1. Mendel and the Gene Idea

2. Two possible explanations existed for how traits are passed from one generation to the next.
Blending hypothesis
Genes from parents blend to make a new set of characteristics

3. Two possible explanations existed for how traits are passed from one generation to the next.
Particulate hypothesis
Genes from parents are discrete units with fixed values for the trait

4. Mendel used the scientific approach to determine how traits are inherited and to identify two laws of inheritance.

5. Not PEAS again! Can’t you study something else for a while?!
What did Mendel find?
Mendel determined that inheritance from the parental generation to the filial generation is particulate.
Mendel used peas to test his ideas.
Not PEAS again! Can’t you study something else for a while?!

6. Mendel used 7 traits in his initial testing.

7. Peas usually self-pollinate, but Mendel controlled all of the reproduction.
By crossing (mating) two true breeding varieties of an organism, scientists can study patterns of inheritance. In this example, Mendel crossed pea plants that varied in flower color.
When pollen from a white flower fertilizes eggs of a purple flower, the first-generation hybrids all have purple flowers. The result is the same for the reciprocal cross, the transfer of pollen from purple flowers to white flowers.

8. Naming the Generations
P refers to the parent (true- breeding) organisms F1 refers to the first generation of offspring from the P generation F2 refers to the generation of offspring produced by breeding two F1 organisms

9. Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation

10. Mendel’s Laws are based on the evidence from his experiments.
Mendel reasoned that
In the F1 plants, only the purple flower factor was affecting flower color in these hybrids
Purple flower color was dominant, and white flower color was recessive

11. Mendel related four concepts in creating his model that explained the 3:1 ratio he found in the F2 generations.

12. First, alternative values of genes (alleles) account for variations in inherited characters
Allele for purple flowers
Locus for flower-color gene
Homologous
pair of
chromosomes
Allele for white flowers

13. Second, for each character an organism inherits two alleles, one from each parent

14. Third, if the two alleles at a locus differ then one, the dominant allele, determines the organism’s appearance
The other allele, the recessive allele, has no noticeable effect on the organism’s appearance

15. Fourth the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes (Meiosis Happens!)

16. Mendel’s Laws Law of Dominance Law of Segregation
If present, a dominant allele will be represented.
Law of Segregation
Alleles segregate during gamete formation.
Law of Independent Assortment
Chromosomes line up randomly and independently in metaphase I
This law came later!

18. A phenotype is a description of the appearance of a gene while a genotype is the genetic code for a trait.

19. Terminology Homozygous- having identical alleles for a trait
Aka: pure or true breeding
Heterozygous- having different alleles for a trait
Aka: hybrid

20. Using a test cross will allow you to figure out if an organism that displays the dominant trait is heterozygous or homozygous.
By mating the unknown organism with an individual that has the recessive trait you can determine the genotype of the original organism.

21. If even one of the offspring displays the recessive trait, the original organism can be determined to be heterozygous.

22. A dihybrid cross allows us to determine that genes are inherited independently.

23. The laws of probability govern Mendelian inheritance.

24. The multiplication and addition rules can be applied to monohybrid crosses
The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities
P(A and B) = P(A)∙P(B)

25. P(A and B) = P(A)∙P(B) Probability of getting a heart = 1 in 4
Probability of getting a king = 1 in 13
Probability of getting a king of hearts = 1 in 52

26. Probability in a monohybrid cross can be determined using this ruleHH Hh hh

27. The multiplication and addition rules can be applied to monohybrid crosses
The rule of addition states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities
P(A or B)= P(A) + P(B)

28. P(A or B)= P(A) + P(B)
Probability of drawing a heart or a spade from a deck of cards.
Probability of drawing a heart = 1 in 4
Probability of drawing a spade = ¼

29. Solving Complex Genetics Problems with the Rules of Probability
We can apply the rules of probability
To predict the outcome of crosses involving multiple characters

30. Combining the rules works as well.
What is the probability of drawing a king of spades or a king of hearts?
P(K♠ or K♥) = P(K)∙P(♠) + P(K)∙P(♥)

31. What is the probability of drawing a king of hearts AND a king of spades.
To make the problem easier, lets say we are using separate decks!
P(K♥ and K♠)=

32. Challenge Problem: What is the probability of getting a royal flush from a single deck of cards?

33. You can look at the outcomes of multiple genes at the same time using a larger Punnett Square
A dihybrid or other multicharacter cross
Is equivalent to two or more independent monohybrid crosses occurring simultaneously
In calculating the chances for various genotypes from such crosses
Each character first is considered separately and then the individual probabilities are multiplied together

34. The Math: x=2n Possible number of different gametes (x)
n is the number of heterozygous traits in the parent
Possible number of different genotypes (x)
n is the number of dominant traits in the individual

35. How many different gametes can be made from the genotype?
AaBbCCDdEEffGg
There are 4 heterozygous traits, so there are 24 or 16 possible gametes

36. How many possible genotypes are possible for the phenotype?
Purple flowered, round, green peas with yellow inflated pods and tall axial flowers.
There are 5 dominant traits so n=5
25=32 different possible genotypes for the phenotype

37. Frequency of Dominant Alleles Dominant alleles
Are not necessarily more common in populations than recessive alleles

38. Inheritance patterns are often more complex than predicted by simple Mendelian genetics. The relationship between genotype and phenotype is rarely simple.

39. The inheritance of characters by a single gene may deviate from simple Mendelian patterns
Multiple types of dominance
Linkage
Multiple alleles
Pleitropy
Sex linkage
Epistasis
Polygenism

40. The Spectrum of Dominance
Complete dominance
Occurs when the phenotypes of the heterozygote and dominant homozygote are identical
In codominance
Two dominant alleles affect the phenotype in separate, distinguishable ways
In incomplete dominance
The phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

41. Complete dominance
Occurs when the phenotypes of the heterozygote and dominant homozygote are identical

42. Codominance occurs
When two dominant alleles affect the phenotype in separate, distinguishable ways

43. Incomplete dominance occurs
When the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

44. Mutation

45. P Generation
F1 Generation
F2 Generation
Red
CRCR
Gametes CR CW x
White
CWCW
Pink
CRCW
Sperm Cw
Eggs
CR CR
CR CW
CW CW

46. Multiple Alleles
Most genes exist in populations in more than two allelic forms

47. The ABO blood group in humans
Is determined by multiple alleles

48. Pleiotropy
In pleiotropy
A gene has multiple phenotypic effects

50. Some traits may be determined by two or more genes

51. In epistasis
A gene at one locus alters the phenotypic expression of a gene at a second locus

52. Polygenic Inheritance
Many human characters
Vary in the population along a continuum and are called quantitative characters

54. Nature and Nurture: The Environmental Impact on Phenotype Another departure from simple Mendelian genetics arises when the phenotype for a character depends on environment as well as on genotype

55. The norm of reaction is the phenotypic range of a particular genotype that is influenced by the environment

56. Multifactorial characters Are those that are influenced by both genetic and environmental factors
The ph of the soil, in conjunction with the genetics of the organism, determine the final phenotype.

57. An organism’s phenotype
Includes its physical appearance, internal anatomy, physiology, and behavior
Reflects its overall genotype and unique environmental history

58. Many human traits follow Mendelian patterns of inheritance
Many human traits follow Mendelian patterns of inheritance. Humans are not convenient subjects for genetic research, however, the study of human genetics continues to advance

59. Pedigree Analysis A pedigree
Is a family tree that describes the interrelationships of parents and children across generations

60. Inheritance patterns of particular traits
Can be traced and described using pedigrees
Can also be used to make predictions about future offspring Ww ww WW or
First generation
(grandparents)
Second generation
(parents plus aunts
and uncles)
Third
generation
(two sisters) Ff ff
FF or Ff FF
Widow’s peak
No Widow’s peak
Attached earlobe
Free earlobe
(a) Dominant trait (widow’s peak)
(b) Recessive trait (attached earlobe)
Figure A, B

61. Many genetic disorders are inherited in a recessive manner
Recessively inherited disorders
Show up only in individuals homozygous for the allele
Carriers
Are heterozygous individuals who carry the recessive allele but are phenotypically normal

62. Cystic Fibrosis Symptoms of cystic fibrosis include
Mucus buildup in the some internal organs
Abnormal absorption of nutrients in the small intestine

63. Sickle-Cell Disease Sickle-cell disease Symptoms include
Affects one out of 400 African-Americans
Is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells
Symptoms include
Physical weakness, pain, organ damage, and even paralysis

64. Mating of Close Relatives
Matings between relatives
Can increase the probability of the appearance of a genetic disease
Are called consanguineous matings

65. Some human disorders are due to dominant alleles
One example is achondroplasia
A form of dwarfism that is lethal when homozygous for the dominant allele

66. Huntington’s disease Is a degenerative disease of the nervous system
Has no obvious phenotypic effects until about 35 to 40 years of age

67. Multifactorial Disorders
Many human diseases
Have both genetic and environment components
Examples include
Heart disease and cancer

68. Genetic Testing and Counseling
Genetic counselors
Can provide information to prospective parents concerned about a family history for a specific disease

69. Counseling Based on Mendelian Genetics and Probability Rules
Using family histories
Genetic counselors help couples determine the odds that their children will have genetic disorders

70. Tests for Identifying Carriers
For a growing number of diseases
Tests are available that identify carriers and help define the odds more accurately

71. Fetal Testing In amniocentesis In chorionic villus sampling (CVS)
The liquid that bathes the fetus is removed and tested
In chorionic villus sampling (CVS)
A sample of the placenta is removed and tested

72. Fetal testing
Figure A, B

73. Newborn Screening
Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States