1. Genetics
Unit 3

2. Mendelian Genetics
Genetics – An aspect of science that deals with the principles of variation and inheritance.
Heredity – The passing of genetic characteristics from one generation to the next (eg. Hair/eye colour)

3. “You get all of your best traits from your mother.”
Genetic Terms
Traits – Distinguishing characteristics which makes
individuals unique (physical, personality, etc.)
“You get all of your best traits from your mother.”
Purebred – An organism descended from ancestors
of a distinct type or breed. They all share similar traits.

4. Gregor Mendel An Austrian Monk Studied Mathematics and Botany
Pioneer in the study of Genetics and Heredity

5. One of Mendel’s Experiments

6. Draw Mendel’s Experiment Here

7. Mendelian Genetics P Generation – Parent generation.
F1 Generation – First filial generation or first set of offspring produced
Hybrid – The result of a cross between two different purebred plants

8. Dominant – A trait which is always expressed, or always appears in the individual
Recessive – A trait which is present but inactive and is therefore not in usually expressed in an individual.

9. Principle of Dominance – Mendel concluded that when 2 different traits are crossed, one trait is always dominate over the other.

10. Mendel’s Experiment AGAIN!

11. Draw Mendel’s Experiment – focusing on F2 generation

12. F2 Generation – The second group of offspring produced
Mendelian Ratio – 3:1 ratio of the occurrence of specific traits in offspring when the parents only differ in one trait.
Monohybrid Cross – A cross where only one trait (ex. Height) is crossed.

13. Monohybrid Cross

14. Law of Segregation
After his initial experiment, Mendel allowed the hybrid F1 plants to self pollinate, producing the second filial generation (F2 generation)
Observed a 3:1 ratio of tall:short plants. Why did this happen?

15. Law of Segregation Mendel made 4 conclusions:
Each parent in the F1 generation starts with 2 hereditary factors, one dominant and one recessive
Only one factor from each parent is contributed to the offspring
Each offspring inherits one factor from each parent. If the dominant factor is present, it will be expressed even if the recessive factor is also present
The recessive factor will be expressed if only recessive factors are present

16. Law of Segregation
Law of Segregation – hereditary traits are determined by pairs of alleles from each parent. These alleles separate during gamete formation, giving each offspring only one allele from each parent.

17. Law of Segregation

18. Law of Segregation
What are these “factors” which Mendel described? We know them today as Genes: the part of the chromosome that governs the expression of a particular trait
Each gene can occur in alternate forms called alleles. Remember the principle of dominance: a dominant allele may prevent the expression of the recessive allele.

19. Law of Segregation
Mendel’s “factors” are inherited as independent units. They are referred to as unit characters
Unit Theory is a term describing Mendel’s “factors” of inheritance (genes), which are inherited as independent units.
When two alleles at the same gene locus are identical, the individual is said to be homozygous
When two alleles at the same gene locus differ, the individual is said to be heterozygous

20. Genetics and Probability
Heads or Tails?
In groups of 3 or 4, complete the Probability activity worksheet

21. Genetics and Probability
Probability – the chance, or likelihood, of a particular outcome
Product Rule – the probability that two or more independent events will occur together is the product of their individual probabilities of occurring alone

22. Punnett Squares
Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

23. Punnett Squares
Dominant Alleles are usually represented by an upper case letter (eg. Purple plant (R))
Recessive Alleles are usually represented by a lower case letter (eg. White plant (r))

24. Punnett Squares Homozygous or Heterozygous? Dominant or Recessive? RR

25. Punnett Squares What is the phenotypic ratio of this cross?
In other words, what is the ratio of purple:white plants?
Phenotype – The appearance of the trait in an organism

26. Punnett Squares What is the genotypic ratio of this cross?
In other words, what is the ratio of homozygous dominant :heterozygous : homozygous recessive (RR:Rr:rr)?
Genotype – The genetic make-up of an organism

27. Punnett Squares
Complete Dominance – a type of inheritance where both heterozygotes and dominant homozygotes share the same phenotype

28. Determining Genotypes
Test Cross – Crossing an individual of unknown genotype with a homozygous recessive individual. Used to determine if an individual expressing a dominant trait is homozygous or heterozygous
Alaskan Malamute example

29. Complex Inheritance Patterns
Mendel’s 2nd Experiment
Does the inheritance of one trait influence the inheritance of a different trait? (eg. Does pea shape influence pea colour?)
Mendel produced purebred pea plants: Round Yellow plants (RY) and Wrinkled Green plants (ry)
Performed a Dihybrid Cross  a cross of two individuals that differ in two traits (pea shape/colour)

30. Dihybrid Cross

31. Law of Independent Assortment
The inheritance of alleles for one trait does not affect the inheritance of alleles for another trait
New combinations of alleles that are not present in either parent

32. Incomplete Dominance
Not all traits are completely dominant or recessive
Incomplete Dominance - The blending of the traits of two different alleles at one gene locus that occurs when neither allele is dominant
Eg. White and Red snapdragons are homozygous; Pink snapdragons are heterozygous

33. Incomplete Dominance

34. Co-Dominance
Similar to incomplete dominance  there is a third phenotype, no definitive dominant or recessive allele
When both alleles of a gene locus are expressed equally (co-dominate), this type of inheritance is known as Co-Dominance

35. Co-Dominance