1. Introduction to Genetics
BIO 1 Chapter 11
Introduction to Genetics

2. 11-1 The Work of Gregor Mendel
Gardener in Austrian monastery
Born 1822
Called the “Father of Genetics”
Used pea plants because
Traits exist as clearly different forms ex: flower is white or purple
Both Male & female parts in plants, so self-fertilization can occur or can cross-pollinate
Small, grow easily, mature quickly
YouTube - Mendel - From the Garden to the Genome

3. Heredity- passing on of characteristics from parents to offspring
Genetics- study of heredity or traits & characteristics

4. Mendel used “Self-pollinating” peas to produce future offspring
Knew that each flower produces both male (sperm –found in pollen) and female (egg) gametes
Fertilized flower’s egg with its own sperm
Produced what he called “true - breeding”
Offspring would be genetically identical

5. Cross Pollination

6. Trait – specific characteristic that varies from one individual to the next
Important that Mendel used traits that were unambiguous

7. Monohybrid crosses- cross 1 pair of contrasting traits
P generation- parents, first two crossed
F1 generation- first offspring, PxP
F2 generation- F1 x F1
Plants that were
products of cross
-pollination are known
as “hybrids.”

8. Mendel’s Hypothesis
For each inherited trait, an individual has 2 copies of the gene, one from each parent
There are alternative versions of genes = alleles (purple, white)
When two different alleles occur together, one of them may be expressed, while one is covered up

9. Short and tall = alleles
Definitions
Mendel concluded that heredity is dictated by chemical factors called genes
(about 100 years later before Watson & Crick and the whole DNA thing)
Genes have alternate forms depending on the plant
These alternate versions of the same gene are called alleles
Plant height = gene
Short and tall = alleles
Both alleles are present.
One type (recessive) can only be expressed if the other (dominant) is not present

10. Definitions Dominant- expressed trait (D) Recessive- not expressed (d)
Homozygous- both letters are same, either both capital or both lowercase (DD or dd)
Heterozygous- one of each, dominant allele is expressed (Dd)
Genotype- set of alleles (DD or Dd or dd)
Phenotype- physical appearance (purple or white flowers)

11. Laws
Law of Segregation- the 2 alleles separate when gametes are formed
Law of Independent Assortment- one trait doesn’t affect the inheritance of another (purple/white flowers has nothing to do with smooth/rough pod)

12. 11-2 Probability and Punnett Squares
Probability – likelihood of an event to take place
What are the chances for a coin to be flipped heads three times in a row?
½ X ½ X ½ = ⅛
Probability explains everything in predicting outcomes of genetic crosses

13. Probability Rules for combining probabilities
1. Probability that one event out of a set of mutually exclusive events will occur is the sum of their probabilities. (Mutually exclusive events cannot occur together.) (Look for the word “or”.)
Ex. What is the probability of rolling a 3 or a 6 on a 6-sided dice?
p = 1/6 + 1/6 = 2/6 or 1/3

14. Probability
Probability that both of two independent events will occur is the product of the independent probabilities of the single events. (Independent events do not affect each other.)(Look for the word “and”.)
Ex. What is the probability that I roll a 1 and a 3 when rolling two 6-sided dice?
p = 1/6 x 1/6 = 1/36

15. Punnett Squares 1 pair of traits: The letters represent alleles
< Homozygous recessive
Homozygous dominant
All offspring are
heterozygous

16. Genotypic
Ratio ? 1. 2.
Phenotypic
Ratio? 3. 4.

20. 7. A heterozygous round seeded plant (Rr) is crossed with a homozygous round seeded plant (RR). What percentage of the offspring will be homozygous (RR)? ____________ A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. What are the genotypes of the parents? __________ x __________ What percentage of the offspring will also be homozygous? ________

21. 9. In pea plants purple flowers are dominant to white flowers
9. 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? ______________ A white flowered plant is crossed with a plant that is heterozygous for the trait. What percentage of the offspring will have purple flowers? _____________ Two plants, both heterozygous for the gene that controls flower color are crossed. What percentage of their offspring will have purple flowers? ______________ What percentage will have white flowers? ___________

22. 12. In guinea pigs, the allele for short hair is dominant
12. In guinea pigs, the allele for short hair is dominant. What genotype would a heterozygous short haired guinea pig have? _______
What genotype would a purebreeding short haired guinea pig have? _______
What genotype would a long haired guinea pig have? ________
13. Show the cross for a pure breeding short haired guinea pig and a long haired guinea pig. What percentage of the offspring will have short hair? __________

23. 14. Show the cross for two heterozygous guinea pigs.
What percentage of the offspring will have short hair? ________
What percentage of the offspring will have long hair? _______
15. Two short haired guinea pigs are mated several times. Out of 100 offspring, 25 of them have long hair.
What are the probable genotypes of the parents? ________ x ___________
Show the cross to prove it!

24. 11-3 Exploring Mendelain Genetics
A. Independent Assortment
1. The Two-Factor Cross: F1
2. The Two-Factor Cross: F2
B. A Summary of Mendel’s Principles
C. Beyond Dominant and Recessive Alleles
1. Incomplete Dominance
2. Codominance
3. Multiple Alleles
4. Polygenic Traits
D. Applying Mendel’s Principles
E. Genetics and the Environment

25. Dihybrid Crosses-
“FOIL” method
AaBb x AaBb

26. P X P
F1 generation=
100% RrYy

27. F1 X F1 = F2 generation
9 round, yellow: 3 round, green: 3 wrinkled yellow: 1 wrinkled, green

28. Practice
RRBb X Rrbb

29. Practice
rrBb X RrBB

31. 3. A male rabbit with the genotype GgBb
3. A male rabbit with the genotype GgBb . Determine the gametes produced by this rabbit (the sperm would have these combinations of alleles) Hint there are 4 combinations.
4. A female rabbit has the genotype ggBb. Determine the gamets (eggs) produced by this rabbit.

32. 5. Use the gametes from #4 and #5 to set up the punnett square below
5. Use the gametes from #4 and #5 to set up the punnett square below. Put the male's gametes on the top and the female's gametes down the side. Then fill out the square and determine what kind of offspring would be produced from this cross and in what proportion.

33. Science Starter:
An aquatic arthropod called a Cyclops has antennae that are either smooth or barbed. The allele for barbs is dominant. In the same organism, resistance to pesticides is a recessive trait.
A Cyclops that is resistant to pesticides and has smooth antennae is crossed with one that is heterozygous for both traits. Show the genotypes of the parents and then complete a punnett square showing the results: ______________ x _______________
_______ have barbed antennae and are not resistant to pesticides
______ have barbed antennae and are resistant to pesticides.
_______ have smooth antennae and are not resistant to pesticides
_______ have smooth antennae and are resistant to pesticides

34. 8. Set up a punnett square for the cross.
9. What are the phenotypic ratios of the offspring?

35. Beyond Dominance and Recessiveness
Not all genes show simple patterns of dominant and recessive alleles. Genetics is more complicated.
The majority of genes have more than 2 alleles.
Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

36. Incomplete Dominance A cross between two 4-o’clock plants:
Red flowered RR
White flowered WW
Which is dominant?
Incomplete Dominance:
Cases in which one allele is not
completely dominant over another

37. Incomplete Dominance Examples
In horses, some of the genes for hair color are incompletely dominant. Genotypes are as follows: brown horses are BB, white horses are WW and a WB genotype creates a yellow-tannish colored horse with a white mane and tail, which is called “palomino”. Show the genetic crosses between the following horses and record the genotypic and phenotypic percentages:
1. Brown x white
2. Brown X palomino
3. Palomino X palomino

38. Codominance
Similar to incomplete dominance however both traits are actually visual instead of blended
Chickens with speckled black spots on white feathers
Humans have gene for protein controlling cholesterol – if heterozygous two forms are made

39. When there are more than two alleles for a particular gene
Multiple Alleles
When there are more than two alleles for a particular gene
Blood type (also demonstrates some codominance)
Polygenic traits
Traits controlled by many genes
Height
SLE (Lupus)
Weight
Eye Color
Intelligence
Skin Color
Many forms of behavior

41. Applying Mendel’s Principles
Good animal to test was fruit fly
Drosophilia melanogaster
Fast reproductive rate/life cycle and produced many offspring

43. Environmental impact on gene expression
Environmental factors/conditions may alter gene expression.
Example: Soil pH and flower color.

44. 11-4 Meiosis A. Chromosome Number B. Phases of Meiosis
1. Meiosis I
2. Meiosis II
C. Gamete Formation
D. Comparing Mitosis and Meiosis

45. Meiosis Process of turning diploid somatic cells into haploid gametes
Must reduce chromosome number so when fertilization takes place we re-establish the regular chromosome number
Humans
Hapolid – sex cells N = 23
Diploid – somatic cells 2N = 46

46. Figure Meiosis
Section 11-4
Meiosis I

47. Figure Meiosis
Section 11-4
Meiosis I
Meiosis I

48. Figure Meiosis
Section 11-4
Meiosis I
Meiosis I

49. Figure Meiosis
Section 11-4
Meiosis I

50. Figure Meiosis
Section 11-4
Meiosis I

51. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

52. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

53. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

54. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

55. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

56. Crossing Over Parts of chromosomes “switch places
A tetrad forms in prophase 1
4 chromosomes to a tetrad

57. Gamete Formation Figure 11-17 on page 278 Males Females
Animals = sperm
Flowering plants = pollen
4 equal sized gametes
Females
Animals = egg
Flowering plants = ovule
Only 1 large egg results from meiosis, the other 3 cells are called polar bodies and not involved in reproduction.

58. Mitosis VS. Meiosis Mitosis Meiosis Purpose Location in Body
Number of Daughter Cells
Change in chromosome number
Number of phases
Number of Cell Divisions
Difference in DNA between parent cell and daughter cell

59. 11-5 Linkage and Gene Maps
Found that some genes were linked to other ones
Seems to violate the rule of independent assortment
Ex: fruit flies – red eyes and miniature wings
Mendel missed this….
He thought the genes independently assorted
Actually it was the chromosomes that do!
Why did he miss it?
6 of the 7 genes he studied in peas were on separate chromosomes
The two that were on the same chromosome were so far apart they independently assorted

60. Gene Maps
Do two genes on the same chromosome mean they are forever linked?
No! Crossing over may put them on separate chromosomes
The further apart genes are the more likely they could be separated during meiosis
Low rate of separation and then recombination means genes are close to one another.