Probability and Inheritance

1
Probability and Inheritance
2
Probability

• The likelihood that a particular event will occur.

3
Percentages

• One way you can express a probability is as a
  percentage.
• Suppose that 3 out of 5 tossed coins landed with
  heads up. Heres how you can calculate what
  percent of the coins landed with heads up
• Write the comparison as a fraction.
• Specific events vs possible events
• 3 out of 5 3/5
• 2. Multiply the fraction by 100 to express it as
  a percentage.
• 3/5 x 100/1 60

4
How is probability associated with genetics?

• Much like the flipping of a quarter, the
  likelihood of alleles is completely random.

5
What is a PUNNETT SQUARE?

• A tool to predict the probability of certain
  traits in offspring that shows the different ways
  alleles can combine
• A way to show phenotype (the trait) genotype
  (the alleles)
• A chart that shows all the possible combinations
  of alleles that can result when genes are crossed

6
Genotype and Phenotype

• Genotype refers to genetic makeup, or what
  alleles the organism has
• Phenotype refers to the physical appearance of an
  organism
• Organisms with the same phenotype may not have
  the same genotype

7
Dominant and Recessive Traits

• When making Punnett squares, capital letters are
  used to represent dominant traits
• P Purple Flower
• always shows up when present
• Lower case letters are used to represent
  recessive traits
• p white flower
• hidden when dominant allele is present

8
Homozygous Heterozygous

• Organisms that have two identical alleles for a
  particular trait (TT or tt) are said to be
  homozygous
• True-breeding
• Organisms that have two different alleles for the
  same trait Tt are heterozygous
• Hybrid

9
A Punnett Square

• In this cross, both parents are heterozygous for
  the trait of seed shape. R represents the
  dominant round allele, and r represents the
  recessive wrinkled allele.

10
Punnett Square 1 breeding 2 homozygous animals
Genotype 100 Bb hybrid brown
B
B
Brown BB
Bb
Bb
b
What is the probability?
Daddy
white bb
Phenotype 100 All brown offspring
b
Bb
Bb
Mommy
11
Punnett Square 2 breeding 1 homozygous animal
and 1 heterozygous animal
Genotype 50 Bb hybrid brown 50 bb white
B
b
Brown Bb
Bb
bb
b
Daddy
white bb
Phenotype 50 brown offspring 50 white offspring
b
Bb
bb
What is the probability?
Mommy
12
Punnett Square 3 breeding 2 heterozygous
animals
Genotype 25 BB brown 50 Bb hybrid brown 25
bb white
B
b
Brown Bb
BB
Bb
B
Daddy
Brown Bb
Phenotype 75 brown offspring 25 white offspring
b
Bb
bb
What is the probability?
Mommy
13
Codominance

• In codominance, the alleles are neither dominant
  nor recessive. As a result, both alleles are
  expressed in the offspring.

14
Incomplete Dominance

• When one allele is NOT completely dominant over
  another (they blend)
• Example In carnations the color red (R) is
  incompletely dominant over white (W). The hybrid
  color is pink.