1. Standard VII- Applying Mendel’s Laws
Biology AHSGE
Standard VII- Applying Mendel’s Laws

2. Heredity The passing of characters from parents to offspring
Genetics- Branch of Biology dealing with heredity
Gregor Mendel- Austrian monk who developed rules of heredity
Experimented with pea plants

3. Mendel’s Experiments
Monohybrid cross- Cross of parents involving one pair of contrasting traits
True breeding- All offspring display one characteristic
P generation- First two individuals crossed
F1 generation (filial)- First offspring from P generation
F2 generation- Second offspring resulting from F1 generation

4. Mendel’s Hypotheses
For each inherited trait, an individual has two copies of the gene- one from each parent.
There are alternative versions of genes- alleles
When two different alleles are present, the individual may completely express one, while the other allele has no observable affect
Dominant- Expressed allele; only one copy needed for expression; capital letter
Recessive- Allele not expressed when dominant allele is present; need both copies for expression; lowercase letter
When gametes are formed, each gene’s alleles separate independently, therefore gametes have one allele for each gene

5. Modern Terms Homozygous- Having two of the same alleles for a gene
Ex: AA, BB, aa or bb
Heterozygous- Having two different alleles for a particular gene
Ex: Aa or Bb
Genotype- The set of alleles for a characteristic or trait (the letters)
Phenotype- The expressed trait or physical appearance of a genotype

6. Laws of Heredity
The Law of Segregation- When gametes are formed, each gene’s alleles separate (segregate) independently, therefore gametes have one allele for each gene
The Law of Independent Assortment- Alleles of different genes separate independently of one another during meiosis

7. Punnett Square
Diagram that predicts the outcome of a genetic cross by considering all possible combinations of gametes in the cross
Test cross- An individual whose phenotype is dominant, but whose genotype is not known, is crossed with a homozygous recessive individual
Monohybrid cross- Cross of parents involving one pair of contrasting traits
Dihybrid Cross- Cross of parents involving two pairs of contrasting traits

8. Monohybrid Cross
Cross a heterozygous, brown-haired woman with a heterozygous, brown-haired man; Brown hair is dominant, while blonde is recessive

9. Probability The likelihood that a specific event will occur
Expressed as percentages or ratios
Probability = number of one kind of possible outcome
total number of all possible outcomes
Genotypic ratio- Ratio of genotypes from a punnett square
Phenotypic ratio- Ratio of phenotypes from a punnett square

10. Punnett Square and Probability
- Probability of offspring with brown hair; blonde
Genotypic Ratio
Phenotypic Ratio

11. Dihybrid Cross
Cross two heterozygous pea plants for seed shape (R= round; r= wrinkled) and color (Y= yellow; y= green); RrYy
1st- Complete a monohybrid cross of the two traits for each parent to determine possible gametes

12. Dihybrid Cross

13. Dihybrid Cross
Calculate the genotypic and phenotypic ratios for the previous cross
Genotypic Ratio
1 RRYY: 3 RRYy: 2 RrYY: 3 RrYy:
1 RRyy: 2 Rryy: 1 rrYY: 2 rrYy: 1rryy
Phenotypic Ratio
9 Round; yellow: 3 Round; green:
3 Wrinkled; yellow: 1 Wrinkled; green

14. Inheritance of Traits
Pedigree- Family history that shows how a trait is inherited over several generations
Circles- female
Squares- male
Horizontal lines show mating
Vertical lines indicate offspring
Completely shaded are affected
Partial shading represents a carrier

15. Pedigree-Albinism

16. Albino

17. Sex-linked Genes Allele is found on the X or Y chromosome
XX- female; XY- male
Mostly carried on X and recessive
Males receiving this on the X would exhibit the condition due to having only one X (Ex: Hemophilia)

18. Hyperchol-esterolemia
Genetic Disorder
Dominant or Recessive
Symptom
Defect
Frequency
Sickle Cell Anemia
Recessive
Poor blood circulation
Abnormal hemoglobin
1/500 (African american)
Hyperchol-esterolemia
Dominant
Excessive cholesterol in blood; heart disease
Abnormal cell surface receptor for cholesterol
1/500
Tay-Sachs Disease
Deterioration of nervous system; death
Defective form of brain enzyme
1/3,500 (Ashkenazi Jews)
Cystic Fibrosis
Mucus clogging or organs; do not survive to old age
Defective chloride-ion transport protein
1/2,500 (Caucasians)
Hemophilia A
Sex-linked recessive
Failure of blood to clot
Defective form of blood-clotting factor
1/10,000 (males)
Huntington’s Disease
Gradual deterioration of brain tissue in middle age
Inhibitor of brain cell metabolism
1/10,000

19. Down’s Syndrome
Chromosomal mutation resulting in mental retardation and physical abnormalities
1 in every 1,000 people born
Having an extra chromosome on the 21st pair of human chromosomes
Trisomy-21
Caused by nondisjunction of the 21st pair during Anaphase I of meiosis