1. Chapter 8 – Mendel & Heredity
Section 1 – The Origin of Genetics
Section 2 – Mendel’s Theory
Section 3 – Studying Heredity
Section 4 – Complex Patterns of Heredity

2. Studies of Characters Character:
genetic trait such as eye color, hair color or skin color
Heredity:
passing on of characters from parents of a species to their offspring
Studying heredity allowed us to figure out ways to breed for the fittest traits or characters

3. Mendel’s Breeding Experiments
Gregor Johann Mendel
An Austrian monk who studied peas more than 100 years ago
Breeding was done 200 years earlier, but Mendel established breeding rules
Genetics:
The branch of biology focused on heredity
Repetition of first experiments focused on flower color (purple & white) more characters used later on
Experimentation included first and second generations

4. Useful Features in Peas
Flower Color: Purple or White
Flower color is a trait
Breeding: Self or Transferred
Male & Female parts in each flower
Self-fertilization
Pollen transfer
Size and Growth of the Pea
Small
Matures quickly
Many offspring

7. Monohybrid Cross Crossing one pair of contrasting traits
Ex: purple and white flowers
Step 1: Self-Pollinate for Several Gen.
True-breeding:
offspring have only one true character
P Generation:
first two true-breeding individuals used in the experiment

8. Monohybrid Cross Cont. Step 2: Cross-Pollination
Crossing the two parents in the P generation to produce the F1 generation
Purple x White
Step 3: F1 Self-Pollinate
The F1 generation self-pollinate to produce the F2 generation
F1 and F2 are compared

10. Mendel’s Results
From the P to F1 generation a contrasting trait disappeared.
The trait reappeared in F2 generation
Ratio:
÷ =3.15
Ratio = 3:1 (purple: white)

11. Mendel’s Hypotheses
Past theory: offspring traits were a blend of their parents’ traits
Mendel’s
An individual has two copies of a gene – one from each parent
Alleles: different versions of a trait
Dominant: expressed form of a trait
Recessive: form not expressed but present
Each gamete contributes one allele to create a two allele offspring

12. Modern Terms Homozygous Heterozygous
When two alleles in a particular gene are displayed as the same
Ex: PP or ww
Heterozygous
When two alleles in a particular gene are displayed differently
Ex: Pp or Ww
PP = homozygous dominant
Ww = homozygous recessive

13. Modern Terms Cont. Genotype Phenotype
Set of alleles an individual contains for a specific character
Phenotype
The physical appearance of a character or trait
Pp => purple flower
Genotype Phenotype

14. Law of Segregation First Law of Heredity
States that – the two alleles of a character segregate (separate) when gametes are formed

15. Law of Independent Assortment
Discovered using dihybrid crosses (crosses featuring two characters)
States that – alleles of different genes separate independently of one another during gamete formation

16. Punnett Squares
A diagram that predicts the outcome of a genetic cross by considering all possible combinations
Parents are put on the top and side of the square
Each of the boxes inside are filled with 2-4 letters depending the type of cross
2 – monohybrid
4 - dihybrid

17. Contrasting Traits Homozygous Traits Heterozygous Traits
YY (yellow) x yy (Green)
All yellow (Yy)
Heterozygous Traits
Yy x Yy (both yellow)
3:1 (yellow: green) ratio

19. Determining Unknown Genotypes
Test cross:
phenotype is dominant (genotype unknown) is crossed with a homozygous recessive.
Outcome:
All yellow = “unknown” = YY
Half green = “unknown” = Yy

20. Probability Likelihood of a specific combination to occur
Ratios or percentages
Equation Probability= number of one kind of possible outcomes total number of all the possible outcomes Probability= number of one kind of possible outcomes total number of all the possible outcomes
Examples:
3:1 (yellow: green) or 75% yellow & 25% green

21. Outcome of a Cross
Combination of two separate events or possibilities are multiplied to achieve a final probability
Example: Tall plant with purple flower
HHPP x HhPp

22. End

23. Inheritance of Traits Pedigree
A family history of how a gene is inherited over several generations
Autosomal
The gene will appear in both sexes equally ex: hair or eye color
Sex-linked
The allele of the gene will only appear on the X or Y gene
ex: Albinism or Red-green colorblindness or Male Pattern Baldness

24. Inheritance of Traits Autosomal Dominant
Every individual with the condition will have a parent with the condition
Recessive
Every individual with the condition can either have one, two or neither parent with the condition
Heterozygous carriers can produce children with the condition

25. Traits cont. Heterozygous or Homozygous Dominant:
The individual will show the dominant allele
Homozygous:
They will show the recessive allele

26. Pedigree Chart Females – circles Males – squares Affected – shaded
Unaffected – blank

27. Comparing Pedigrees Recessive Dominant
If two affected parents have an unaffected child
Occurs more often in a pedigree = more shaded individuals
If two unaffected parents have an affected child
If two unaffected people have an affected child, it is a recessive pedigree: R is the dominant wild type allele and r is the recessive mutant allele. Both parents are Rr and the affected child is rr.

28. Comparing Pedigrees Autosomal Dominant Autosomal Recessive
All unaffected are homozygous recessive (ex. dd)
The affected parents of an unaffected child must be heterozygotes Dd, since they both passed a d allele to their child.
All affected are homozygous recessive
If two unaffected mate and have an affected child, both parents must be Rr heterozygotes

33. End

34. Influenced by Several Genes
Polygenic Influence
When several genes influence a character
May be located on the same or different chromosomes to cause influence
Examples:
Eye color, height, weight, hair color and skin color
Think about your license and what information it provides to remember these

35. Incomplete Dominance
When an individual displays a phenotype that is intermediate of the parent’s phenotypes
Flowers: Red & White
Intermediate?
Pink
Hair: Straight & Curly
Wavy

36. Blood Types Group A antigen B antigen Plasma A Present Not present
B antibody B
Not Present
A antibody AB
No antibody O
A & B antibody

37. Multiple Alleles Genes that have three or more alleles Blood Type Gene
ABO blood groups
Determined by IA, IB and i

39. A IA i IAIA B IB i IBIB AB IAIB O ii Blood Type First Genotype
Second Genotype A
IA i
IAIA B
IB i
IBIB AB
IAIB O ii

42. Genetics & Environment

43. Influenced by the Environment
Pigmentation in Fur in Foxes (Opposite in Siamese cats)
Warm temperatures express a deeper color
Genes are fully functioning
Cold temperatures express a lighter color
Loss of gene function

44. Humans Height – influenced by nutrition
Skin color – influenced by light exposure
Personality – influenced by temperature (response to environment)

45. Genetic Disorders Sickle Cell Anemia
Recessive genetic disorder that produces a defective protein hemoglobin
Allows for less oxygen to be carried through the blood
Protects against the disease - Malaria
Malaria – protozoan attacks red blood cells

46. Genetic Disorders Cystic Fibrosis
Recessive disease which causes a defective gene that makes a protein that allows Cl to move in and out of the body
Fatal – as airways are blocked by mucus build-up
Malaria – protozoan attacks red blood cells

47. Genetic Disorders Hemophilia
Recessive and sex-linked disorder – blood is unable to clot
Mutation on an X gene = Hemophilia A
Son receives a mutated X from mother

48. Genetic Disorders Huntington’s Disease
Dominant allele on a autosome gene
Causes memory and muscle control loss, severe mental illness and eventually death
Passed from one generation to next as diagnosis is in late 30s to 40s
See chart on page 181