Download presentation
Presentation is loading. Please wait.
Published byJob Mills Modified over 8 years ago
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...
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.