Mendelian Genetics
Gregor Johann Mendel (1822-1884)
 Austrian monk
 Studied the inheritance of traits in ____________
 Developed the laws of ______________
 Mendel's work was not recognized until the turn of the 20th century
 Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants
 He found that the plants' offspring retained __________ of the parents
 Called the ___________________
Particulate Inheritance
 Mendel stated that physical traits are inherited as “______________”
 Mendel did not know that the “particles” were actually ____________________________
Genetic Terminology
 _____________ - any characteristic that can be passed from parent to offspring
 _____________- passing of traits from parent to offspring
 _____________- study of heredity
Types of Genetic Crosses
 Monohybrid cross - cross involving a__________ trait e.g. flower color
 Dihybrid cross - cross involving _________ traits e.g. flower color & plant height
Punnett Square
 Used to help solve ________________ problems
 Allow geneticists to predict the possible _______________ & ________________ of offspring
Genes
 ______________- two forms of a gene (dominant & recessive)
 _____________ - stronger of two genes expressed in the hybrid; represented by a capital letter (R)
 _____________ - gene that shows up less often in a cross; represented by a lowercase letter (r)
More Terminology
 _________________ - gene combination for a trait (e.g. RR, Rr, rr)
 _________________ - the physical feature resulting from a genotype (e.g. red, white)
Genotype & Phenotype in Flowers
 Genotype of alleles:
R = red flower
r = yellow flower
 All genes occur in ___________, so 2 ____________ affect a characteristic
 Possible combinations are:
Genotypes:
RR
Rr
rr
Phenotypes:
RED
RED
YELLOW
Genotypes
 ________________ genotype - gene combination involving 2 dominant or 2 recessive genes
(e.g. RR or rr)
o also called __________
 ________________ genotype - gene combination of one dominant & one recessive allele
(e.g. Rr)
o also called ____________
Genes and ___________________ determine characteristics
Mendel’s Pea Plant Experiments
Why peas, Pisum sativum?
 Can be grown in a small area
 Produce lots of ___________________
 Produce ____________ plants when allowed to self-pollinate several generations
 Can be artificially ________________________
Reproduction in Flowering Plants
 Pollen contains _____________
o Produced by the stamen
 Ovary contains ______________
o Found inside the flower
 Pollen carries sperm to the eggs for __________________
 __________-fertilization can occur in the same flower
 __________-fertilization can occur between flowers
Mendel’s Experimental Methods
 Mendel ____________________________ flowers using a paintbrush
 He could snip the ________________ to prevent self-pollination
 Covered each flower with a cloth bag
 He traced traits through the several generations
How Mendel Began
 Mendel produced __________ strains by allowing the plants to self-pollinate for several
generations
Eight Pea Plant Traits
 Seed shape --- Round (R) or Wrinkled (r)
 Seed Color ---- Yellow (Y) or Green (y)
 Pod Shape --- Smooth (S) or wrinkled (s)
 Pod Color --- Green (G) or Yellow (g)
 Seed Coat Color ---Gray (G) or White (g)
 Flower position---Axial (A) or Terminal (a)
 Plant Height --- Tall (T) or Short (t)
 Flower color --- Purple (P) or white (p)
Did the observed ratio match the theoretical ratio?
 The theoretical or expected ratio of plants producing round or wrinkled seeds is
3 __________ : 1 _______________
 Mendel’s observed ratio was 2.96:1
 The discrepancy is due to _______________ error
 The larger the sample the more nearly the results approximate to the theoretical ratio
Generation “Gap”
 P1 Generation = the ___________________ generation in a breeding experiment.
 ________________ = the first-generation offspring in a breeding experiment. (1st filial generation)
o From breeding individuals from the P1 generation
 _______________ = the second-generation offspring in a breeding experiment.
(2nd filial generation)
o From breeding individuals from the F1 generation
Following the Generations
 Pure plants are ___________________ (TT or tt)
 Hybrid plants are _____________________ (Tt)
Monohybrid Crosses
P1 Monohybrid Cross
 Trait: Seed Shape
 Alleles: R – Round
r – Wrinkled
 Cross: Round seeds x Wrinkled seeds
RR
x
rr
RR R
RR R
o
o
o
o
Genotype: _______
Phenotype: __________
Genotypic Ratio: ________________
Phenotypic Ratio: ________________
P1 Monohybrid Cross Review
 Homozygous dominant x Homozygous recessive
 Offspring all _____________________ (hybrids)
 Offspring called ______ generation
 Genotypic & Phenotypic ratios are ______________________
F1 Monohybrid Cross
 Trait: Seed Shape
 Alleles: R – Round
r – Wrinkled
 Cross: Round seeds x Round seeds
Rr
x
Rr
RR R
RR R
o
o
o
o
Genotype: _______
Phenotype: __________
Genotypic Ratio: ________________
Phenotypic Ratio: ________________
F1 Monohybrid Cross Review
 Heterozygous x heterozygous
 Offspring:
______% Homozygous dominant RR
______% Heterozygous Rr
______% Homozygous Recessive rr
 Offspring called F2 generation
 Genotypic ratio is _______________
 Phenotypic Ratio is ______________
…And Now the F2 Cross
 Mendel then crossed a __________ & a ______________ from his F2 generation
 This is known as an F2 cross
 There are two possible F2 crosses:
Homozygous ________________ x Hybrid
Homozygous ________________ x Hybrid
F2 Monohybrid Cross (1st)
 Trait: Seed Shape
 Alleles: R – Round
r – Wrinkled
 Cross: Round seeds x Round seeds
RR
x
Rr
RR R
RR R
o
o
o
o
Genotype: _______
Phenotype: __________
Genotypic Ratio: ________________
Phenotypic Ratio: ________________
F2 Monohybrid Cross (2nd)
 Trait: Seed Shape
 Alleles: R – Round
r – Wrinkled
 Cross: Wrinkled seeds x Round seeds
rr
x
Rr
RR R
RR R
o
o
o
o
Genotype: _______
Phenotype: __________
Genotypic Ratio: ________________
Phenotypic Ratio: ________________
F2 Monohybrid Cross Review
 Homozygous x heterozygous (hybrid)
 Offspring:
______% Homozygous RR or rr
______% Heterozygous Rr
Practice Your Crosses
 Work the P1, F1, and both F2 Crosses for two of the other Seven Pea Plant Traits
Mendel’s Laws
Results of Monohybrid Crosses
 Inheritable factors or _____________ are responsible for all heritable characteristics.
 Phenotype is based on _________________.
 Each trait is based on ______ genes, one from the mother and the other from the father.
 True-breeding individuals are ____________________ (both alleles are the same)
Law of Segregation
 During the formation of gametes (eggs or sperm), the two alleles responsible for a trait
________________ from each other.
 Alleles for a trait are then "recombined" at _________________, producing the genotype for the
traits of the offspring.
Law of Independent Assortment
 Alleles for _________________ traits are distributed to sex cells (& offspring) independently of
one another.
 This law can be illustrated using _______________crosses.
Dihybrid Cross
 A breeding experiment that tracks the inheritance of ________ traits.
 Mendel’s “Law of Independent Assortment”
A. Each pair of alleles segregates ________________________ during gamete formation
B. Formula: 2n (n = # of heterozygotes)
Equation
 The formula 2n can be used, where “n” = the number of heterozygous traits.
Ex: TtRr, n=2
2
 2 or 4 different kinds of gametes are possible.
TR, tR, Tr, tr
Question:
How many gametes will be produced for the following allele arrangements?
Remember: 2n (n = # of heterozygotes)
1.
RrYy
2.
AaBbCCDd
3.
MmNnOoPPQQRrssTtQq
Answer:
1. RrYy: 2n = _______ = ______ gametes
RY Ry rY ry
2. AaBbCCDd: 2n = _______ = ______ gametes
ABCD ABCd AbCD AbCd
aBCD aBCd abCD abCD
3. MmNnOoPPQQRrssTtQq: 2n = _______ = _______ gametes
Dihybrid Cross
Traits: Seed shape & Seed color
Alleles: R = round, r = wrinkled, Y = yellow, y = green
RrYy x RrYy
Round/Yellow: _____
Round/green: _____
wrinkled/Yellow: _____
wrinkled/green: _____
________________ phenotypic ratio
Test Cross
 A mating between an individual of _______________ genotype and a homozygous recessive
individual.
o Example: bbC___ x bbcc
BB = brown eyes
CC = curly hair
Bb = brown eyes
Cc = curly hair
bb = blue eyes
cc = straight hair
 Possible results:
bC
b___
bc
bC
OR
b___
bc
Incomplete Dominance
 F1 hybrids have an appearance somewhat in between the ________________ of the two parental
varieties.
 Example: snapdragons (flower)
 red (RR) x white (rr)
RR = red flower
rr = white flower
produces the F1 generation
All Rr = pink
(heterozygous pink)
Codominance
 Two alleles are _________________ (multiple alleles) in heterozygous individuals.
 Example: blood type
1.
type A = IAIA or IAi
2.
type B = IBIB or IBi
3.
type AB= IAIB
4.
type O = ii
Codominance Problem
 Example:
homozygous male Type B (IBIB) x heterozygous female Type A (IAi)
_______ = IAIB
_______ = IBi
Another Codominance Problem
 Example: male Type O (ii) x female type AB (IAIB)
_______ = IAi
_______ = IBi

Question:
o If a boy has a blood type O and his sister has blood type AB, what are the genotypes and
phenotypes of their parents?
 boy - type O (ii)
 girl - type AB (IAIB)
Answer:
Parents:
genotypes = ________ and _________
phenotypes = _____ and _____
Sex-linked Traits
 Traits (genes) located on the ________ ________________
 Sex chromosomes are X and Y
 _______ genotype for females
 _______ genotype for males
 Many sex-linked traits carried on _____ chromosome
Sex-linked Trait Problem
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY
x
XrXr
Remember: the Y chromosome in males does not carry traits.
 RR = red eyed
 Rr = red eyed
 rr = white eyed
 XY = male
 XX = female
Sex-linked Trait Solution:
________ red eyed female
________ white eyed male
Female Carriers
 In a sex-linked trait (like hemophilia), women are ______________, and men display the
phenotype more often.