1. Warm-up (use pencil today)
1.What type of cross does the visual below represent? (Hint: see word wall terms) 2. How many traits are being crossed? 3. What are the genotypes of the traits being crossed? 4. What words from the word wall represent the parent genotypes?

2. PART 2

3. Mendel’s experimentation with peas continued:
Mendel performed another set of crosses in which he used peas that differed from each other in two traits rather than only one.
A cross involving two pairs of contrasting traits is called a dihybrid cross (because di means “two”). example: seed shape (smooth vs. wrinkled) and seed color (yellow vs. green).
Mendel wanted to find out if the two traits would stay together in the next generation (do they influence one another).
After Mendel experimented with the dihybrid crosses, he found that alleles sorted independently.
“Mendel’s Law of Independent Assortment”: two alleles for different traits can segregate independently during the formation of gametes.

4. How do we use a Punnett square to conduct Dihybrid Crosses?
We start by determining the possible gamete combination of each parent’s genotype.

5. The Independent Alignment of Different Pairs of Homologous Chromosomes At Meiosis Accounts for the Principle of Independent Assortment
The alignment of one pair of homologs is independent of any other.
Principle of Independent Assortment: The assortment of one pair of genes into gametes is independent of the assortment of another pair of genes.

6. There are 2 possible gametes: rE and re
To determine the number of different gametes a parent can have, we use the acronym FOIL (First – Outer – Inner – Last) with the pair of traits.
rrEe rE re rE re
There are 2 possible gametes: rE and re

7. There are 2 possible gametes: Re and RE
To determine the number of different gametes a parent can have, we use the acronym FOIL (First – Outer – Inner – Last) with the pair of traits.
RREe RE Re RE Re
There are 2 possible gametes: Re and RE

8. There is 1 possible gamete:
#3. Possible Gametes:
To determine the number of different gametes a parent can have, we use the acronym FOIL (First – Outer – Inner – Last) with the pair of traits.
RREE RE RE RE RE
There is 1 possible gamete:
All gametes are RE

9. Determine the different types of gametes
Hint: Use the FOIL method.
Parent genotype Number of gamete variations
TTYY =
one (TY)
#4.
TtYY =
#5.
two (TY and tY)
TtYy
#6. =
four (TY,Ty, tY, ty,)

10. There are 4 total different gametes
Determining Gametes:
What are the different possible gametes combinations for these parents (R=round, r=wrinkled, T=tall, t=short) ?
RRTT x RrTt RT
RT, Rt, rT, rt
There are 4 total different gametes

11. RRTT RRTt RrTT RrTt RRTT RRTt RrTT RrTt RRTT RRTt RrTT RrTt RRTT RRTt
#7. Determine the possible gametes and offspring by completing the cross below (R=round, r=wrinkled, T=tall, t=short).
RRTT x RrTt RT Rt rT rt
RRTT
RRTt
RrTT
RrTt RT
Genotypic ratio?
4 RRTT
4 RRTt
4 RrTT
4 RrTt RT
RRTT
RRTt
RrTT
RrTt
Phenotypic ratio?
RRTT
RRTt
RrTT
RrTt RT
16 Round/Tall
RRTT
RRTt RT
RrTT
RrTt

12. RrTT RrTt RrTT RrTt RrTt Rrtt RrTt Rrtt RrTT RrTt RrTT RrTt RrTt Rrtt
#8. Determine the possible gametes and offspring by completing the cross below (R=round, r=wrinkled, T=tall, t=short).
rrTt x RRTt RT Rt RT Rt
RrTT
RrTt
RrTT
RrTt rT
Genotypic ratio?
4 RrTT
8 RrTt
4 Rrtt
RrTt
Rrtt
RrTt
Rrtt rt
Phenotypic ratio?
RrTT
RrTt
RrTT
RrTt rT
12 Round/Tall
4 Round/short rt
RrTt
Rrtt
RrTt
Rrtt

13. RRTT RRTt RrTT RrTt RRTt RRtt RrTt Rrtt RrTT RrTt rrTT rrTt RrTt Rrtt
#9. Determine the possible gametes and offspring by completing the cross below (R=round, r=wrinkled, T=tall, t=short).
RrTt x RrTt RT Rt rT rt
Genotypic ratio?
RRTT
RRTt
RrTT
RrTt RT
1 RRTT
2 RRTt
2 RrTT
4 RrTt
1 RRtt
2 Rrtt
1 rrTT
2 rrTt
1 rrtt
RRTt
RRtt
RrTt
Rrtt Rt rT
RrTT
RrTt
rrTT
rrTt
Phenotypic ratio?
9 Round/Tall
3 Round/short
3 wrinkled/Tall
1 wrinkled/short rt
RrTt
Rrtt
rrTt
rrtt

14. RESPONSE BOARD ASSESSMENT ARE YOU READY?

15. Warm-up
According to the table above which of the following
phenotypes would probably occur in all the offspring
from the parents shown above?
Solid gray fur c. Green eyes
Striped gray fur d. Blue eyes

16. A pea plant with the genotype TtWW is crossed with a pea plant with the genotype ttWw. How many different genotypes can be expressed in the offspring? 1 2 3 4

17. 2. What is the probability of producing a long haired, tabby cat?
Two cats heterozygous for short hair and tabby striping mate. Short hair is dominant over long hair. Tabby striping is dominant over plain coat What is the phenotypic ratio?
9 Short/Tabby
3 Short/Plain
3 long/Tabby
1 long/plain
2. What is the probability of producing a long haired, tabby cat?
3 out of 16

18. 3. If you want to create a purebreed of long haired, tabby striped cats, you would choose kittens with which genotype(s)?

19. Online Dihybrid Cross Practice

20. Why Did Mendel Conclude That The Inheritance of one Trait is Independent of Another?
Phenotype Ratio:
9 yellow/smooth
3 yellow/wrinkled
3 green/smooth
1 green/wrinkled
Because it’s the only way to explain the pattern of inheritance.

21. What Works for Peas Also Works for Humans
Consider a cross between parents heterozygous for both deafness and albinism.
This is the same 9:3:3:1 ratio seen for Mendel’s cross involving pea color and shape.

22. Going Beyond Dominant and Recessive
There are always exceptions to the rule…

23. + + + +
Ask students: How does this situation illustrate inheritance of traits that differs from what we’ve explored so far with dominant and recessive traits?
Have students think, pair, share. The point we want to reach is that inheritance does not always follow simple mendelian dominant / recessive +

24. RED Flower x WHITE Flower ---> PINK Flower
Some alleles are related through
Incomplete Dominance WW
white
a cross between organisms with two different phenotypes produces hybrid offspring with a third phenotype that is a blending of the parental traits. 
Remember Incomplete Dominance
RED Flower x WHITE Flower ---> PINK Flower

25. red x white ---> red & white spotted
Codominance A.
A cross between two different phenotypes produces a third phenotype where both traits appear “together” in a hybrid offspring. B.
A. Cross between a homozygous red flower and a homozygous white flower.
B. Cross between homozygous IA blood type and homozygous IB blood type.
Remember codominance
red x white ---> red & white spotted

26. Codominance cont’d
Cross between a homozygous black horse and a homozygous white horse. W W BW B B

27. Incomplete or Codominant?+

28. Incomplete or Codominance?X

29. Polygenic Inheritance –
when a single trait is influenced by many genes

30. Polygenic Inheritance
Examples: Height Hair texture Skin color eye color

31. Pleiotropy – When One Allele Influences Many Traits
Examples:
Sickle Cell Anemia
Albinism

32. Traits (phenotypes) associated with the sickle cell allele.
Anemia, infections, weakness, impaired growth, liver and spleen failure, death.
Traits (phenotypes) associated with the sickle cell allele.
Pleiotropy in Action

33. Human Blood Type Inheritance Summary
Human blood type exhibits Non-Mendelian inheritance
It is inherited with multiple alleles (IA, IB, i)
Alleles A and B are codominant (IAIB). Heterozygous individuals for IAIB have Type AB blood.
Have students reference graphic organizer (they should label AB phenotype as “codominant”)

34. Can Receive Blood From:
Multiple Alleles
Many genes are present in 3 or more alleles (versions). This is known as multiple alleles.
The human ABO blood group is determined by three alleles (IA, IB, and i) of a single gene.
Blood Type
Genotype
Can Receive Blood From: A
IAIA
IAi AA AO
A or O B
IBIB
IBi BB BO
B or O AB
IAIB
A, B, AB, O O ii OO

35. Human Blood Types

36. Sex-Linked Traits
Characteristics that are inherited from genes found on the sex chromosomes.

37. Sex-Linked Traits Sex Determination
Females – XX
Males – XY
Almost all sex-linked traits are found on the X chromosome
Y chromosome contains very few genes and is mainly involved in sex determination

38. Intro to Human a Karyotype

39. Normal Male and Female Karyotypes
See page 341 in your biology textbook
In a human karyotype, the first 22 pairs of chromosomes are the autosomes. The 23rd pair of chromosomes are the sex chromosomes

40. Examples of X-linked traits:
1. Color Blindness
2. Hemophilia
3. Muscular Dystrophy

41. Colorblindness
A person with normal color vision sees a number seven in the circle above.
Those who are color blind usually do not see any number at all.

42. Colorblindness RED-GREEN COLORBLINDNESS:
People with red-green color blindness see either a three or nothing at all.
Those with normal color vision see an 8.

43. Hemophiliac carrier XHXh Colorblind carrier XCXc
Carrier – person who has one recessive allele and one dominant allele for a trait or heterozygous for that trait.
Example
Hemophiliac carrier XHXh
Colorblind carrier XCXc

44. Sex-linked punnett square
Question: What is the probability that a carrier female and a colorblind male will have a girl who is colorblind
(c = colorblind, C = normal)? Xc Y
XCXc
XCY
XcXc
XcY XC Xc

46. Human Pedigree
See page in your biology textbook