Transcript Section 11-1

Section 11-1
Analyzing Inheritance
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.
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Section:
Section 11-1
Parents
First Generation
Second Generation
Long stems  short stems
All long
787 long: 277 short
Red flowers  white flowers
All red
705 red: 224 white
Green pods  yellow pods
All green
428 green: 152 yellow
Round seeds  wrinkled seeds All round
5474 round: 1850 wrinkled
Yellow seeds  green seeds
6022 yellow: 2001 green
All yellow
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?
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Section:
Section Outline
Section 11-1
11–1 The Work of Mendel
A. Gregor Mendel’s Peas
B. Genes and Dominance
C. Segregation
1. The F1 Cross
2. Explaining the F1 Cross
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Section:
Section 11-1
11–1 The Work of Mendel
•
•
•
•
Gregor Mendel (1822-1884) was a monk at a
monastery in Brunn, Austria
He taught school and did other chores, but in
his spare time he set out to study plant
breeding
He started breeding pea plants about 1855
He wanted to learn the rules of heredity so that
better varieties could be produced
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Section:
Section 11-1
11–1 cont.
•
•
•
Mendel’s original pea plants were true-breeding.
– When allowed to self-pollinate they produced
offspring identical to themselves
Mendel wanted to cross-pollinate the plants and
study the results
Mendel studied seven different pea plant traits
(specific characteristic that varies from individual to
individual) with 2 contrasting characteristics
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Section:
Figure 11-3 Mendel’s Seven F1 Crosses
on Pea Plants
Section 11-1
Seed Coat
Color
Pod
Shape
Pod
Color
Smooth
Green
Seed
Shape
Seed
Color
Round
Yellow
Gray
Wrinkled
Green
White
Constricted
Round
Yellow
Gray
Smooth
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Section:
Flower
Position
Plant
Height
Axial
Tall
Yellow
Terminal
Short
Green
Axial
Tall
Section 11-1
11–1 cont.
•
•
Mendel called each original pair of plants
the
P Generation (parental) and the offspring
of these the F1 generation (first filial)
Mendel produced hybrids when he crossed
parents with different traits; and to his
surprise the offspring only resembled one of
the parents
Go to
Section:
Principles of Dominance
Section 11-1
P Generation
Tall
Go to
Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Principles of Dominance
Section 11-1
P Generation
Tall
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Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Section 11-1
11–1 cont.
•
Mendel drew 2 conclusions from this
experiment:
1.Biological inheritance is determined by
factors that are passed from one generation
to the next; today known as genes
2.Principle of Dominance which states that
some alleles (different forms of a gene) are
dominant and others are recessive
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Section:
Section 11-1
11–1 cont.
•
•
Dominant alleles will always exhibit that form
of the trait and is represented with a capital
letter
ex. (T) - Tall
Recessive alleles will only exhibit that form of
the trait if the dominant allele is not present
and is represented with a lower case letter
ex. (t) - short
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Section:
Section 11-1
11–1 cont.
•
Mendel then allowed his F1 hybrid plants to
self-pollinate to produce an F2 generation
(second filial)
– Traits controlled by the recessive alleles
reappeared in ¼ of the F2 generation
– Mendel explained that the dominant allele
masked the recessive allele in the F1
generation and due to the segregation of
alleles during gamete formation reappeared
in the F2 generation
Go to
Section:
Principles of Dominance
Section 11-1
P Generation
Tall
Go to
Section:
Short
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
Section 11-1
F1
Generation
Gametes
F2
Generation
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Section:
T
t
T
t
T
t
T
t
T T
T t
T t
t t
Section 11-2
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.
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Section:
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?
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Section:
Section Outline
Section 11-2
11–2 Probability and Punnett Squares
A.
B.
C.
D.
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Section:
Genetics and Probability
Punnett Squares
Probability and Segregation
Probabilities Predict Averages
Section 11-2
11–2 Probability and Punnett Squares
•
Probability is the likelihood that a particular
event will occur and Mendel realized that the
principles of probability could be used in
predicting the outcomes of genetic crosses
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Section:
Section 11-2
11–2 cont.
•
Punnett Squares can be used to predict and
compare the genetic variations that will result
from a cross
– The gametes are shown along the top and
left side
– Possible gene combinations of the offsping
appear in the boxes
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Section:
Tt X Tt Cross
Section 11-2
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Section:
Tt X Tt Cross
Section 11-2
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Section:
Section 11-2
11–2 cont.
•
•
Homozygous organisms are true-breeding
which means they have two identical alleles
for a particular trait
Ex. TT
Heterozygous organisms are hybrids that
have two different alleles for the same trait
Ex. Tt
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Section:
Section 11-2
11–2 cont.
Genotype vs. Phenotype
The genotype is the actual genetic makeup
of the traits, while the phenotype is the
actual physical characteristics of an organism
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Section:
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Section:
Section Outline
Section 11-3
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
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Section:
11-3 Exploring Mendelian Genetics
After proving that alleles segregate in the formation of
gametes, Mendel wanted to know if they did so
independently – did the segregation of one pair of alleles
affect the segregation of other pairs?
Two-Factor Cross – F1
- Mendel crossed homozygous round yellow peas
(RRYY) with wrinkled green peas (rryy).
- F1 were all round yellow (RrYy)
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Section:
Two-Factor – F2
- Mendel knew F1’s were heterozygous for both traits
- when allowed to self-fertilize the F1 gave rise to F2’s w/ a
definite ratio
- this led Mendel to his Principle of Independent Assortment
- alleles for different characteristics segregate independently of
each other – so as long as genes for two traits are on
different chromosomes every combination of alleles is
possible.
Go to
Section:
Figure 11-10 Independent Assortment in Peas
Section 11-3
Go to
Section:
Concept Map
Section 11-3
Gregor
Mendel
concluded
that
experimented
with
Pea
plants
“Factors”
determine
traits
Some alleles
are dominant,
and some alleles
are recessive
which is
called the
Law of
Dominance
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Section:
Alleles are
separated during
gamete formation
which is
called the
Law of
Segregation
Incomplete Dominance
* when neither allele is dominant over the other
- heterozygotes differ phenotypically from either
homozygote
Ex.: Four O’clock plants
- RR = red
- WW = white
- RW = pink
** this is not blending because red and white
flowers will reappear.
Go to
Section:
Figure 11-11 Incomplete Dominance in
Four O’Clock Flowers
Section 11-3
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Section:
Figure 11-11 Incomplete Dominance in
Four O’Clock Flowers
Section 11-3
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Section:
Codominance
* situation in which both alleles contribute to the
phenotype
- both are expressed if present
Ex.: chickens – white and black feathers are
codominant
- heterozygotes produce both white and black
feathers
** A and B alleles in human blood types
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Section:
Multiple Alleles
* when a gene has more than two alleles
- each individual still only gets two of the possible
alleles that exist in the population
Ex.: Human blood groups
- three alleles = A, B, O
- A and B are codominant
- O is recessive
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Section:
Polygenic Traits
* traits which are influenced by several genes
- results in a wide range of phenotypes
Ex.: Human height, skin color, color in eyes of
fruitflies
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Section:
Section 11-3
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?
Go to
Section:
Section 11-3
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.
Go to
Section:
Applying Mendel’s Principles
* Mendel’s principles apply to all organisms
- Thomas Hunt Morgan – began use of fruitflies
- ideal organism
- fast breeder
- lots of young
- many observable traits
- small size
- Environment also affects development of
organisms
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Section:
Sex Linkage
- genes located on autosomes behave as we have studied
- genes located on the sex chromosomes often exhibit a unique
pattern of inheritance.
- in mammals females have two X-chromosomes (XX)
- in mammals males have an X and a Y chromosome (XY)
- the Y chromosome has a gene (SRY) that makes the
embryo male
- but Y has fewer genes than X and so males only get one
copy of some genes on the Y
- genes that males only get one copy of are sex-linked and are
expressed more often in males than females
- color-blindness, muscular dystrophy
Go to
Section:
Section Outline
Section 11-4
11–4 Meiosis
A.Chromosome Number
B.Phases of Meiosis
1. Meiosis I
2. Meiosis II
C. Gamete Formation
D. Comparing Mitosis and Meiosis
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Section:
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Section:
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Section:
Interest Grabber
Section 11-4
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.
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Section:
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Section:
Interest Grabber continued
Section 11-4
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?
Go to
Section:
Crossing-Over
Section 11-4
Go to
Section:
Crossing-Over
Section 11-4
Go to
Section:
Crossing-Over
Section 11-4
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Section:
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Section:
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Go to
Section:
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Go to
Section:
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Go to
Section:
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Go to
Section:
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Go to
Section:
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Go to
Section:
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
Interest Grabber
Section 11-5
Forever Linked?
Some genes appear to be inherited together, or “linked.” If two genes
are found on the same chromosome, does it mean they are linked forever?
Study the diagram, which shows four genes labeled A–E and a–e, and
then answer the questions on the next slide.
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Section:
Interest Grabber continued
Section 11-5
1. In how many places can crossing over result in genes A and b being on
the same chromosome?
2. In how many places can crossing over result in genes A and c being on
the same chromosome? Genes A and e?
3. How does the distance between two genes on a chromosome affect the
chances that crossing over will recombine those genes?
Go to
Section:
Section Outline
Section 11-5
11–5
Linkage and Gene Maps
A. Gene Linkage
B. Gene Maps
Go to
Section:
Comparative Scale of a Gene Map
Section 11-5
Mapping of Earth’s
Features
Mapping of Cells,
Chromosomes, and Genes
Cell
Earth
Country
Chromosome
State
Chromosome
fragment
City
People
Go to
Section:
Gene
Nucleotide
base pairs
Figure 11-19 Gene Map of the Fruit Fly
Section 11-5
Exact location on chromosomes
Go to
Section:
Chromosome 2
Videos
Click a hyperlink to choose a video.
Meiosis Overview
Animal Cell Meiosis, Part 1
Animal Cell Meiosis, Part 2
Segregation of Chromosomes
Crossing Over
Video 1
Meiosis Overview
Click the image to play the video segment.
Video 2
Animal Cell Meiosis, Part 1
Click the image to play the video segment.
Video 3
Animal Cell Meiosis, Part 2
Click the image to play the video segment.
Video 4
Segregation of Chromosomes
Click the image to play the video segment.
Video 5
Crossing Over
Click the image to play the video segment.
Go Online
The latest discoveries in genetics
Interactive test
Articles on genetics
For links on Punnett squares, go to www.SciLinks.org and enter the
Web Code as follows: cbn-4112.
For links on Mendelian genetics, go to www.SciLinks.org and enter
the Web Code as follows: cbn-4113.
For links on meiosis, go to www.SciLinks.org and enter the Web
Code as follows: cbn-4114.
Interest Grabber Answers
1. In the first generation of each experiment, how do the characteristics of the
offspring compare to the parents’ characteristics?
All offspring had the same characteristic, which was like one of the
parents’. The other characteristic seemed to have disappeared.
2. How do the characteristics of the second generation compare to the
characteristics of the first generation?
Both characteristics appeared in this generation. The characteristic that
had “disappeared” in the first generation did not appear as often as the
other characteristic. (It appears about 25 percent of the time.)
Interest Grabber Answers
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?
Results will vary, but should be close to 5 heads and 5 tails.
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?
The results for 20 tosses may be closer to the predicted 10 heads and 10 tails.
3. If you compiled the results for the whole class, what results would you expect?
The results for the entire class should be even closer to the number predicted
by the rules of probability.
4. How do the expected results differ from the observed results?
The observed results are usually slightly different from the
expected results.
Interest Grabber Answers
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.
Check students’ answers to make sure they are realistic.
2. What can you observe about the heights of the ten people?
Students should notice that there is a range of heights in humans.
3. Do you think height in humans is controlled by 2 alleles, as it is in pea
plants? Explain your answer.
No, height does not seem to be controlled by two alleles, as it is in pea
plants. Height in humans can vary greatly and is not just found in tall and
short phenotypes.
Interest Grabber Answers
1. How many chromosomes would a sperm or an egg contain if either one
resulted from the process of mitosis?
46 chromosomes
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?
46 + 46 = 92; a developing embryo would not survive if it contained 92
chromosomes.
3. In order to produce a fertilized egg with the appropriate number of
chromosomes (46), how many chromosomes should each sperm and egg
have?
Sperm and egg should each have 23 chromosomes.
Interest Grabber Answers
1. In how many places can crossing over result in genes A and b being on the
same chromosome?
One (between A and B)
2. In how many places can crossing over result in genes A and c being on the
same chromosome? Genes A and e?
Two (between A and B and A and C); Four (between A and B, A and C, A
and D, and A and E)
3. How does the distance between two genes on a chromosome affect the
chances that crossing over will recombine those genes?
The farther apart the genes are, the more likely they are to be recombined
through crossing over.
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