1. Bio.B.2- Genetics
CHAPTER 11

2. B2: Genetics
Describe and/ or predict observed patterns of inheritance i.e. dominant, recessive, co-dominant, incomplete dominance, sex- linked, polygenic and multiple alleles.

3. B2 Vocabulary genetics homozygous fertilization heterozygous trait
hybrid
gene
allele
Principle of dominance
segregation
Gamete
probability
homozygous
heterozygous
phenotype
genotype
punnett square
incomplete dominance
codominance
multiple allele
polygenic trai

4. Review… What are the four macromolecules?
1. Carbohydrates
2. Proteins
3. Lipids
4. Nucleic Acids
Which of the four macromolecule is responsible for an individuals unique characteristics?
Nucleic acids - DNA

5. Introduction Genetics = study of heredity
Heredity = transfer of characteristics from parent to offspring

6. Gregor Mendel: Father of Modern Genetics Studied Pea Plants
Observed recurring patterns
Pea plants made good subjects to study because mendel could control breeding, the plants would produce many offspring plants in just one growing season and all of the traits he studies were “either-or” traits.

7. What Mendel Knew… A trait is a specific characteristic
EX: pea color, pea shape, flower color

8. What Mendel Knew… Mendel could control fertilization
Self-pollination – one plant fertilizes itself
Cross-pollination – two different plants

9. What Mendel Knew…
“true-breeding” plants always produced offspring plants that had the same trait as the parent
EX: a true-breeding purple flower plant produces plants that also have purple flowers

10. What Mendel Knew… A “hybrid” = a cross between two different plants
Offspring showed the characteristic of one parent

11. What Mendel Saw 1st generation parental trait disappears
2nd generation parental trait reappears in a 3:1 ratio

12. What Mendel saw P-generation True-breeding
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P-generation
True-breeding
When self pollinated, always produce offspring plants with identical traits
Ex: a true-breeding purple plant ALWAYS produces plants with purple flowers

13. F1 generation (hybrids)
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F1 generation (hybrids)
F1 Generation
Produced by crossing pure-bred P plants
Always saw the same results (parental trait disappears)

14. F2 generation Produced by self-pollination of F1 plants
Mendel
F2 generation
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Produced by self-pollination of F1 plants
Always saw the same results (parental trait reappears) in a specific ratio 14 14 14 14 14 14 14

15. Mendel’s Conclusions:
Traits are determined by “factors” that get passed from one generation to the next
Factors = genes

16. Mendel’s Conclusions:
There are different “forms” of a gene that account for variations in inherited characteristics
Forms = alleles
EX: purple allele or white allele

17. Mendel’s Conclusions:
For each trait, an organism inherits two alleles (one from each parent)
The alleles may be identical or they may be different
Homozygous = two identical alleles
Heterozygous = two different alleles

18. Mendel’s Conclusions:
Physical appearance (phenotype) is influenced by the alleles inherited for the trait (genotype)
some “alleles” are dominant and some are recessive
One dominant allele will give the dominant trait
Need two recessive alleles to have the recessive trait
Letters used to differentiate alleles
dominant = uppercase
recessive = lowercase

19. Mendel’s Conclusions:
Alleles segregate during gamete formation
Gamete = reproductive cell that contributes to the new organism
Each parent contributes only one allele to their offspring

21. Gene (A) or Allele (B) Hair color…….. Brown hair….... Purple flowers.
Flower color….
Tall plant………
Plant height…..
Tail length…….
Long tail……….
GENE
ALLELE

22. Homozygous (A) or Heterozygous (B)
AA …….
Bb …….
BB …….
bb …….
Rr …….
dd …….
Homozygous Dom.
Heterozygous
Homozygous Rec.

23. Genotype (A) or Phenotype (B)
AA …….
Blue eyes
heterozygous Bb
Freckles
Visible trait
Genotype
Phenotype

24. Dominant Trait (A) or Recessive (B)
AA …….
Bb …….
BB …….
bb …….
Rr …….
dd …….
Dominant
Recessive

25. Applying Mendel’s Principles
11.2

26. Probability
Probability = the likelihood that a particular event will occur
The way alleles separate during gamete formation is just as random as a coin toss
Therefore, probability can be used to predict genetic outcomes.

27. Punnett Squares: mathematical tool used to predict genetic outcomes
Axes of grid = possible gamete genotypes of parents
Grid boxes = possible genotypes of offspring
Reminders
Genotype = genetic makeup (alleles)
Phenotype = physical appearance
When constructing Punnett Squares, ALWAYS
Define the terms
Define the genotypes of the parents
Analyze the results

28. Punnett Squares can be used to explain Mendel’s results…
F1 generation

29. Punnett Squares can be used to explain Mendel’s results…
F1 generation

30. Punnett Squares can be used to explain Mendel’s results…
F2 generation

31. Practice with Punnett squares
For Simple Dominance Practice Problems, Click Here
Practice with Punnett squares
11.2

32. Exceptions to Mendel Incomplete Dominance Codominance Multiple Alleles
Sex-linked Traits
Polygenic traits
Epistasis
Interaction of environment and genotype

33. Incomplete Dominance Neither allele is completely dominant
Heterozygote has a blended phenotype

34. Codominance
Both alleles get expressed
Heterozygote has both traits

35. Multiple Alleles Trait with more than two alleles in a population
Example – Blood Types
3 different alleles (A, B, O)
A and B alleles are codominant
O allele is recessive

37. Heterozygous for the A allele
Homozygous for the A allele

38. Read Only

39. Sex-Linked Genes (X-linked)
Carried on the sex chromosomes (female = XX; male = XY)
More common in males
XY = only need one allele for trait to be present
Females need two copies of allele for trait to be present
Can be carriers of the trait (heterozygous genotype)
Passed from mother to son
Examples include colorblindness and hemophilia

43. Polygenic Traits
Traits that are determined by the interaction of 2 or more genes
Ex: Skin color, eye color, height, etc

44. Practice with Punnett squares