Living Things - Ms. D. Science C.G.P.A.

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Genetics and DNA: The Science of Heredity
Ms. De Los Rios
7th Grade
12.3 Probability and Heredity
Essential Question:
Why Don’t Offspring always look like their Parents?
How is Probability Related to Inheritance?
What Are Phenotype and Genotype?
Pgs. 420-425
Probability and Heredity – Vocabulary
Probability – A number that describes how likely it is that a particular
event will occur
Punnett square – A chart that shows all the possible combinations of
alleles that can result from a genetic cross
Pedigree – A chart that shows the presence or absence of a trait
according to the relationships within a family across several
generations
Phenotype – An organism’s physical appearance, or visible traits
Genotype – An organism’s genetic makeup, or allele combinations
Homozygous – Having two identical alleles for a particular gene
Heterozygous – Having two different alleles for a particular gene
My Planet Diary p.420
Storm on the Way?
Have you ever watched a
hurricane form?
Weather forecasters at the National
Hurricane Center (NHC) in Miami,
Florida, have. From May 15 to
November 30, the NHC Operations
Area is staffed around the clock with
forecasters. They study data from
aircraft, ocean buoys, and satellites
to develop computer models. These
models predict the probable paths of
a storm. If the probability of a certain
path is high, the NHC issues a
warning that helps save lives and
reduce damage.
Probability and Heredity – My Planet Diary p.420
Storm on the way?
Local weather forecasters
often talk about the percent
chance for rainfall. What do
you think they mean?
_________________________________________________
_________________________________________________
_________________________________________________
What is probability? Pg.421
• Probability is a number that describes how likely it is that an event
will occur
• Ex: probability that a tossed coin will land on heads = 50%
• The laws of probability predict what is likely to occur, not what will
occur
• The more trials you do, the closer your actual results will be to those
predicted by probability
• When tossing a coin, one toss does not affect the result of the next
toss – each event occurs independently
Do the math!
Step 1: write the comparison as a fraction 3 out of 5 = 3/5
Step 2: Calculate the number value of the fraction 3/5 = 0.6
Step 3: multiply this number by 100%
0.6 x 100% = 60%
Punnett Squares and Pedigrees P.422-423
• A Punnett square is a chart that shows all the possible ways alleles can
combine in a genetic cross
• In a genetic cross, the combination of alleles that parents can pass on to
an offspring is based on probability
• The boxes in the Punnett square show the possible combinations of
alleles that the offspring can inherit
• A pedigree is a chart or “family tree” that shows the presence or absence of
a trait according to the relationships within a family across several
generations
• Doctors us pedigrees to trace and diagnose genetic disorders
Probability and Heredity – Figure 1 p. 422-423
1. Determine the probability that an
offspring will have wrinkled seeds.
____________________________________
2. Determine the probability that an
offspring will have round seeds.
____________________________________
Assess Your Understanding pg. 423
1a. Review- What is probability?__________________________
___________________________________________________
b. Apply Concepts- What is the probability that a cross between a hybrid
pea plant with round seeds and one with wrinkled seeds will produce
offspring with wrinkled seeds? (Draw a punnett square on another
paper to find the answer)
___________________________________________________
I get it! Now I know that the combination of alleles parents can pass to
offspring ___________________________________
___________________________________________________
What are Phenotype and Genotype p.424
phenotype
genotype
An organism’s phenotype is its
physical appearance or, visible
traits
An organism’s genotype is its genetic
makeup or allele
Identical Alleles
SS or ss
Homozygous
Different alleles
An organism that has two identical
alleles for a trait is said to be
homozygous for that trait.
Ss
Heterozygous
An organism that has two different
alleles for a trait is said to be
heterozygous for that trait. Ss
Recall that Mendel used the term
hybrid to describe
heterozygous
What are Phenotype and Genotype p.424
The allele for smooth pea pods (S) is
dominant. Therefore those with the
phenotype of smooth pods can have two
genotypes, SS or Ss
The plants with a phenotype of
pinched pods would only only have one
genotype, ss
Apply it! p. 425
Mendel’s principles apply to many other organisms.
Example: In guinea pigs, black fur color (B) is
Dominant over white fur color (b). Suppose a pair
Of black guinea pigs produces several litters of
Pups during their lifetimes. The graph shows the
Phenotypes of the pups. Write a title for the graph.
1.How many black pups were produced? How
many white pups?
______________________________________
2. What are the possible genotypes of the offspring?
____________________________
3. What can you conclude about the genotypes of the parent guinea pigs? Explain
your answer.
______________________________________________________________________
______________________________________________________________________
Assess Your Understanding pg. 425
2a. Relate Cause and Effect- Explain how two organisms can have the
same phenotype but different genotypes.
_________________________________________________________
___________________________________________
b. Challenge- In their lifetime, two guinea pigs produce 40 black pups
and 40 white pups. On a separate sheet of paper, make a Punnett
square and find the likely genotypes of these parents.
__________________________________________
___________________________________________________
I get it, Now I know that phenotype and genotype are terms that
describe __________________________________________
___________________________________________________

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