1. Dihybrid Crosses - looking at 2 traits

2. Mendel’s dihybrid crosses:
Mendel also performed crosses involving two pairs of traits, e.g., seed shape (smooth vs. wrinkled) and color (yellow vs. green).
If alleles sort independently, four possible phenotypes (2n) appear in the F2 generation in a 9:3:3:1 ratio.
“Mendel’s Principle of Independent Assortment”:
Alleles for different traits assort independently of one another.
Modern formulation of independent assortment:
Genes on different chromosomes behave independently in gamete production.

3. 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.

4. RREE All gametes are RE RE RE RE RE Possible Gametes:
To determine the number of different gametes a parent can have use the FOIL method.
RREE RE RE RE RE
All gametes are RE

5. You have 2 possible gametes: Re and RE
To determine the number of different gametes a parent can have use the FOIL method.
RREe Re RE RE Re
You have 2 possible gametes: Re and RE

6. You have 2 possible gametes: rE and re
To determine the number of different gametes a parent can have use the FOIL method.
rrEe re rE rE re
You have 2 possible gametes: rE and re

7. Number and kind of gametes
How many gametes?
To determine the number of different gametes a parent can have use the FOIL method.
Number and kind of gametes
TTYY =
one TY
TtYY =
two TY and ty
TtYy =
four TY, Ty, tY, ty

8. There are 4 total different gametes
Possible Gametes (sperm/egg):
If I cross:
What are the different possible gametes for these parents??
RRTT x RrTt RT
RT, Rt, rT, rt
There are 4 total different gametes

9. I have 4 possible offspring
If I cross:
What are the possible gametes?
RRTT x RrTt RT Rt rT rt
RRTT
RRTt
RrTT
RrTt RT
I have 4 possible offspring

10. I have 4 possible offspring
If I cross:
What are the possible gametes and offspring?
rrTt x RRTt RT Rt
RrTT
RrTt rT
RrTt
Rrtt rt
I have 4 possible offspring

11. I have 16 possible offspring
If I cross:
What are the possible gametes?
RrTt x RrTt RT Rt rT rt
RRTT
RRTt
RrTT
RrTt RT
RRTt
RRtt
RrTt
Rrtt Rt
I have 16 possible offspring
9:3:3:1 rT
RrTT
RrTt
rrTT
rrTt rt
RrTt
Rrtt
rrTt
rrtt

12. Because it’s the only way to explain the pattern of inheritance!
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!

13. 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.

14. January 10, 2012 Get your homework out on your desk! Warm Up #1:
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?
(SHOW ALL WORK!)
a. 1 b. 2 c. 3 d. 4

15. Warm Up #2
If a corn plant has a genotype of Ttyy, what are the possible genetic combinations that could be present in a single grain of pollen (sperm, male gamete) from this plant?
a. Ty, ty
b. TY, ty
c. TY, Ty, ty
d. Ty, ty, tY, TY

16. Warm Up #3
3. The pea plant produces plants of two different sizes and seeds that are two different shapes. Tall pea plants (T) are dominant to dwarf pea plants (t) and round seeds (R) are dominant to wrinkled seeds, r. Two plants heterozygous for both traits are mated. What fraction of their offspring will be dwarf and have wrinkled seeds?
(SHOW ALL WORK!)

17. Great job on your quizzes!
Hand back quizzes and work – review most common mistakes.
Tonight: Talk to your parents about their blood type. Write down each parent and yours if you know yours. Turn this in tomorrow for extra credit.
What do you know about blood types?

18. Multiple Alleles
More than two allelic forms of a gene that code for a trait
Phenotype is still determined by a pair of alleles! The gene pool simply contains more than two.
These alleles can be expressed in various ways:
Complete dominance
Co-dominance
Incomplete dominance

19. Multiple Alleles: Human Blood Type
Blood Type is Coded by Multiple Alleles A, B, and O.
*A and B are co-dominant.
*A and B are completely dominant over O.
Genotypes AA AO BB BO AB OO
Phenotypes
Type A
Type B
Type AB
Type O
*The genes cause the production of a cell surface protein A or B.
Type O cells have neither protein, so Type O individuals are Universal DONORS. Which individuals are Universal RECEPIENTS (have both proteins)?

20. Type A
Type B
Type AB
Type O
No antibodies

21. The AB phenotype (genotype IA IB) is an example of codominance!!
Multiple Alleles
Many genes are present in 3 or more versions (alleles) – this is known as multiple alleles.
The human ABO blood group is determined by three alleles (IA, IB, and i) of a single gene.
The AB phenotype (genotype IA IB) is an example of codominance!!

22. Codominance
The human ABO blood group illustrates another genetic phenomenon – codominance.
Codominance occurs when the phenotype associated with each allele is expressed in the heterozygote – both are expressed!

23. Problem 1
1. In humans, the blood types A, B, AB and O are determined by three alleles. A man who has AB blood marries a woman with O blood. What are the genotypes and phenotypes of the offspring?

24. Problem 2
2. A man who is heterozygous type A marries a woman who is heterozygous type B. What percentage of their offspring will be Type 0?

25. Problem 3
3. If a man with blood type B, one of whose parents had blood type O, marries a woman with blood type AB. What percentage of their children should have blood type B?

26. Problem 4
4. A man with type O blood and a woman with type AB blood get married. One of their children needs an operation. This child has type B blood. Can the child safely receive a blood transfusion from either parent? If not, why?

27. Multiple Alleles: Whose Baby ?
A major mix-up occurred. Have the babies been returned
to the correct set of parents? 1
Baby A - Type O Blood Baby B - Type B Blood
Smiths - Types O and AB Jones - Types A and B 2
Baby C - Type AB Blood Baby D - Type A Blood
Squares -Types AB and AB Angles -Types AB and O

28. 1/13/11: Warm Up
Both Mrs. Smith and Mrs. Jones had babies the same day in the same hospital. Mrs. Smith took home a baby girl, whom she named Shirley. Mrs. Jones took home a baby girl, whom she named Jane. However, Mrs. Jones began to suspect that her child had been accidentally switched with another baby in the nursery.
Mr. Smith – type A Mr. Jones – type A
Mrs. Smith – type B Mrs. Jones – type A
Shirley – type O Jane – type B
**Did a mix-up occur? SHOW YOUR WORK!!!

29. Sex – Linked Genes Review: What are the two sex chromosomes?
What is a woman’s genotype?
What is a man’s genotype?
Which do you think there are more of – x-linked genes or y-linked genes?
Who do you think inherits sex-linked disorders more – males or females?

30. X-linked Genetics Genes that are located on the
X chromosome but not the Y
MALES receive only ONE copy
FEMALES receive TWO copies

31. Color Blind Test
Are you red-green colorblind?
Lets find out…

32. Sex- Linked Inheritance
A male always receives a sex-linked condition from his mother, from whom he inherits an X chromosome.
A female must receive 2 alleles, one from each parent, for the trait to be expressed.
X-linked disorders are often recessive.

33. Sex-linked ( X-linked) disorders
Color –blindness
Hemophilia – protein for blood clotting is missing
Duchenne Muscular dystrophy- progressive wasting of muscles
(There are about 205 X-linked recessive disorders)

34. More males than females are affected by this type of disorder. WHY?
Color-blindness
Father
(normal vision)
Male
Female
Son
(normal vision)
Daughter
(normal vision)
Mother (carrier)
Daughter
(carrier)
Son
(colorblind)
More males than females are affected by this type of disorder. WHY?

35. True or False?
The X chromosome carries alleles that are not on the Y chromosome. Therefore, a recessive allele on the X chromosome is expressed in males.
Certain traits that have nothing to do with the gender of the individual are controlled by genes on X chromosomes.
Males have 2 X chromosomes, and therefore, X-linked recessive alleles are expressed.

36. Solving X-linked Problems
How do you know if x-linked?
Know color-blindness and hemophilia are!
Make Punnet Square using XX and XY
Attach alleles to X’s ONLY
To help determine percentages, circle the male offspring

37. Let’s Practice
1. Both the mother and the father of a male hemophiliac appear to be normal. From whom did the son inherit the allele for hemophilia? What are the genotypes of the mother, the father, and the son?

38. 2. A woman is color blind. What are the chances that her sons will be color blind? If she is married to a man with a normal vision, what are the chances that her daughters will be color blind? Will be carriers?

39. Cont…
3. A husband and a wife give birth to a baby girl. Mom’s vision was normal, so she assumed the baby’s would be normal too. However, she gave birth to a color-blind daughter. What can you deduce about the girl’s parentage?

40. Cont…
4. A man with normal color vision marries a woman who carries the recessive gene, although her vision is normal. What percentage of male children will be colorblind? What about females?

41. Cont…
5. If a hybrid female for the colorblind trait marries a colorblind male, what percentages of offspring will be colorblind?

42. Paternity Suit
6. One of the sons from question #5 is involved in a paternity suit. The child in question is a cb female. The judge rules that the child could not possibly belong to this man. Which sons, of problem #5, was involved in this case? Give his genotype and phenotype and tell how you know.

43. Sex-Linked Problems
Finish for homework!!!!

44. Article Anticipation Guide
Read the statements on your guide and mark your educated guesses in the boxes
Skin Color and Genetics Article

45. Polygenic Inheritance – when a Single Trait is
Polygenic Inheritance – when a Single Trait is influenced by many genes
Examples:
Height Hair texture
3. Skin color eye color

46. Types of Traits – Single Gene
Some traits are controlled by single gene
Expressed as “either/or”
Discontinuous Variation

47. Types of Traits – Polygenic Traits
Polygenic Traits are controlled by the additive effects of 2 or more genes
Shows a range of phenotypes
Continuous Variation

48. Types of Traits Example: A Biology Class
Single Gene Trait
Polygenic Trait
Discontinuous Variation
Continuous Variation

49. Human Population - Skin Color
Types of Traits – Polygenic Traits
Human Population - Skin Color
Controlled by many genes
A given individual can have as many as six alleles (possibly more!) for pigmentation

50. Polygenics
What are other traits that are coded for by MANY genes????

51. Multifactorial Traits
Influenced by genetic and environmental factors
*Even with a the same genetic make-up, environment can affect the phenotype, as seen in the Hydrangea above. The color variation is a reaction to acid in the soil. Similar environmental influence is observed in humans such as skin color and body build, giving even identical twins slight differences.

52. Review Problems Gametes:
For each of the diploid genotypes presented below, determine all of the possible haploid gametes.
a. Rr
b. RrYy
c. RrYyBb

53. Example 1
In turkeys a R produces a bronze color and is dominant over red color. Another dominant gene H, results in normal feathers; its recessive allele h produces feathers without webbing. Two heterozygous bronze turkeys with normal feathers were mated.
What kind of problem is this? ___________________
Give the genotypes of P:_________________
Give the genotypes of F1:________________
Give the phenotypes of F1:_______________

54. Example 2 In pea plants purple flowers are dominant to white flowers.
If two white flowered plants are cross, what percentage of their offspring will be white flowered?  ______________
What kind of inheritance is this? __________
Monohybrid or dihybrid? ________________

55. Example 3
A cross between a blue-flowered plant and a white-flowered plant gives all pale-blue-flowered plants.
What kind of inheritance is this?___________
What are the genotypes of the offspring?_______
Monohybrid or dihybrid?_________________

56. Example 4
A father and mother claim they have been given the wrong baby at the hospital! Both parents are blood type A. The baby they have been given is blood type O. Could they have the right baby?
What kind of inheritance is this?___________
P genotypes: ______________

57. Example 5
In a certain cactus, prickly spines can be two-pronged or one-pronged. If a one-pronged cactus is crossed with a two-pronged cactus, the F1 generation has a both types of spines, some are two-pronged, some are one-pronged.
What kind of inheritance is this?___________
Monohybrid or dihybrid?_________________
Give the genotypes of P:_________________
Give the genotypes of F1:________________

58. Example 6
Located on the X chromosome of a cat is a gene that codes for deafness. This gene is recessive. A black female cat that is is heterozygous for deafness (Dd) is crossed with a yellow male cat that is not deaf.
What type of problem is this?_____________
P genotypes:__________________________

59. Human Traits
Genetic counselors analyze how the trait is passed from one generation to the next. They construct pedigree charts that show the pattern of inheritance for a particular condition, and show if a disorder is dominant or recessive.

60. Pedigree Chart

61. Genetic Disorders
Autosomal ( non-sex linked) Dominant- individuals with alleles AA or Aa will have the disorder.
Autosomal Recessive – individuals with alleles aa with have the disorder.

62. Autosomal Disorders
Do you remember what an autosome was?

63. Autosomal Dominant Disorders:
Dwarfism known as achondroplasia
Huntington’s disease
Autosomal Recessive Disorders:
Phenylketonuria ( PKU)
Tay-Sachs disease
Cystic Fibrosis
Albinism
Incompletely dominant disorders:
- Sickle-Cell disease

64. Ways to recognize autosomal dominant disorders:
Affected children usually have an affected parent.
Two affected parents can produce an unaffected child.
Two unaffected parents will not have affected children.
Inheritance Pattern I:

65. Ways to recognize autosomal recessive disorders:
Most affected children have normal parents.
Two affected parents will always have affected children.
Affected individuals with homozygous normal mates will have normal children.
Inheritance Pattern II:

66. Dominant or recessive?

67. Dominant or recessive?

68. Dominant or recessive?

69. Dominant or recessive?

70. Sex – Linked Pedigrees Y – linked (ONLY males will inherit) X – linked
Male infertility
X – linked
Hemophilia
Red/Green Color Blindness MS

71. Pedigree Analysis