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

Genetics and DNA: The Science of Heredity Ms. De Los Rios

7th Grade

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?

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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

1. Determine the probability that an offspring will have wrinkled seeds.

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

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Probability and Heredity – Figure 1 p. 422-423

Assess Your Understanding pg. 423

1a. Review- What is probability?__________________________

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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)

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I get it! Now I know that the combination of alleles parents can pass to offspring ___________________________________

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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 AllelesSS or ss

Homozygous

Different alleles

SsHeterozygous

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. SsRecall that Mendel used the term

hybrid to describe heterozygous

What are Phenotype and Genotype p.424

Mendel’s principles apply to many other organisms. Example: In guinea pigs, black fur color (B) isDominant over white fur color (b). Suppose a pairOf black guinea pigs produces several litters of Pups during their lifetimes. The graph shows thePhenotypes 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.____________________________________________________________________________________________________________________________________________

Apply it! p. 425

Assess Your Understanding pg. 425

2a. Relate Cause and Effect- Explain how two organisms can have the same phenotype but different genotypes.

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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. __________________________________________

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I get it, Now I know that phenotype and genotype are terms that describe __________________________________________

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