1. Heredity Part 1: Genetics
Biology 10.1

3. Gregor Mendel
1800’s Austrian (NOT AUSTRALIAN) monk, mathematician, and scientist
Began working in the garden at his monastery
Father of Genetics
His work led to an understanding of how traits are passed from parents to offspring
The passing of traits from parents to offspring is called heredity
Primarily worked with a variety of garden peas
Noticed several traits that appeared to follow certain patterns of inheritance.

4. Mendel’s Pea Plant Traits

5. Mendel’s Observations
Mendel mated pea plants together until he got plants that were true- breeding
Also known as pure-bred
Organisms that always pass on a certain trait
Ex. Purple plant that always has purple offspring
Once he had established 2 true-breeding lines for each trait, he mated them together
For example, true-breeding yellow seed and true-breeding green seeds.
He noticed that all of the offspring looked like one of the parents, but not the other (Ex. All yellow, no green)
Called them hybrids because they got one gene from each parent

6. Generations in Crosses
P=Parental generation
First ones to be crossed
F1=1st Filial generation
Filial=children
F2=2nd Filial generation
Grandchildren

7. Mendel’s Observations continued
He then self-pollinated each of the offspring
He noticed that most looked like the parent, but some did not

8. Mendel’s Hypotheses
He hypothesized that one of the traits was overpowering the other
He called these traits dominant
Because the other trait was not expressed in the first generation, but reappeared in the second, he hypothesized that the trait was still there, but was being overpowered by the dominant trait
He called these traits recessive

9. Example of Mendel’s Experiment-Yellow and Green seeds
Mendel developed a true-breeding line of plants with yellow seeds and a true-breeding line of plants with green seeds.
He took one yellow-seeded plant and one green-seeded plant and mated them together.
All of the offspring had yellow seeds
He then took each of these yellow-seeded plants, and self- pollinated them
¾ of the offspring had yellow seeds and ¼ of them had green seeds.
He concluded that Yellow was dominant and green was recessive

10. Results of Mendel’s Experiment
Mendel’s experiments continually showed that ¾ of the plants showed the dominant trait, and ¼ showed the recessive trait
3:1 ratio

11. Mendel’s Laws of Inheritance
Law of Segregation
For any particular trait, the pair of alleles from each parent separate and only one allele passes from each parent to an offspring
Recall that we have 23 pairs of chromosomes (one set from mom and one set from dad)
During meiosis, one of these are sorted into each gamete (sex cell)
Which one winds up in each is random.
Law of Independent Assortment
Different pairs of alleles for one trait are passed to offspring independently of alleles for other traits
Most traits are not linked in any way. You could get your mom’s blue eyes without getting her blonde hair, height, etc.

12. Mendel’s Principle of Dominance
Alleles can be dominant or recessive
Dominant alleles mask, or cover up, recessive alleles
Recessive alleles can only be expressed if the offspring receives 2 of the recessive alleles
Any time a dominant allele is present, it will be expressed

13. Symbols for alleles
Dominant alleles are represented by capital letters
Example: A, B, C, D
Recessive alleles are represented by lowercase letters
Example: a, b, c, d
The gene is represented by a single letter, and dominant and recessive alleles of the gene are shown by whether they are capital or lowercase

14. You try it: Indicate whether the following are dominant or recessiveP E e

15. You try it: Indicate whether the following are dominant or recessive
T-dominant
d-recessive
P-dominant
E-dominant
e-recessive

16. Homozygous vs Heterozygous
Recall that organisms get 2 alleles-1 from each parent
Homozygous-2 of the same alleles for a trait
“Homo” means same
Example: TT or tt
Can be homozygous dominant (TT) or homozygous recessive (tt)
Heterozygous- 2 different alleles for a trait
“Hetero” means different
Example: Tt or tT
Note: The latter is rarely used, but will sometimes be the result in a Punnett Square

17. You Try It: Indicate whether the following are heterozygous, homozygous dominant, or homozygous recessive. TT Tt tT tt

18. You Try It: Indicate whether the following are heterozygous, homozygous dominant, or homozygous recessive.
TT-homozygous dominant
Tt-heterozygous
tT-heterozygous
Tt-homozygous recessive

19. Punnett Squares Tool to predict results of a cross (mating)
Usually a 2x2 grid
Can be larger if including more traits
Couple different types
Monohybrid cross (one trait)
Dihybrid cross (2 traits)
Trihybrid cross (3 traits)-Gets too time consuming for this class
And more that are too complicated to be done by hand and are instead done using computers

21. Punnett Squares Show Probability
Not actuality
Coin flip
If you flip a coin, what is the chance that it comes up heads?
50%
If you flip it again, what is the chance it will come up heads a second time?
And so on
If there is a 1 in 4 chance that your offspring will have blue eyes, and you have 3 children with brown eyes, will the 4th for certain have blue eyes?

22. Using Punnett Squares Draw example
Begin by drawing a 2x2 grid
Place one parent’s alleles on top
Place the other parent’s alleles on the left side
Bring ones on the top down
Bring one on the left across A A a A a A a a A a A a

23. Practice Problem
A pea plant with genotype Rr is mated with a pea plant with genotype rr. What genotypes could the offspring have?

24. R r r R r r r r R r r r Practice Problem Begin by drawing a 2x2 grid
Place one parent’s alleles on top
Place the other parent’s alleles on the left side
Bring ones on the top down
Bring one on the left across R r r R r r r r R r r r

25. Genotype and Phenotype
Genotype-The genes (alleles) that an organism has
Geno=Gene
Example: Aa, BB, cc
Phenotype-The expression (appearance) of the genotype
Ph-Physical
Example: Green eyes, brown hair, tall

26. You try it: Indicate whether the following are genotypes or phenotypes.Aa
Blue eyes
Rolling tongue TT

27. You try it: Indicate whether the following are genotypes or phenotypes.
Aa-genotype
Blue eyes-phenotype
Rolling tongue-phenotype
TT-genotype

28. Principles of heredity
Traits are controlled by alleles (different versions of a gene) on a chromosome
An allele can be dominant or recessive
When a pair of chromosomes separate during meiosis, the different alleles for a trait move into different gametes

29. Practice Problem #1
A person with brown eyes (BB) has a child with a person with blue eyes (bb). What is the chance that the child will have blue eyes?

30. Practice problem #2
2 people with brown hair (BB) have a child. What is the chance that they will have a child with brown hair?

31. Practice Problem #3
A heterozygous brown dog mates with a homozygous recessive white dog. What is the chance that their puppies will be white?

32. Practice Problem #4
Tongue-rolling is a dominant trait. If two people heterozygous for tongue-rolling have a child, what is the chance that it will not be able to roll its tongue.

33. Practice Problem #5
Red hair is recessive to all other hair colors. Can 2 people with brown hair have a child with red hair?

34. Dihybrid Crosses Deals with 2 traits Little bit more complicated
Looking at 2 genes, so 4 possible alleles
Little bit more complicated
Punnett Square will be 4x4
16 possible offspring combinations
Principle of Dominance is still followed
F1 generation will still show dominant phenotype
F2 generation will have a ratio of 9:3:3:1

35. How to set up Punnett Square
One allele from each trait will join with one for the other trait, and will give 4 allele combinations
EX: AaBb  AB, Ab, aB, ab
Do for both parents
Draw a 4x4 grid
Place alleles for one parent on top, the other on the side
Solve like other Punnett Square, only make sure to bring both alleles down and across

36. Example of Dihybrid Cross
If you cross a pea plant with genotype Rryy and one with rrYY, what are the possible genotypes of the offspring?
1st plant allele combinations: Ry, Ry, ry, ry
2nd plant allele combinations: rY, rY, rY, rY
Draw 4x4 grid
One parent’s alleles on top, the other on the left side

38. You try it! Tall is dominant to short and Wide is dominant to narrow
If you crossed 2 heterozygotes, what number of the offspring would display each of the phenotypes?
Tall wide: _________________
Tall narrow: _______________
Short wide: _______________
Short narrow: _____________