1. Basic Concepts in Genetics
Mendel and the Gene Idea
Basic Concepts in Genetics

2. What Is heredity
The passing on of characteristics from parents to offspring
Trait
physical characteristic
Genetics
is the study of heredity

3. Chromosome Logical Structure
Gene – segments of DNA that code for the basic units of heredity and are transmitted from one generation to the next
Allele – genes that reside at the same locus on homologous chromosomes
Alleles are the result of mutation!!!!!!

4. Genotypes Phenotypes
At each locus (except for sex chromosomes) there are 2 genes. These constitute the individual’s genotype at the locus. The alleles that are present.
The expression of a genotype is termed a phenotype. For example, hair color, weight, or the presence or absence of a disease.

5. genotype Genotype Gene(s) responsible for the trait
The alleles that are present on each homologous chromosome that code for the trait

6. Phenotype Phenotype Expression of the characteristic The trait
The way we “look”
Red hair or Brown hair
The expression of the gene

7. Patterns of Inheritance
Gregor Mendel
( ) is the called the “Father of Genetics”
Researched with garden peas
Developed the ideas that are the basis of genetics

8. Mendel used peas…
Characters (inherited characteristic) are in two distinct forms (such as white and purple color) called traits.
Not many traits
Easy to keep track
The male and female gametes are enclosed within the same flower – He could control the fertilization process
Self-fertilization
Cross-pollination
The garden pea is small, grows easily, matures quickly and produces many offspring.

9. Mendelian genetics Height - short or TALL Seed color - green or YELLOW
Mendel studied a number of characteristics in pea plants including:
Height - short or TALL
Seed color - green or YELLOW
Seed shape - wrinkled or ROUND
Seed coat color - white or GRAY
Pod shape - constricted or SMOOTH
Pod color - yellow or GREEN
Flower position - terminal or AXIAL

10. Mendel was a careful researcher
Carefully controlled experiments
Studied one trait at a time
Kept detailed data
Cross - combining gametes from parents with different traits
The offspring are called hybrids
offspring of parents with different traits
A monohybrid cross is one that looks at only one trait (let’s look at plant height – tall or short)
Cross fertilization
Pollen from one plant to fertilize another plant

11. Mendel’s monohybrid crosses
Step One:
Mendel allowed the peas to self-pollinate for several generations.
What Did Mendel Find?

12. Mendel’s monohybrid crosses
Step One:
Each variety was true-breeding for a particular character.
tall plants only produced tall plants
These plants served as the parental generation.
The P generation is the first two individuals that are crossed in a breeding experiment

13. Mendel’s monohybrid crosses
Step Two:
Mendel cross-pollinated two P generation plants with different traits
The offspring were the first filial generation or F1 generation
Mendel recorded the traits of the offspring
What Did Mendel Find?

14. Mendel’s monohybrid crosses
Tall plant crossed with short plants produced all tall offspring
Purple flowers crossed with white flowers produced all purple offspring

15. Mendel’s monohybrid crosses
Step Three:
Finally, Mendel allowed the F1 generation to self-pollinate.
He called the offspring of the F1 generation, the second filial generation, or F2 generation
Again, Mendel recorded the traits of the offspring
What Did Mendel Find?

16. Mendel’s monohybrid crosses
The short plants reappeared!!!!!!
Mendel found that 3 out of 4 (¾) of the offspring were tall & 1 out of 4 (¼) were short

17. Mendel’s monohybrid crosses
Mendel found the same 1:3 ratio (1 out of 4) in the other traits as well!

18. Mendel’s results
He discovered different laws and rules that explain factors affecting heredity

19. Theory of Heredity
Before Mendel, people thought offspring were a blend of traits
Tall x short = medium
Mendel’s experiments did not support this theory
Mendel’s work led him to the understanding that traits are carried in pairs (one from each parent)

20. questions What did Mendel cross? What are traits? What are gametes?
What is fertilization?
What is heredity?
What is genetics?

21. Mendel’s 4 hypotheses Hypotheses 1
For each inherited character, an individual has two copies of each gene
One on each chromosome
Alternative versions of genes account for variations in inherited characters.
Alleles are different versions of genes that impart the same characteristic.

22. Mendel’s 4 hypotheses Hypotheses 2
Gametes (sperm or egg) carry only one allele as a result of pair separation during meiosis
Offspring inherit 2 alleles, 1 from each parent for each characteristic (i.e. height, color, etc.)

23. Mendel’s 4 hypotheses Hypotheses 3 The Rule of Dominance
Some genes (alleles) are dominant and others are recessive
The dominant allele, is fully expressed in the organism's appearance
The recessive allele, has no noticeable effect on the organism's appearance.

24. Mendel’s 4 hypotheses Hypotheses 4
The two genes for each character segregate during gamete production.
The genes are sorted into separate gametes, ensuring variation. 
This sorting process depends on genetic recombination

25. mendel’s First law of heredity
Law of Random Segregation A parent randomly passes only one allele for each trait to each offspring

26. Mendel’s second law of heredity
Law of Independent Assortment
Different gene pairs assort independently in gamete formation.
This Law is only true for genes on separate chromosomes!

27. Law of independent assortment
P GENERATION -True Breeding Parent Plants
All purple (PP)
All white (pp)
Gametes will be either P or p
FIRST FILIAL GENERATION F1
F1 are all purple because of dominance (Pp)
SECOND FILIAL GENERATION F2
F2 results in a mathematically predictable 3:1 ratio

28. Mendelian Inheritance patterns
Involve genes directly influencing traits
Obey Mendel’s laws
Law of segregation
Law of independent assortment
Include
Dominant / recessive relationships
Gene interactions
Phenotype-influencing roles of sex and environment
Most genes of eukaryotes follow a Mendelian inheritance pattern

29. Predicting Inheritance
To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes.
Each allele is represented by a letter
UPPERCASE/CAPITAL letters are used to represent dominant genes.
lowercase letters are used to represent recessive genes.
Homozygous - the two alleles for a trait are the same (AA or aa)
Heterozygous - the two alleles for a trait are different (Aa)

30. Predicting Inheritance
For example:
T = represents the gene for TALL in pea plants
t = represents the gene for short in pea plants
So:
TT & Tt both result in a TALL plant, because T is dominant over t.
t is recessive.
tt will result in a short plant.

31. PUNNETT SQUARES A diagram that predicts the outcome of a genetic cross
It considers all the possible combinations of gametes
1ST DRAW A BIG SQUARE AND DIVIDE IT IN 4’S
WHY E COLI?
What do you like to eat?
WHEN YOU EAT YOU NEED ENZYMES TO BREAK DOWN THE FOOD YOU EAT
EXPLAIN WHAT ENZYMES ARE
THEY BREAK DOWN FOOD
LIKE GLUCOSE AND LACTOSE
WHAT ARE GLUCOSE AND LACTOSE?

32. PUNNETT SQUARES The alleles from one parent go here.
The alleles from the other parent go here.

33. PUNNETT SQUARES T t

34. PUNNETT SQUARES T t

35. PUNNETT SQUARES T t

36. PUNNETT SQUARES T t Tt

37. PUNNETT SQUARES T t Tt

38. PUNNETT SQUARES
F1 generation T t Tt

39. Interpreting the Results
The genotype for all the offspring is Tt.
The genotype ratio is:
Tt – 4:4 = 100% heterozygous
The phenotype for all the offspring is tall.
The phenotype ratio is:
tall – 4:4 = 100% tall T t Tt

40. PUNNETT SQUARES
F2 generation T t TT Tt tt

41. Interpreting the Results
This time the ratios are different! Tt.
The genotype ratio is:
TT – 1: Tt – 2: tt – 1:4
1:2:1
2 – homozygous
2 – heterozygous
The phenotype ratio is:
TT, Tt, Tt = 3 tall
tt = 1 short
3:1 – tall : short T t TT Tt tt

42. Laws of probability help explain genetic events
Genetic ratios are most properly expressed as probabilities:
Probabilities range from
0 - an event is certain NOT to happen
1.0 - an event is certain to happen

43. Predicting Outcomes-probability
The likelihood that a specific event will occur
Probability = # of one kind of possible outcome
total # of all possible outcomes
a coin lands on “heads”
1 outcome
Total possible outcomes
= 2
heads or tails
Possibility that the coin will land on heads = 1/2

44. Product law For simultaneous outcomes (this AND that)
What is the chance that you will roll snake eyes with two dice? (1 and 1)
Chance of rolling 1 with first die = 1/6
Chance of rolling 1 with second die = 1/6
Chance of rolling two 1’s = 1/6 X 1/6 = 1/36

45. Sum law For outcomes that can occur more than one way (this OR that)
What is the chance that you will roll either a 1 or a 6 with one die?
Chance of rolling 1 = 1/6
Chance of rolling 6 = 1/6
Chance of rolling 1 or 6 = 1/6 + 1/6 = 2/6 = 1/3

46. What fraction would we expect to be
Probabilities
Multiplication Rule
The probability that two independent events, A and B, are realized simultaneously is given by the product of their separate probabilities
What fraction would we expect to be
Round AND Green
3/4 x 1/4 = 3/16

47. What fraction would we expect to be
Probabilities
Addition Rule
The probability that one or the other of two mutually exclusive events, A or B, is the sum of their separate probabilities
What fraction would we expect to be
(Round and Green) OR
(wrinkled and yellow)
3/ /16 = 6/16

48. Dihybrid cross F1 produces equal amounts of 4 possible genotypes
F2 reveals even more genotypic possibilities (9:3:3:1)
Dihybrid cross is equivalent to two monohybrid crosses (12:4 or 3:1)
Illustrates the Law of Independent Assortment

49. NON-MENDELIAN INHERITANCE
Many genes do not follow a Mendelian inheritance pattern
Incomplete Dominance
Co-dominance
Multiple alleles
Pleiotropy
Polygenic Inheritance
Lethal Dominance
Environmental Influence on Gene Expression

50. Incomplete dominance
The phenotype of the heterozygous genotype is intermediate between the phenotypes of the homozygous genotypes
E.g. snapdragons
Heterozygotes differ from homozygotes
Predictable 1:2:1 ratio
Different than “blending” hypothesis
No testcross necessary

51. codominance
Both alleles are dominant and affect the phenotype in two different but equal ways
Andalusian chickens show this pattern of inheritance.
If you cross a black (BB) chicken
With a white (WW) chicken
You get black+white speckled (BW) chicken

52. Multiple alleles More than two possible alleles controlling one trait
Example3 alleles in blood type – OAB
4 possible phenotypes = O, A, B, AB
6 possible genotypes
Note:
this is also an example of co-dominance

53. Multiple alleles Genes that have more than two alleles
More than two alleles exist in a given population
However, any one individual only has two of these alleles
Example - Coat color in rabbits (4 alleles)
Chinchilla Rabbit
Himalayan Rabbit
Full Color Rabbit
Albino Rabbit

54. Pleiotropy Gene influences multiple characteristics
A singe gene influences more than one phenotypic trait.
Genes that exert effects on multiple aspects of physiology or anatomy are pleiotropic

55. Polygenic Inheritance
Multiple genes have an additive effect on a single character in the phenotype
Example: Skin Color or height
Usually is described by a bell-shaped curve with majority clustered in the middle

56. Examples of Polygenic Inheritance

57. Lethal dominance T/t x T/t = T/T T/t t/t 1 : 2 : 1 ratio at conception
0 : 2 : 1 ratio at birth

58. Characters influenced by the environment
pH of the soil will change the color of hydrangea flowers from blue to pink

59. Characters influenced by the environment
Temperature will affect color change in fur

60. Characters influenced by the environment
Body temperature affects color in Siamese cats
Height is affected by nutrition

61. How do we determine inheritance of human traits
Pedigree Analysis
In humans, pedigree analysis is used to determine individual genotypes and to predict the mode of transmission of single gene traits

62. Some examples of dominant and recessive traits in humans (at one gene locus)

63. Autosomal dominant traits
Huntington disease is a progressive nerve degeneration, usually beginning about middle age, that results in severe physical and mental disability and ultimately in death
Every affected person has an affected parent
Two unaffected parents will not produce affected children. (aa x aa)
Both males and females are affected with equal frequency.
Pedigrees show no Carriers.

64. Examples of autosomal dominant disorders
Dwarfism
Polydactyly and Syndactyly
Hypertension
Hereditary Edema
Chronic Simple Glaucoma – Drainage system for fluid in the eye does not work and pressure builds up, leading to damage of the optic nerve which can result in blindness.
Huntington’s Disease – Nervous system degeneration resulting in certain and early death. Onset in middle age.
Neurofibromatosis – Benign tumors in skin or deeper
Familial Hypercholesterolemia – High blood cholesterol and propensity for heart disease
Progeria – Drastic premature aging, rare, die by age 13. Symptoms include limited growth, alopecia, small face and jaw, wrinkled skin, atherosclerosis, and cardiovascular problems but mental development not affected.

65. Autosomal recessive traits
Albinism = absence of pigment in the skin, hair, and iris of the eyes
Most affected persons have parents who are “normal” (Aa x Aa)
The parents are heterozygous for the recessive allele and are called carriers (Aa)
Approximately 1/4 of the children of carriers are affected (aa)
Close relatives who reproduce are more likely to have affected children.
Both males and females are affected with equal frequency.
Pedigrees show both male and female carriers.

66. Examples of autosomal recessive traits
Congenital Deafness
Diabetes Mellitus
Sickle Cell anemia
Albinism
Phenylketoneuria (PKU) – Inability to break down the amino acid phenylalanine. Requires elimination of this amino acid from the diet or results in serious mental retardation.
Galactosemia – enlarged liver, kidney failure, brain and eye damage because can’t digest milk sugar
Cystic Fibrosis – affects mucus and sweat glands, thick mucus in lungs and digestive tract that interferes with gas exchange, lethal.
Tay Sachs Disease – Nervous system destruction due to lack of enzyme needed to break down lipids necessary for normal brain function. Early onset and common in Ashkenazi Jews; results in blindness, seizures, paralysis, and early death.

67. Why we look the way we look...
Mendel and Heredity