1. Genetics
Explain the basic rules and processes associated with the transmission of genetic characteristics

2. Describe the evidence for dominance, segregation and the independent assortment of genes on different chromosomes, as investigated by Mendel

3. Introduction Heredity Genetics Gregor Mendel
is the passing of traits from parents to offspring
Genetics
is the study of the patterns of inheritance as hereditary characteristics or traits
Gregor Mendel
the "father of modern genetics“
an Austrian monk
published his completely new and thoroughly documented ideas of inheritance in 1866

4. Introduction
His model was so simple that scientists who read it at that time considered it "trivial“
it received little attention and no recognition until it was rediscovered in 1900 after his death (simultaneously by 3 different people)
In the meantime,
chromosomes had been named
their movements during mitosis and meiosis observed and described

5. Introduction
1902
scientists realized that chromosomes moved precisely as reported by Mendel
Once the connection between chromosomes and heredity was established, the science of genetics was reborn
Mendel was the first person to realize that genetic traits are inherited as separate particles

6. Introduction He did not actually see these particles
but he predicted their existence based on patterns of inheritance
He proposed that organisms have a pair of "factors" for each trait
one from each parent
We NOW know that the particles of inheritance are segments of DNA
which we call genes

7. Mendel's Experiments Mendel worked with garden peas
available in many different varieties
E.g. pure breeding tall, pure breeding dwarf
Pea flowers contain both male and female parts and normally self-pollinate
but can easily be artificially cross-pollinated with other pea plants
Mendel crossed plants of two varieties with contrasting traits (such as tall and dwarf) to see what would happen.

8. Mendel's Experiments
Mendel worked with seven traits, each which occurred in two distinct forms
Mendel began by studying crosses involving only one trait at a time
Example: Flower color
P1: (parental generation)
pure-breeding red flowered plants X pure-breeding white flowered plants
F1: (first filial generation)
red-flowered hybrids (genetically mixed offspring)
F2: (second filial generation)
3/4 red-flowered and 1/4 white-flowered

9. Mendel's Laws
Inherited characteristics are controlled by pairs of factors
genes
one from each parent.
One gene may “mask” the effect of another.
The gene which is expressed is dominant, while the one which is masked is recessive.
Pairs of genes segregate during gamete formation
so each sex cell contains only one member of a pair of genes.

10. Terms Alleles Homozygous Heterozygous
Two or more alternate forms of a gene, which produce contrasting effects for a certain trait
e.g. red (R) and white (r) for flower colour of peas
Homozygous
having two of the same allele
eg. red/red (RR)
purebred
Heterozygous
having two different alleles eg. red/white (Rr)

11. Terms Genotype Phenotype Purebred Hybrid
the genetic makeup of an individual
Phenotype
the expression of the genes, or appearance of an individual
Purebred
an organism having all homozygous gene pairs
Hybrid
an organism having at least one heterozygous gene pair

12. Terms Monohybrid Dihybrid
an organism having only one heterozygous gene pair
Dihybrid
an organism having two heterozygous gene pairs

13. Monohybrid Cross Purebred Red Purebred White Phenotypes x Rr Rr Rr Rr
Genotypes Rr Rr Rr Rr
F1 Genotypes

14. Monohybrid Punnet Square
Genotype of Parent #2
Male
Female R R
Gametes !! r Rr Rr
Genotype of
Parent #1 r Rr Rr

15. Monohybrid Cross Purebred Red Purebred White Phenotypes x Rr Rr Rr Rr
Genotypes Rr Rr Rr Rr
F1 Genotypes Rr x Rr
F1 Self Pollenate RR Rr rR rr
F2 Genotypes

16. Monohybrid Cross Purebred Red Purebred White Phenotypes x Rr Rr Rr Rr
Genotypes Rr Rr Rr Rr
F1 Genotypes Rr x Rr
F1 Self Pollenate RR Rr Rr rr
F2 Genotypes

17. The phenotypic ratio for a monohybrid cross is always 3:1
dominant trait : recessive trait

18. Predicting the Outcome of a Genetic Cross
When we know the genotypes of parents used in a genetic cross, we can predict the genotypes of the offspring and their expected ratios
Must use a Punnett square is used
named after some guy named Punnett
A geneticist
Basically it’s a just a fancy chart

19. Monohybrid Punnet Square
Genotype of Parent #2
Male
Female R R
Gametes !! r Rr Rr
Genotype of
Parent #1 r Rr Rr

20. Practice

21. If an organism has the dominant phenotype, how can you determine whether it is homozygous or heterozygous?

22. Test Cross You conduct a test cross. For example:
Mate it with an organism of a known genotype and see what you get.
The only known genotype that is observable is HOMOZYGOUS RECESSIVE (rr)
For example:
determine whether a red-flowered pea plant is homozygous or heterozygous

23. Test Cross P: Red flowered X White-flowered R? rr
F1: Suppose the cross produces all red flowers
  Rr Rr Rr Rr
If no offspring showing the recessive phenotype are produced, the unknown parent must be …
homozygous

24. Purebred Red Purebred White Phenotypes x Rr Rr Rr Rr RR rr Genotypes
F1 Genotypes

25. Test Cross P: Red flowered X White-flowered R? rr
F1: Suppose the cross produces 50% red flowers and 50% white flowers
The only way a white flower could appear is if it received a recessive allele from the unknown parent.
The unknown parent must be …
HETEROZYGOUS

26. Rr x rr P1 Rr Rr rr rr
F1 Genotypes

27. Dihybrid Cross
In addition to his monohybrid crosses, Mendel performed dihybrid crosses of plants with two different pairs of contrasting alleles
In one experiment, Mendel crossed plants homozygous for seeds that were both round and yellow with plants homozygous for wrinkled, green seeds

28. Dihybrid Cross All the F1 offspring had round, yellow seeds
Self-fertilization of the F1 plants produced and F2 generation of seeds with the following phenotypes:
315 round yellow
108 round green
101 wrinkled yellow
32 wrinkled green

29. Dihybrid Cross To find the ratio among the F2 phenotypes,
we take the number of offspring in the smallest category and divide it into the number of offspring in the other categories:
then the quotient is rounded to the nearest whole number

30. Dihybrid Cross
Thus Mendel determined the phenotypic ratio in the F2 generation to be 9:3:3:1
This is the ratio typical of a dihybrid cross in which both pairs of alleles show a dominant-recessive relationship

31. Dihybrid Cross
Mendel explained these data by assuming that the genes governing seed color and seed shape move independently during gamete formation
In the process of independent assortment, each pair of alleles behaves as it would in a monohybrid cross - independently of the other pair 
A dihybrid can produce four possible gene combinations (with equal probability)
If the alleles are:
R = round r = wrinkled
Y = yellow y = green
The possible gamete combinations are
RY Ry rY ry

32. Dihybrid Cross RRYY x rryy RY ry RrYy RY, Ry, rY, ry Parent:
P Gametes:
F1:
F1 Gametes:
F2:
RRYY x rryy
 RY ry
RrYy
 RY, Ry, rY, ry
9/16 round, yellow (R_Y_)
3/16 round, green (R_yy)
3/16 wrinkled, yellow (rrY_)
1/16 wrinkled, green (rryy)

35. Practice

36. Multiple Alleles & Incomplete Dominance

37. Compare ratios and probabilities of genotypes and phenotypes for dominant and recessive, multiple, incomplete dominant, and codominant alleles
Explain the relationship between variability and the number of genes controlling a trait

38. Multiple Alleles
The genes which we have studied so far have only two different alleles:
Many genes actually exist in more than two allelic forms,
Although only two genes control coat colour in rabbits it is controlled by a series of four alleles for the same gene:
C Full colour
Cch Chinchilla
ch Himalayan
c Albino

39. Multiple Alleles
The dominance hierarchy of these alleles is C > Cch > ch > c
Determine the genotypes for the following phenotypes:
Phenotype Possible Genotype
Full color
Chinchilla
Himalayan
Albino
C + any of the 4
Cch+ anything but C
ch ch, ch c
c c

40. Incomplete Dominance
In some cases, a heterozygous organism shows a blending of genes because neither gene is dominant:
this is termed incomplete dominance
for example, in snapdragons, neither the red nor the white allele is dominant…

41. Red Flowers x White Flowers
Incomplete Dominance
Parent:
F1:
F2:
Red Flowers x White Flowers
Pink Flowers
¼ Red flowers
½ Pink flowers
¼ White flowers
RR x rr
Rr, Rr, Rr, Rr RR Rr rr

42. Codominance
If two different alleles each contribute to a phenotype, they are termed codominant
One of the best-known example of codominant genes occurs in humans, and determine ABO blood types
There are three possible alleles: IA IB i

43. Codominance Blood Type
Phenotype
Possible Genotypes A
IA IA, IA i B
IB IB, IB i AB
IA IB O
i i

48. Practice

49. Chromosome Mapping
Explain the influence of gene linkage and crossing over on variability

50. Chromosomal Theory of Inheritance
Chromosome Mapping
Chromosomal Theory of Inheritance
Genes are located on chromosomes
Chromosomes undergo segregation during meiosis
Chromosomes assort independently during meiosis
Each chromosome contains many different genes

51. Random Assortment

52. Chromosome Mapping
Each chromosome contains hundreds or thousands of genes
Genes located on the same chromosome are inherited together,
they are part of a single chromosome that is passed along as a unit
such genes are said to be linked

53. Chromosome Mapping
during meiosis, chromosomes may exchange segments of DNA by crossing-over
A A a a
B B b b
C C c c
D D d d
E E e e
F F f f

54. Chromosome Mapping
during meiosis, chromosomes may exchange segments of DNA by crossing-over
A A a a A a A a
B B b b B B b b
C C c c C C c c
D D d d D D d d
E E e e E e E e
F F f f F f F f

55. Crossing Over

56. Chromosome Mapping
The closer two genes are on a chromosome, the fewer the possible points of crossover are between them, and the less frequently such a cross-over will occur
In other words, if two genes are close together on a chromosome it is likely they will stay together and not be exchanged between chromatids during meiosis
To determine the location of genes along a chromosome is called MAPPING a chromosome

57. Chromosome Mapping A chromosome map indicates
The order in which specific genes occur on a chromosome
The distances between the genes

58. Chromosome Mapping Example:
In Drosophila, the following data was obtained from genetic crosses: 
13% recombination between bar eye and garnet eye
High percentage recombination indicates that these two genes are far apart from each other
High likelihood that crossing over will occur between these two genes.
7% recombination between garnet eye and scalloped wings
These two genes are closer together than bar eye and garnet eye
6% recombination between scalloped wings and bar eye

59. Chromosome Mapping This data can be used to map the chromosome:
 Bar eye Scalloped wings Garnet eye
6 units units
13 units

60. Chromosome Mapping

61. Sex Determination
There are two chromosomes involved in the determination of sex of most animals,
the sex chromosomes (X & Y)
Any other chromosome not involved in sex determination is called an autosome
for example, humans have 22 pairs of autosomes and 1 pair of sex chromosomes
in most mammals, females are homozygous and have 2 X chromosomes, while males are heterozygous and carry an X and a Y chromosome

62. Sex Determination Female = XX Male = XY
Females can produce eggs carrying only an X chromosome,
Males produce sperm carrying either an X or a Y chromosome (50% of each)
Thus, it is the male who determines the sex of his offspring !

63. Sex Linkage
Compare the pattern of inheritance produced by genes on the sex chromosomes to that produced by genes on autosomes, as investigated by Morgan and others.

64. every white-eyed fly was male!
A True Story
One day a geneticist named Thomas Hunt Morgan discovered a mutant white-eyed male fly among his hundreds of red-eyed flies. He bred the white-eyed male with several red-eyed females and observed the offspring: as expected, all the F1 flies had red eyes, showing red to be the dominant allele. He allowed the F1 generation to interbreed freely and observed the F2 generation. Again, as expected, the ratio of red-eyed flies to white-eyed flies was 3:1, except that …
every white-eyed fly was male!

65. Explanation … X-chromosome
Morgan concluded that the gene controlling eye-colour was carried on the…
X-chromosome

66. Sex Linkage
Like other chromosomes, the sex chromosomes carry many genes
Some of the regions of the X-chromosome have a homologous region on the Y- chromosome
There are also large non-homologous portions:
That is, the X chromosome carries some genes that have no counterparts on the Y chromosome

67. Sex Linkage
Genes for sex-linked traits are carried on the X chromosome but not on the Y chromosome
Therefore in a male, the gene on the X chromosome is expressed whether it is dominant or recessive
In a female, she must have two recessive alleles to have the recessive phenotype

68. Fly Solution R = Red r = white XR XR = Red eyed Female
Xr Xr = White eyed Female
XR Y = Red eyed Male
Xr Y = White eyed Male

69. Fly Solution P White Eyed Male F1 F2 XR XR x Xr Y XR Xr x XR Y XR XR

70. Example of hemophilia trait – (h) recessive disease

71. Sex Linkage Some sex-linked traits in humans are Colour vision
Hemophilia
Duchenne's Muscular Dystrophy

72. Sex-Influenced Genes

73. Sex Influenced Genes
The main role of sex hormones is to influence the reproductive system and its related organs,
These hormones, however, also affect many other parts of the body
Genes that are expressed to a greater or lesser degree as a result of the level of sex hormones are called sex-influenced genes.

74. Sex Influenced Genes These genes are usually located on the autosomes
Males and females with the same genotype may differ greatly in phenotype because the levels of sex hormones
For example:
A bull may have a gene for high milk production, but he will not produce milk because he has low levels of female hormones.

75. Sex Influenced Genes
In humans, the gene for male pattern baldness is autosomal and sex-influenced
A man will become bald even if he has only one allele for baldness, because
the male sex hormones somehow stimulate the expression of the allele
In a woman, however, the allele acts as a recessive allele so that she must have two balding genes before she loses her hair

76. Lethal Alleles

77. Lethal Alleles
If An organism has a mutation that destroys the genetic code for a protein essential to life, the organism will often die prematurely.
This gene that fails to code for a functional protein is called a lethal allele
It is possible for lethal alleles to be dominant, but most are rapidly eliminated from a population because they cause death before the individual carrying the allele reproduces.

78. Lethal Alleles
An exception of a lethal dominant allele that remains in a population is the one responsible for Huntington's Disease in humans, because this allele is not expressed until later in life ( years of age)
An example of a recessive lethal allele in humans is the one for Brachydactyly:
Heterozygotes have a short middle finger bone that makes the fingers appear to have only two bones instead of three
Homozygous babies lack fingers and have abnormal development of the skeleton that result in death in infancy

80. Homozygous

81. Lethal Alleles Some human examples of lethal alleles are:
Sickle cell anemia
Tay-sachs disease
Cystic fibrosis
Huntington's disease

82. Pedigrees

83. Pedigrees

84. Pedigrees
Because geneticists are unable to manipulate the mating patterns of people, they must analyze the results of matings that have already occurred.
As much information as possible is collected about a family's history for a particular trait, and this information is assembled into a family tree describing the interrelationships of parents and children across the generations
This is called a pedigree

86. Pedigrees
From a pedigree you should be able to determine if a particular trait is dominant or recessive, sex-linked or autosomal
A pedigree not only helps us understand the past but also helps us predict the future
Geneticists, physicians, and genetic counselors use pedigrees
for analysis of genetic disorders
to advise prospective parents of genetic risks involved  
Complete the pedigree studies on page 632 and page 611 as a class.