1. Jim Twins

2. Mendelian Genetics
Integrated Biology

3. What is genetics? What is heredity?
Science of heredity and the mechanisms by which traits are passed from parent to offspring.
The passing on of characteristics from parent to offspring.
Inherited characteristics = “traits”
What is heredity?

4. Who was Gregor Mendel? Monk Studied mathematics, taught science
early on in life
Tended the gardens (at monastery in
Austria)
Observed growth of plants 
garden peas, Pisum sativum
1st to predict how traits were transferred from one generation to another
Father of Modern Genetics

5. Why pea plants?
1. 7 easy traits to study – could examine one variable at a time

6. Why pea plants? 2. Grows many generations in a short period of time
3. Lots of offspring are produced in a short period of time

7. Why pea plants? 4. Reproduce sexually
Similar to other organisms (i.e. humans)
Male and female parts in every flower
Plant sperm = pollen ; eggs = contained in ovary

9. Why pea plants? 5. Can control mating 
self – pollination / fertilization or
cross pollination
Self = flower fertilizes itself
Cross = flower fertilized by another flower
Mendel hand-pollinated flowers w/a
paintbrush
He snipped the stamens (contain pollen) to
stop self-pollination

10. Mendel’s Conclusions: Rule of Unit Factors
Each organisms has 2 factors that control its trait
Review  different forms of genes = alleles
Ex: height (short vs. tall)

11. Mendel’s Conclusions: Law of Segregation
“Factors “ (genes) that occur in homologous pairs are separated during gamete formation and recombined at fertilization
Alleles segregate separately!

12. Mendel’s Conclusions: Law of Dominance
One allele (letter) is dominant over another
observed trait
A dominant trait will overpower a recessive trait

13. Mendel’s Conclusions: Law of Independent Assortment
Genes for different traits (i.e. hair color, eye color) are inherited independently of each other
Don’t influence each other’s inheritance
Example 
P1: Round Yellow x Wrinkled Green
F1: all Round Yellow
F2: 9 Round Yellow, 3 Round Green,
3 Wrinkled Yellow, 1 Wrinkled Green

14. Which law? Which law is proven by the following examples:
Alleles R and r separate
Alleles Rr and Yy separate

15. Chromosomes, Genes, Alleles
Chromosome  rodlike structures in cells that contain hereditary information
Genes  distinct unit of hereditary information found on a chromosome
Alleles  alternate form of a gene (one from mom, one from dad)
i.e. gene = height  allele: T, for tallness ; t, for shortness

16. Alleles : Refresher For height  tall versus short Can have:
2 alleles for tallness
2 alleles for shortness
1 allele for tallness, 1 allele for shortness
** located on different chromosomes – 1 from mom, 1 from dad **

17. Dominance vs. Recessiveness
DOMINANT  ALWAYS shown if allele is present
One or two uppercase letters (TT, Tt)
RECESSIVE  shown ONLY if both alleles are recessive
2 lowercase letters (tt)
*Mendel’s tall plants (T) are dominate over short plants (t)

18. Recap: Use SAME letters for different alleles (of the same gene)
Uppercase = dominant
Lowercase = recessive
Dominant (capital letter) always written first

19. Genotype vs. Phenotype GENOTYPE  Genetic makeup ; Allele comb.
what the actual genes are
ex: TT , Tt, or tt
PHENOTYPE  Physical appearance ;
what is actually shown/seen
ex: tall, short
* results from genotype *

20. Homozygous vs. Heterozygous
HOMOZYGOUS  Both alleles are the SAME
(TT, tt) aka: purebred
*can either be homozygous dominant or homozygous recessive
HETEROZYGOUS  alleles are DIFFER.
(Tt) aka: hybrid

21. Let’s try it!
When a pea plant is homozygous for tallness, what would its genotype be?
When a pea plant is homozygous for shortness, what would its genotype be?
When a pea plant is heterozygous, what would its genotype be?

22. Genotypic ratio vs. Phenotypic ratio
Genotypic ratio- the ratio of the genotypes that appear in an offspring.
What is the genotypic ratio in this Punnett Square?
Phenotypic ratio- the ratio of phenotypes produced by the cross.
What is the phenotypic ratio in this Punnett Square?

23. Genotype/Phenotype Homozygous/Heterozygous WORKSHEET

24. Punnett Squares
Short hand way to find expected proportions of possible genotypes (and phenotypes) in offspring of a cross
Monohybrid  1 allele considered in cross
Dihybrid  2 alleles considered in cross

25. Probability Method of calculating the expected outcome of an event
Just like in math!
Can be expressed as  decimal, percentage, fraction, or ratio
Probability = Number of times an event is expected to happen
Number of times an event could happen
The results predicted by probability are MORE likely to occur when there are MANY trials

26. Probability Chosen outcome / all possible outcomes 1/6
Fraction  1 / 6
Ratio  1 : 5 ( 1 to 5 )
Percentage  16.7%

27. Mendel’s Monohybrid Crosses
Crossed tall pea plants with short pea plants
Mono = one ; hybrid = differ by a single trait
Only one allele will be seen
Mendel did monohybrid crosses with all 7 pairs of traits
Yielded the same results in each cross!
What was the result??

28. Mendel’s Cross: Parents F1 = filial  “daughter, son” of parents
F2 = filial  “daughter, son” of first generation
CLUE:
Your parents = P1
You = F1
Your children = F2

29. Mendel’s Cross: Parents : TALL x SHORT F1: TALL
Cross-pollination
F1: TALL
Self-pollination
F2: (3) TALL : (1) SHORT
Parents : PURPLE x WHITE
Cross-pollination
F1: PURPLE
Self-pollination
F2: (3) PURPLE: (1) WHITE

30. Mendel’s Cross: 1 trait always disappeared in the F1 generation
RESULT 
1 trait always disappeared in the
F1 generation
But, that trait always reappeared in the F2 generation
In the ratio of 1 : 4 ( ¼ , 25% )

31. Mendel’s Monohybrid Crosses:

32. Baby Steps to Creating a Punnett Square
Determine the genotype of the parent organisms
Write down your “cross” (mating)
Draw a “p” square known as a Punnett Square
“split” the letters of the genotype for each parent and put them outside the “p” square
Determine the possible genotypes of the offspring by filling in the “p”-square
Summarize the results (Genotypes and phenotypes of the offspring)
Write on your paper how awesome your teacher is 

33. Monohybrid Cross Homozygous x Homozygous Homozygous x Homozygous

34. Monohybrid Crosses Homozygous x Heterozygous
Half of the offspring would be homozygous dominant
Half of the offspring would be heterozygous dominant
What would a Punnett Square for this cross look like?

35. Monohybrid Crosses Heterozygous x Heterozygous
The genotypic ratio would be:
The phenotypic ratio would be:

36. Dihybrid Crosses Homozygous x Homozygous

37. Dihybrid Crosses Heterozygous x Heterozygous

38. Review Questions: What is genetics? Heredity??
Why did Mendel use pea plants?
Differentiate between self-pollination and cross-pollination
AKA purebred? AKA hybrid?
The “F” in F1 and F2 refers to what?
What observation did Mendel make for all monohybrid crosses?
What does the rule of unit factors state? Rule of dominance?
What is an allele?
Differentiate between dominant and recessive.
Differentiate between genotype and phenotype.
Differentiate between homozygous and heterozygous.
What does the law of segregation state? Law of independent assortment?
Define probability and state the various ways it can be expressed.