Living Things

1
Genetics and DNA The Science of Heredity Ms. De
Los Rios 7th Grade
12.3 Probability and Heredity Essential
Question Why Dont Offspring always look like
their Parents? How is Probability Related to
Inheritance? What Are Phenotype and
Genotype? Pgs. 420-425
2
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 organisms physical appearance, or
  visible traits
• Genotype An organisms genetic makeup, or
  allele combinations
• Homozygous Having two identical alleles for a
  particular gene
• Heterozygous Having two different alleles for a
  particular gene

3
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.

4
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?
• _________________________________________________
• _________________________________________________
• _________________________________________________

5
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

6
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

7
Probability and Heredity Figure 1 p. 422-423

• Determine the probability that an offspring will
  have wrinkled seeds.
• ____________________________________
• 2. Determine the probability that an offspring
  will have round seeds.
• ____________________________________

8
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
  ___________________________________
• __________________________________________________
  _

9
What are Phenotype and Genotype p.424
phenotype genotype
An organisms phenotype is its physical appearance or, visible traits An organisms genotype is its genetic makeup or allele
Identical Alleles SS or ss Homozygous Different alleles Ss Heterozygous
An organism that has two identical alleles for a trait is said to be homozygous for that trait. 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
10
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

11
Apply it! p. 425

• Mendels 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.
• 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.
• __________________________________________________
  __________________________________________________
  ________________________________________

12
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 __________________________
  ________________
• __________________________________________________
  _