1. Genes and Heredity

2. Gregor Mendel “The Father of Genetics”
Performed classic experiments with peas to discover the basic laws of heredity
Chose garden peas because they had characteristics that appeared in one of two forms
Also, peas could be self-fertilizing or cross fertilizing
Discovered that some traits were more frequent than others, regardless if trait came from female or male plant
He concluded that some genes dominate others

3. Mendel’s Peas

4. Laws of Heredity
Through carefully recording his results, Mendel was apply to determine basic laws of heredity:
Inherited factors are controlled by genes, which occur in pairs
One gene can mask the effects of another
During the formation of gametes, the paired genes separate (this is known as the law of segregation), thus sex cells only contain 1 gene for each trait, where as a zygote contains 2 genes for each trait

5. Alleles Are two or more alternate forms of a gene
For example, plants have two alleles for seed shape, round and wrinkled
Represented using letters, i.e. T or t represent alleles

6. Represented in genetics using a capital letter (R)
Dominant Genes
Dominant genes are displayed in the presence of recessive genes
For example, in peas, the tall gene dominates over the short gene
When a seed inherits one gene from each parent, it has two genes that code for the same trait
However, the dominant gene will be the one that is displayed in the organism
In peas, the plant would be tall, if it inherited a tall gene, even if it also inherited the gene for shortness
Represented in genetics using a capital letter (R)

7. Recessive Genes Represented in genetics using lower case letters (r)
Recessive genes are displayed in the absence of dominant genes
Thus, an organism must inherit TWO recessive genes to display the recessive trait
Represented in genetics using lower case letters (r)

8. Genotype
Genotype refers to the genes an individual contains for a particular trait
For example, a pea seed may contain the genes for tallness and for shortness
Genotype = TT or Tt or tt

9. Phenotype Phenotype refers to the observable traits of an individual
For example, even though a plant has the genes for shortness and tallness, the observable characteristic is tallness
Phenotype = tall or short

10. TT (homozygous dominant) tt (homozygous recessive)
GENOTYPE: Homozygous
Homozygous is the term that refers to an organism that has two copies of the gene that are the same
Two dominant, or two recessive genes
Both tall genes, or both short genes
TT (homozygous dominant)
tt (homozygous recessive)

11. GENOTYPE: Heterozygous
Heterozygous refers to the term when an individual has two different genes that code for the same trait
One dominant and one recessive
One tall gene, and one short gene
Tt (heterozygous for ___ trait)

12. Single Trait Inheritance
A monohybrid cross consists of contrasting single trait inheritance (one gene – 2 alleles)
For example, a cross between a female with genotype Bb and a male with genotype bb.
Possible offspring can be represented with a Punnett square
Can then be used to calculate frequency

13. Probability: indicates PREDICTED outcome
Actual/Observed outcome:
Ratio of offspring actually observed (imagine that!!)
**Will usually be very CLOSE in numbers to a predicted outcome**
Ratio
Fraction
Percentage

15. Monohybrid Cross (AA; Aa; aa)
The punnett square can help determine the likely genotypes and phenotypes of the offspring.
Ex. Cross between TT and Tt
Ex. Cross between Ww and ww
Ex. Cross between BB and bb

16. Pattern in monohybrid crosses GENOTYPE
TT x tt
TT x Tt
Tt x Tt
Tt x tt
TT x TT or tt x tt
100% Tt
50%TT; 50% Tt (1:1)
25%TT; 50%Tt; 25% tt
Or (1:2:1)
50% Tt; 50% tt (1:1)
100%TT or 100% tt

17. Pattern in monohybrid crosses PHENOTYPE
TT x tt
TT x Tt
Tt x Tt
Tt x tt
TT x TT or tt x tt
100% Dominant
75% D; 25% r
Or 3:1 (D:r)
50% D; 50%r (1:1)
100%D or 100% r

18. Test Cross
When the genotype of the parent is unknown, (i.e. they have one dominant allele, but the other allele is unknown), a test cross can help determine the unknown genotype
Why would we want to determine genotype this way??
What is the purpose of knowing genotype?

20. Mendel used the following notation to designate generations
Generation Notation
Mendel used the following notation to designate generations
P = parental generation (first cross)
F1 = filial generation (offspring of P)
F1 is the outcome of the Punnett square for the parental cross
F2 = outcome of Punnett square for F1
And so on..

21. EXAMPLES: QUESTION TIME!!!
The ability to curl your tongue up on the sides/roll your tongue (T ) is dominant to not being able to roll your tongue (t). (a) A woman who can roll her tongue marries a man who cannot. Their first child has his father’s phenotype.
Predict the genotypes of the mother, father, and child.
(b) Determine the probability that their second child will not be able to roll her or his tongue.

22. Long stems are dominant over short stems for pea plants
Long stems are dominant over short stems for pea plants. A heterozygous long-stem plant is crossed with a short-stem plant.
Determine and identify the genotypic and phenotypic ratio of the F1 progeny from the cross.

23. Dominant and Recessive
STOP LAMB
Part 1 -Monohybrid
Dominant and Recessive

24. Other Patterns of Inheritance (single trait) (Other than simply DOMINANT AND RECESSIVE)
Most traits are not controlled by simply 2 allele genes
Some traits can be a combination of multiple allele genes
Examples:
Dominance Hierarchy (act like D/r)
Incomplete Dominance (MIXING)
Codominance (BOTH SHOW)

25. Dominance Hierarchy E1 > E2 > E3 > E4
A dominance hierarchy consists of multiple phenotypes, with genes that are rated in terms of how dominant they are
E1 > E2 > E3 > E4

26. E1 > E2 > E3 > E4 Consider the fruit fly:
E1 is the dominant gene, over E2, E3 and E4
Example
E1 > E2 > E3 > E4

27. Multiple Alleles – Blood Types
4 blood types are controlled by ONE GENE with 3 alleles
Blood type is determined by the antigen marker on the RBC’s
Blood type designation – see DATA SHEET
GENE is designated I
Blood type is designated by superscript letter (A or B) or by i
IA = A antigen
IB = B antigen
(IAand IB are co-dominant – both are displayed)
i = no antigen (recessive to IAand IB)

28. Part 2A – Multiple Alleles/Dominance Hierarchy

29. Incomplete Dominance
Incomplete dominance occurs when two genes interact, and neither one is dominant to the other
When both alleles are inherited, a third, new phenotype is displayed
The new phenotype is produced by an interaction between two alleles (an individual who is heterozygous for alleles that show incomplete dominance will have an intermediate phenotype)
Ex. Pink colour in flowers
Cr = Red, Cw = White
Two pink flowers (incomplete dominance) crossed
CrCw x CrCw = 2 pink, 1 red, 1 white

30. Incomplete Dominance
“mixing paint”

31. Co-dominance Co-dominance is a form of incomplete dominance
Occurs when both phenotypes are displayed at the same time (co- dominant alleles are both expressed in a heterozygous individual)
Ie. Roan colour in animals

32. Co-dominance

33. END FOR TODAY
Do this on the weekend!!!