1. Mendel, Monohybrid cross, types of dominance, multiple alleles, lethal alleles, X inactivation
Ch 7 – PP3

2. Key words from Cell reproduction
Sexual reproduction
Asexual reproduction
Gametes
Diploid (2n)
Haploid (n)
Prokaryote chromosomes
Plasmids
Binary fission
Semi conservative replication
Cell cycle
Mitosis
Meiosis
Cytokinesis
DNA helicase
Parental strand
Replication fork
DNA polymerase
DNA ligase
Apoptosis

3. Gregor Mendel
A priest, mathematician and an expert in agriculture, a rad dude
Particularly interested in breeding practices in plants
In 1856, he carried out a number of breeding experiments on pea plants in the garden at his monastery, in what is now the Czech Republic

4. Mendelaen Genetics
The conclusions Mendel drew from his experiments form the basis on which the study of genetics is still based

5. Peas, peas peas
Peas plants are self fertilising, ie pollen from one flower, fertilises ovules of the same flower
Mendel prevented this, and so he was artificially crossing the pea plants, choosing characteristics he wanted to study

6. Explain what this means?
Tall or Short
Tall Stem pea plant
Autosomal dominant
Short stem pea plant
Autosomal recessive
Explain what this means?

7. Monohybrid Cross True breeding Tall with Short
True breeding – when crossed amongst themselves only give rise to offspring that look like the parents (Homozygous)
Monohybrid cross – crossing of organisms that differ in just one trait. That is – just one gene locus
H = Tall
h = Short X P HH hh

8. Monohybrid Cross True breeding tall with short H h Hh Hh X P HH hh
P = Parental Generation F1
All F1
offspring are heterozygous
F1 = First Filial Generation Hh Hh Hh Hh

9. Monohybrid Cross Cross two of the F1 generation H h HH Hh X F1 Hh Hh
Genotype ratio
HH : Hh : hh
1 : : 1 F2
Phenotype ratio
Tall : Short :
F2 = Second Filial Generation hh HH Hh Hh

10. Mendel bred thousands of pea plants and looked at many traits
Dominant traits are underlined

11. True Breeding
One way to establish if tall pea plant (or any other dominant trait) is homozygous dominant or heterozygous, is to self pollinate it.
If F1 are all tall, we conclude HH.
If there is a mixture, then must be Hh
Exactly the same result occurs if the organism is crossed with another that is Homozygous for the same trait – said to breed true
Applies to homozygous dominant or homozygous recessive – same at the same locus

12. Test Cross
How do we determine the same thing for animals where self pollination is not possible?
We cross the unknown individual with an individual who is homozygous recessive for the trait
If there are any offspring with recessive phenotype, then the unknown genotype must have been heterozygous.

13. Test Cross 1 Unknown genotype bred with Homozygous recessive. H ? h
Hh hh X P H? hh
P = Parental Generation F1
Ratios Depend on Geno type of parental genotype.
F1 = First Filial Generation Hh Hh hh hh

14. Test Cross 1 Unknown genotype bred with Homozygous recessive. H ? h
Hh Hh X P H? hh
P = Parental Generation F1
Ratios Depend on Geno type of parental genotype.
F1 = First Filial Generation Hh Hh Hh Hh

15. Snapdragon flowers Crossing white with red snapdragon
We expect one colour to be dominant
We get pink flowers!

16. Partial Dominance Or incomplete dominance Neither allele is dominant
The phenotype is neither of the alleles but some sort of half-way form

17. Partial Dominance
Red colour (CR) in snapdragon flowers and white colour (CW)are an example of incomplete dominance. CR CW
CRCW P
CRCR CWCW F1
CRCW CRCW CRCW CRCW

18. Partial Dominance
What will you get if you cross two plants from the F1 generation? CR CW
CRCR
CRCW
CWCW CR CW F1
CRCW CRCW F2
CRCR CRCW CRCW CWCW

19. Partial Dominance X
Cremello Chestnut
Palomino

20. Codominance
Both alleles in the genotype are expressed in the phenotype.
Neither is dominant

21. Mixture of red and white hairs
Codominance X
Red
White
Roan
Mixture of red and white hairs

22. Models of types of Dominance
Co-dominance
Partial/Incomplete dominance

23. Activities
Worksheets
Alleles
Basic genetic cross
Monohybrid cross

24. ABO Blood Groups Multiple alleles Another example of co-dominance
Multiple alleles = three or more alleles exist in population but only two are inherited at a time
Another example of co-dominance
Alleles found at the same locus

25. ABO Blood Groups Three alleles IA and IB are codominant
IA (produces A antigens on red blood cells)
IB (produces B antigens on red blood cells)
i (produces no antigens on red blood cells)
IA and IB are codominant
IA and IB are dominant over i

26. ABO Blood Groups Possible blood types IAIA IAIB IBIB IBi ii A AB B O
Genotypes
IAIA
OR IAi
IAIB
IBIB OR
IBi ii
Phenotypes
(blood type) A AB B O

27. Summary of types of dominance
Pg 229 of your text

28. Blood type Game.

29. Sexy Genes Sex linked alleles
Carried on Heterosome (X and Y chromosome)

34. Colour blindness On Moodle. Colour Blindness word Doc.
Please to be submitted underneath.
Am you Clr Blind?
How am to be see no clr ? Can does like Doge?
who know clr Boy or is not boy?

35. Lethal Alleles In mice, yellow coat colour Y is dominant to grey y
What phenotype ratio do you expect to get from crossing two mice heterozygous for coat colour?

36. We expect. . . X Yy Yy :

37. We observe . . . X Yy Yy :

38. Lethal Alleles The combination YY is lethal
Results in yellow to grey ratio of 2:1
Huntingtons Disease in Humans is as a result of lethal allele and results in deterioration of nervous system at around age 40

39. X-inactivation Females have two X chromosomes In embryonic development
One X chromosomes turns off
This is random
The inactive X chromosome condenses
Becomes a dark staining Barr body
X-inactivation causes females not to have twice as many X chromosome gene products as males

40. X-inactivation In cats
One X chromosome carries the orange allele of fur color and the other X chromosome carriers the black allele for fur color.
Depending on which of the X chromosomes is inactivated early in embryonic development, patches of fur descending from these original cells express the color from the X chromosome that has not been inactivated

41. Tortoiseshell Cat
What can you infer about the sex of this cat?

42. Activities Worksheets Multiple Alleles blood groups
Dominance of Alleles
Lethal Alleles
Plus 11 past exam questions

43. 2006 Exam 2

48. 2007 Exam 2
2008 Exam 2

50. 2009 Exam 2

51. 2011 Exam 2