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Probability and Genetics
Pages 84 - 89
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Open your notebook
Have pen or pencil ready
Listen carefully during presentation
You will take notes and answer
questions!!
• At the end of presentation
you will answer the review questions
• It will be a quiz grade…!!!
Probability and Genetics
pages 84 - 89
Principles of Probability
• Likelihood that a particular event will occur
• In genetics it is the likelihood a particular
trait will show up in the organism/you
• PROBLEM:
3 out of 10 coins landed heads up. What % is
this?
3 X 100% = 30%
10
1
Punnett Square
• The Punnett square is a diagram designed by
Reginald Punnett and used by biologists
Mom
determine the probability of an offspring
having a particular genotype
• It is made by comparing all the possible
combinations of alleles from the mother with
those from the father
Dad
Punnett Square
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R = round face / dominant
r = oval face / recessive
Mom has round face Rr
Dad has oval face rr
Two children have round face
Rr 2:4
• Two children have oval face
rr 2:4
Mom
Dad
Genotype
and
Phenotype
• Phenotype – physical traits,
those you can see
• Genotype – genetic makeup or
allele combinations, inside the
nucleus
• A = Red feathers/ Dominant
• a = blue feathers/ recessive
• Feather color is the Phenotype
• AA aa or Aa is the Genotype
QUESTION
What is the Phenotype or feather color
of the 4 little birds?
• All the little birds are Red
Dad
Two types of Genotype
1. Homozygous Genotype or Ho
• Both alleles are Dominant TT SS CC
• Both alleles are recessive
tt ss cc
Both alleles are the same…
2. Heterozygous Genotype or He
• One allele is Dominant the other is recessive
Tt
Ss
Cc
Both alleles are different…
Phenotypes and Genotypes
• In Purple people eaters, one-horn is
dominant and no horns is recessive.
• H = one horn/ Dominant allele
• h = no horn/ recessive allele
• QUESTIONS:
- What are the phenotypes of the children?
2 have one horn, 2 have no horn
- What are the genotypes of the children?
2 are Hh ( Horn) 2 are hh (no horn)
SOLVE THIS PROBLEM
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Mom has blue eyes with bb
genotype or allele combination
B
b
Dad has Brown eyes with
b
B
b
b
b
Bb genotype or allele
combination
b Bb b b
• What is the Phenotype for
each child?
• What are the allele combinations
or genotype for each child? _: % are Bb or bb
CAN YOU PREDICT BEFORE YOU CLICK?
ANSWERS for Eye colors
GENOTYPE
PHENOTYPE
2 Children have Bb
2 Children have
Brown eyes
2:4
50 %
2 Children have bb
2 Children have
Blue eyes
2:4
50%
Describing Allele Combinations
• Homozygous Genotype
1. Both alleles are either:
a. DOMINANT AA
b. recessive aa
• Heterozygous Genotype
1. One allele is dominant A
the other is recessive a
Question
What is the Phenotype of the
4 offsprings?
• 3 are Red feathers
• 1 is blue feathers
What is the genotype for each parent
and the little birds?
• Mom is?
Homozygous Dominant
• Dad is ?
homozygous recessive
• Do all the little birds have the
same genotype?
YES…!
• What is their genotype?
Heterozygous Dominant
• Do they have the recessive allele
for blue feathers?
YES…!
Codominance
• Codominance
a. The alleles for a trait are neither
dominant or recessive
b. In this case both alleles are expressed or
show up as physical trait or Phenotype
c. See Figure 10, page 89
Both black and white feathers show in the
offsprings
Cystic Fibrosis
If both parents are carriers of the recessive allele for the disorder
but parents do not have the disease the probability all of their
children of inheriting Cystic Fibrosis is:
25% or 1: 4 chance of having the recessive disorder
50% or 2 : 4 chance of being a healthy carrier
25% or 2 : 4 chance of being healthy and not have the recessive allele
Review questions
1
. What is the Punnett Square?
Answer: A diagram that shows the probability or a
chance of a trait showing up in an offspring
2. What is an allele?
Answer: A specific form of a trait
3. True or False: We can see our genotype?
Answer: FALSE The genotype is what our genes
are for a specific trait
What is the Phenotype?
Answer: It is the visible trait, you can see it:
Example: Eye color, body shape…..
4.
5. Which trait is seen in the organism?
Dominant or Recessive ?
Answer: The Dominant Trait if the organism has it
6. When is the only time the recessive trait or allele shows?
Answer: When the organisms doesn’t have the
Dominant trait or allele
7. True or False: A heterozygous or He trait has
both Dominant and recessive allele.
Answer: TRUE Bb for brown eyes
Review questions
8. What is Codominance?
Answer: When the alleles are neither dominant
nor recessive. Both alleles or traits
show up