ed.
Genotypes and Phenotypes PhenotypePhenotype – the way that the
organism lookslooks and behaves.
PhenoPheno (physical) (physical) typetype (model) (model)
Genotypesenotypes – the combination of alleles (genes)alleles (genes) in the organism.
GenGen (birth) (birth) typetype (model) (model)
Genotypes and Phenotypes AlleleAllele – the different forms of a gene
ex: Blue eyes or Brown eyes Alleles can be dominant or recessive
DominantDominant The trait covers up (masks) the
recessive trait Symbol is a capital letter (T)
RecessiveRecessive The trait is masked by the dominant
allele Symbol is a lowercase letter (t)
Genotypes and Phenotypes
PhenotypePhenotype
Genotype Genotype
AllelesAlleles
Genotypes and Phenotypes Homozygous dominant:
Homo (same)
Homozygous recessive:
Heterozygous: Hetero (different)
Crossing traits HybridHybrid: a cross between plants with
different traits like tall and short. Mendel’s first cross he called a
monohybridmonohybrid cross. (Mono means one) Later Mendel began crossing plants
with 2 traits. These crosses were called dihybriddihybrid crosses.
Testcross: Breeding an individual of unknown genotype to a homozygous homozygous recessiverecessive individual to reveal the unknown genotype
Parent generat
ion
Filial (son or
daughter) generation
2nd Filial
generation
Grandchildren
Children
Parents
Law of segregation:Law of segregation: the 2 alleles for each trait (on homologous chromosomes)will segregatesegregate (separate)(separate) with the formation of the gametes gametes during meiosis.
Mendel’s Laws of Inheritance
Mendel’s Laws of Inheritance Law of independent assortment: Law of independent assortment:
Each trait (or gene) is inherited Each trait (or gene) is inherited independently of the other independently of the other traitstraits.
In other words, all blondes do not have blue eyes.
Punnett Squares In 1905, Reginald PunnettPunnett, an
English biologist, devised a shorthand way of predicting the outcomes of the various crosses.
These are called Punnett squares.
Monohybrid crosses
Genotypes
Phenotypes
Bb: 100% Bb
100% White
B: White
b: Black
BB
bb
Bb Bb
Bb Bb
B B
b
b
gametes
Monohybrid crosses
Genotypes
Phenotypes
BB: 25%Bb: 50%bb: 25%
White: 75%(BB and Bb)black: 25%
B: White
b: BlackBB Bb
Bb bb
Genotypic ratio1:2:1
Phenotypic ratio3:1
B b
B
b
gametes
Monohybrid crosses
Genotypes
PhenotypesBB: 0%
Bb: 50% bb: 50%
Genotypic ratio
0:1:1
50% White50% Black
Phenotypic ratio
1:1
BB: White
bb: Black
Bb
bb
B b
b
b
Bb bb
Bb bb
gametes