1. Mendel's
Genetics

2. The Terms

4. Gene – composed of DNA. The sequence of bases in DNA will code for the production of protein (trait).
Allele – one of the two genes responsible for a specific trait; symbolized by letters
T, t

5. Locus – the position of the gene on the chromosome
Gene Pool – all the genes of a population
Dominant – the “stronger” gene shown up in the offspring (capital letter)
Recessive – the “weaker” gene that doesn’t necessarily show up in the offspring (lowercase)

6. Homozygous – have two of the same alleles (pure) for the trait
TT, tt
Heterozygous – have two different genes for the trait (hybrid) Tt
Tt will tend to show stronger trait

7. Homozygous
Heterozygous

8. What is Homozygous? Homozygous (pure)
Having a pair of identical genes for a trait
Ex: Tall (T) = TT, or tt

9. What is Heterozygous? Heterozygous (hybrid)
Having two different genes (alleles) for a trait
Ex: Tt

10. Phenotype – physical appearance of the individual
Ex: brown hair, blue eyes, widow’s peak, etc.
Genotype – the genetic makeup of the individual
Ex: Is the person homozygous dominant, homozygous recessive, or heterozygous

11. Phenotype

12. Phenotype Phenotype – the physical and observable characteristics
Ex: Tall, short, brown eyes, blond hair, freckles

13. Genotype

14. Genotype
Genotype – the genetic makeup of an individual
Ex: TT, Tt, tt

15. Gregor
Mendel

16. Gregor Mendel Gregor Mendel (1860’s) father of genetics
He used pea plants because
Few Traits
Easy to Grow
Had a lot of offspring
Reproduce quickly
He came up with a couple of laws for determining heredity

17. Mendel’s Laws we will be discussing are:
The Law of Dominance
The Law of Segregation
The Law of Independent Assortment

18. The Law
of Dominance

19. Law of Dominance
In a cross between 2 pure contrasting traits (tall vs. short), only one of these traits appear in the next generation
This is called the DOMINANT TRAIT
The one that does not appear is called the RECESSIVE TRAIT
(Tongue-curling is dominant)

20. LAW OF DOMINANCE

21. Attached Earlobes are Dominant and free earlobes are Recessive
                                        
                                        
Attached Earlobes are Dominant and free earlobes are Recessive

22. Widow’s Peak is Dominant and no widow’s peak is Recessive
                                        
Widow’s Peak is Dominant and no widow’s peak is Recessive

23. A Fruit Fly with red eyes is Dominant and white eyes is Recessive

24. The Law
of Segregation

25. History:
Mendel worked with pea plants and selected seven traits to study that each occurred in two different forms.
For instance, one trait he studied was pod color.
Some pea plants have green pods and others have yellow pods.
Since pea plants are capable of self fertilization, Mendel was able to produce true-breeding plants.
A true-breeding yellow-pod plant for example would only produce yellow-pod offspring.
Mendel then began to experiment to find out what would happen if he cross-pollinated a true-breeding yellow pod plant with a true-breeding green pod plant.
He referred to the two parental plants as the parental generation (P generation) and the resulting offspring were called the first filial or F1 generation

26. Law of Segregation
When Mendel performed cross-pollination between a true-breeding yellow pod plant and a true-breeding green pod plant, he noticed that all of the resulting offspring, F1 generation, were green.

27. Law of Segregation
He then allowed all of the green F1 plants to self-pollinate. He referred to these offspring as the F2 generation.
Mendel noticed a 3:1 ratio in pod color.
About 3/4 of the F2 plants had green pods and about 1/4 had yellow pods.

28. Law of Segregation:
From these experiments Mendel formulated what is now known as Mendel's law of segregation.
This law states that allele pairs (genes) separate or segregate during gamete formation (meiosis), and randomly unite at fertilization

29. The Law
of Independent
Assortment

30. Independent Assortment
This principle states that two or more pairs of alleles for a trait separate when gametes are formed. These allele pairs are then randomly united at fertilization.

31. Mendel performed dihybrid crosses in plants that were true-breeding for two traits. For example, a plant that had green pod color and yellow seed color was cross-pollinated with a plant that had yellow pod color and green seeds. In this cross, the traits for green pod color (GG) and yellow seed color (YY) are dominant. Yellow pod color (gg) and green seed color (yy) are recessive. The resulting offspring (Figure A) or F1 generation were all heterozygous for green pod color and yellow seeds (GgYy).

33. Punnett
Square

34. The Punnett Square
Determines the probability of obtaining various results in genetic crosses
Ex: cross a heterozygous tall (Tt) and a heterozygous tall (Tt)

35. Cross 2 Heterozygous Traits:

38. Cross a homozygous freckles with heterozygous freckles
F = Freckles
f = no freckles

39. Genotypes:
50% homozygous dominant
50% heterozygous
Phenotypes:
100% Freckles

40. Monohybrid Cross
Crossing one trait
Ex: Crossing height

41. Cross a heterozygous freckles with heterozygous freckles
F = Freckles
f = no freckles

42. Genotypes:
25% homozygous dominant
50% heterozygous
25% homozygous recessive
Phenotypes:
75% Freckles
25% No Freckles

43. Dihybrid Cross
Crossing 2 traits
Ex: crossing height and color

44. Backcross

45. Backcross – Is done to determine the genotype of an organism
Unknown genotype x Pure recessive
B = black
b = white

46. Incomplete
Dominance

47. Incomplete Dominance PINK
With incomplete dominance we get a blending of the dominant & recessive traits so that the third phenotype is something in the middle (red x white = pink).
Ex: Cross a pure red snapdragon (RR) and a pure white snapdragon (WW) (notice that only capital letters are used)
Offspring Phenotype: ____________________
Neither trait dominates the other, which is why it is called incomplete dominance
PINK

48. Cross a pink snapdragon (RW) with a pink snapdragon (RW)
R = Red
W = White
Results:

50. Chickens

51. Andalusian Chickens

52. Codominance

53. Codominance
In Codominance, both of the dominant traits appear together in the phenotype
Ex: Roan cattle
Cross a homozygous red coat cow (RR) and a homozygous white coat cow (WW)

55. Roan Cattle

56. Cross a homozygous red cow (RR) with a homozygous white cow (WW)
R = Red
W = White
Results:

57. Multiple
Alleles

58. Multiple Alleles
If there are 4 or more possible phenotypes for a particular trait, then more than 2 alleles for that trait must exist in the population
We call this “multiple alleles”
Ex: Human blood type
Blood type exists as four possible phenotypes: A, B, AB, and O
There are 3 alleles for the gene that determines blood type:
IA = Type A
IB = Type B
i = Type O
Note that according to the symbols used, that the allele for “O” (i) is recessive to the alleles for “A” and “B”

60. Blood Type:
Cross a man with AB blood (IAIB) and a woman with type O blood (ii)

61. Blood Type:
A man with AB blood is married to a woman with AB blood. What blood types will their children be and in what proportion?

62. What
Determines
Gender?

63. Gender
Chromosomes determine everything from hair color and eye color to gender.
Whether you are a male or female depends on the presence or absence of certain chromosomes.
Human cells contain 23 pairs of chromosomes for a total of 46.
There are 22 pairs of autosomes and one pair of sex chromosomes.
The sex chromosomes are the X chromosome and the Y chromosome.
These chromosomes determine gender.

64. Males determine Gender?
Sperm cells in humans and other mammals contain one of two types of sex chromosomes.
They are either X or Y.
The female gametes or eggs however, contain only the X sex chromosome.
Therefore, the sperm cell determines the sex of an individual
If a sperm cell containing an X chromosome fertilizes an egg, the resulting zygote will be XX or female.
If the sperm cell contains a Y chromosome, then the resulting zygote will be XY or male.

65. Karyotype of a normal male with 22 pairs of autosomes and one pair of sex chromosomes.