Download Genetics

Genetics
Why You Look the Way
You Do
George Radcliffe
Centreville Middle School
April, 2008
CONTENTS
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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”
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Asexual reproduction
Sexual reproduction
Mitosis – normal cell division
Meiosis
Gamete
Fertilization
Pollination
Gene
Trait
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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.
Contents
Vocabulary
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
Mitosis
Normal Cell Division
Makes 2 copies of any cell
Meiosis
Makes gametes
Makes eggs, sperm, pollen
Produces two cells
Produces four gametes
All the DNA is found in
each cell.
½ of the parent DNA is
found in gamete.
46 chromosomes
23 pairs
23 chromosomes
1 from each pair
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.
Contents
Vocabulary
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.
Contents
Vocabulary
Genotypes and Phenotypes
• Let’s
show this in a chart.
• Trait: Eye color
• Alleles: B and b
Genotype
(the genes)
BB
Phenotype
(what it looks like)
Brown
bb
Blue
Bb
Brown
Contents
Vocabulary
Genotypes and Phenotypes
• Let’s
look at another trait.
• Trait: Height of a pea plant
• Alleles: T and t
• T – gene for tallness
Genotype
(the genes)
t – gene for short plant
TT
Phenotype
(what it looks like)
Tall plant
tt
Short plant
Tt
Tall plant
Let’s Review
TT
Tall plant
tt
Short plant
Tt
Tall plant
• 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
Let’s Review
TT
Tall plant
tt
Short plant
Tt
???? plant
• 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
Contents
Genotype and Phenotype Practice
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).
T = tall
t = short
G = green leaves
Genotype
Phenotype
g = yellow leaves
P = purple flowers
Gg
green leaves
p = white flowers
gg
yellow leaves
R = round peas
r = wrinkled peas
Genotype and Phenotype Practice
Genotype
Pp
Phenotype
purple flowers
T = tall
t = short
G = green leaves
rr
wrinkled peas
g = yellow leaves
Rr
round peas
P = purple flowers
TtGg
Pprr
TTggppRr
tall plants with green
leaves
purple flowers and
wrinkled peas
p = white flowers
R = round peas
r = wrinkled peas
tall plants, yellow peas, white
flowers, and round peas
Contents
Homozygous and Heterozygous
TT (homozygous)
Tall plant
Tt (homozygous)
Short plant
Tt (heterozygous)
Tall plant
• 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
Vocabulary
Contents
“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).
Putting it All Together
TT
Tall plant
tt
Short plant
Tt
Tall plant
• 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.
Monohybrid inheritance
Let the allele for round seeds be:
Let the allele for wrinkled seeds be:
Parents phenotype
genotype
round seeds
RR
Gametes (pollen, eggs)
R
R
Offspring
R (dominant allele)
r (recessive allele)
x
round seeds
RR
R
R
Gametes
Gametes
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.
Possibility # 1
Gametes
Gametes
R
R
R
R
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.
Possibility # 2
Gametes
Gametes
R
R
R
R
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.
Possibility # 3
Gametes
Gametes
R
R
R
R
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.
Possibility # 4
Gametes
Gametes
R
R
R
R
Monohybrid inheritance
Let the allele for round seeds be:
Let the allele for wrinkled seeds be:
Parents phenotype
genotype
round seeds
RR
R (dominant allele)
r (recessive allele)
x
round seeds
RR
Gametes
Offspring
All possibilities
are the same: RR.
Offspring phenotypes
Offspring genotypes
Gametes
R
R
R
RR
RR
R
RR
RR
100% plants producing round seeds
100% heterozygotes RR
Monohybrid inheritance – Part 2
Let the allele for round seeds be:
Let the allele for wrinkled seeds be:
Parents phenotype
genotype
wrinkled seeds
rr
r
x
r
Gametes (eggs, pollen)
Offspring
R (dominant allele)
r (recessive allele)
wrinkled seeds
rr
r
r
Gametes
Gametes
r
r
rr
r
rr
r
rr
rr
Offspring phenotypes
100% plants producing wrinkled seeds
Offspring genotypes
100% heterozygotes rr
Monohybrid inheritance – Part 3
Let the allele for round seeds be:
Let the allele for wrinkled seeds be:
R (dominant allele)
r (recessive allele)
Parents phenotype
genotype
x
Gametes
round seeds
RR
R
wrinkled seeds
rr
r
R
r
Gametes
Offspring
Gametes
R
r
Rr
r
Rr
R
Rr
Rr
Offspring phenotypes
100% plants producing round seeds
Offspring genotypes
100% heterozygotes Rr
Contents
Heterozygous Cross
Let the allele for round seeds be:
Let the allele for wrinkled seeds be:
R (dominant allele)
r (recessive allele)
Parents phenotype
genotype
x
Gametes
round seeds
Rr
R
round seeds
Rr
r
R
r
Offspring
Gametes
Gametes
Offspring phenotypes
Gametes
Gametes
RR
RR
RR
rr
Rr
rr
Rr
rr
75% plants producing round seeds
25% plants producing wrinkled seeds
Offspring genotypes
50% Rr
25% RR
25% rr
Prediction vs. Actual
Gametes
Gametes
R
r
R
RR
Rr
r
Rr
rr
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.
Contents
Prediction vs. Actual
• 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
Contents
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 If plant is heterozygous Rr
Parents
phenotype round x wrinkled
genotype
RR
rr
gametes
R
R
r
Parents
phenotype
genotype
gametes
r
Offspring
round x wrinkled
Rr
rr
R
r
r
r
Offspring
gametes
gametes
R
R
r
Rr
Rr
r
Rr
Rr
Offspring
gametes
gametes
R
r
r
Rr
rr
r
Rr
rr
Offspring
phenotype
100% round
phenotype 50% round/50% wrinkled
Genotype
100% Rr
genotype
50% Rr
50% rr
Let’s Try a Couple Problems!
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.
Gametes
Gametes
g
g
T = tall
t = short
G = green leaves
g = yellow leaves
P = purple flowers
G
p = white flowers
g
R = round peas
r = wrinkled peas
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!
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.
Gametes
T = tall
t = short
G = green leaves
g = yellow leaves
Gametes
g
g
G
Gg
Gg
p = white flowers
g
gg
gg
R = round peas
P = purple flowers
r = wrinkled peas
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
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.
Gametes
Gametes
T = tall
t = short
G = green leaves
g = yellow leaves
P = purple flowers
p = white flowers
R = round peas
r = wrinkled peas
1.
What percentage of the plants will be green?
2.
What is the ratio of green to yellow plants?
Practice Problem #2
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.
Gametes
T = tall
t = short
G = green leaves
g = yellow leaves
Gametes
G
g
G
GG
Gg
p = white flowers
g
Gg
gg
R = round peas
P = purple flowers
r = wrinkled peas
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
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.
Gametes
Gametes
T = tall
t = short
G = green leaves
g = yellow leaves
P = purple flowers
p = white flowers
R = round peas
r = wrinkled peas
1.
What percentage of the plants will be yellow?
Practice Problem #3
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.
Gametes
T = tall
t = short
G = green leaves
g = yellow leaves
Gametes
G
G
P = purple flowers
g
Gg
Gg
p = white flowers
g
Gg
Gg
R = round peas
r = wrinkled peas
1.
What percentage of the plants will be yellow? 0%
Practice Problem #4
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.
Gametes
Gametes
T = tall
t = short
G = green leaves
g = yellow leaves
P = purple flowers
p = white flowers
R = round peas
1.
What percentage of the plants will be white?
2.
What is the ratio of purple to white flowers?
r = wrinkled peas
Practice Problem #4
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.
Gametes
T = tall
t = short
G = green leaves
g = yellow leaves
Gametes
P
p
P
PP
Pp
p = white flowers
p
Pp
pp
R = round peas
P = purple flowers
r = wrinkled peas
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.
B.
C.
D.
fertilization
mitosis
conjugation
meiosis
Review Questions
2. In asexual reproduction
A.
B.
C.
D.
Gametes are produced.
Fertilization occurs.
An identical cell is produced.
A cell with ½ of the DNA is
produced.
Review Questions
3. In sexual reproduction, meiosis
produces
A.
B.
C.
D.
A zygote.
A cell with ½ of the DNA
A cell with double the DNA
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.
B.
C.
D.
None will be tall.
50% will be tall.
75% will be tall.
100% will be tall.
Review Questions
5. What is the genotype of a
homozygous tall plant?
T = tall
t = short
G = green leaves
A.
B.
C.
D.
TT
Tt
tt
None of the above
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?
T = tall
t = short
G = green leaves
A.
B.
C.
D.
Green leaves
Yellow leaves
Green and yellow leaves
It depends on who gave
the G gene.
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. PP
B. Pp
T = tall
t = short
G = green leaves
g = yellow leaves
P = purple flowers
p = white flowers
C. Either PP or Pp
R = round peas
D. Neither PP or Pp
r = wrinkled peas
Review Questions
8. Which of the below could
be the genotype for a
short plant with purple
flowers?
A. TtPP
B. ttPp
C. TTpp
D. 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.
B.
C.
D.
100%
50%
25%
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?
T = tall
t = short
G = green leaves
g = yellow leaves
P = purple flowers
A.
B.
C.
D.
0%
25%
50%
75%
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.
B.
C.
D.
4:1
3:1
2:1
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
T = tall
t = short
G = green leaves
g = yellow leaves
A.
B.
C.
D.
100% will be green.
25% will be yellow.
50% will be green.
None will be yellow.
P = purple flowers
p = white flowers
R = round peas
r = wrinkled peas
Review Questions
13. If you breed a Rr plant with a
RR plant,
T = tall
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 = short
G = green leaves
g = yellow leaves
P = purple flowers
p = white flowers
R = round peas
r = wrinkled peas
Review Questions
14. Which of the below gene
set represents a gamete?
T = tall
t = short
A.
B.
C.
D.
TtGg
Tt
TT
T
G = green leaves
g = yellow leaves
P = purple flowers
p = white flowers
R = round peas
r = wrinkled peas
Review Questions
15. Challenge Question: How
many tall and green plants
will result from breeding
Ttgg with TTgg?
T = tall
t = short
G = green leaves
A.
B.
C.
D.
100%
50%
None
Depends on other
variables
g = yellow leaves
P = purple flowers
p = white flowers
R = round peas
r = wrinkled peas
Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
D
C
B
D
A
A
C
B
9. D
10. A
11. D
12. B
13. B
14. D
15. C
Contents
Vocabulary