Patterns of HeredityPatterns of Heredity(Chapter 4 pp. 98-(Chapter 4 pp. 98-127)127)T. GilbertT. Gilbert

77thth Life Science Life Science

Objective(s): TSWObjective(s): TSW

Explain the relationship between traits Explain the relationship between traits and heredity.and heredity.

Describe the experiments of Gregor Describe the experiments of Gregor Mendel.Mendel.

Explain the difference between dominant Explain the difference between dominant and recessive traits.and recessive traits.

Terms to LearnTerms to Learn HeredityHeredity: the passing of genetic traits from : the passing of genetic traits from

parents to offspringparents to offspring Dominant traitDominant trait: the trait observed in the : the trait observed in the

first generation when parents that have first generation when parents that have different traits are breddifferent traits are bred

Recessive traitRecessive trait: a trait that reappears in : a trait that reappears in the second generation after disappearing the second generation after disappearing in the first generation when parents with in the first generation when parents with different traits are breddifferent traits are bred

Mendel and His PeasMendel and His Peas

Why don’t you look like a whale?Why don’t you look like a whale? Simple answer, neither of your parents Simple answer, neither of your parents

are whales.are whales. But there’s more to this answer than But there’s more to this answer than

meets the eye.meets the eye. Heredity is the passing of traits from Heredity is the passing of traits from

parents to offspring.parents to offspring. Passing of traits is more complicated Passing of traits is more complicated

than you think.than you think.

HeredityHeredity Passing of traits is complicated.Passing of traits is complicated. You might have curly hair, while both of You might have curly hair, while both of

your parents have straight hair.your parents have straight hair. Your eyes may be black, while both your Your eyes may be black, while both your

parents have brown eyes.parents have brown eyes. How does this happen?How does this happen? This has been studied for years. Gregor This has been studied for years. Gregor

Mendel, over 150 years ago, performed Mendel, over 150 years ago, performed important experiments.important experiments.

His work laid the foundation for finding His work laid the foundation for finding answers to these questions.answers to these questions.

Who was Gregor Mendel?Who was Gregor Mendel?

Born in 1822 in AustriaBorn in 1822 in Austria Entered a monastery at the age of 21Entered a monastery at the age of 21 Monks taught science and performed many Monks taught science and performed many

experiments.experiments. Received formal training in teaching but Received formal training in teaching but

could not pass test.could not pass test. Returned to monastery where he Returned to monastery where he

discovered the principles of hereditydiscovered the principles of heredity

AssignmentAssignment

Read pages 100-107 in textbooks.Read pages 100-107 in textbooks. As you read, use one of the notetaking As you read, use one of the notetaking

strategies described on page 100 under strategies described on page 100 under “Choose Your Own Strategy.” (Main idea “Choose Your Own Strategy.” (Main idea webs, combination notes, or mind maps)webs, combination notes, or mind maps)

You may mix and match the strategies.You may mix and match the strategies. Turn in at the end of class.Turn in at the end of class.

Genes are on chromosome pairs.

Gene Heredity Allele Homolog Individuals _______ their genes from

their parents.

Genes are on chromosome pairs.

Genes can occupy a specific location on a chromosome and code for a specific characteristic or product.

Individuals inherit genes from their parents.

Most traits are not coded for by one gene.

Some characteristics are coded for by many genes.

Genes are on chromosome pairs.

Unraveling the MysteryUnraveling the Mystery

Working with pea plants, Mendel knew that Working with pea plants, Mendel knew that patterns of inheritance were not always clear.patterns of inheritance were not always clear.

For example, sometimes traits that appeared For example, sometimes traits that appeared in one generation (parents) was not present in one generation (parents) was not present in the next generation (offspring). in the next generation (offspring).

Mendel noticed these kinds of patterns in Mendel noticed these kinds of patterns in several other living things, too.several other living things, too.

Unraveling the Mystery Unraveling the Mystery (cont.)(cont.)

To keep his investigation simple, Mendel To keep his investigation simple, Mendel decided to study only one kind of decided to study only one kind of organism- garden pea plants.organism- garden pea plants.

Self-Pollinating Peas- Chosen because Self-Pollinating Peas- Chosen because grow quickly, different kinds available, grow quickly, different kinds available, self-pollinate.self-pollinate.

Self-Pollinating PeasSelf-Pollinating Peas

Self-pollinatingSelf-pollinating plant has both male and plant has both male and female reproductive structures.female reproductive structures.

Pollen from one flower can fertilize the Pollen from one flower can fertilize the ovule of the same flower or the ovule of ovule of the same flower or the ovule of another flower of the same plant.another flower of the same plant.

Why is it important for pea plants to self-Why is it important for pea plants to self-pollinate? pollinate?

Self-Pollinating Peas Self-Pollinating Peas (cont.)(cont.)

Because eggs (in an ovule) and sperm (in Because eggs (in an ovule) and sperm (in pollen) from the same plant combine to make a pollen) from the same plant combine to make a new plant, Mendel was able to grow true-new plant, Mendel was able to grow true-breeding plants.breeding plants.

True-breeding plantTrue-breeding plant- When it self-pollinates, all - When it self-pollinates, all offspring will have the same trait as the parent.offspring will have the same trait as the parent.

For example, a true-breeding plant with purple For example, a true-breeding plant with purple flowers will always have offspring with purple flowers will always have offspring with purple flowers.flowers.

Self-Pollinating Peas Self-Pollinating Peas (cont.)(cont.)

Pea plants can cross-pollinate.Pea plants can cross-pollinate. In In cross-pollinationcross-pollination, pollen from one , pollen from one

plant fertilizes the ovule of a flower on a plant fertilizes the ovule of a flower on a different plant.different plant.

Several ways cross-pollination can Several ways cross-pollination can happen:happen:

1.1.AnimalsAnimals

2.2.WindWind

School to Home: School to Home: Describing TraitsDescribing Traits

How would you describe yourself?How would you describe yourself? Would you say that you are tall or short, have Would you say that you are tall or short, have

curly hair or straight hair?curly hair or straight hair? Make a list of some of your physical traits.Make a list of some of your physical traits. Make a second list of traits that you were not Make a second list of traits that you were not

born with, such as “caring” or “good at born with, such as “caring” or “good at soccer.”soccer.”

Talk to your family about your lists.Talk to your family about your lists. Do they agree with your descriptions?Do they agree with your descriptions?

CharacteristicsCharacteristics Mendel studied only one characteristic at a Mendel studied only one characteristic at a

time.time. Mendel used plants that had different traits Mendel used plants that had different traits

for each of the characteristics he studied.for each of the characteristics he studied. CharacteristicCharacteristic- a feature that has different - a feature that has different

forms in a population. Example- hair colorforms in a population. Example- hair color Different forms, such as brown or red hair, Different forms, such as brown or red hair,

are called are called traitstraits..

Mix and MatchMix and Match

Mendel was careful to use plants that were Mendel was careful to use plants that were true breeding for each of the traits being true breeding for each of the traits being studied.studied.

By doing so, Mendel would know what to By doing so, Mendel would know what to expect if his plants were to self-pollinate.expect if his plants were to self-pollinate.

Mendel decided to find out what would Mendel decided to find out what would happen if he bred, or crossed, two plants happen if he bred, or crossed, two plants that had different traits of a single that had different traits of a single characteristic.characteristic.

Mix and Match (cont.)Mix and Match (cont.)

To be sure the plants cross-pollinated, he To be sure the plants cross-pollinated, he removed the anthers of one plant so that removed the anthers of one plant so that the plant could not self-pollinate.the plant could not self-pollinate.

Mendel then used pollen from another Mendel then used pollen from another plant to fertilize the plant.plant to fertilize the plant.

This step allowed Mendel to select which This step allowed Mendel to select which plants would be crossed to produce plants would be crossed to produce offspring.offspring.

Mendel’s First Mendel’s First ExperimentsExperiments

Crossed pea plants to study 7 different Crossed pea plants to study 7 different characteristicscharacteristics

Each cross, Mendel used plants that Each cross, Mendel used plants that were true breeding for different traits for were true breeding for different traits for each characteristic.each characteristic.

For example, he crossed plants that had For example, he crossed plants that had purple flowers with plants that had white purple flowers with plants that had white flowers. flowers.

Mendel’s First Mendel’s First Experiments (cont.)Experiments (cont.)

The offspring from such a cross are called The offspring from such a cross are called first-first-generationgeneration plants. plants.

All of the first generation plants in this cross All of the first generation plants in this cross had purple flowers.had purple flowers.

What happened to the trait for white flowers?What happened to the trait for white flowers? Mendel got similar results for each cross.Mendel got similar results for each cross. One trait was always present in the first One trait was always present in the first

generation, and the other trait seemed to generation, and the other trait seemed to disappear.disappear.

Mendel’s First Mendel’s First Experiments (cont.)Experiments (cont.)

Mendel chose to call the trait that Mendel chose to call the trait that appeared the appeared the dominant traitdominant trait..

The other trait seemed to fade into the The other trait seemed to fade into the background leading Mendel to call it the background leading Mendel to call it the recessive traitrecessive trait..

To find out what happened to the To find out what happened to the recessive trait, Mendel performed recessive trait, Mendel performed another set of experiments.another set of experiments.

Mendel’s Second Mendel’s Second ExperimentsExperiments

Mendel allowed the first-generation plants to Mendel allowed the first-generation plants to self-pollinate.self-pollinate.

Results: The recessive trait for white flowers Results: The recessive trait for white flowers reappeared in the second generation.reappeared in the second generation.

Mendel did this same experiment on each of Mendel did this same experiment on each of the 7 characteristics.the 7 characteristics.

In each case, some of the second-In each case, some of the second-generation plants had the recessive trait.generation plants had the recessive trait.

Ratios in Mendel’s Ratios in Mendel’s ExperimentsExperiments

Mendel decided to count the number of plants Mendel decided to count the number of plants with each trait that turned up in the second with each trait that turned up in the second generation in hopes of explaining his results.generation in hopes of explaining his results.

The recessive trait did not show up as often The recessive trait did not show up as often as the dominant trait.as the dominant trait.

Mendel figured out the ratio of dominant to Mendel figured out the ratio of dominant to recessive traits.recessive traits.

A ratio is a relationship between two different A ratio is a relationship between two different numbers that is often expressed as a fraction.numbers that is often expressed as a fraction.

Math PracticeMath Practice

Calculate the dominant-to-recessive ratio Calculate the dominant-to-recessive ratio for each characteristic.for each characteristic.

Do you notice anything interesting about Do you notice anything interesting about the ratios?the ratios?

Round to the nearest whole number.Round to the nearest whole number. Are the ratios all the same, or are they Are the ratios all the same, or are they

different? different?

Gregor Mendel- Gone but Gregor Mendel- Gone but Not ForgottenNot Forgotten

Mendel realized that his results could be explained Mendel realized that his results could be explained only if each plant had two sets of instructions for only if each plant had two sets of instructions for each characteristic.each characteristic.

Each parent would then donate one set of Each parent would then donate one set of instructions.instructions.

In 1865, Mendel published his findings; however, In 1865, Mendel published his findings; however, his ideas were overlooked or misunderstood until his ideas were overlooked or misunderstood until approximately 30 years after his death. approximately 30 years after his death.

Once his ideas were rediscovered and Once his ideas were rediscovered and understood, the door was opened to modern understood, the door was opened to modern genetics.genetics.

SummarySummary Heredity is the passing of traits from parents to Heredity is the passing of traits from parents to

offspring.offspring. Gregor Mendel made carefully planned experiments Gregor Mendel made carefully planned experiments

using pea plants that could self-pollinate.using pea plants that could self-pollinate. When parents with different traits are bred, dominant When parents with different traits are bred, dominant

traits are always present in the first generation. traits are always present in the first generation. Recessive traits are not visible in the first generation Recessive traits are not visible in the first generation but reappear in the second generation.but reappear in the second generation.

Mendel found a 3:1 ratio of dominant-to-recessive Mendel found a 3:1 ratio of dominant-to-recessive traits in the second generation.traits in the second generation.