1. Mendelian Genetics

2. Genetics: The Basics Allele- An alternative form of a gene
Diploid organisms have one copy on each homologous chromosome
Represented by letters:
Capital letter = dominant form
Lower case letter = recessive form
Example= Eye Color
Controlled by 2 alleles
Blue Eyes = bb
Brown eyes= Bb or BB

3. Dominant allele-fully expressed in the organism's appearance
Recessive allele-no noticeable effect on the organism's appearance

5. Genetics: The Basics
Heterozygous: Have 2 different forms of the allele
Example:
Brown Eyes = Bb = heterozygous
Homozygous: Have 2 of the same forms of the allele
Blue Eyes = bb = homozygous recessive
Brown Eyes = BB = homozygous dominant

6. Genetics: The Basics Genotype = the genetic makeup of an organism
Example = BB, Bb, bb
Phenotype = the physical expression of genes
Example =
Brown Eyes = phenotype of either the BB or Bb genotype
Blue Eyes= phenotype of the bb genotype
Remember that phenotype is not necessarily an appearance-
It can be things like enzyme production, behavior, etc!!
It is ANY expression of a gene!!

7. Gregor Mendel *1843 entered monastery
* studied at Univ. of Vienna
*1857 started breeding garden peas
* 1860 started forging data!!

8. Do units of inheritance retain integrity (preserved) or blend????
MENDEL'S MAIN QUESTION
Do units of inheritance retain integrity (preserved) or blend????
Sample Question: If you cross a purple flower with a white flower are these flower colors retained in future crosses or are they blended to form an intermediate color?

11. 2 plants crossed Self-fertilized
Law of Segregation-two alleles for a character are packaged into separate gametes
2 plants crossed
Self-fertilized

13. Mendel's findings Purple flowers White flowers
1. Alternative version of genes (alleles) account for variations in inherited characters
Homologous chromosomes
Purple flowers
White flowers

14. Mendel's findings maternal paternal Purple flowers White flowers
2. For each character, an organism inherits two alleles, one from each parent.
maternal
Homologous chromosomes
paternal
Purple flowers
White flowers

15. Mendel's findings recessive dominant Purple flowers White flowers
3. If two alleles differ, the dominant allele is fully expressed in the organism's appearance.
recessive
dominant
Purple flowers
White flowers

16. Mendel's findings
4. The two alleles for each character segregate during gamete production.
dominant
recessive
Seed shape PP pp
Gametes P p

17. Punnett Square
Predicts the results of a genetic cross between individuals with known genotypes

18. Rules for Genetic Problems
1. Identify traits (alleles) and assign letters to represent the various traits: capital letters for dominant traits; lower case letters for recessive traits.
2. Set up parental cross.
3. Draw individual gametes with corresponding letter for trait.
4. Identify F1 offspring phenotype and genotype.
5. Setup F1 cross.
6. Draw individual gametes with corresponding letter for trait.
7. Set up Punnett square to identify individual genotypes and phenotypes for F2 offspring.

19. EXAMPLE: SEED COLOR dominant recessive CC cc c C c C C C c CC c 3 Cc1

20. EXAMPLE: POD SHAPE dominant recessive SS ss s S s S S S s SS s 3 Ss Ss1

21. Monohybrid Cross
Follows single trait

22. Test Cross
Breeding a homozygous recessive with a dominant phenotype (unknown genotype) can determine an unknown allele.

23. In pea plants, spherical seeds (S) are dominant to dented seeds (s)
In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds?
F1 generation, test cross: Ss Ss
What is the genotypic ratio?
What is the phenotypic ratio?

24. The test cross
To identify the genotype of yellow-seeded pea plants as either homozygous dominant (YY) or heterozygous (Yy), you could do a test cross with plants of genotype _______.
A. y
B. Y
C. yy
D. YY
E. Yy

25. Predicting the results of a test cross
A test cross is used to determine if the genotype of a plant with the dominant phenotype is homozygous or heterozygous. If the unknown is homozygous, all of the offspring of the test cross have the __________ phenotype. If the unknown is heterozygous, half of the offspring will have the __________ phenotype.
A. dominant, recessive
B. recessive, dominant

26. Question: How are two traits inherited?
DIHYBRID CROSS
Experimental Approach: A cross involving two true-breeding traits.
System: Pea Plants; seed color (Y/y)
and seed shape (S/s).

27. F1 Generation

28. F1 Generation

29. F1 Generation
Each of the male gametes types (SY, Sy, sY, sy) can fuse with each of the female gametes types (SY, Sy, sY, sy).
16 possible combinations of gametes are possible.
We will see that there are 9 possible genotypes and 4 possible phenotypes.
4. The two parental phenotypes, and
two new phenotypes were obtained.

30. Dihybrid Cross
Follows two traits
9:3:3:1 RATIO

31. The phenotypes of two independent traits show a 9:3:3:1 ratio in the F2generation. coat color is indicated by B (brown, dominant) or b (white)
tail length is indicated by S (short, dominant) or s (long).
If the children mate with each other, in the F2 generation all combinations of coat color and tail length occur: 9 are brown/short (purple boxes), 3 are white/short (pink boxes), 3 are brown/long (blue boxes) and 1 is white/long (green box).

32. Dihybrid Cross
In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and disk-shaped fruit (D) is dominant over sphere-shaped fruit (d)..  If a squash plant true-breeding for white, disk-shaped fruit  is crossed with a plant true-breeding for yellow, sphere-shaped fruit,  what will the phenotypic and genotypic ratios be for:
a. the F1 generation?     b. the F2 generation?

33. Genotypic ratios:  1/16 will be homozygous dominant for both traits (WWDD) 2/16 will be homozygous dominant for color and heterozygous for shape (WWDd) 2/16 will be heterozygous for color and homozygous dominant for shape (WwDD) 1/16 will be homozygous dominant for color and homozygous recessive for shape (WWdd) 4/16 will be heterozygous for both traits  (WwDd) 2/16 will be heteozygous for color and homozygous recessive for shape (Wwdd) 1/16 will be homozygous recessive for color and homozygous dominant for shape (wwDD) 2/16 will be homozygous recessive for color and heterozygous for shape (wwDd) 1/16 will be homozygous recessive for both traits (wwdd)
This is a 1:2:2:1:4:2:1:2:1 genotypic ratio
Phenotypic ratios: 9/16 will have white, disk-shaped fruit 3/16 will have white, sphere-shaped fruit 3/16 will have yellow, disk-shaped fruit 1/16 will have yellow, sphere-shaped fruit
This is a 9:3:3:1 phenotypic ratio
 WD
 Wd wD wd
 WWDD
 WWDd
WwDD
WwDd
 WWdd
Wwdd
wwDD
wwDd
wwdd

34. Law of Segregation-
Every individual possesses a pair of alleles for any particular trait and that each parent passes a randomly selected copy (allele) of only one of these to its offspring. 

36. Law of Independent Assortment- Separate genes for separate traits are passed independently of one another from parents to offspring. These allele pairs are then randomly united at fertilization. 

37. The relationship between the genotype and phenotype is rarely simple.
Inheritance that diverges from Mendel's inheritance
GENE INTERACTIONS
The relationship between the genotype and phenotype is rarely simple.
* Each character is rarely controlled by one gene
*Each gene usually has more than two alleles, with one not always being dominant over the other

38. Traits are separable in further crosses
Incomplete Dominance
Heterozygotes show a distinct intermediate phenotype, not seen in homozygotes
Traits are separable in further crosses
Not BLENDED

39. Most genes have more than two alleles in a population. (IA, IB, I)
In CODOMINANCE, both alleles are expressed and functional, though they may be different.
Most genes have more than two alleles in a population. (IA, IB, I)

40. Pleiotrophic
Most genes affect more than one phenotypic character.

41. Pleiotropy:Albinism
A single defect in one of the enzymes catalyzing tyrosine to melanin can affect multiple phenotypic characters, from eye color to skin color to hair color.

42. Epistasis
A gene at one locus alters the phenotypic expression of a gene at a second locus.
bb with dominant C allele
results in brown mouse

43. Polygenic Inheritance
Additive effect of two or more genes on a single phenotypic character.
SKIN COLOR
Controlled by at least 4 different genes

46. Sex-linked traits In humans, 2 of our 46 chromosomes are
classified as sex chromosomes
Females = XX
Carried on ova
Males = XY
Carried on sperm
In females, only 1 X chromosome is active
Sex linked traits usually aren’t expressed-
In males, their only X chromosome is active
No other X chromosome to block sex linked trait

47. Sex-linked traits
In humans, the genes for colorblindness are both located on the X chromosome with no corresponding gene on the Y.
Strawberries as they would appear to someone who is red/green colorblind.

48. Sex Linked Traits Alleles are expressed on each of the sex chromosomes
Female: XAXA or XAXa or XaXa
Male: XAY or XaY
Setting up a punnet square for sex-linked traits:
Mom= XAXa Dad = XAY XA Xa XA Y

49. Mom is carrier, dad does not have x-linked recessive disorder
Mom isn’t carrier, dad has x-linked recessive disorder

50. Sex Linked Traits Can a female end up with an X-linked trait????
Example = Sex-linked baldness
assume that baldness (b) is recessive
Full head-o-hair (B) is dominant

51. .
Hemophilia is an X-linked recessive disorder characterized by the inability to properly form blood clots.

52. Y Linked Traits

53. Recessive Allele Disorders

54. Dominant Allele Disorders
Achondroplasia
*Form of dwarfism (dominant allele)
*Heterozygous/
Homozygous dominant individuals have dwarf phenotype
*99.99% of population are homozygous recessive

55. Dominant Allele Disorders Polydactyly
*Heterozygous/
Homozygous dominant individuals have 6 finger phenotype
*399 out of 400 have 5 digits/appendage: homozygous recessive

56. Pedigree Analysis
Information about presence/absence of phenotypic trait is collected from individuals in a family across generations.

57. Having the past help predict the future

58. RECESSIVE TRAIT (Allelic to left column)
DOMINANT TRAIT
RECESSIVE TRAIT (Allelic to left column)
Brown eyes PTC taster Widow's Peak  Middigital hair Tongue roller Detached earlobe A and B blood type (codominant) Pattern baldness (dominant in males)
Blue eyes (more complex, simplified here) PTC non taster Lack Widow’s peak Hairless mid digits Cannot roll tongue Attached earlobe Type O blood type Pattern baldness (recessive in females)

59. Common Heritable Traits

60. Common Heritable Traits

61. Common Heritable Traits

62. Common Heritable Traits

63. Common Heritable Traits

64. Case Study: In Sickness and In Health Greg and Olga’s Trip to the Genetic Counselor
Work in groups of 3-4
Write down answers to turn in

65. Part 1: Pedigree Construction 10 minutes
What would the pedigree of Greg and Olga’s families look like?

67. Part 2: Autosomal Dominant Traits 10 minutes
What is an autosome???
Do autosomal dominant disorders skip generations?
Could Greg or his mother be a carrier of the gene that causes myotonic dystropy (MD)? Why?
Is there a possibility that Greg’s aunt or uncle is homozygous for the MD gene? Why?
Symptoms of MD sometimes don’t show up until after age 50. What is the possibility that Greg’s cousin has inherited the MD gene?
What is the possibility that Greg and Olga’s children will inherit the MD gene?

68. Part 3: Autosomal RecessiveTraits 10 minutes
What are the hallmarks of an autosomal recessive trait (list four)?
What is it about the inheritance pattern of factor VIII deficiency seen in Greg and Olga’s pedigree that point toward it not being an autosomal recessive trait?

70. Part 4: Sex-Linked Inheritance 10 minutes
What are the characteristics of X-linked inheritance?
Why does a son never inherit his father’s defective X chromosome?
What is required for a female to display a sex-linked recessive trait?
Referring to the pedigree you drew in Part 1, mark the persons who are carriers of the factor VIII deficiency gene.
What is the chance that Olga carries the gene for factor VIII deficiency? Calculate the probability that she will pass it to her offspring. Will male children be affected in a different way than female children?
What is the chance that Greg carries the factor VIII gene? Can he pass the gene on to his sons? His daughters? How will each be affected?