1. MendelianMendelian
GeneticsGenetics
Section 10-2Section 10-2
Pages 277-282Pages 277-282

2. Gregor MendelGregor Mendel
 Austrian monk and plant breederAustrian monk and plant breeder
 He joined the monastery in 1843He joined the monastery in 1843
 He carried out the first importantHe carried out the first important
studies of hereditystudies of heredity
 He was the first person toHe was the first person to
succeed in predicting howsucceed in predicting how
traits are transferred from onetraits are transferred from one
generation to the next.generation to the next.
 He published his findings inHe published his findings in
1866.1866.

3. 3
Why peas?Why peas?
Can be grown in a smallCan be grown in a small
areaarea
Produce lots ofProduce lots of
offspringoffspring
Produce pure plantsProduce pure plants
when allowed to self-when allowed to self-
pollinate for severalpollinate for several
generationsgenerations
Can be artificially cross-Can be artificially cross-
pollinatedpollinated

4. Why Peas?
 Peas contain both gametes in the
same flower
 Pollen contains sperm produced by
the stamen
 Ovary contains eggs inside the flower
 Pollen carries sperm to the eggs forPollen carries sperm to the eggs for
fertilizationfertilization
Self-fertilizationSelf-fertilization can occur in the samecan occur in the same
flowerflower
Cross-fertilizationCross-fertilization can occur betweencan occur between
flowersflowers 4

5. Genetic TermsGenetic Terms
 Heredity – the passing on ofHeredity – the passing on of
characteristics from parents tocharacteristics from parents to
offspringoffspring
 Genetics – the branch of biologyGenetics – the branch of biology
that studies hereditythat studies heredity
 Traits – characteristics that areTraits – characteristics that are
inheritedinherited

6.  PP11 generation – “parent” - the originalgeneration – “parent” - the original
true-breeding parentstrue-breeding parents
 FF11 generation – “filial” (or son orgeneration – “filial” (or son or
daughter) offspring of the parentdaughter) offspring of the parent
plantsplants
 FF22 or “second filial generation” (oror “second filial generation” (or
granddaughter or grandson)granddaughter or grandson)
Mendel’s Experiments- Terms

7. Mendel’s Experiments
First Generation (FFirst Generation (F11))
Mendel grew seeds from a crossMendel grew seeds from a cross
between green-seed and yellow-seedbetween green-seed and yellow-seed
plants. All of the offspring had yellowplants. All of the offspring had yellow
seeds.seeds.
Second Generation (FSecond Generation (F22))
Mendel allowed the plants in the 1Mendel allowed the plants in the 1stst
generation to self pollinate. ¾ of thegeneration to self pollinate. ¾ of the
plants had yellow seeds and ¼ had green.plants had yellow seeds and ¼ had green.
 Ratio of 3:1 (3 yellow to 1 green)Ratio of 3:1 (3 yellow to 1 green)

8. 8

9. 9

10. AllelesAlleles
Alleles- alternative form of a single geneAlleles- alternative form of a single gene
passed from generation to generation.passed from generation to generation.
Organisms have 2 genes that control each trait.Organisms have 2 genes that control each trait.
These genes are located on theThese genes are located on the
chromosomeschromosomes
Dominant trait – appears in the FDominant trait – appears in the F11 generationgeneration
Recessive trait – disappears in the FRecessive trait – disappears in the F11
generationgeneration

11. A plant could have:A plant could have:
2 alleles for tallness (TT)2 alleles for tallness (TT)
2 alleles for shortness (tt)2 alleles for shortness (tt)
1 allele for tallness and 1 for shortness (Tt)1 allele for tallness and 1 for shortness (Tt)
The 2 alleles are located on different copiesThe 2 alleles are located on different copies
of a chromosome – one copy inheritedof a chromosome – one copy inherited
from the female parent and one from thefrom the female parent and one from the
male parentmale parent

12. Rule of dominanceRule of dominance
Pea plants that have at least 1 allele forPea plants that have at least 1 allele for
tallness (TT or Tt) are tall because thetallness (TT or Tt) are tall because the
allele for tallness is dominant over theallele for tallness is dominant over the
allele for shortnessallele for shortness
The only way a plant can be short is ifThe only way a plant can be short is if
both height alleles are for a short plant (tt)both height alleles are for a short plant (tt)
 HomozygousHomozygous – an organisms 2 alleles for– an organisms 2 alleles for
a trait are the same (TT, tt)a trait are the same (TT, tt)
 HeterozygousHeterozygous - an organisms 2 alleles for- an organisms 2 alleles for
a trait are different (Tt)a trait are different (Tt)

13. Phenotypes & GenotypesPhenotypes & Genotypes
2 organisms can look alike2 organisms can look alike
but have different genebut have different gene
combinationscombinations
 PhenotypePhenotype – the way an– the way an
organism looks andorganism looks and
behaves (tall or short)behaves (tall or short)
 GenotypeGenotype – the gene– the gene
combination an organismcombination an organism
contains (TT, Tt, tt)contains (TT, Tt, tt)

14. Law of SegregationLaw of Segregation
Law of Segregation- two alleles for each traitLaw of Segregation- two alleles for each trait
separate during meiosis.separate during meiosis.
 A TT plant can only produce T gametesA TT plant can only produce T gametes
 A Tt plant can produce both T gametes andA Tt plant can produce both T gametes and
t gametest gametes
 A tt plant can only produce t gametesA tt plant can only produce t gametes
The 2 alleles come together duringThe 2 alleles come together during
fertilization.fertilization.

16. TT Tt
TT TT Tt Tt
TtTTTT Tt
T T
T T t
t
T
T
segregation
segregation
fertilization
fertilization
gametes
gametes
P
F1
F2
Segregation of Alleles

17. Mendel’s CrossesMendel’s Crosses
 Hybrid – offspring of parents that haveHybrid – offspring of parents that have
different traitsdifferent traits
 Mono – means oneMono – means one
 Di- means twoDi- means two
 Monohybrid crosses – the two parentMonohybrid crosses – the two parent
plants differ by a single trait (height)plants differ by a single trait (height)
 Dihybrid cross – parents differ by twoDihybrid cross – parents differ by two
traits (height and color)traits (height and color)

18. Monohybrid Cross (Seed color)
Genotype-
1 YY, 2 Yy, 1yy
or 1:2:1
Phenotype-
3 Yellow, 1 Green
or 3:1

19. Punnett SquaresPunnett Squares
• 1905, Reginald Punnett, an English1905, Reginald Punnett, an English
biologist, devised the shorthand way ofbiologist, devised the shorthand way of
finding the expected proportions offinding the expected proportions of
possible genotypes in the offspring of apossible genotypes in the offspring of a
crosscross
• Used to predict the possible genotypes ofUsed to predict the possible genotypes of
offspringoffspring
• In reality, you don’t get the exact ratio ofIn reality, you don’t get the exact ratio of
results shown in the squareresults shown in the square

20. Punnett Square-Monohybrid CrossPunnett Square-Monohybrid Cross

21. Punnett SquarePunnett Square
T t
T TT Tt
t Tt tt

22. 22
• Trait: Seed ShapeTrait: Seed Shape
• Alleles:Alleles: RR – Round– Round rr – Wrinkled– Wrinkled
• Cross:Cross: RoundRound seeds xseeds x RoundRound seedsseeds
• RrRr xx RrRr
Monohybrid CrossMonohybrid Cross
R
r
rR
RR
rrRr
Rr
Genotype:Genotype: RR, Rr, rrRR, Rr, rr
PhenotypePhenotype: Round &Round &
wrinkledwrinkled
G.Ratio:G.Ratio: 1:2:11:2:1
P.Ratio:P.Ratio: 3:13:1

23. 23
• Trait: Seed ShapeTrait: Seed Shape
• Alleles:Alleles: RR – Round– Round rr – Wrinkled– Wrinkled
• Cross:Cross: RoundRound seeds xseeds x RoundRound seedsseeds
• RRRR xx RrRr
Monohybrid CrossMonohybrid Cross
R
R
rR
RR
RrRR
Rr
Genotype:Genotype: RR, RrRR, Rr
PhenotypePhenotype: RoundRound
GenotypicGenotypic
Ratio:Ratio: 1:11:1
PhenotypicPhenotypic
Ratio:Ratio: All alikeAll alike

24. 24
• Trait: Seed ShapeTrait: Seed Shape
• Alleles:Alleles: RR – Round– Round rr – Wrinkled– Wrinkled
• Cross:Cross: WrinkledWrinkled seeds xseeds x RoundRound seedsseeds
• rrrr xx RrRr
Monohybrid CrossMonohybrid Cross
r
r
rR
Rr
rrRr
rr
Genotype:Genotype: Rr, rrRr, rr
PhenotypePhenotype: Round &Round &
WrinkledWrinkled
G. Ratio:G. Ratio: 1:11:1
P.Ratio:P.Ratio: 1:11:1

25. 25
Law of Independent AssortmentLaw of Independent Assortment
 Alleles forAlleles for differentdifferent traits are distributed totraits are distributed to
sex cells (& offspring) independently of onesex cells (& offspring) independently of one
another.another.
 This law can be illustrated usingThis law can be illustrated using dihybriddihybrid
crossescrosses..

26. Dihybrid Cross (Seed color and shape)
Phenotypes:
9 Round and
Yellow
3 Wrinkled and
Yellow
3 Round and
Green
1 Wrinkled and
Green or 9:3:3:1
ratio

27. Punnett Square-Dihybrid Cross

28. 28
Dihybrid CrossDihybrid Cross
• Traits: Seed shape & Seed colorTraits: Seed shape & Seed color
• Alleles:Alleles: R round
r wrinkled
Y yellow
y green
RrYy x RrYy
RY Ry rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry
All possible gamete combinationsAll possible gamete combinations

29. 29
Dihybrid CrossDihybrid Cross
RYRY RyRy rYrY ryry
RYRY
RyRy
rYrY
ryry

30. 30
Dihybrid CrossDihybrid Cross
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic
ratio
RYRY RyRy rYrY ryry
RYRY
RyRy
rYrY
ryry

31. 31
Dihybrid CrossDihybrid Cross
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1

32. 32
Summary of Mendel’s lawsSummary of Mendel’s laws
LAWLAW
PARENTPARENT
CROSSCROSS
OFFSPRINGOFFSPRING
DOMINANCEDOMINANCE TT x ttTT x tt
tall x shorttall x short
100% Tt100% Tt
talltall
SEGREGATIONSEGREGATION
Tt x TtTt x Tt
tall x talltall x tall
75% tall75% tall
25% short25% short
INDEPENDENTINDEPENDENT
ASSORTMENTASSORTMENT
RrGg x RrGgRrGg x RrGg
round & greenround & green
xx
round & greenround & green
9/16 round seeds & green pods9/16 round seeds & green pods
3/16 round seeds & yellow3/16 round seeds & yellow
podspods
3/16 wrinkled seeds & green3/16 wrinkled seeds & green
podspods
1/16 wrinkled seeds & yellow1/16 wrinkled seeds & yellow
podspods