1. Introduction to Mendelian Genetics
Chapter
Introduction to Mendelian Genetics

2. Introduction to Genetics
11-1 Work of
Gregor Mendel
11-2 Probability &
Punnett Squares
Introduction to Genetics
11-3 Exploring
Mendelian Genetics
11-3 Exceptions to
Mendelian Genetics

3. Genetics Vocabulary Seed shape, seed color, plant height
Genetics – the study of passing on of genes from parent to offspring
Gene = part of DNA coding for trait
Trait = Characteristic
Seed shape, seed color, plant height
Allele = alternate forms of a gene
Eye color: blue, green, brown, hazel, etc.
Trait/ Gene
Allele
Seed Shape
Round
Wrinkled
Seed Color
Yellow
Green
Plant Height
Tall
Short

4. Gregor Mendel & Pea Plants
7 traits each with 2 contrasting alleles
seed shape, seed color, plant height, pod color, pod shape, seed coat color, flower position
Self-pollination (also known as true-breeding) vs. Cross-pollination (also known as selective breeding)

5. Mendel’s 1st experiment
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.

6. Mendel’s 1st Conclusion
Law of Dominance
Dominant allele v. Recessive allele
Capital letter = dominant (ex: tall= T)
Lowercase letter = recessive (ex: small= t)
Each individual has 2 alleles (homologous)
TT =Tall
Tt = Tall
tt = small
Genotype = gene combination (represented by alphabet letters)
Phenotype = Physical appearance (represented by words)

7. Mendel’s 2nd Experiment
F1 generation x F1 generation
Tall (____) x Tall (____)
2nd Experiment Results

8. Mendel’s 2nd Conclusion
Law of segregation
Alleles separate during gamete formation (meiosis)
Homologous chromosomes separate!! (phase?)
Review
Tall (____) x Tall (____)
Phenotype:
3 tall & 1 short

9. Genetic Terminology Alleles in pair alike Alleles inherited
Genotype: Gene make-up
Alleles inherited
Ex: Height:
Phenotype: Physical appearance
TT=
Tt=
tt=
Homozygous = Purebred
Alleles in pair alike
Homozygous Dominant
Ex: Height
Genotype= TT
Phenotype= Tall
Homozygous Recessive
Genotype= tt
Phenotype= small
Heterozygous = Hybrid
Alleles in pair different
Genotype= Tt
Phenotype=Tall
TT, Tt, tt
Tall
Tall
Short

10. Predicting Monohybrid Crosses: Height
Gametes
Punnett Square = diagram to predict offspring
Larger # offspring closer to expected
Monohybrid cross = cross of one trait
Homozygous Dominant x Homozygous Recessive
Step 1: determine parents
Height TT x tt
Step 2: Put parents on punnett square
Step 3: Predict
Step 4: Genotypic & Phenotypic ratios
Genotypic- 0 TT:4 Tt: 0 tt
Phenotypic- 4 Tall: 0 Short t T t T
T t

11. Punnett Monohybrid Cross: Height
Homozygous Dominant x Heterozygous
Step 1: ID parents
Step 2: add parents to Punnett
Step 3: Predict
Step 4: Genotypic & Phenotypic ratios
Genotypic ratio = ____________
Phenotypic ratio = ____________
Homozygous recessive x Heterozygous
Genotypic ratio = _______________
Phenotypic ratio = ______________

12. Punnett Monohybrid Cross
Heterozygous x Heterozygous
Genotypic ratio = ____________
Phenotypic ratio = ____________
Testcross
Determine unknown genotype of phenotypic dominant trait
Unknown Dominant x recessive OR
Ratios Ratios

13. Punnett Dihybrid Crosses
Cross 2 pairs of contrasting traits
Ex: seed texture & seed color at same time
Hom. Round &Yellow x Hom. Wrinkled & Green
Step 1: determine parents
RRYY x rryy
Step 2: determine possible gametes (* independent assortment)
RRYY RY, RY, RY, RY
rryy ry, ry, ry, ry
Step 3: Set-up Punnett Square
Step 4: Predict
Step 5: Phenotypic ratios

14. Dihybrid Cross Punnett Square
Phenotypic Ratios
Round Yellow =16
Round Green = 0
Wrinkled Yellow=0
Wrinkled Green=0
Ratio 16:0:0:0 RY ry
RrYy

15. Dihybrid Cross Phenotypic Ratio: Heterozygous x Heterozygous
Round Yellow=
Round Green=
Wrinkled Yellow=
Wrinkled Green=
Ratio:
WHY & HOW?
Heterozygous x Heterozygous

16. Mendel’s 3rd Conclusion
Law of independent assortment
Alleles on separate chromosomes separate independently of each other during meiosis
AKA homologous chromosomes separate independently of each other (phase?)
Accounts for genetic variation!!
Review of possible gametes in dihybrid cross
RRYY RY, RY, RY, RY
rryy ry, ry, ry, ry
Due to Law of
Independent assortment

17. Mendel Summary Traits determined by genes & are passed on
Most sexually reproducing adults have 2 copies of each gene (AKA 2 alleles) one from each parent
Law of Dominance vs Recessive
Law of Segregation
Law of Independent Assortment

18. Artificial Selection
Selective Breeding – known as artificial selection, people select the traits they want to have passed on.
Inbreeding – can cause genetic defects because the DNA is too similar to each other.
Hybridization – A mix of two
different traits