Essential knowledge: The chromosomal basis of … · Dominant phenotype, unknown genotype: PP or...
Transcript of Essential knowledge: The chromosomal basis of … · Dominant phenotype, unknown genotype: PP or...
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Essential knowledge: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring
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Objective: You will be able to construct a representation that connects the process of meiosis to the passage of traits from parent to offspring.
Do Now:
Turn to page 206 in your textbook
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Some genetic vocabulary
Character: a heritable feature, such as flower color
Genes code for characters
Trait: a variant of a character, such as purple or
white flowers
Alleles are the alternative traits
Turn to a partner and come up with 3 genes for
human characteristics
Provide 2 alleles for each
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Individual Activity
Create a drawing of a pea plant cell undergoing meiosis
The cell contains the 4 chromosomes seen below during
the G1 phase of the cell cycle.
Follow the movements of the genes and alleles carefully.
Include both cells of meiosis II
Y = Yellow color
y = Green color
R = Round shape
r = Wrinkled shape
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Work with a partner
Do all of your gametes have a “Y” as opposed to a “y”? Find
where in your drawings this occurred.
Randomly put your finger on one of your gametes
If your egg cell fused with your partners sperm cell, what
color would the pea have? (This is fertilization)
Repeat the process with another pair of gametes
What percent chance is their in forming a zygote that
would have yellow color? Green?
How would the percentages change if “R’s” were used?
Y = Yellow color
y = Green color
R = Round shape
r = Wrinkled shape
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Objective: You will be able to construct a representation that connects the process of meiosis to the passage of traits from parent to offspring.
Do Now:
Take out your drawings
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Find someone that had different gametes than you
• Figure out exactly where in the drawings the difference began
Randomly put your finger on one of your gametes
If your egg cell fused with your partners sperm cell, what
color AND shape would the pea have? (This is fertilization)
Repeat the process with another pair of gametes
What percent chance is their in forming a zygote that would
be:
• Yellow AND Round
• Yellow and Wrinkled
• Green AND Round
• Green and Wrinkled
Y = Yellow color
y = Green color
R = Round shape
r = Wrinkled shape
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Punnett Squares
Rules of probability can be applied to analyze
passage of single gene traits from parent to
offspring
YY x yy
Law of
Segregation
Law of
Independent
Assortment
YyRr x YyRr
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Monohybrid Cross (Segregation)
• Refers to the mating of two heterozygous individuals
involving one gene
Yy x Yy
Dihybrid Cross (Independent Assortment)
• Refers to the mating of two heterozygous individuals
involving two genes
YyRr x YyRr
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Phenotype
vs.
Genotype
Mate a pea plant that is
heterozygous for pod shape
with a plant that is
homozygous recessive
Mate a pea plant that is axial
for flower position with one
that is terminal.
What do you need to know?
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Figure 11.7 Technique
Predictions
Dominant phenotype, unknown genotype:
PP or Pp?
Eggs
Sperm
½ offspring purple and
½ offspring white
Recessive phenotype, known genotype:
pp
If purple-flowered parent is PP
If purple-flowered parent is Pp
Eggs
Sperm
All offspring purple
Results
or
or
p p
P
p
Pp
pp
Pp
pp
p p
P
P
Pp
Pp
Pp
Pp
The
Testcross
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Objective: You will be able to apply mathematical routines to
determine patterns of inheritance.
Do Now:
A new way to solve genetic problems
• Turn to page 234 and try question 6(a).
• Work with a partner to complete the following
problems in this order: – 6 (b-d)
– 12
– 11
– 9
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• Pedigree charts can be used to determine
Mendelian patterns of inheritance.
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Figure 11.14a
WW
or
Ww
ww
ww ww
ww ww
Ww Ww
Ww Ww
Widow’s peak
ww Ww
1st generation (grandparents)
3rd generation (two sisters)
2nd generation (parents, aunts, and uncles)
Affected male
Affected female
Male
Female
Key
Mating
Offspring, in birth order (first-born on left)
(a) Is a widow’s peak a dominant or recessive trait?
No widow’s peak
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Figure 11.14b
Affected male
Affected female
Male
Female
Key
Mating
Offspring, in birth order (first-born on left)
1st generation (grandparents)
3rd generation (two sisters)
2nd generation (parents, aunts, and uncles)
Attached earlobe Free earlobe
FF
or
Ff
ff
ff ff
Ff ff
Ff FF or
Ff
Ff Ff
ff Ff
(b) Is an attached earlobe a dominant or recessive trait?
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• What would you look for in a pedigree chart to determine if a trait
was dominant and not recessive?
• Does this trace a dominant or recessive trait?
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• What would you look for in a pedigree chart to determine if a trait
was dominant and not recessive?
• Does this trace a dominant or recessive trait?
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Objective: You will be able to solve problems involving
sex-linked traits.
• Do Now:
– Draw a Punnett square that proves which gender is
responsible for the sex of the child.
– List two examples of sex linked-traits in humans
5
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Autosomes versus Sex Chromosomes
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Sex-linked genes exhibit unique patterns of
inheritance
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Some traits are determined by genes on sex chromosomes
• Some traits are sex limited, and expression depends on the sex
of the individual, such as: • Milk production in female mammals
• Male pattern baldness in males
• Color Blindness
• Hemophilia
• In mammals and flies, the Y chromosome is very small and
carries few genes
• Sex-linked genes reside on sex chromosomes (X in humans)
• In mammals and flies, females are XX and males are XY; as
such, X-linked traits are always expressed in males
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Do Now:
Take out your meiosis drawings from a few last week
Objective: You will be able to apply mathematical routines to
determine patterns of inheritance involving gene linkage.
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Gene Linkage
• Genes that are adjacent and close to each other on the
same chromosome tend to move as a unit.
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Gene Linkage
• A cell in G1
• How is this different from independent
assortment?
Y y
R r
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Are these two genes linked?
Mate: YyRr x yyrr
Start by drawing the chromosomes and their
genes for the highlighted individual above
OR
• If they are linked, what should the F1 ratio be?
• If they are not linked what should the F1 ratio be?
Unlinked Linked
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Experiment
P Generation
(homozygous)
Wild type (gray body, normal wings)
F1 dihybrid testcross
Wild-type F1 dihybrid
(gray body, normal wings)
b b vg vg
b b vg vg
b b vg vg
b b vg vg
Double mutant (black body, vestigial wings)
Homozygous recessive (black body, vestigial wings)
If the two genes are on the same chromosome
(linked), what is the expected F1 ratio
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Figure 12.9b
b b vg vg b b vg vg b b vg vg b b vg vg
Eggs
Sperm
b vg
b vg b vg b vg b vg
Wild-type (gray-normal)
Black- vestigial
Gray- vestigial
Black- normal
Experiment
Testcross
offspring
PREDICTED RATIOS
Genes on different
chromosomes:
Genes on same
chromosome:
Results : 965 944 206 185 : :
: : :
: : : 1 1 1 1
1 1 0 0
?
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Gene Linkage
• The probability that they will segregate as a unit is a
function of the distance between them.
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Y y
R r
Which would show more crossing over?
R Y y
r
O
R
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• The recombination frequency is the percentage of the
offspring that were a result of crossing over
• Which scenario would produce offspring with the highest
recombination frequency?
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Do Now:
Compile of list of human disorders that are
linked to genetics
Objective: You will be able to pose questions about ethical,
social or medical issues surrounding human genetic disorders.
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Certain human genetic disorders can be attributed to the
inheritance of single gene traits or specific
chromosomal changes, such as nondisjunction.
Examples: – Sickle cell anemia (rec.)
– Tay-Sachs disease(rec.)
– Huntington’s disease (dom.)
– X-linked color blindness(rec.)
– Trisomy 21/Down syndrome
– Klinefelter’s syndrome
Single gene traits
Nondisjunction
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Figure 12.13-3 Meiosis I
Nondisjunction
Meiosis II
Non- disjunction
Gametes
Number of chromosomes
Nondisjunction of homo- logous chromosomes in meiosis I
(a) (b) Nondisjunction of sister chromatids in meiosis II
n 1 n 1 n 1 n − 1 n − 1 n − 1 n n
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Figure 12.15
Trisomy 22/Down Syndrome
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Figure 12.14
(a) Deletion (c) Inversion
A deletion removes a chromosomal segment.
(b) Duplication (d) Translocation
An inversion reverses a segment within a chromosome.
A translocation moves a segment from one chromosome to a nonhomologous chromosome.
A duplication repeats a segment.
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Many ethical, social and medical issues surround human
genetic disorders.
Examples
– Reproductive issues
– Civic issues such as:
• Ownership of genetic information
• Privacy
Work with a partner to pose FIVE questions about ethical, social
or medical issues surrounding human genetic disorders.
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Do Now:
Objective: You will be able to explain deviations from Mendel’s
model of the inheritance of traits.
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Essential knowledge: The inheritance pattern of many
traits cannot be explained by simple Mendelian genetics
• Many traits are the products of multiple genes and/or
physiological processes.
– Examples include:
– Sex-linkage
– Incomplete dominance
– Codominance
– Polygenic inheritance
• Patterns of these traits don’t follow ratios predicted
by Mendel’s laws.
• They can be identified by quantitative analysis where
phenotypic ratios differ from predicted ratios.
How does this deviate from Mendel’s patterns?
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Make some predictions of what you would expect if these
example followed the inheritance pattern of Mendel.
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? How does this deviate
from Mendel’s patterns?
Predict what would
happen in the F2
generation.
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Figure 11.10-3
Eggs
½ ½
½
½
P Generation
F1 Generation
Gametes
F2 Generation
Gametes
Sperm
White CWCW
Pink CRCW
Red CRCR
CWCW
CRCW CRCR
CW CR
CW CR
½ ½ CW CR
CW
CR
CRCW
Incomplete
Dominance
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Red Bull
RR White Cow
WW
Make some predictions of what you would expect if these
example followed the inheritance pattern of Mendel.
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Red Bull
RR White Cow
WW
Roan Cattle
How does this
deviate from
Mendel’s patterns?
Predict what would
happen in the F2
generation.
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Figure 11.11
Carbohydrate
(b) Blood group genotypes and phenotypes
Allele
Red blood cell appearance
Genotype
none B A
IB
Phenotype (blood group)
i IA
IAIB ii IAIA or IAi IBIB or IBi
B A O AB
(a) The three alleles for the ABO blood groups and their carbohydrates
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Figure 11.13
Eggs
Sperm
AaBbCc AaBbCc
Phenotypes:
0 Number of dark-skin alleles: 1 2 3 4 5 6
1 64
1 64
6 64
6 64
1 64
15 64
15 64
20 64
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
Polygenic
Inheritance
How would you
know if a
phenotype was
likely controlled by
many genes?
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Some traits result from nonnuclear inheritance
• Chloroplasts and mitochondria are randomly assorted to gametes and
daughter cells; thus, traits determined by chloroplast and mitochondrial
DNA do not follow simple Mendelian rules.
• In animals, mitochondrial DNA is transmitted by the egg and not by the
sperm; as such, mitochondrial-determined traits are maternally inherited.
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Figure 4.17
Free ribosomes in the mitochondrial matrix
Mitochondrion
Intermembrane space
Matrix
Cristae
DNA
Outer membrane
Inner membrane
0.1 m
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Figure 4.18
Intermembrane space
Ribosomes
Inner and outer membranes
1 m
Stroma
Granum
DNA
Chloroplast
Thylakoid
(a) Diagram and TEM of chloroplast
50 m
(b) Chloroplasts in an algal cell
Chloroplasts (red)
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A poker-dealing machine is supposed to deal cards at random, as if from an
infinite deck.
In a test, you counted 1600 cards. What would be your expected values for
each suit?
You observed the following:
Spades 404
Hearts 420
Diamonds 400
Clubs 376
• Are these discrepancies too much to be random? Or are they in the realm
of probability?
• Scientists use chi-square as a statistical method that assesses the goodness
of fit between observed values and those expected.
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Category
(Suit)
Observed (o) Expected (e) (o-e)2/e
Spades
Hearts
Diamonds
Clubs
X2 =
∑
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Spades (404 -400)2/400 = 0.04
Hearts (420-400)2/400= 1.0
Diamonds (400-400)2/400= 0.0
Clubs (376-400)2/400= 1.44_____
X2 = 2.48
So…are these discrepancies too much to be random? Or are they
in the realm of probability?
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Do Now:
Objective: You will be able to use the chi square test to determine if
there are significant differences between expected and observed results.
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In the garden pea, yellow cotyledon color is dominant to green,
and inflated pod shape is dominant to the constricted form. In a
dihybrid mating, the progeny appeared in the following numbers:
556 yellow, inflated
193 green, inflated
184 yellow constricted
61 green, constricted
Total offspring is 994
Do these genes assort independently? Support your answer using
Chi-square analysis.
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Figure 12.UN03b
Dihybrid x homozygous recessive
mating
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The Null Hypothesis
• A null hypothesis(H0) is a hypothesis that says there
is no statistical significance between the two
variables.
• It is usually the hypothesis a researcher or
experimenter will try to disprove or discredit.
• An alternative hypothesis is one that states there is a
statistically significant relationship between two
variables.
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• Let's say you feed chocolate to a bunch of chickens,
then look at the sex ratio in their offspring. – If you get more females than males, it would be a tremendously
exciting discovery: female chickens are more valuable than male
chickens in egg-laying breeds
– You might look at 48 offspring of chocolate-fed chickens and see 31
females and only 17 males.
– You need to ask "What's the probability of getting a deviation from the
null expectation
– Only when that probability is low can you reject the null hypothesis.
The goal of statistical hypothesis testing is to estimate the probability of
getting your observed results under the null hypothesis.