GeneticsWhy You Look the Way

You Do

George RadcliffeCentreville Middle SchoolApril, 2008

CONTENTS

• Vocabulary• Asexual Reproduction• Sexual Reproduction• Mitosis vs. Meiosis• The Gene• Genotypes and Phenotypes• Punnett Square – Predicting Offspring• Practice Problems• Review Quiz

VOCABULARY YOU NEED TO BE ABLE TO SPEAK “GENETICS”

• Asexual reproduction• Sexual reproduction• Mitosis – normal cell division

• Meiosis• Gamete• Fertilization• Pollination• Gene• Trait

• Allele• Dominant• Recessive• Genotype• Phenotype• Homozygous• Heterozygous• Punnett Square

Asexual Reproduction

• The gene is a strand of DNA that makes a particular protein, enzyme, or pigment.

• In asexual reproduction, all of the DNA comes from your 1 parent.

• If an asexually reproducing plant had yellow flowers, what percentage of its offspring will have yellow flowers?

• Answer: 100% of the offspring will have yellow flowers.

Contents

The Gene and Sexual Reproduction

• The gene is a strand of DNA that makes a particular protein, enzyme, or pigment.

• ½ of your DNA comes from the mother’s egg.

• ½ comes from the father’s sperm.

• These half cells are produced by the process of meiosis.

• Each of these ½ cells (egg, sperm or pollen) is called a gamete.

• When the two halves combine (fertilization) you have a complete set of DNA. (½ + ½ = 1)

• Thus you actually have two of each gene. Vocabulary

Plants and Sexual Reproduction• Plants usually reproduce sexually, too.

• The female half of the DNA is found in the egg.

• The male half comes from the pollen.

• Insects or wind carries the pollen from one flower to another. This pollination leads to fertilization of the egg.

• This fertilized egg is called a zygote. The zygote has a complete set of DNA.

VocabularyContents

Mitosis vs. Meiosis

• Go to the following PBS website listed below. Either run the flash animation, or use the non-Flash version.

• Answer: how is meiosis different from mitosis?

• Link: PBS Meiosis/Mitosis Site

Mitosis vs. Meiosis

• How is meiosis different from mitosis?

• Answer: In the beginning, they are the same, one cell dividing into two complete cells. In meiosis the two cells then each divide into 2 half cells.

• If you missed this, go back (hit “P”), and run the animation again.

Comparison of meiosis and mitosis

Normal Cell Division

All the DNA is found in each cell.

½ of the parent DNA is found in gamete.

Makes eggs, sperm, pollenMakes 2 copies of any cell

Produces two cells Produces four gametes

46 chromosomes

23 pairs

23 chromosomes

1 from each pair

Mitosis Meiosis

Makes gametes

Let’s See if We’ve Got it All Straight.• Question: What is the process that produces normal cells?

• Answer: Mitosis

• Question: What is the process that produces eggs, sperm, and pollen?

• Answer: Meiosis

• Question: What is a gamete?

• Answer: a sex cell: egg, sperm, or pollen

• Question: How much DNA does a pollen or egg have?

• Answer: ½ of the normal DNA

• Question: How much DNA does a zygote have?

• Answer: full amount of DNA

The Gene

• Let’s see how genes work.

• Let’s look at human eye color.

• The gene is represented by the letter B.

• There are 2 alleles for this gene; that means that there are 2 ways that eye color can be.

• Eye color can be brown; we show this gene with a B.

• Eye color can also be blue; we show this gene with a b.

• Remember: You get a gene from each parent; so you have 2.

VocabularyContents

Which Gene Does Your Cell Listen to?

• If you have 2 brown genes (BB), your eyes are obviously brown.

• If you have 2 blue genes (bb), your eyes are obviously blue.

• But what happens if you have one of each gene?

• The dominant gene wins out.

• Brown (B) is the dominant gene; that’s why it is represented with a capital letter.

• Thus a person with Bb genes has brown eyes.

• The blue gene (b) is recessive; that means it is hidden or masked by the dominant gene, BUT it can be passed on to the offspring.

VocabularyContents

Genotypes and Phenotypes

• Let’s show this in a chart.

• Trait: Eye color

• Alleles: B and b

Genotype(the genes)

Phenotype(what it looks like)

BB Brown

bb Blue

Bb Brown

VocabularyContents

Genotypes and Phenotypes• Let’s look at another trait.

• Trait: Height of a pea plant

• Alleles: T and t

• T – gene for tallness t – gene for short plant

Genotype(the genes)

Phenotype(what it looks like)

TT Tall plant

tt Short plant

Tt Tall plant

Let’s Review

• Question: What is the trait?

• Answer: height of pea plant

• Question: What are the alleles for height?

• Answer: T and t

• Question: What is the dominant allele?

• Answer: T

TT Tall plant

tt Short plant

Tt Tall plant

Let’s Review

• Question: What is genotype for a short plant?

• Answer: tt

• Question: What is the phenotype for TT?

• Answer: tall

• Question: What is the phenotype for Tt?

• Answer: tall since T is dominant

TT Tall plant

tt Short plant

Tt ???? plant

Contents

Genotype and Phenotype Practice

Genotype

Phenotype

Gg

gg

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Let’s do some practice using the 4 pairs of pea plant genes shown at the right. For each genotype listed, give the phenotype (what it looks like).

green leaves

yellow leaves

Genotype and Phenotype Practice

Genotype Phenotype

Pp

rr

Rr

TtGg

Pprr

TTggppRr

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

purple flowers

wrinkled peas

round peas

tall plants with green leaves

purple flowers and wrinkled peas

tall plants, yellow peas, white flowers, and round peas

Contents

Homozygous and Heterozygous

• Let’s add 2 more words to the mix.

• Homozygous means both genes are the same.

• Heterozygous means both genes are different,

• “Homo” = the same “Hetero” = different

• “zygous” refers to the zygote, the first cell formed from the fertilization of the egg by the sperm.

• Another word for a heterozygous (Tt) is hybrid, one of each gene).

TT (homozygous) Tall plant

Tt (homozygous) Short plant

Tt (heterozygous) Tall plant

Vocabulary

Contents

Putting it All Together

• What is the homozygous genotype for a tall plant?

• Answer: TT

• What is the heterozygous genotype for a tall individual?

• Answer: Tt

• What is the heterozygous genotype for a short individual?

• Answer: impossible; Tt is can’t be short.

TT Tall plant

tt Short plant

Tt Tall plant

Monohybrid inheritanceLet the allele for round seeds be: R (dominant allele)Let the allele for wrinkled seeds be: r (recessive

allele)

Parents phenotype round seeds x round seedsgenotype RR RR

Gametes (pollen, eggs)

OffspringGametes

Gametes

R R R R

We call this a Punnett Square.

We’ll use this to show the 4 ways that the gametes from the 2 parents can combine.

Monohybrid inheritance• Let’s watch this in action.• With these gametes, there are 4 possibilities;

that’s why there are 4 boxes in the Punnett Square.

Gametes

Gametes

R

R

R R

Possibility # 1

Monohybrid inheritance• Let’s watch this in action.• With these gametes, there are 4 possibilities;

that’s why there are 4 boxes in the Punnett Square.

Gametes

Gametes

R

R

R R

Possibility # 2

Monohybrid inheritance• Let’s watch this in action.• With these gametes, there are 4 possibilities;

that’s why there are 4 boxes in the Punnett Square.

Gametes

Gametes

R

R

R R

Possibility # 3

Monohybrid inheritance• Let’s watch this in action.• With these gametes, there are 4 possibilities;

that’s why there are 4 boxes in the Punnett Square.

Gametes

Gametes

R

R

R R

Possibility # 4

Monohybrid inheritanceLet the allele for round seeds be: R (dominant allele)Let the allele for wrinkled seeds be: r (recessive

allele)

Parents phenotype round seeds x round seedsgenotype RR RR

Offspring

Offspring phenotypes 100% plants producing round seeds

Offspring genotypes 100% heterozygotes RR

Gametes

Gametes R R

R RR RR

R RR RRAll possibilities are the same: RR.

Monohybrid inheritance – Part 2

Let the allele for round seeds be: R (dominant allele)Let the allele for wrinkled seeds be: r (recessive

allele)

Parents phenotype wrinkled seeds x wrinkled seedsgenotype rr rr

Gametes (eggs, pollen)

Offspring

Gametes

Gametes

r r r r

Offspring phenotypes 100% plants producing wrinkled seeds

Offspring genotypes 100% heterozygotes rr

Gametes

Gametes r r

r

r

Gametes

Gametes r r

r rr rr

r rr rr

Monohybrid inheritance – Part 3

Let the allele for round seeds be: R (dominant allele)Let the allele for wrinkled seeds be: r (recessive allele)

Parents phenotype round seeds x wrinkled seedsgenotype RR rr

Gametes

OffspringGametes

Gametes

R R r r

Offspring phenotypes 100% plants producing round seeds

Offspring genotypes 100% heterozygotes Rr

Gametes

Gametes r r

R

R

Gametes

Gametes r r

R Rr Rr

R Rr Rr

Heterozygous Cross

Let the allele for round seeds be: R (dominant allele)Let the allele for wrinkled seeds be: r (recessive allele)

Parents phenotype round seeds x round seedsgenotype Rr Rr

Gametes

Offspring

Gametes

Gametes

R r R r

Offspring phenotypes 75% plants producing round seeds

25% plants producing wrinkled seeds

Offspring genotypes 50% Rr 25% RR 25% rr

Gametes

Gametes R r

R

r

Gametes

Gametes R r

R RR Rr

r Rr rr

Contents

Prediction vs. Actual

Predicted Offspring phenotypes 75% plants producing round seeds

25% plants producing wrinkled seeds

Ratio 3:1 Round seeds: wrinkled seeds

• This is what we predict, just like we predict that 1 out of 2 coin flips will be heads.

• Actual results can be different.

• If we bred the plants above many times, we would at least get close to a 3:1 ratio.

Gametes

Gametes R r

R RR Rr

r Rr rr

Contents

Prediction vs. Actual

Contents

• To see how predicted can vary from what actual happens. Let’s look at coin flips.• Because there is a 50:50 chance of heads turning up, ½ or 50% of coin flips will be heads.• This obviously doesn’t happen, but if you flip the coin enough, you will approximate 50%.• Go to the website below, and flip coins different numbers of time. Notice that when you flip 10,000 times, you will always get close to 50%.• Return here when you’re done.

Go to Coin Toss Probability

How can you tell if a parent is RR or Rr?To test whether a plant producing round seeds is homozygous RR or heterozygous Rr it can be crossed with a homozygous rr plant

If plant is homozygous dominant RR

Parents phenotype round x wrinkledgenotype RR rrgametes

Offspring

If plant is heterozygous Rr Parents phenotype round x wrinkledgenotype Rr rrgametes

OffspringR R r r

R r r r

gametesgametes R R

r Rr Rrr Rr Rr

gametesgametes R r

r Rr rrr Rr rr

Offspring

phenotype 100% round

Genotype 100% Rr

Offspring

phenotype 50% round/50% wrinkled

genotype 50% Rr 50% rr

Let’s Try a Couple Problems!

Gametes

Gametes g g

Gg

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: Gg and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be yellow?

2. What is the ratio of green to yellow plants?

Let’s Try a Couple Problems!

Gametes

Gametes g g

G Gg Gg

g gg gg

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: Gg and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be yellow? 50%

2. What is the ratio of green to yellow plants?1:1 ratio of green: yellow

Practice Problem #2

Gametes

Gametes

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: Gg and Gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be green?

2. What is the ratio of green to yellow plants?

Practice Problem #2

Gametes

Gametes G g

G GG Gg

g Gg gg

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: Gg and Gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be green? 75%

2. What is the ratio of green to yellow plants?3:1 ratio of green: yellow

Practice Problem #3

Gametes

Gametes

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: GG and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be yellow?

Practice Problem #3

Gametes

Gametes G Gg Gg Gg

g Gg Gg

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: GG and gg. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be yellow? 0%

Practice Problem #4

Gametes

Gametes

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: Pp and Pp. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be white?

2. What is the ratio of purple to white flowers?

Practice Problem #4

Gametes

Gametes P p

P PP Pp

p Pp pp

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Two plants are cross pollinated: Pp and Pp. What will the resulting offspring look like? Work out the problem using a Punnett Square like the one below on scrap paper.

1. What percentage of the plants will be white? 25%

2. What is the ratio of purple to white flowers?3:1 ratio of purple: white Contents

Review Questions

• Number a ¼ sheet of paper from 1 to 15.

• Answer the questions with no assistance.

• Score your paper with the key; consider 11 or more correct as OK.

• Go back into the PowerPoint to correct your errors.

Review Questions

1. What process produces the gametes?

A. fertilizationB. mitosisC. conjugationD. meiosis

Review Questions

2. In asexual reproduction

A. Gametes are produced.B. Fertilization occurs.C. An identical cell is produced.D. A cell with ½ of the DNA is

produced.

Review Questions

3. In sexual reproduction, meiosis produces

A. A zygote.B. A cell with ½ of the DNA C. A cell with double the DNAD. A cell with the same DNA as the

parent’s cell.

Review Questions

4. A plant with Tt genes reproduces asexually. What will its offspring look like?

A. None will be tall.B. 50% will be tall. C. 75% will be tall.D. 100% will be tall.

Review Questions

5. What is the genotype of a homozygous tall plant?

A. TTB. TtC. ttD. None of the above

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions

6. What is the phenotype of a Gg plant?

A. Green leavesB. Yellow leavesC. Green and yellow leavesD. It depends on who gave

the G gene.

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions

7. Which of the below could be the genotype for a plant with purple flowers?

A.PPB.Pp

C. Either PP or Pp

D. Neither PP or Pp

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions

8. Which of the below could be the genotype for a short plant with purple flowers?

A.TtPPB. ttPpC. TTppD. Ttpp

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions

9. A cutting is taken from a pea plant. Thus the plant reproduces asexually. The parent has TtGg genes. What percentage of the offspring will be tall with yellow leaves?

A. 100%B. 50%C. 25%D. 0%

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions

10. If a homozygous tall and heterozygous tall plant are cross pollinated, what percentage of the offspring will be short?

A. 0%B. 25%C. 50%D. 75%

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions

11. What will be the ratio of round peas to wrinkled peas if a Rr plant is bred with a rr plant?

A. 4:1B. 3:1C. 2:1D. 1:1

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions

12. Predict the result of breeding: Gg and Gg

A. 100% will be green.B. 25% will be yellow.C. 50% will be green.D. None will be yellow.

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions13. If you breed a Rr plant with a

RR plant,

A. You will get all homozygous offspring.

B. You will get no wrinkled plants since round is dominant.

C. 75% of the offspring will be round since wrinkled is recessive.

D. You will get all heterozygous offspring.

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions14. Which of the below gene

set represents a gamete?

A. TtGgB. TtC. TTD. T

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Review Questions15. Challenge Question: How

many tall and green plants will result from breeding Ttgg with TTgg?

A. 100%B. 50%C. NoneD. Depends on other

variables

T = tall

t = short

G = green leaves

g = yellow leaves

P = purple flowers

p = white flowers

R = round peas

r = wrinkled peas

Answer Key

1. D2. C3. B4. D5. A6. A7. C8. B

9. D10. A11. D12. B13. B14. D15. C

Contents Vocabulary