1. Chapter 9 - Introduction to Genetics
Genetics – the branch of Biology that studies heredity – how traits are passed on.

3. Chromosomes
Humans have 46 chromosomes arranged in 23 pairs (44 autosomes and 2 sex chromosomes)
Chromosomes are made up of DNA and Proteins
Chromosomes and therefore the DNA can be divided into genes
Genes are short segments of DNA

4. Chromosome with genes

6. Karyotype-a picture of chromosomes

7. Allele – alternate form of a gene
Example: Brown/blue, tall/short
can be represented by a letter
Example: Brown – B
Blue - b

8. Homologous Chromosomes
Determines eye
color
Genes
Determines hair
color

9. Brown Allele
Blue Alleles
Blue Allele b b b B
One pair of your chromosomes
for eye color
One pair of your chromosomes
for eye color

10. Brown Allele
Blue alleles
Blue Allele b b b B
Homozygous – alleles are the same
Heterozygous – alleles are
different

11. Homozygous (pure) The two alleles are the same
The two letters are the same
BB or bb
Homozygous Dominant – BB
Homozygous Recessive - bb

12. Heterozygous (hybrid)
The two alleles are different
The two letters are different Bb

13. Dominant Gene A gene that will be expressed if it is present
Examples – brown, tall, green, purple
Written as a capital letter

14. Recessive Gene
A gene that will only be expressed if there are two alleles present
Recessive genes are not expressed if there is a dominant gene present
Short, blue, yellow, white
Written as a lower case letter

15. Genotype The two alleles an organism has What the genes “say”
Ex. BB, Bb, bb

16. Phenotype Physical appearance of an organism
The result of the expression of the genes
Example: tall, short, brown, blue

17. The Goal
The goal of genetics is to determine the possible offspring that can be produced from two parents
The likelihood of an outcome is determined through the laws of probability

18. Probability The likelihood that a specific event will occur
Can be expressed as a decimal, percent or a fraction

19. Equation for Probability
Number of times an event
is expected to happen
Probability =
The number of opportunities
for an event to happen

20. Probability Example You flip a coin once
The probability of getting tails is ½
You flip a coin twice
The probability of getting tails twice is 1/4 1 1 1 = X 4 2 2

21. T H or
First Flip
Second Flip
If I got Tails on the first flip I can either get heads or tails
On the second flip H T

22. Second
Probability of getting:
First H
1/4 H T
1/4 H
1/4 T T
1/4

23. Gametes Egg or sperm Haploid Contains half the number of chromosomes
One gene from each homologous pair

25. Early Ideas on Heredity
Until the 19th century it was thought that the reason people look like their parents is because they were a blend of both parents.
The work of Gregor Mendel changed the views of how characteristics are passed on from 1 generation to the next.

26. Gregor Mendel Born in 1822 in Austria
Studied at the University of Vienna
Became a priest and lived in a monastery
He was in charge of the garden and he studied pea plants

27. Gregor Mendel Pea flowers have both male and female parts
They normally produce seeds through self-pollination
The pollen from the male flower part fertilizes the egg from the female flower part of the same flower
These seeds would inherit all their characteristics from the single plant that bore them

28. Gregor Mendel
Mendel figured out that self-pollination could be prevented
He cut the male parts off of 1 plant and the female parts off another plant
Then he pollinated the 2 plants by dusting the pollen from one onto the flower of the other
This is known as cross-pollination
Produces seeds with the characteristics of both plants

29. Gregor Mendel Mendel had a stock of peas that were purebred
They would only produce offspring that were identical to them
He decided to cross plants with different characteristics to produce hybrids
He studied a few isolated characteristics to simplify his experiments

30. Cross pollination

31. Gregor Mendel Pea Traits Studied Seed Shape Seed Color Seed Coat Color
Pod Shape
Pod Color
Flower Position
Plant Height
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
White
Constricted
Terminal
Short

32. Genetic Crosses
When doing genetic crosses it is important to keep tract of the generations
P1 – parents
F1 – children of the parents (P1)
F2 – Children of the F1’s

33. GG gg Gg gg GG Gg

34. A Genetic Cross Punnett Square – used to predict the possible outcomes
of a cross

35. AA aa aa Male produces one type of sperm with the gene A
        
        
Male produces one
type of sperm with
the gene A
Female produces one
type of egg with
the gene a

36. The Baby Elephants will be..Aa Aa Aa Aa

37. Monohybrid Cross a a Aa A A

38. How to fill in the Punnett Square

39. Monohybrid Cross Cross where one trait is looked at
Dark elephant vs. light elephant

40. Aa Aa Male produces two Female produces two types of sperm with
        
        
Male produces two
types of sperm with
the gene A or a
Female produces two
type of eggs with
the gene A or a

41. The Baby Elephants will be..Aa AA aa Aa

43. Genotypic Ratio Ratio of the offspring's genotypes Genotypic Ratio:
1:2:1
EE – 1
Ee – 2
ee – 1

44. Phenotypic Ratio Ratio of the offspring's phenotypes Phenotypic ratio:
3:1
3 – smooth
1- wrinkled

45. Phenotypes?
Genotypic Ratio?
Genotypes?
Phenotypic Ratio?

46. Law of Segregation
A pair of genes is segregated or separated during the formation of gametes

47. Law of Independent Assortment
Genes for different characteristics are not connected
They are inherited independently

48. Dihybrid Cross
A cross between individuals that involves two pairs of contrasting traits
Look at hair color and eye color at the same time
Look at height and color at the same time

49. Dihybrid Cross Punnett Square

50. AABB
aabb AB ab ab AB AB AB ab ab

51. Sperm
Egg AB ab
Fertilization
AB ab
AaBb
Genes in the fertilized egg

52. Dihybrid Cross Two traits are crossed at the same time
Color and height
A=tall a=short
B=Yellow b=white
AaBb x AaBb

53. B AB A b Ab aB B b ab a How to find genes for the gametes
of a dihybrid cross B AB A b Ab aB B a b ab

54. ab ab ab ab
AaBb AB AB AB AB

55. AaBb
Genotypic Ratio:
Phenotypic Ratio:

56. What if the Dihybrid cross has heterozygous parents?
How do you find the gametes?

57. AaBb
AaBb AB AB Ab Ab aB ab aB ab

59. B=black
b=brown
S=Short hair
S=long hair

62. Dihybrid Heterozygous Cross Genotypic Ratio
1:2:1:2:4:2:1:2:1

63. Testcross
When an individual of unknown genotype is crosses with a homozygous recessive individual
B? x bb

65. The End