Transcript Bio1001ch10W

QUIZ
Name___________________
Meiosis
1. End result
1n or 2n?
2. Daughter cells
Distinct or identical?
3. Chiasmata?
Yes or no?
4. # of divisions
5. Purpose
Growth or germ cells?
Mitosis
QUIZ
Name___________________
Meiosis
1. End result
1n or 2n?
2. Daughter cells
Distinct or identical?
3. Chiasmata?
Yes or no?
4. # of divisions
5. Purpose
Growth or germ cells?
Mitosis
1n
2n
distinct
identical
Yes
No
2
1
Germ cells
Growth
Chapter 10
Observable Patterns of
Inheritance
•Attached or detached earlobes depends on
a single _____
•A gene has two molecular forms (______)
•Inherit one form each _______
•Dominant allele specifies detached
earlobes
Earlobe Variation
• You inherited one allele for this gene
from each parent
• _______ allele specifies detached
earlobes
• __________ allele specifies attached
lobes
Early Ideas About Heredity
How are traits transmitted?
• _______________ theory– Genetic material mixes much like
yellow and blue paint makes ____
Problem:
– Would expect variation to
________
– Yet variation in traits _______
Gregor Mendel
• Strong background in plant breeding and
mathematics- __________
• Using pea plants, found indirect but
observable evidence of how parents
transmit ____to offspring
The Garden Pea Plant
•Self-pollinating
•______________ (different alleles
not normally introduced)
•Can be experimentally ____________
What is a gene?
• Units of information about specific ____
• Passed from _________ to offspring
• Each has a specific location (_____) on
a chromosome
What is an allele?
•Different ________________ of a gene
•Arise by _____________
•Dominant allele ___________ a
recessive allele that is paired with it
Vocabulary
• _____________ - An organism with two _______
alleles for a character (e.g. AA or aa)
• ___________- An organism with two
____________ alleles for a character (e.g. Aa)
• ________ - A description of an organism’s ______
• ________ - A description of its ______________
•Example- For flower color in peas, both PP and
Pp plants have the same phenotype (purple) but
different genotypes (homozygous and
heterozygous).
Mendel cross-pollinated peas
_________________
_________________
P1 x P2
F1
The F2 generation revealed two
principles of heredity:
1. _____________________
F1 x F1
2._______________________
_________________
F2
Mendel’s
Monohybrid
Cross Results
F2 plants showed
dominant-torecessive ratio that
averaged 3:1
5,474 round
1,850 wrinkled
6,022 yellow
2,001 green
882 inflated
299 wrinkled
428 green
152 yellow
705 purple
224 white
651 long stem
207 at tip
787 tall
277 dwarf
Mendel’s Law of Segregation
1. An individual inherits a unit of
information (_______) about a trait
from each parent
2. During gamete formation, the alleles
_________ from each other
1. Law of segregation
• A ________________ predicts the results of a
genetic cross between individuals of known
genotype.
Purple
White
PP x pp
Call the dominant allele “P”
Call the recessive allele “p”
All Pp
F1
Purple
Pp x Pp
P
P
Predicts 75% purple: 25% white
Or 3:1 ratio
F2
p
p
Dihybrid Cross
• Experimental cross between individuals
that are homozygous for different
versions of two traits
purple
flowers,
tall
TRUEBREEDING
PARENTS:
AABB
GAMETES:
AB
x
AB
white
flowers,
dwarf
aabb
ab
ab
AaBb
F1 HYBRID
OFFSPRING:
All purple-flowered, tall
Phenotypic Ratios in F2
AaBb
X
AaBb
Four Phenotypes:
– Tall, purple-flowered
(9/16)
– Tall, white-flowered
(3/16)
– Dwarf, purple-flowered (3/16)
– Dwarf, white-flowered (1/16)
9:3:3:1
is magic
ratio in
dihybrid
cross
Explanation of Mendel’s
Dihybrid Results
If the two traits
are coded for
by genes
on separate
chromosomes,
sixteen gamete
combinations
are possible
1/4
AB
1/4
Ab
1/4
aB
1/4
ab
1/4
AB
1/4
Ab
1/4
aB
1/4
ab
1/16
1/16
1/16
1/16
AABB AABb AaBB AaBb
1/16
1/16
1/16
1/16
AABb AAbb AaBb Aabb
1/16
1/16
1/16
1/16
AaBB AaBb aaBB aaBb
1/16
1/16
1/16
1/16
AaBb Aabb aaBb aabb
Law of independent assortment
Metaphase I
A
A a
a
B
B b
b
OR
A
A a
a
b
b B
B
Metaphase II:
Gametes:
A
A
a
a
A
A
a
a
B
B
b
b
b
b
B
B
B
A
B
A
1/4 AB
b
a
b
a
1/4 ab
b
A
b
A
1/4 Ab
B
a
B
a
1/4 aB
•two “units” for the first trait were to be assorted
into gametes ____________ of the two “units” for
the other trait
Impact of Mendel’s Work
• Mendel presented his results in ____
• Paper received _______________
• Mendel discontinued his experiments in
1871
• Paper rediscovered in ______ and
finally appreciated
Dominance Relations
• _____________dominance
• ____________ dominance
– Heterozygote phenotype is somewhere
___________that of two homozyotes
• _________________
– Non-identical alleles specify two
______________ that are both
expressed in ________________
Examples of recessive disorders
1. ___________________ -one of every 2,500
whites of European descent.
– One in 25 whites is a _______________
– The normal allele codes for a membrane protein
that transports Cl- between cells and the
environment.
– If these channels are defective or absent, there are
abnormally high extracellular levels of chloride that
causes the mucus coats of certain cells to become
thicker and stickier than normal.
– This mucus build-up in the pancreas, lungs,
digestive tract, and elsewhere favors bacterial
infections.
– Without treatment, affected children die before five,
but with treatment can live past their late 20’s.
Examples of recessive disorders
2. Tay-Sachs disease
– Caused by a dysfunctional enzyme that fails to
break down specific brain lipids.
– Symptoms- seizures, blindness, and
degeneration of motor and mental performance
a few months after birth.
– Child dies after a few years.
– Among Ashkenazic Jews (those from central
Europe) this disease occurs in one of 3,600
births, about 100 times greater than the
incidence among non-Jews or Mediterranean
(Sephardic) Jews.
__________________ Dominance
Flower Color in Snapdragons:
Pink-flowered plant X Pink-flowered plant
(heterozygote)
(heterozygote)
White-, pink-, and red-flowered plants
in a 1:2:1 ratio
Pink flowers have one normal and one
____________allele
Codominance
Genetics of ABO Blood Types: ______Alleles
• Gene that controls ABO type codes for
enzyme that dictates structure of a
glycolipid on blood cells
• Two alleles (IA and IB) are ________
when paired
• Third allele (i) is _________ to others
• Type A - IAIA or Iai
• Type B - IBIB or IBi
• Type AB - IAIB
• Type O - ii
ABO and Transfusions
• Recipient’s immune system will attack
blood cells that have an unfamiliar
glycolipid on surface
• Type __ is universal donor because it
has neither type A nor type B glycolipid
Pleitropy
• Alleles at a ______ locus may have
effects on _______________ traits
• Classic example is the effects of the
mutant allele at the _______________
that gives rise to sickle-cell anemia
•HbS homozygotes produce only the
___________hemoglobin; suffer from
sickle-cell anemia
At low ___ levels, cells with only HbS hemoglobin
“sickle” and stick together- clog __________•Eye disease, infection, heart disease
Fig. 10.12, p. 161
Albinism
•________ production is completely blocked
•Homozygous recessive at the gene
locus that codes for _____
Human Variation
• Some human traits occur as a few
________types
– Attached or detached earlobes
– Many genetic disorders
• Other traits show continuous variation
– ________
– Weight
– Eye color
(line of bell-shaped curve indicates
continuous variation in population)
Range of values for the trait
Number of individuals with
some value of the trait
Number of individuals with
some value of the trait
Describing Continuous
Variation
Range of values for the trait
Temperature Effects
on Phenotype
• Himalayan rabbits are
Homozygous for an allele
that specifies a heatsensitive version of an
enzyme in melaninproducing pathway
• Melanin is produced in
cooler areas of body