1. UNIT 8 Genetics and Genetic Engineering

2. A. Definition =
The study of how genes are passed from parent to offspring (heredity) and how genes cause variation in the traits of organisms.

3. B. The Father of Genetics
The first individual to conduct extensive research on how genes work was
Gregor Mendel
*Between 1856 and 1863, Mendel cultivated and tested approx. 29,000 pea plants to discover how certain traits were passed from one generation to another.

5. * Some of the traits he studied in peas were the height of the plants, the color of the flowers, and the shape of the seeds (peas).

6. Pea Plant Characteristics
Easy to grow
Multiple offspring
Characteristics

7. Selective Cross Pollination

9. The Law of Dominance and Recessive in genes for a trait.
Mendelian Genetics
Based on his research, Mendel proposed several genetics theories, one being :
The Law of Dominance and Recessive in genes for a trait.
*A pattern of heredity in which 1 gene/allele is expressed = the Dominant gene.

10. Mendelian Genetics
Also proposed the
Law of Independent Assortment = if the genes for two different traits are located in different non-homologous chromosomes, they separate randomly during meiosis and are inherited independent of each other

11. Parent or P Generation. F1 Generation. F2 Generation.
Cross Pollination
F1 Generation.
Self Pollination
F2 Generation.

12. C. The Role of DNA and Chromosomes
REVIEW:
1. During cell division, DNA forms chromosomes.
Each chromosome contains many genes made of nucleotides.
Each gene controls the production of a protein in the organism which creates a trait (characteristic).

13. D. Chromosomes and Genes
1. Most traits are controlled by
2 genes.
* One of the genes was inherited from mother, while the other gene was inherited from father.

14. * Different alleles can result in
a. ALLELES = versions of genes for a single trait.
* Different alleles can result in
slightly different proteins which can then result in different effects on the trait.
Example: Brown eye allele = brown eye protein
Blue eye allele = blue eye protein

15. Allele ~ Different versions of a gene that
Each person has 2 copies of every gene—one copy from mom and a second copy from dad.
Allele ~ Different versions of a gene that
is responsible for controlling a trait.

16. Different form of a gene
Allele
Different form of a gene P
Mom’s Chromosome p
Dad’s Chromosome

17. VOCABULARY
*Homozygous = the alleles for the trait result in the production of the same proteins. “Purebred”; used to describe a genotype
Examples of symbols for homozygous
genotypes: HH tt BB
XHXH

18. *Heterozygous = different alleles for the trait result in the production of the different proteins. “hybrid”; used to describe a genotype.
Examples of symbols for heterozygous genotypes: Hh Tt CS
XhXH

19. *Phenotype = a description of the effects of the alleles on a trait.
Examples:
Blue eyes
Tall Height
Has Cystic Fibrosis

20. *Genotype = an identification of the exact alleles an individual has for a trait.
Examples:
Eye color = bb
Height = Tt
Disease = NN
XhY

21. Mendelian Genetics: Simple Dominance
One of the two alleles for a trait hides the effects of the other allele = strong = dominant allele
The symbol for a dominant trait is written as a capital letter (T, R, B, W)

22. The other allele (the one that is hidden by the dominant allele) is weaker and is called the recessive allele.
The symbol for the recessive allele is written as a lower case letter (t, r, b, w)
When an individual has one of each of the alleles (Tt, Rr, Bb, Ww), only the dominant allele shows, recessive is hidden by the dominant allele.

23. An example of a pea plant trait discovered by Mendel
In pea plants, the trait for height is controlled by two alleles.
The tall allele is dominant over the short allele, which is recessive
Symbols: T for the tall allele, t for the short allele

24. Pea plants have the following gene combinations to control how high they grow
Bill Nye Video: Genes
Possible 2 gene combinations a pea plant can have
The height of the pea plant based on its genes
TT (homozygous)
Tt (heterozygous)
tt (homozygous)
Tall
Short
The exact genes an individual has for a trait = genotypes
The effects of the genes on an individual = phenotypes

25. E. Punnett Squares
A Punnett Square is a chart used to figure out all of the possible gene combinations in an offspring based on the genes from its parents.
Example: TT
T T t tt

26. Homozygous tall pea plant crossed with a homozygous short pea plant
Write the two genes from the other parent across the top
T T
Write the two genes from one parent along the side. t
Fill in the boxes inside the Punnett Square with the two letters on the outside of each box (bring top one down and side one across).
The letters inside each smaller box represent the genes an offspring could POSSIBLY inherit.

27. Possible genotypes and % chance each could occur
Possible phenotypes and
Tt = 100%
Tall = 100%

28. Incomplete Dominance
Of the alleles that control the trait, neither gene is dominant or recessive.
Heterozygous individuals have a blending of the alleles
Creating a third phenotype

29. Incomplete Dominance Example
Snapdragons
Two alleles control
flower color
R produces red colored
flowers
W produces white
colored flowers
Heterozygous
individuals have PINK

30. Normal tail

31. No tail

32. Short tail (bobtail)

33. Cat Traits:

34. cats

35. colorpoint

36. Codominant Traits
Of the alleles that control a trait, neither gene is dominant or recessive.
Heterozygous individuals will express both alleles at the same time
Creating a third phenotype
Example:
Human ABO Blood Type (also a multiple allele trait)

38. Human ABO Blood Groups
3 alleles control human blood type, each human inherits 2 of these alleles
Alleles:
IA = produces the antigen A protein on the RBCs
IB = produces the antigen B protein on the RBCs
IA and IB are co-dominant alleles = when both are inherited, both are fully expressed
- i = recessive allele, no antigen on RBCs

39. Human ABO Blood Groups
The immune system produces antibodies against antigens it does not recognize
When a foreign antigen is present, the immune system attacks and causes Agglutination = clumping of the blood cells.

41. Human ABO Blood Groups
Chart:

42. O + 37% 47% 53% 39% O - 8% 4% 1% A + 33% 24% 29% 27% A - 7% 2% 0.5%
White
African/
American
Hispanic
Asian
O +
37%
47%
53%
39%
O - 8% 4% 1%
A +
33%
24%
29%
27%
A - 7% 2%
0.5%
B + 9%
18%
25%
B -
0.4%
AB + 3%
AB -
0.3%
0.2%
0.1%

43. Sex-linked Traits Most traits are carried on the autosomes
A few traits are carried by the sex chromosomes
Most of these are on the X chromosome and
Some of these are recessive and disease-causing
Example:
Duchenne muscular dystrophy is an X linked recessive trait
XD: a dominant normal gene
Xd: chromosome carrying the recessive trait for the disorder

44. Sex-linked Trait Example
Possible Genotypes
Possible Phenotypes

45. Other Sex-linked Traits
Hemophilia- blood doesn’t clot properly
Red-Green Colorblindness –difficulty distinguishing between reds, greens, browns and oranges.; also commonly confuse different types of blue and purple hues. TEST

48. Multiple alleles
A trait having more than 2 versions of the genes for the trait Example: *Human ABO Blood Type Trait

49. Example = Rabbit Fur Color
The color of rabbit fur is conditioned by four different alleles
C = brown-red fur (wild type)
g = gray fur (chinchilla color)
h = black and white (Himalayan)
a = albino
In this case the dominance relations are
C > g > h > a
(the symbol > means “dominates over”).

50. Wild type color

51. Gray (chinchilla) color

52. Himalayan Color

53. Albino color

54. Dihybrid Cross
A cross showing the inheritance of two different traits at the same time. *each parent genotype will have 4 alleles, two for each trait *One allele for each trait will occur in the gametes each parent creates. All possibilities must be determined. (= 4 possibilities per parent) *requires a 16 box Punnett Square **SEE EXAMPLE with pea plant traits**

55. Dihybrid Pea Plant Cross
Trait = Seed shape
-R = round
-r = dented
Trait = Seed Color
Y = yellow
y = green
Cross 2 pea plants that are heterozygous for seed shape and for seed color.

56. RrYy X RrYy

57. Punnett Square Analysis:

58. G. Polygenic Traits
Traits controlled by more than two genes (usually by many different genes) on different chromosomes described as polygenes. Each has its own alleles.
Examples:
Human height (180 genes?)
Human weight
Human skin color
Fur color in dogs

59. Epistasis =
A circumstance where the expression of one gene is affected by the expression of one or more independently inherited genes.

60. Coat color in Labrador Retrievers
*Allele of coat color gene: B = dominant = Black b = recessive = brown *Epistasis gene: EE or Ee = does not suppress the black or brown allele ee = suppresses both the black and brown alleles

61. BB = black Lab, no chocolate gene Bb = black Lab, carries chocolate gene bb = chocolate Lab, no black gene
Yellow is produced by the presence of a recessive epistatic gene which has the effect of masking the black or chocolate genes.
EE or Ee = no suppression of coat color ee = suppresses the coat color = Yellow.

62. So.... EEBB =Black EEBb =Black EeBB =Black EeBb =Black
eeBB =Yellow eeBb =Yellow eebb =Yellow
EEbb =Chocolate
Eebb =Chocolate