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Essential Questions: How is the study of genetics related to the characteristics of life? PowerPoint PPT Presentation

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Georgia Standards: SB2d. Explain the relationship between changes in DNA and the appearance of new traits. SB2c. Using Mendel’s Laws, explain the role of meiosis in reproductive variability. Essential Questions: How is the study of genetics related to the characteristics of life?

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Essential Questions: How is the study of genetics related to the characteristics of life?

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Georgia Standards:SB2d. Explain the relationship between changes in DNA and the appearance of new traits. SB2c. Using Mendel’s Laws, explain the role of meiosis in reproductive variability

Essential Questions:

How is the study of genetics related to the characteristics of life?

How do you predict the probability of various genotypes inherited and the expressed phenotypes?

How does meiosis generate variation in offspring?


  • What is Genetics?

  • What do you think of when you hear the word genetics????

11-1 Warm-up: Analyzing Inheritance

Section 11-1

  • Offspring resemble their parents.

  • Offspring inherit genes for characteristics from their parents.

  • To learn about inheritance, scientists have experimented with breeding various plants and animals.

  • In each experiment shown in the table on the next slide, two pea plants with different characteristics were bred. Then, the offspring produced were bred to produce a second generation of offspring. Consider the data and answer the questions that follow.

Go to Section:

Parents (P)

Long stems  short stems

Red flowers  white flowers

Green pods  yellow pods

Round seeds  wrinkled seeds

Yellow seeds  green seeds

First Generation (F1)

All long

All red

All green

All round

All yellow

Second Generation (F2)

787 long: 277 short

705 red: 224 white

428 green: 152 yellow

5474 round: 1850 wrinkled

6022 yellow: 2001 green

11-1 Warm-up: Analyzing Inheritance

1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics?

2. How do the characteristics of the second generation compare to the characteristics of the first generation?

Go to Section:

Gregor Mendel: Father of Genetics

  • Gregor Mendel (1860’s) an Austrian Monk

  • Gregor Mendel used pea plants and a quantitative approach to collect data.

  • Mendel studied seven different pea plant traits. A trait is a specific characteristic, such as seed color or plant height, that varies from one individual to another.

Important terms

  • Genotype- genetic make-up of an organism (allele combinations= AA or Aa)

  • Phenotype- physical trait that is visible.

  • Allele- different forms of a gene

    Ex. Aa- A and a

Gregor Mendel’s Experiment:

  • Mendel crossed plants with each of the 7 contrasting traits and studied their offspring.

  • Mendel called each original pair of plants the P (parental) generation.

  • He called the offspring of the P generation, the F1, or “first filial,” generation. Filius is the Latin word for “son.”

    • These pea plants were cross pollinated.

    • The offspring of crosses between parents with different traits are called hybrids.

Gregor Mendel’s Experiment:

cross-pollination, male sex cells in pollen from the flower on one plant fertilize the egg cells of a flower on another plant.

Self-pollination- male sex cells in pollen are used to fertilize the egg of the same flower.

Gregor Mendel’s Conclusions:

  • Genes and Dominance

    • Mendel’s first conclusion was that biological inheritance is determined by factors (genes) that are passed from one generation to the next.

      • Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms.

      • The different forms of a gene are called alleles

Gregor Mendel’s Conclusions:

  • Mendel’s second conclusion is called the principle of dominance, which states that some alleles are dominant and others are recessive.

    • An organism with a dominant allele for a particular form of a trait will always have that form.

    • An organism with a recessive allele for a particular form of a trait will have that form only when the dominant allele for the trait is not present.

During gamete formation, alleles are segregated from each other so that each gamete carries only a single copy of each gene.

Each F1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness.

The alleles are paired up again when gametes fuse during fertilization.

Segregation of Alleles:

Checkpoint Questions:

  • What are dominant and recessive alleles?

  • What is segregation? What happens to alleles during segregation?

    3. What did Mendel conclude determines biological inheritance?

    4. Describe how Mendel cross-pollinated pea plants.

    5. Why were true-breeding pea plants important for Mendel’s experiments?

Height in pea plants is controlled by one of two alleles; the allele for a tall plant is the dominant allele, while the allele for a short plant is the recessive one.

What about people? Are the factors that determine height more complicated in humans?

1. Make a list of 10 adults whom you know. Next to the name of each adult, write his or her approximate height in feet and inches.

2. What can you observe about the heights of the ten people?

3. Do you think height in humans is controlled by 2 alleles, as it is in pea plants? Explain your answer.


11-2 Warm-up: Tossing Coins

Section 11-2

  • If you toss a coin, what is the probability of getting heads? Tails? If you toss a coin 10 times, how many heads and how many tails would you expect to get? Working with a partner, have one person toss a coin

  • ten times while the other person tallies the results on a sheet of paper. Then, switch tasks to produce a separate tally of the second set of 10 tosses.

Go to Section:

Interest Grabber continued

11-2 Warm-up: Tossing Coins

Section 11-2

1. Assuming that you expect 5 heads and 5 tails in 10 tosses, how do the results of your tosses compare? How about the results of your partner’s tosses? How close was each set of results to what was expected?

2. Add your results to those of your partner to produce a total of 20 tosses.

Assuming that you expect 10 heads and 10 tails in 20 tosses, how close are these results to what was expected?

3. If you compiled the results for the whole class, what results would you expect?

4. How do the expected results differ from the observed results?

Go to Section:

11-2: Probability and Punnett Squares

  • The principles of probability can be used to predict the outcomes of genetic crosses.

  • The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square. (See note sheet)

This Punnett square shows the probability of each possible outcome of a cross between hybrid tall (Tt) pea plants.

Genotype: 25% TT, 50% Tt, 25%tt (1:2:1)

Phenotype: 75% Tall, 25% short (3:1)

Punnett square

Punnett Squares

  • Organisms that have two identical alleles for a particular trait—TT or tt in this example—are said to be homozygous

  • Organisms that have two different alleles for the same trait are heterozygous (Ex: Tt)

  • Homozygous organisms are true-breeding for a particular trait. Heterozygous organisms are hybrid for a particular trait.

Punnett Squares

  • All of the tall plants have the same phenotype, or physical characteristics.

  • They do not, however, have the same genotype, or genetic makeup.

Dihybrid Cross:

Shows inheritences of two traits at once

F1 Mendel crossed plants that were homozygous dominant for round yellow peas with plants that were homozygous recessive for wrinkled green peas. All of the F1 offspring were heterozygous dominant for round yellow peas.

The cross did not indicate whether genes assort, or segregate, independently.

A Dihybrid Cross: F1

A combination of alleles were produced that were not found in either parent

This means that genes for different traits can segregate independently during the formation of gametes. (Independent Assortment)

Did this mean that the two dominant alleles would always stay together? Or would they “segregate independently.”

Alleles are

separated during

gamete formation




Some alleles

are dominant,

and some alleles

are recessive

Law of


Law of


Concept Map



experimented with

concluded that



genes for different traits can segregate independently during the formation of gametes

which is called the

which is called the

Law of



which is called the

Go to Section:

Genes determine inheritance of biological characteristics.

Genes are passed from parents to offspring

Some forms of the gene may be dominant and others may be recessive.

In most sexually reproducing organisms, each adult has two copies of each gene—one from each parent. These genes are segregated from each during gamete formation.

The alleles for different genes usually segregate independently of one another.

A Summary of Mendel’s Principles

Exceptions to Simple Dominance

  • Does the segregation of one pair of alleles affect the segregation of another pair of alleles?

  • For example, does the gene that determines whether a seed is round or wrinkled in shape have anything to do with the gene for seed color? Must a round seed also be yellow?

Exceptions to the Laws:

  • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

  • incomplete dominance occurs when one allele is not completely dominant over another

  • In incomplete dominance, the heterozygous phenotype is somewhere in between the two homozygous phenotypes.

Some alleles are neither dominant nor recessive.

In four o’clock plants, for example, the alleles for red and white flowers show incomplete dominance.

Heterozygous (RW) plants have pink flowers—a mix of red and white coloring

Incomplete Dominance 

In codominace, both alleles contribute to the phenotype of the organism.

For example, in cattle the allele for red hair is codominant with the allele for white hair.

Cattle with both alleles are roan, or pinkish brown, because their coats are a mixture of both red and white hairs.

In certain varieties of chickens, the allele for black feathers is codominant with the allele for white feathers.

Heterozygous chickens appear speckled with black and white feathers.


Many genes have more than two alleles and are therefore said to have multiple alleles.

This does not mean that an individual can have more than two alleles. It only means that more than two possible alleles exist in a population.

One of the best-known examples is coat color in rabbits.

A rabbit’s coat color is determined by a single gene that has at least four different alleles.

Many other genes have multiple alleles

human genes for blood type

Multiple Alleles

Many traits are produced by the interaction of several genes.

Traits controlled by two or more genes are said to be polygenic traits, which means “having many genes.”

Different combinations of alleles for these genes produce very different eye colors.

Polygenic traits often show a wide range of phenotypes.

Ex: skin color, eye color for fruit flies, height (humans)

Polygenic Traits 

Most traits are controlled by two or more genes and are, therefore, called polygenic traits.

Each gene of a polygenic trait often has two or more alleles.

As a result, one polygenic trait can have many possible genotypes and even more possible phenotypes.

Polygenic Traits:

EX: height (A bell-shaped curve is also called a normal distribution)

Checkpoint Point Questions:

1. Explain what independent assortment means.

2. Describe two inheritance patterns besides simple dominance.

3. What is the difference between incomplete dominance and codominance?

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