1. Chapter 14 – Genetics and the Work of Mendel
Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas
used good experimental design
used mathematical analysis
collected data & kept detailed records
excellent example of scientific method

2. Genes, Alleles and Dominance
Trait – specific characteristic
Mendel studied 7 different pea plant traits
What are some examples? Plant Height, Seed Shape, Pod Color

3. Genes, Alleles and Dominance
Genes – the chemical factors that determine traits (the segment of DNA) ex. pea plant: height
Alleles – different forms of a gene from each parent ex. pea plants: tall and short (T or t)

4. Principle of Dominance
Principle of dominance: some alleles are dominant and others are recessive
Dominant allele – the trait is always shown
Capital letter (T = tall)
Recessive allele – the trait that will only show if there is no dominant allele
Lower case letter (t = short)

5. Genes, Alleles and Dominance
Heterozygous – organisms that have 2 different alleles for the same trait
Hybrid for that trait
Ex: Tt
Homozygous – organisms that have 2 identical alleles for a particular trait
True-breeding for a particular trait
Ex: TT or tt

6. Genes, Alleles and Dominance
Phenotype – physical characteristics
Ex: tall, short, yellow, green
Genotype – genetic make-up
Ex: TT, Tt, tt
Tall plants have the same phenotype (tall), but not the same genotype (TT or Tt)

7. Mendel crossed plants to study offspring
P generation – (parents) – tall TT x short tt
F1 generation – (offspring of P) tall Tt x tall Tt
F2 generation – (offspring of F1) 3 tall TT Tt Tt, 1 short tt

8. Law of Segregation Segregation = separation
The alleles for tall vs. short separate during the formation of gametes – sex cells
Each gamete (sperm or egg) carries one allele for each gene

9. The Two-factor Cross: F1
4 alleles (2 genes) at the same time (cross true breeders – P generation)
Provides the hybrid plants (F1 generation)
Crossed a homozygous RRYY (round yellow peas) with a homozygous rryy (wrinkled, green peas)

10. The two factor cross: F2
F1 – yields all offspring heterozygous for both traits
F2 – heterozygous parents crossed
F2 – yields 9:3:3:1
ratio

11. Law of Independent Assortment
Independent assortment – genes segregate independently during the formation of gametes
Helps account for many genetic variations in organisms
Seed shape & color gene do not influence each other

12. Law of Independent Assortment
NOTE: Independent assortment only works if genes are on different chromosomes or are far apart on the same chromosome (unlinked)

13. Law of Independent Assortment
Unlinked Genes – on different chromosomes, the two genes assort into gametes independently of each other. Follows expected ratio of 9:3:3:1 for heterozygous cross
Linked Genes – on the same chromosomes, do not assort into gametes independently, unexpected phenotypic ratios.
A/b and a/B are on the same chromosome, so they are linked

14. Genetics and Probability
Probability – the likelihood a particular event will occur.
Ex: probability of flipping a coin to heads = ½ or 50%
Probability of heads 3 times in a row = ½ x ½ x ½ = 1/8 - can be multiplied together
The greater the number or trials, the closer to the expected ratio
Past outcomes do not affect future outcomes

15. Beyond Dominant and Recessive Alleles
Genes can act in various ways
Dominant vs. Recessive – one allele completely masks another allele.
Incomplete Dominance
Definition : one allele is not completely dominant over another
Ex: flowers – white x red flowers = pink flowers

16. Beyond Dominant and Recessive
3. Codominance
Definition: both alleles contribute to the phenotype of the organism
Ex: chicken feather – black and white alleles = black and white feathers
Colors don’t blend like incomplete dominance (roan horse and cow).

17. Multiple Alleles Definition: more than two alleles
(more than 2 alleles exist in a population not an individual) Blood Types
Ex: human’s blood type
AB type is codominant

18. Polygenic Traits
Definition: traits that are controlled by 2 or more genes
Ex: fruit fly red eyes - 3 genes involved in making pigment
Diff. combo of genes produce different eye colors
Ex: Human skin color – more than 4 different genes
Human height – more than 50 genes

19. Genetics and the Environment
Genes provide a plan for development, but how the plan unfolds also depends on the environment:
Ex. Butterflies have different wing colors depending on when they hatch
Hydrangea flowers are different colors depending on soil pH.

20. Probability – Rules of Multiplication and Addition (pg
Probability – Rules of Multiplication and Addition (pg in your text)
Parents: PpYyRr x Ppyyrr
What fraction of offspring from this cross would be expected to exhibit the recessive phenotypes for at least two of these traits?
The genotypes:
ppyyRr
ppYyrr
Ppyyrr
PPyyrr
ppyyrr