1. Genetics
November 28, 2018

2. I. Important Genetics Vocabulary
Heredity: the passing on of characteristics from parents to offspring
Example: eye color
Trait: characteristic that is inherited
Example: blue, brown, green eyes, etc.

3. Gene: A region of DNA that controls a hereditary characteristic
Let’s do an example:
Let’s take the gene for hair color
How many different genes are present in this room?
Alleles: Different forms of genes
For the gene for hair color how many different alleles do each of you have? 2

4. Phenotype: the way an organism looks physically
Genotype: the gene combination an organism has
Homozygous: an organism’s 2 alleles are the same
We call this a purebred
2 capital letters would be homozygous dominant
2 lowercase letters would be homozygous recessive
Problem: You can’t always know an organism’s genotype simply by looking at its phenotype

5. Genotype (cont.)
Heterozygous: An organism’s 2 alleles for a trait are different
These are called hybrids
Homozygous
Heterozygous

6. II. Where did it all begin?
Gregor Mendel ( )
Mendel was an Austrian monk
Used pea plants to study the inheritance of traits

7. Mendel (cont.)
Mendel Animation

8. B. Mendelian Vocab
Mendel looked at plants over generations, so lets give each generation a name…
PARENTAL GENERATION (P1)
These are the first two pea plants crossed.
Pea plants can SELF FERTILIZE so sometimes both parents are the SAME plant!

9. Mendelian Vocab (cont.)
The offspring of the parental generation are called the F1 generation
If we then cross plants from the F1 generation, we get an F2 generation and so on… F1 P

10. C. Mendel’s Experiment
Mendel took two pea plants that were identical in every way except for their height, one was short and one was tall.
What is this generation called? P1

11. He cross pollinated them and took a look at their offspring.

12. When he planted the seeds from the cross pollination the plants that were produced were all tall.
As you recall, this was his F1 generation

13. Next, Mendel allowed the tall plants in the F1 generation to self pollinate. He then planted these seeds and grew 1000 plants.
Mendel found in this F2 generation that ¾ of the plants grew tall and ¼ were short.

14. 6. Why was this a big discovery for Mendel?
1 trait of a pair seemed to disappear in the F1 generation, only to reappear unchanged in ¼ of the F2 plants.

15. d. Mendel’s Conclusions
Gregor Mendel didn’t know much if anything about DNA or what it was, and he didn’t even know how much you know…so what was Mendel’s big conclusion after seeing his offspring?
He figured out that each organism must have 2 factors that control each of its traits.

16. III. Mendel’s Laws
Law of Dominance: In a heterozygous individual, the dominant allele will be expressed and the recessive allele will be hidden
Law of Segregation: During meiosis, homologous pairs are separated and each gamete only receives one allele
Law of Independent Assortment: During meiosis, homologous pairs separate RANDOMLY and INDEPENDENTLY of each other

17. IV. The Rule of Dominance
In Mendel’s F1 offspring plants, there were only tall plants even though one of the parents was a short plant.
1 of the alleles is dominant over the other.

18. The observed trait is dominant and the trait that disappeared is recessive.
In Mendel’s example which is the dominant trait and which is the recessive trait?
The allele for tallness is dominant
The allele for shortness is recessive

19. What does it mean to be Dominant or Recessive?

20. How many of you have 6 fingers on each hand?
6 fingers are dominant

21. How many of you have a widow’s peak?
Widow’s peak is dominant

22. How many of you have attached ear lobes?
Attached earlobes are recessive

23. How many of you have the ability to roll your tongue?
Rolling your tongue is dominant

24. How many of you have a straight thumb?
Straight thumb is recessive

25. How many of you have blue eyes?
Blue eyes are recessive

26. How many of you can taste PTC paper?
PTC tasting is dominant

27. How many of you have freckles?
Having freckles are dominant

28. How many of you have a cleft chin?
Having a cleft chin is recessive

29. How many of you have a second toe longer than your big toe?
Having a longer second toe is dominant

30. Which way do your thumbs cross each other when you are clasping your hands together?
Left thumb on top is dominant

31. How many of you have an immunity to poison ivy?
Poison ivy immunity is dominant

32. The Rule of Dominance (cont.)
We label or designate alleles with letters.
For example, a letter T for the trait of height
An uppercase letter is used for the dominant allele (T for tall)
A lowercase letter is used for the recessive allele (t for short)

33. Using the letter T what can you say about the possible alleles that the following people have on the genes on their chromosomes?

34. V. Mendel’s Law of Segregation
Mendel’s law of segregation explains the results of his cross between F1 tall plants. He concluded that the 2 alleles for each trait must separate when sex cells are formed. A parent, therefore, passes on at random only one allele for each trait to each offspring.
When does this happen in Meiosis?
Meiosis I (Metaphase I)

35. Meiosis Review How many chromosomes do we have in our cells?
How many came from Mom?
How many from Dad?
How many alleles for hair color did you receive from your mother?
How many alleles for hair color did you receive from your father?
If you have 2 alleles for hair color how come half of my head isn’t blonde and half isn’t brown?

37. Let’s revisit Meiosis again
What happens in Metaphase 1
The law of independent assortment
Genes for different traits (for example seed shape and seed color) are inherited independently of each other.
In our class example we used hair color
We saw depending on how homologous pairs randomly lined up with each other that you could tons of different combinations.

38. VI. Punnett Squares
In 1905, Reginald Punnett, an English biologist, devised a way of finding the expected proportions of possible genotypes in the offspring of a cross.
If you know the genotypes of the parents, you can use a Punnett square to predict the possible genotypes of their offspring.

39. t t T T t T t T t T t C. Monohybrid Cross
Let’s consider Mendel’s first monohybrid cross between his pure-breeding Tall plants and his pure-breeding short plants. (P1  F1)
Each letter (allele) separates into a possible gamete (sex cell).
t t T
T t
T t
T t
T t

40. 3. Mendel’s Second Monohybrid Cross
Now let’s look at Mendel’s second monohybrid cross between his heterozygous F1 generation self-pollinating themselves. (F1  F2)
T t T t
T T
T t
T t
t t

41. D. Probability
Punnett squares show all of the possible combinations of gametes and the likelihood that each will occur.
In reality, however, you don’t get the exact ratio of results shown in the square. That’s because genetics is like flipping a coin, meiosis leaves it up to chance.
After completing a Punnett square you are able to calculate the probabilities of what offspring will be produced.