1. Unit 3
Genetics

2. What is Genetics? Genetics is the study of heredity.
Heredity is how traits are passed down from generation to generation.
Gregor Mendel
“Father of Genetics”.
He studied the way characteristics are passed on in pea plants in the 1800’s.

3. Mendel’s Discovery
Mendel discovered that a pea plant’s characteristics such as height, seed color and pod color are determined by an inheritance factor. He observed 14 different characteristics
These inheritance factors where later called genes. Genes are a unit of heredity. They contain the instructions for a trait.
A trait is a characteristic (color, height) coded for by two or more genes.

4. Fourteen Traits of Pea Plants:
Flower Color
Pink Flower
White Flower
Seed Color
Yellow Seed
Green Seed
Seed Shape
Round Seed
Wrinkled Seed
Pod Color
Green Pod
Yellow Pod
Pod Shape
Smooth Pod
Wrinkled Pod
Flower Position
Along Stem
At the Tip
Plant Size
Tall Plant
Short Plant

5. Types of Genes Allele: 2 forms of a gene Dominant:
The gene that covers up the effect of the other one.
Use a capital letter. Example “T” or “G”
Recessive:
The effect of the gene is hidden (unless two are present).
Use a lower case letter. Example “t” or “g”

6. Mendel developed true breeding plants for each trait because true bred plants always gave the same results every time.
PURE
PURE
PURE
He found when breeding different pure forms of the same trait that one trait would always show up while the other one did not. It was for this reason that he labeled the trait that always showed up in these crosses DOMINANT and the trait that did not show up RECESSIVE
RECESSIVE
PURE
DOMINANT
PURE
All
Dominant
But NOT
PURE

7. He tested many characteristics and found that this was true for all of the traits. They had a dominant trait and a recessive trait.
He did his experiment again using the offspring from the first cross. His results were very strange. From two parents showing the dominant trait, he got offspring that showed the recessive trait.
WEIRD
Not Pure
Not Pure
????
Offspring from the Pink and White Cross
This proved that the parents and offspring have 2 genes for each trait. How else could the parents have offspring that showed different traits than the parents.

8. Females are listed by XX.
DNA makes up genes. Genes make up chromosomes.
DNA
GENES
Chromosomes
There are 23 pairs (46 total) chromosomes in each non-sex cell for humans. 23 chromosomes in sex cells.
Females are listed by XX.
Males are listed by XY.
Genetic disorders:
Tay-Sachs: Caused by a gene mutation on chromosome 15
Down Syndrome: An extra copy of chromosome 21 is present.
Look up other genetic disorders.

9. Describing Traits
Traits are ways to describe living things.
We are going to focus on human traits during genetics.
Traits that we may discuss include: hair color, eye color, blood type.
Phenotype: What the organism looks like. Its Physical makeup. Examples : Tall, Short, round or wrinkled
Genotype: The genetic make-up of a trait. What 2-letter gene combination it is made from.
Examples TT, Tt, tt

10. Cross Pure Tall with Pure Short
Punnett Square: Determine the probability that offspring will or will not have a given trait.
Pure Tall plant ( T T ) crossed with a Pure Short Plant ( t t )
Each parent can give one trait gene to the offspring so each offspring will get half their trait genes from each parents. The chances of any parent giving a particular trait gene are random. We always start off with what we know in a KEY:
Then we show the cross:
Key:
T- Tall Plant
t – Short Plant
Cross Pure Tall with Pure Short
T T X t t
The Pure Short parent can give a t or a t
The Pure Tall parent can give a T or a T.
We put these on a grid and see what possible outcomes we can get…

11. T T X t t t t t t t t T T T T T T T The Phenotype of the offspring is:
One parent goes on the top of the box and the other goes on the side
T T
T T X t t t T t T t
You fill in the squares with the appropriate letter
The possible offspring will appear in the boxes
By looking at these results, you can see that the offspring will all be Tall but not Pure Tall.
They are all mixed. This is called Hybrid. T t T t
The Phenotype of the offspring is:
100 % TALL
The Genotype of the offspring is:
100% mixed… We call this Hybrid T t

12. Describing Genes
When we write genes we use one letter (G or g, T or t, etc.)
Traits or characteristics are determined by one or more pair of genes.
Half of your genes come from your mother and half of your genes come from your father.
Purebred or Homozygous : Both genes are the same.
Example: TT or tt are BOTH Homozygous. It doesn’t matter if they are dominant or recessive…just that they are the same.
Hybrid or Heterozygous : Both genes are different.
Example Tt is Heterozygous. Heterozygous offspring always show the dominant trait.

13. Punnett Squares practice
We looked at green seeds and yellow seeds. If both plants are homozygous, what are their genotypes?
Key: G – Green seeds
g – Yellow seed
Plant 1 (green) = GG
Plant 2 (yellow) = gg
Identify the genes that are present in each plants’ sex cells. GG gg G G g g

14. We are now going to determine the possible genotypes and
We are now going to determine the possible genotypes and phenotypes of the offspring using a Punnett Square.
GG x gg
Genotype g g
gg =
0/4 = 0%
Gg =
4/4 = 100% Gg Gg G
GG =
0/4 = 0%
Phenotype Gg Gg G
Green =
4/4 = 100%
Yellow =
0/4 = 0%

15. GG Gg Gg gg G g G g Parents = Gg X Gg
Determine the genotype and phenotype probabilities for a cross between two heterozygous plants from the previous problem.
Parents = Gg X Gg
Genotype G g
gg =
1/4 = 25%
Gg =
2/4 = 50% GG Gg G
GG =
1/4 = 25%
Phenotype
Green =
3/4 = 75% Gg gg
Yellow =
1/4 = 25% g

16. When you look closely at it, there are only six crosses that deal with two alleles. They are: (using G and g as example traits)
GG x GG Pure Dominant x Pure Dominant
GG x Gg Pure Dominant x Hybrid
GG x gg Pure Dominant x Pure Recessive
Gg x Gg Hybrid x Hybrid
Gg x gg Hybrid x Pure Recessive
gg x gg Pure Recessive x Pure Recessive
If you can memorize these six crosses and their phenotype and genotype ratios, you will never see a genetics problem you can’t solve.
Also remember that anything crossed with a Pure Recessive is a Test Cross. It is a control to show what recessive traits you may have.

17. Practice Problem
Mendel also studied the heights of pea plants during his experiments.
He determined that tall pea plants were dominant over short pea plants.
Step 1: Create a key. Pick a letter to represent genes.
Dominant = Tall (T)
Recessive = short (t)
Use the key to help you answer the following questions:
1. Determine the phenotype of a plant that is Tt.
2. Determine the genotype of a homozygous small plant.
3. Would a heterozygous plant show the dominant or recessive trait?

18. Dominant = Tall (T) Recessive = short (t)
Determine the phenotype of a plant that is Tt.
Phenotype means what it looks like. It will be tall because it has one dominant gene (T).
2. Determine the genotype of a homozygous small plant.
Genotype means genetic make-up. Homozygous means the same and small is recessive (small letter).The answer is tt.
3. Would a heterozygous plant show the dominant or recessive trait?
Heterozygous means different. (Tt) The answer is dominant because there is at least one big T. To show recessive you have to have two small t’s.

19. Vocabulary Practice Problems
1. Brown hair is dominant over blonde.
A. Create a key for the traits.
B. What would the genotype for a blonde be?
C. What would the phenotype be for a person that is
heterozygous?
2. Freckles is dominant over non-freckles. Mom is purebred for freckles. Dad is heterozygous for freckles.
B. Determine the genotypes for Mom and Dad.
C. Could any of their children NOT have freckles? Explain your answer.

20. Maybe Baby Directions 1. Determine baby’s gender:
Female: XX Male: XY
Dad determines gender by flipping a coin:
Heads: X Tails: Y
2. Name the child. (Use father’s last name)
3. Determine genes for the child
Each partner flips a coin.
Heads: 1st allele (A or L1) Tails: 2nd allele (a or L2)
Circle all your results on data sheet
You must flip the coin multiple times when there is more than one letter for a trait!!! Ex. Eye and hair color
Three different letters means you flip three times!!!!!

21. Maybe Baby Directions
4. You now have to record the genotypes and phenotypes for the alleles you determined yesterday.
Make sure you read carefully. Not all traits are going to be seen. Put NA in the genotype and phenotype box if that trait is not visible for your child.
5. Get your data sheet signed by the teacher after you sketch the characteristics.
6. Begin drawing your child as a teenager. USE PENCIL!!!! You need to draw front view and side view of your child. Your drawing must include:
Your child’s name on the front.
All 30 characteristics between the two drawings.
Your name and your partner’s name on the back.
Star your name on the back!!!!

22. 1A. Key: B = brown = dominant
b = blonde = recessive
1B. Blonde is recessive. “bb”
1C. Heterozygous means different.
Phenotype means what it looks like.
“Brown hair”
2A. Key: F = freckles = dominant
f = non-freckles = recessive
2B. Mom = FF Dad = Ff
2C. There is no possibility that any of their children could not have freckles. Mom has two big F genes, which means she will always give her children a F. Therefore all of the children will have freckles. You need two little f’s for non-freckles.

23. Pedigree Chart
Follows the passing of a trait from generation to generation. Looks like a family tree.
= male
= female
Shaded shape means that the recessive trait is expressed.
Half shaded shape means that they are a carrier of the trait.
Carriers have one gene but do not express or show the trait.

24. marriage Generation 1 parents Generation 2 children
Oldest child to the left
Youngest child to the right
Number of rows = number of generations
Count from the top to the bottom

25. Normal skin is dominant over albino skin.
How many males?
How many females?
How many generations?
How many marriages? 5 1 2 6 3 4 5 8 10 9 7 11 6 Nn 4 Nn 3 Nn N_ Nn nn
Normal skin is dominant over albino skin.
Key:
Normal = N = dominant
Albino = n = recessive
Recessive trait is colored in! Nn nn nn N_ nn

26. Page 6 in Packet N = normal vision = dominant
n = nearsighted = recessive
Shaded = recessive trait 1 2 nn N _ 4 3 N n nn 9 8 6 7 5 nn nn N n nn N n 11 12 10
Page 6 in Packet nn N n N n

27. Green seeds are dominant over yellow seeds
Green seeds are dominant over yellow seeds. A homozygous recessive plant (1) is mated with a homozygous dominant plant (2).
Make a key.
Determine the genotypes of the two plants.
Determine the phenotype of the two plants.
Could their offspring have yellow seeds? Explain.
What is a trait?
How many chromosomes do human sex cells have?

28. More Pedigree Practice
Dimples are dominant over non-dimples
Shaded areas represent the recessive trait.
Make a key!
How many males?
How many females?
How many generations?
How many marriages?
How many children did the parents in the first generation have?
How many males have dimples?
How many females do not have dimples?

29. 2 1 15 14 13 9 7 5 3 4 6 8 10 11 12

30. 2 1 15 14 13 9 7 5 3 4 6 8 10 11 12 Dd dd Dd dd Dd dd Dd Dd dd dd dd
D = dimples = dominant
d = non-dimples = recessive
8 males
7 females
3 generations 2 1 15 14 13 9 7 5 3 4 6 8 10 11 12
3 marriages
3 children
5 males have dimples
4 females don’t have dimples. Dd dd Dd dd Dd dd Dd Dd dd dd dd dd Dd Dd Dd

31. Pedigree Chart Practice
Widow’s peak is dominant over non-widow’s peak
Make a key What is the dominant trait?
Determine genotypes for all. 5. How many males have a widow’s peak?
How many generations are there? 6. How many marriages are shown?

32. I II III IV Key: W= widow’s peak = dominant w = non- peak = recessive
c) 4 generations
d) Having the widow’s peak is dominant.
e) 5 males have a widow’s peak.
f) 4 marriages Ww

33. Vocabulary Quiz
Free (unattached) earlobes are dominant over attached earlobes. Mom is heterozygous and Dad is homozygous recessive. Use this information to answer the questions below.
Make a key.
Determine the genotypes:
Mom = Dad =
Determine the phenotypes:
Is it possible for their children to have attached earlobes? Why or why not?
What is the difference between a gene and a trait?

34. Make a key.
How many marriages are present?
How many generations are shown?
How many males are albino?
How many females are normal?
How many children did 3 and 4 have in the first generation?

35. Genetics Vocabulary Problem
Red flowers are dominant over white flowers. A heterozygous plant (1) is crossed with a homozygous dominant plant (2).
Make a key.
What are the phenotypes of both plants?
What are the genotypes of both plants?
Is it possible for the new plants to have white flowers? Explain.
What is the trait being studied?
Who is Gregor Mendel? Why is he important?

36. Cell Division Mitosis: Occurs in body cells.
One cell divides into two.
Both cells have the same genetic material as the parent cell.
Four chromosomes
Four chromosomes copied
Four chromosomes go into each cell during division
Four chromosomes in each identical cell

37. Cell Division Meiosis: Occurs in sex cells (egg and sperm).
One cell divides into four.
The four daughter cells have ½ the genetic material as the parent cell.
Stage 1:
Stage 2:

38. Pedigree Chart Quiz Questions
Make a key.
Determine the genotypes for each person using your key.
How many males are there?
How many females are there?
How many marriages are present?
How many generations are shown?
How many males are PTC non-tasters?
How many females are PTC tasters?
How many children did 1 and 2 from the first generation have?

39. Tt tt tt Tt T t t t Parents = Tt X tt
Determine the genotype and phenotype probabilities for a cross between a heterozygous plant and a short plant. The trait we are studying is plant height. Tall is dominant over short.
Parents = Tt X tt
T = tall = dominant
t = short = recessive
Genotype T t
TT =
0/4 = 0%
Tt =
2/4 = 50% t Tt tt
tt =
2/4 = 50%
Phenotype
Tall =
2/4 = 50% t tt Tt
Short =
2/4 = 50%

40. Punnett Square Practice Problems
Normal skin pigment is dominant over albino. Show a cross of an albino man with a heterozygous normal woman.
Brown eyes are dominant over blue eyes. Using a Punnett Square, determine the probability that the offspring will be homozygous recessive if both parents are heterozygous dominant.
Determine the genotypes for the individuals in the pedigree chart below. Widow’s peak is dominant over non-peak.
Make a key
Determine genotypes
Determine number of generations
What is the dominant trait?
How many males have peak?
How many marriages?

41. n n Nn N Nn n nn nn 1. Key: N = normal = dominant
n = albino = recessive
Parents: Male = nn Female = Nn n n
Genotype
NN=
0/4 = 0% Nn
Nn =
2/4 = 50% N Nn
nn =
2/4 = 50%
Phenotype
normal =
2/4 = 50% n nn nn
albino =
2/4 = 50%

42. B b Bb B BB b Bb bb 2. Key: B = brown = dominant b = blue = recessive
Parents: Male = Bb Female = Bb B b
Genotype
BB=
1/4 = 25% Bb
Bb =
2/4 = 50% B BB
bb =
1/4 = 25%
Phenotype
brown =
3/4 = 75% b Bb bb
blue =
1/4 = 25%

43. Parent cross = ________ x ________ Genotype
_____ = _______ = _____ %
______
______
Phenotype
_______ = _______ = _____ %
______

44. Red flowers is dominant over white flowers.
A plant (1) is homozygous dominant is crossed with a heterozygous plant (2). Use a Punnett Square to determine the probability that the offspring will be white.
Use a Punnett Square to determine the probability the offspring will be white if two heterozygous plants were crossed.
A homozygous dominant plant (3) is crossed with a homozygous recessive plant (4). Determine the probability the offspring will be red using a Punnett Square.

45. Tall is dominant over short. Recessive trait is shaded. 19 13 14 15 16 2 4 3 5 6 7 8 10 11 12
Make a key How many males are tall?
Determine the genotypes. 5. How many females are short?
How many marriages. 6. How many generations?

46. Vocabulary Quiz
Free earlobes are dominant over attached earlobes. Mom is heterozygous and Dad is homozygous recessive. Use this information to answer the questions below.
Make a key.
Determine the genotypes:
Mom = Dad =
Determine the phenotypes:
Is it possible for their children to have attached earlobes? Why or why not?
What is the difference between a gene and a trait?

47. Sex-linked traits
Sex-linked traits are caused by genes found on the X chromosome.
Sex-linked traits are recessive.
Fewer females are afflicted with these traits because they have two X chromosomes and the other is usually normal.
Males only have one X chromosome, so when they inherit the sex-linked gene, they display the trait.
Examples: color-blindness, hemophilia XX
XX-
X-X- XY
X-Y
Normal
female
Carrier
female
Afflicted
female
Normal
male
Afflicted
male

48. Sex-linked traits practice problems
A man normal for blood clotting marries a woman who is a carrier for hemophilia. What are the chances they will have a child with hemophilia? Use a Punnett Square to prove your answer.
What is the probability that a woman with normal vision who marries a color-blind man will have a color-blind child?
A man with normal vision and a woman with normal vision have three sons. Two of the sons have normal vision and one of them is color-blind. What are the probable genotypes of the parents?

49. Intermediate Inheritance
Not all traits are either dominant or recessive.
For some traits, heterozygous individuals are different than both homozygous parents.
Codominance
Incomplete Dominance
Both alleles are blended in heterozygous offspring
Both are different capital letters
Both alleles are expressed in heterozygous offspring
Both alleles are dominant
Both are different capital letters
Red flowers = RR
White flowers = WW
Pink flowers = RW
Red coat = CR CR
White coat = CW CW
Roan coat = CR CW
(both red and white are seen)

50. Multiple Alleles: Phenotype Genotype(s) A IA IA , IA i B IB IB, IB i
When there are more than 2 (multiple) alleles for a trait.
Examples: Human blood groups have 3 alleles. (A, B, O)
A and B are both dominant, O is recessive
The possible combinations of these blood alleles are:
Phenotype
Genotype(s) A
IA IA , IA i B
IB IB, IB i AB
IA IB O ii

51. Dihybrid Crosses Study two traits at the same time.
Determine the outcome for both traits together.
A pure tall plant with blue flowers is mated with a short plant with white flowers. Determine the genotypes and phenotypes of the offspring. Tall and blue flowers are both dominant traits.
TTBB X
ttbb
Parents:
T =
tall
ttbb
TTBB
t =
short tb tb TB TB
B =
blue
b =
white

52. Genotype Phenotype Tall and blue = 100% TtBb = 100% TtBb TtBb TtBb

53. Now mate two of the offspring to determine the possible genotypes and phenotypes.
EXTRA CREDIT!!!
You must show ALL possible
genotypes and phenotypes!
Genotype
TtBb X TtBb
ttbb
= 1/16 = 6.25%
ttBb
= 2/16 = 12.5% TB Tb TB Tb tB tb
ttBB
= 1/16 = 6.25%
Ttbb
= 2/16 = 12.5% tB tb TB
TTBB
TTBb
TtBB
TtBb
TtBb
= 4/16 = 25%
TtBB
= 2/16 =12.5% Tb
TTBb
TTbb
TtBb
Ttbb
TTbb
= 1/16 = 6.25% TB
TTBb
= 2/16 = 12.5%
TTBB
= 1/16 = 6.25% Tb tB
TtBB
TtBb
ttBB
ttBb
Phenotype
Tall, blue = 9/16 (56.25%)
Short, blue = 3/16 (18.75%)
Tall, white = 3/16 (18.75%)
Short, white = 1/16 (6.25%) tB tb
TtBb
Ttbb
ttBb
ttbb tb

54. Incomplete dominance & Codominance
When a mouse with black fur is crossed with a mouse with white fur, all F1 generation offspring have gray fur. What are the probable genotypes and phenotypes for the F2 generation? Is this an example of codominance or incomplete dominance?
What would the possible genotypes and phenotypes be for a cross between a roan-coated cow (CR CW) and a red-coated cow (CR CR)? Is this an example of codominance or incomplete dominance?

55. Blood Type Problems
A couple preparing for marriage have their blood typed. They are both AB. They are curious about the possible blood types their children might have. What are the possible phenotypes of their children?
A type A person marries a type A person. Their firstborn has type O blood. What are the genotypes of the parents and the child?
A wealthy elderly couple die together in an accident. Soon a man shows up to claim their fortune, claiming he is their long lost son. Other relatives dispute the claim. Hospital records show that the deceased couple were blood types AB and O. The person claiming to be their son is type O. Do you think this man is an impostor? Explain why.