1. Observable Patterns of Inheritance
Mendelian Genetics & Monohybrid Crosses

3. Mendel’s First Experiment
He crossbred pure tall and pure short plants. These plants were called the parental generation (P).
This experiment is called a monohybrid cross because it focuses on only one inherited characteristic.
 Mendel's Hypothesis: Mendel expected to see offspring plants of medium height.

4. Mendel’s First Experiment
The hybrid offspring from P were called first filial generation (F1)‏
Mendel's Observations: all of the offspring were tall
 Mendel's Conclusion:
dominant trait = tallness,
recessive trait = shortness,
the recessive trait is not expressed in first generation

5. Principle of Dominance
When an organism is hybrid (cross bred) for a pair of contrasting traits, it shows only the dominant trait.

6. Mendel’s Second Experiment
Mendel allowed the F1 plants to mature and self-pollinate. Their offspring were called the second filial generation (F2).
Mendel's Observations:
¾ of the plants were tall,
¼ of the plants were short

7. Mendel’s Second Experiment
Mendel's Conclusion:
offspring inherit two “factors” for each characteristic (e.g. height), one from each parent,
the F1 DID inherit contrasting factors only the dominant factor is expressed

8. Principle of Segregation
Hereditary characteristics are determined by distinct factors (genes) that occur in pairs.
These paired factors segregate from one another and are distributed into different sex cells.
Each sex cell has an equal probability of possessing either of the pair.

9. Tracking Generations Parental generation P mates to produce
First-generation offspring F1
mate to produce
Second-generation offspring F2

10. Genes Units of information about specific traits
Passed from parents to offspring
Each has a specific location (locus) on a chromosome

11. Alleles Different molecular forms of a gene Arise by mutation
Dominant allele masks a recessive allele that is paired with it

12. Allele Combinations Homozygous having two identical alleles at a locus
AA or aa
Heterozygous
having two different alleles at a locus Aa

13. Genotype & Phenotype
Genotype refers to particular genes an individual carries
Phenotype refers to an individual’s observable traits
Cannot always determine genotype by observing phenotype

14. Impact of Mendel’s Work
Mendel presented his results in 1865 to a small Austrian audience
Paper received little notice
Mendel discontinued his experiments in 1871
Paper rediscovered in 1900 and finally appreciated

15. Mendel’s work applied today MONOHYBRID CROSSES
Monohybrid crosses are used to determine the probability of certain genetics outcomes in offspring.
Mendel is famous for his discovery that there are 2 factors for each trait called alleles.
Genes can be dominant or recessive 15

16. 4 Expectations for Genetic Problems
After reading the problem, determine the genotype of the parents
Indicate the different possible gametes
Show possible combinations using a punnett square and state the genotypic and phenotypic ratios
Answer the questions in sentence form 16

17. Capital letters represent the dominant trait
Rules for Crosses
Capital letters represent the dominant trait
Small letters represent the recessive trait
Usually the first letter of the allele is used (ie. T (tall) 17

18. Let’s Practice: Monohybrid Cross problems
1) a) Mendel crossed a purebred tall (TT) plant with a purebred dwarf (tt) plant. What are the possible genotypes for this cross?   F1 P1 P2
Genotype
Phenotype
Possible Gametes 18

19. b) If two F1 plants are crossed, what is the probability of having a dwarf plant?19

20. 2) In humans, the allele A, for pigment formation is dominant to the allele a, for inability to form pigment. aa individuals are albino. Determine the expected genotypic and phenotypic ratios expected from a cross between two individuals heterozygous for this trait. F1 20

21. 3). Some people are PTC tasters (T) and some are non-tasters (t)
3) Some people are PTC tasters (T) and some are non-tasters (t). What is the probability of a grandchild being a non-taster if his paternal grandfather is a homozygous dominant taster, his paternal grandmother is a non-taster and his mother a non-taster?
Start with the known info:
paternal grandfather = TT (taster)
paternal grandmother = tt (non-taster)
Father =
Mother = tt (non-taster) P1 P2
Geno tt
Pheno
non-taster
Gametes t F1 21