Go to Section:

CP Biology

Chapter 10 - Genetics

Go to Section:

11-1: The Work of Mendel

•“Father of Genetics”•Austrian monk, spent time teaching high school age students and tended to the monastery garden.•YouTube - Mendel - From the Garden to the Genome

Go to Section:

•“self-pollinating” peas – Mendel used to produce future offspring

– Knew that each flower produces both male (sperm –found in pollen) and female (egg) gametes

– Fertilized flower’s egg with its own sperm• ASEXUAL REPRODUCTION!• Produced what he called a “true breed”• Offspring would be identical genetically

Go to Section:

Go to Section:

•Then experimented with cross-pollination– Cut the pollen bearing anther off of the flowers and

applied pollen from different flowers to the stigma (part that catches pollen)

Go to Section:

Go to Section:

So with cross-pollination what did Mendel expect?

A: Probably a blend of both parents.

What did he get?

A: Not really what he expected.

Go to Section:

Genes and Dominance

• Trait – specific characteristic that varies from one individual to the next– Important that Mendel used traits that were unambiguous

• Mendel’s seven traits:

1. Seed coat color

2. Seed color

3. Seed shape

4. Pod color

5. Pod shape

6. Plant height

7. Flower position

Go to Section:

•Crossed true breeds with each other (P generation – “parental”)

•Offspring known as F1

•Plants that were products of cross-pollination known as “hybrids.”

•F1 generation was not a blend of parental char.•Instead….

Go to Section:

Mendel’s Monohybrid Cross – P to F1

A Punnett square, something we’ll cover in a moment.

Huh?!?....all yellow seeds!!!

Go to Section:

In fact………here’s what happened with the rest of the traits.

Go to Section:

Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall

Section 11-1

Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants

Go to Section:

•Mendel concluded that heredity is dictated by chemical factors called genes (it would be almost 100 years later before Watson & Crick and the whole DNA thing)

•Genes have alternate forms depending on the plant– These alternate versions of the same gene are

called alleles

Plant height = geneShort and tall = alleles

•Both alleles are present.•One type (recessive) can only be expressed if the other (dominant) is not present

•All these are found on chromosomes!!

Go to Section:

Genes, Alleles, and Chromosomes

Go to Section:

Segregation

•What happened to the other traits?

•Self-pollinated the F1 plants

•The “other” (recessive) traits reappeared in the F2

– He was floored, I’m sure…

Go to Section:

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

Go to Section:

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

Go to Section:

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

Go to Section:

Go to Section:

Segregation (cont.)

•How did the alleles get separated (segregated)?– Mendel suggested the alleles segregated when

the gametes formed.– So every sperm or egg cell has one version

(allele) for that gene• Some (50%) have allele for tall, others (50%)

have allele for short

Go to Section:

Genes, Alleles, and Chromosomes

Go to Section:

Tossing Coins

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.

Section 11-2

Interest Grabber

Go to Section:

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?

Section 11-2

Interest Grabber continued

Go to Section:

11–2 Probability and Punnett Squares

A. Genetics and Probability

B. Punnett Squares

C.Probability and Segregation

D.Probabilities Predict Averages

Section 11-2

Section Outline

Go to Section:

11-2: Probability and the Punnett Square

•Probability – likelihood of an even to take place– What are the chances for a coin to be flipped

heads three times in a row?

½ X ½ X ½ = ⅛

•Probability explains everything in predicting outcomes of genetic crosses.

Go to Section:

Punnett Squares

•Possible gene combinations are represented showing a Punnett Square.

•Homozygous – same allele (SS or ss)•Heterozygous - different allele (Ss)

•Genotype – genetic makeup (SS, Ss, ss)•Phenotype – physical feature observed (Smooth, wrinkled)

Go to Section:

Go to Section:

Go to Section:

Go to Section:

Go to Section:

Go to Section:

Go to Section:

Go to Section:

Probability and Segregation

Consistency is Good

Characters investigated by Mendel

No matter what the characteristic, Mendel observed a 3:1 ratio of characteristics in the F2.

Go to Section:

Monohybrid Crosses Yielded Consistent Results

Therefore, the Principle of Segregation indeed is a general principle of genetics.

Go to Section:

Probabilities Predict Averages

•More the times you flip the coin, the closer it will be to the expected result•Consequently the more offspring that an organism has, the closer the results will be to the averages.

•This is why scientists perform MANY experiments.– Avoid the small percentage event and assume it is

the trend.

Go to Section:

Height in Humans

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?

Section 11-3

Interest Grabber

Go to Section:

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.

Section 11-3

Interest Grabber continued

Go to Section:

11–3 Exploring Mendelian Genetics

A. Independent Assortment

1. The Two-Factor Cross: F1

2. The Two-Factor Cross: F2

B. A Summary of Mendel’s Principles

C.Beyond Dominant and Recessive Alleles

1. Incomplete Dominance

2. Codominance

3. Multiple Alleles

4. Polygenic Traits

D.Applying Mendel’s Principles

E. Genetics and the Environment

Section 11-3

Section Outline

Go to Section:

Independent Assortment•Mendel wondered if alleles for separate genes influenced each other when they segregate.

– Ex: Does a round seed always have to be yellow, or can it be green?

•Two-factor cross– Followed two separate genes from generation to

generation

Independent Assortment of Alleles

Go to Section:

Two Factor Cross

•Crossed true bred round/yellow (RRYY) pea plants with wrinkled/green (rryy) plants

•F1 – 100% round/yellow (RrYy)

– No surprise to Mendel•Mendel hypothesized there was dependent assortment, therefore predicted 3:1 ratio in the F2 (just like in the first experiment)

– 3 round/yellow : 1 wrinkled/green

Go to Section:

Go to Section:

Fig. 10.12a Dihybrid cross: F1 generation

Go to Section:

Fig. 10.12b Dihybrid cross: F2 generation

Ratio:

9:3:3:1

Go to Section:

Beyond dominance and recessiveness

•Incomplete dominance– Hybrids (heterozygous) exhibit blend of traits– 4 o’clock plants

• Red and white produce heterozygous pink plants

Go to Section:

Section 11-3

Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

Go to Section:

Section 11-3

Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

Go to Section:

Codominance•Similar to incomplete dominance however both traits are actually visual instead of blended

– Chickens with speckled black spots on white feathers

– Humans have gene for protein controlling cholesterol – if heterozygous two forms are made.

MOO

Go to Section:

Multiple Alleles

•When there are more than two alleles for a particular gene

– Blood type (also demonstrates some codominance)

Polygenic traits

•Traits controlled by many genes– Height

– SLE (Lupus)

– Weight

– Eye Color

– Intelligence

– Skin Color

– Many forms of behavior

Go to Section:

Go to Section:

Go to Section:

Go to Section:

Applying Mendel’s Principles

•Good animal to test was fruit fly– Drosophilia melanogaster

•Fast reproductive rate/life cycle and produced many offspring

Go to Section:

Go to Section:

Environmental impact on gene expression                        • Environmental factors/conditions may alter gene expression.

 Example: Soil pH and flower color.

Go to Section:

Go to Section:

How Many Chromosomes?

Normal human body cells each contain 46 chromosomes. The cell division process that body cells undergo is called mitosis and produces daughter cells that are virtually identical to the parent cell. Working with a partner, discuss and answer the questions that follow.

Section 11-4

Interest Grabber

Go to Section:

1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?

2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?

3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

Section 11-4

Interest Grabber continued

Go to Section:

11–4 Meiosis

A. Chromosome Number

B. Phases of Meiosis

1. Meiosis I

2. Meiosis II

C.Gamete Formation

D.Comparing Mitosis and Meiosis

Section 11-4

Section Outline

Go to Section:

11-4 Meiosis

•Process of turning diploid somatic cells into haploid gametes•Must reduce chromosome number so when fertilization takes place we re-establish the regular chromosome number

– Humans• Hapolid – sex cells N = 23• Diploid – somatic cells 2N = 46

N = chromosome number

Go to Section:

Go to Section:

Go to Section:

Phases of meiosis

Meiosis I and II

Go to Section:

Go to Section:

Go to Section:

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Go to Section:

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Crossing over

•Parts of chromosomes “switch places”

•Meiosis

Go to Section:

Section 11-4

Crossing-Over

Go to Section:

Section 11-4

Crossing-Over

Go to Section:

Section 11-4

Crossing-Over

Go to Section:

Mitosis vs. meiosis

Go to Section:

11–5 Linkage and Gene Maps

A. Gene Linkage

B. Gene Maps

Section 11-5

Section Outline

Go to Section:

11-5: Linkage and Gene Maps

•Found that some genes were linked to other ones– Seems to violate the rule of independent

assortment– Ex: fruit flies – red eyes and minature wings

Go to Section:

•Mendel missed this….– He thought the genes independently assorted

• Actually it was the chromosomes that do!• Why did he miss it?

– 6 of the 7 genes he studied in peas were on separate chromosomes

– The two that were on the same chromosome were so far apart they independently assorted

Go to Section:

Gene Map

•Do two genes on the same chromosome mean they are forever linked?

– No! Crossing over may put them on separate chromosomes

•The further apart genes are the more likely they could be separated during meiosis

•Low rate of separation and then recombination means genes are close to one another.

Go to Section:

Exact location on chromosomes Chromosome 2

Section 11-5

Figure 11-19 Gene Map of the Fruit Fly