1. Mendel and the Gene Idea

2.  To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes.  Each allele is represented by a letter  UPPERCASE/CAPITAL letters are used to represent dominant genes.  lowercase letters are used to represent recessive genes.  Homozygous (AA or aa)  Homozygous - the two alleles for a trait are the same (AA or aa)  Heterozygous (Aa)  Heterozygous - the two alleles for a trait are different (Aa)

3.  For example:  T = represents the gene for TALL in pea plants short  t = represents the gene for short in pea plants  So:  TT & Tt both result in a TALL plant, because T is dominant over t.  t is recessive.  tt will result in a short plant.

4.  A diagram that predicts the outcome of a genetic cross  It considers all the possible combinations of gametes  1 ST DRAW A BIG SQUARE AND DIVIDE IT IN 4’S

5. The alleles from one parent go here. The alleles from the other parent go here.

6. TT t t

7. TT tt tt

8. TT ttt ttt

9. TT tTt ttt

10. TT t t

11. TT t t F 1 generation

12. Tt  The genotype for all the offspring is Tt.  The genotype ratio is:  Tt – 4:4 = 100% heterozygous tall  The phenotype for all the offspring is tall.  The phenotype ratio is:  tall – 4:4 = 100% tall TT tTt t

13. Tt TTTTt t tt F 2 generation

14.  This time the ratios are different! Tt.  The genotype ratio is:  TT – 1:4 Tt – 2:4 tt – 1:4  1:2:1  2 – homozygous  2 – heterozygous  The phenotype ratio is:  TT, Tt, Tt = 3 tall  tt = 1 short  3:1 – tall : short Tt TTTTt t tt

15. LAWS OF PROBABILITY HELP EXPLAIN GENETIC EVENTS  Genetic ratios are most properly expressed as probabilities:  Probabilities range from  0 - an event is certain NOT to happen  1.0 - an event is certain to happen

16.  The likelihood that a specific event will occur  Probability  Probability = # of one kind of possible outcome total # of all possible outcomes  a coin lands on “heads”  1 outcome  Total possible outcomes  = 2  heads or tails  Possibility that the coin will land on heads = 1/2

17. PRODUCT LAW  For simultaneous outcomes (this AND that)  What is the chance that you will roll snake eyes with two dice? (1 and 1)  Chance of rolling 1 with first die = 1/6  Chance of rolling 1 with second die = 1/6  Chance of rolling two 1’s = 1/6 X 1/6 = 1/36

18. SUM LAW  What is the chance that you will roll either a 1 or a 6 with one die?  Chance of rolling 1 = 1/6  Chance of rolling 6 = 1/6  Chance of rolling 1 or 6 = 1/6 + 1/6 = 2/6 = 1/3  For outcomes that can occur more than one way (this OR that)

19. 19 Multiplication Rule The probability that two independent events, A and B, are realized simultaneously is given by the product of their separate probabilities What fraction would we expect to be Round AND Green 3/4 x 1/4 = 3/16

20. 20 Addition Rule The probability that one or the other of two mutually exclusive events, A or B, is the sum of their separate probabilities What fraction would we expect to be (Round and Green) OR (wrinkled and yellow) 3/16 + 3/16 = 6/16

21. MENDEL AND HEREDITY Why we look the way we look...