1. MENDELIAN GENETICS Mendel’s work
Monohybrid inheritance and principal of segregation
Dihybrid inheritance and the principal of independent assortment
Test cross

2. INTRODUCTION Explaining the mechanism of inheritance
The mechanism relates to the numbers of characteristic of inheritance
The simple characteristic leads to the simpler crossing over mechanism and ration
This is followed by excluding the mutation effects that will be discussed later (chapter 4)

3. GREGOR MENDEL Study in University of Vienna
His parents has a small farm in Austria

4. GREGOR MENDEL (cont) Austrian monk
Studied the inheritance of traits in pea plants
Developed the laws of inheritance
Mendel's work was not recognized until the turn of the 20th century

5. GREGOR MENDEL (cont)
Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants
He found that the plants' offspring retained traits of the parents
Called the “Father of Genetics"

7. MENDEL’S PEA PLANT TRAITS

8. GREGOR MENDEL (cont)
Mendel stated that physical traits are inherited as “particles”
Mendel did not know that the “particles” were actually Chromosomes & DNA

9. GENETIC TERMINOLOGIES
Character – heritable feature that varies among individuals
Trait – each variant for the character
True-breeding – Plants homozygous for a characteristic are true-breeding (Self-pollinate)
Hybridization – mating or crossing over of two true-breeding varieties
P generation – parental generation/parent
F1 generation – first filial generation (son)
F2 generation – second filial generation

10. GENETIC TERMINOLOGIES (cont)
Allele- alternate version of a gene
Homozygote – pair of identical alleles for a character
Heterozygote – two different alleles for a character (Bb)
Dominate allele – expressed in the heterozygote
Recessive allele – not expressed in the heterozygote
Homozygous dominant- BB
Homozygous recessive - bb
Genotype – genetic makeup
Phenotype – appearance of an organism

11. TYPES OF GENETIC CROSS
Monohybrid cross - cross involving a single trait e.g. flower colour
Dihybrid cross - cross involving two traits e.g. flower colour & plant height

12. PUNNET SQUARE
Diagrammatic device for predicting the allele composition of offspring from a cross between individuals of known genetic makeup.
3 steps / generation = P gen, F1 gen, F2 gen
Heterozygous allele - ?
Homozygous allele - ?
Phenotype - ?
Genotype - ?

13. PUNNET SQUARE (cont)
Can be used for monohybrid and also dihybrid cross.

15. LAW OF INHERITANCE Gregor Mendel introduce 2 laws Law of Segregation
Law of Independent Assortment

16. LAW OF SEGREGATION Inherit only ONE characteristic @ Monohybrid
Producing 3:1 of phenotypic inheritance
Mendel use a large group of sample size to explain this law
Leads to a development of a model known as Mendel’s Model

17. MENDEL MODEL Four concepts in law of segregation
Alternative versions of genes account for variations in inherited characteristics
For each character, an organism inherit two alleles, one from each parent
If the two alleles at a locus differ, then one, the dominant allele, determines the organism’s appearance; the other, the recessive allele, has NO noticeable effect in the organism’s appearance
The two alleles for a heritable character segregate (separate) during gamete formation and end up in different gametes

18. 1 . ALTERNATIVE VERSIONS OF GENES ACCOUNT FOR VARIATIONS IN INHERITED CHARACTERISTICS
Have 2 choices of alleles
Existing in two version
Depending on the phenotypic or characteristic derive in the genetic make up
Eg. Purple flower and white flower

19. 2. FOR EACH CHARACTER, AN ORGANISM INHERIT TWO ALLELES, ONE FROM EACH PARENT
Each somatic cell in a diploid organism has two sets of chromosome
Genetic locus represent twice in diploid cell, once in homolog of a specific pair of chromosome

20. 3. IF THE TWO ALLELES AT A LOCUS DIFFER, THEN ONE, THE DOMINANT ALLELE, DETERMINES THE ORGANISM’S APPEARANCE; THE OTHER, THE RECESSIVE ALLELE, HAS NO NOTICEABLE EFFECT IN THE ORGANISM’S APPEARANCE
The plant have more purple colour due to its dominant allele, vice versa

21. 4. THE TWO ALLELES FOR A HERITABLE CHARACTER SEGREGATE (SEPARATE) DURING GAMETE FORMATION AND END UP IN DIFFERENT GAMETES
An egg or sperm gets only one of the two alleles that are present in the somatic cell of the organism making the gamete
The correspond depending on the types of reproduction between meiosis and mitosis
Further discussion after test cross

22. Example of MONOHYBRID CROSS

23. P1 Monohybrid Cross r r Rr Rr R R Rr Rr Genotype: Rr Phenotype: Round
Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr r r
Genotype: Rr
Phenotype: Round
Genotypic Ratio: All alike
Phenotypic Ratio: All alike Rr Rr R R Rr Rr

24. P1 Monohybrid Cross Review
Homozygous dominant x Homozygous recessive
Offspring all Heterozygous (hybrids)
Offspring called F1 generation
Genotypic & Phenotypic ratio is ALL ALIKE

25. F1 Monohybrid Cross R r RR Rr R r Rr rr Trait: Seed Shape
Alleles: R – Round r – Wrinkled
Cross: Round seeds x Round seeds
Rr x Rr R r
Genotype: RR, Rr, rr
Phenotype: Round & wrinkled
G.Ratio: 1:2:1
P.Ratio: 3:1 RR Rr R r Rr rr

26. F1 Monohybrid Cross Review
Heterozygous x heterozygous
Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr
Offspring called F2 generation
Genotypic ratio is 1:2:1
Phenotypic Ratio is 3:1

27. HOW DOES THE PEAS LOOK LIKE?

29. Genotypic Ratio &
Phenotypic Ratio

30. TEST YOURSELF! Between blue flower, BB and yellow, yy
Between small leaf, ff and big leaf, Ff

31. LAW OF INDEPENDENT ASSORTMENT
TWO characteristics at the same Dihybrid cross
Eg. Leaf colour and leaf size
Using both dominant and recessive alleles in each of the characteristics.

32. INDEPENDENT ASSORTMENT in CHROMOSOME
ndependent Assortment: Mendelian theory that, as meiosis ends, genes on pairs of homologus chromosomes have been sorted out for distribution into one gamete or another, independently of gene pairs on other chromosomes.

33. Mendel performed dihybrid crosses in plants that were true-breeding for TWO traits.
E.g a plant with green pod colour and yellow seed, cross-pollinated with a plant that had yellow pod colour and green seeds.
Green pod colour = GG
Yellow seed colour = YY
Yellow pod colour = gg
Green seed colour = yy
The resulting F1 generation were all heterozygous for green pod colour and yellow seeds (GgYy)

34. DIHYBRID CROSS
Involves two pairs of contrasting traits

36. copyright cmassengale
DIHYBRID CROSS
Round/Yellow: 9 Round/green: wrinkled/Yellow: 3 wrinkled/green: 1
Phenotypic ratio 9:3:3:1
copyright cmassengale

37. DIHYBRID CROSS RrYy x RrYy RY Ry rY ry RY Ry rY ry
Traits: Seed shape & Seed colour
Alleles: R round r wrinkled Y yellow y green
RrYy x RrYy
RY Ry rY ry
RY Ry rY ry
All possible gamete combinations

38. DIHYBRID CROSS RY Ry rY ry RY Ry rY ry

39. DIHYBRID CROSS RY Ry rY ry Round/Yellow: 9 Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic
ratio
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy

40. HYPOTHESIS/CONCLUSION
The alleles of seed colour and seed shape sort into gametes independently of each other.
Phenotypic ratio for IA = 9:3:3:1

41. TEST CROSS
To determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait.
If all offspring display the dominant phenotype, the individual in question is homozygous dominant; if the offspring display both dominant and recessive phenotypes, then the individual is heterozygous

42. TEST CROSS (cont)
In some sources, the ‘test cross’ is defined as being a type of backcross between the recessive homozygote and F1 generation.
F1 progeny are mated back to one of their parents (or to individual with a genotype identical to the parent)
Backcross is often used synonymously with testcross.

43. TEST CROSS
A mating between an individual of unknown genotype and a homozygous recessive individual.
Example: bbC__ x bbcc
BB = brown eyes
Bb = brown eyes
bb = blue eyes
CC = curly hair
Cc = curly hair
cc = straight hair bC
b___ bc

44. copyright cmassengale
TEST CROSS
Possible results: bC
b___ bc
bbCc C bC
b___ bc
bbCc
bbcc or c
copyright cmassengale

46. If the plant being tested is homozygous
If the plant being tested is heterozygous

47. G?W? X ggww (G=yellow; g=green; W=round; w=wrinkled)
What will the expected phenotypic ratios be for the above testcross?

49. SUMMARY of MENDEL’S LAW
PARENT CROSS
OFFSPRING
DOMINANCE / True-breeding
TT x tt tall x short
100% Tt tall
SEGREGATION
Tt x Tt tall x tall
75% tall 25% short
INDEPENDENT ASSORTMENT
RrGg x RrGg round & green x round & green
9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods