1. 11-1 The Work of Mendel
What does every living thing inherit from their parents?
Genetics – the study of heredity
Look around at your classmates and make a list of some of the traits that are inherited.

2. What did Mendel already know…
Each flower produces pollen (sperm) and egg cells
Cross fertilization (sexual) – male and female cells join
Self-pollination (asexual) – pollen fertilizes eggs from same plant
Mendel’s pea plants were true-breeding
A tall plant with green seeds would produce a tall plant with green seeds

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

4. 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)

5. 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)

6. True-breeding for a particular trait
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

7. 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)
Why are TT and Tt genotypes for tallness, but tt is not???

8. 11-2 Probability and Punnett Squares
Mendel realized…the principles of probability could be used to explain the results of genetic crosses.

9. Genetics and Probability
Probability – the likelihood a particular event will occur.
Ex: probability of flipping a coin to heads = ½ or 50%
Probability of head 3 times in a row = ½ x ½ x ½ = 1/8
The greater the number or trials, the closer to the expected ratio
Past outcomes do not affect future outcomes
Alleles segregate randomly (like a coin)

10. Principle of Segregation
Segregation = separation
The alleles for tall vs. short separate during the formation of gametes – sex cells
Each gamete carries one allele for each gene

11. The Two-factor Cross: F1
4 alleles (2 genes) at the same time
Provides the hybrid plants (F2 generation)
Crossed a homozygous RRYY (round yellow peas) with a homozygous rryy (wrinkled, green peas)

12. 11.3 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

13. 11.3 Beyond Dominant and Recessive
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

14. 11.3 Multiple Alleles Definition: more than two alleles
(more than 2 alleles exist in a population not an individual) Blood Types
Ex: rabbit’s coat color
Ex: human’s blood type

15. 11.3 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

16. 11.3 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.

17. Mendel Questions
Using tall and short pea plants and the letters T = dominant and t = recessive describe Mendel’s F1 generation and F2 generation.
Provide the genotype and phenotype for each of four offspring from each generation. You do not need to use a punnett square.

18. Meiosis

19. Ttrr x ttRr

20. ttRr x TtRr

21. Questions Genetics is the study of ________.
Alternate characteristics of an organism such as height, hair color, eye color, etc. are called _______.
Why did pea plants make such a good subject for Mendel to study?
What does “true breeding” mean?

22. Considering the allele related to short and tall pea plants.
Plants of the P generation (tall) will produce only_____________ if not crossed with plants having other alleles.
Describe the phenotype (what we can see) of Mendel’s F1 Generation.
What was the genotype (use letters “T” and “t”) for Mendel’s F1 generation?
How did the F2 generation suggest that genes were simply segregated, not lost?