1. end result 1n or 2n? 2. daughter cells distinct or identical? 3. chiasmata? yes or no?...
TRANSCRIPT
1. End result 1n or 2n?
2. Daughter cells Distinct or identical?
3. Chiasmata?Yes or no?
Meiosis Mitosis
4. # of divisions
5. PurposeGrowth or germ cells?
QUIZ Name___________________
1. End result 1n or 2n?
1n 2n
2. Daughter cells Distinct or identical?
identicaldistinct
3. Chiasmata?Yes or no?
Meiosis Mitosis
NoYes
4. # of divisions 2 1
5. PurposeGrowth or germ cells?
GrowthGerm cells
QUIZ Name___________________
Observable Patterns of Inheritance
Chapter 10
•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
• _______________ theory-– Genetic material mixes much like
yellow and blue paint makes ____
Problem:
– Would expect variation to ________
– Yet variation in traits _______
How are traits transmitted?
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).
_________________
P1 x P2_________________
F1_________________
Mendel cross-pollinated peas
F1 x F1
F2
The F2 generation revealed two principles of heredity:1._____________________
2._______________________
Mendel’s Monohybrid Cross Results
787 tall 277 dwarf
651 long stem
207 at tip
705 purple 224 white
152 yellow428 green
299 wrinkled882 inflated
6,022 yellow 2,001 green
5,474 round 1,850 wrinkled
F2 plants showed dominant-to-recessive ratio that averaged 3:1
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
• A ________________ predicts the results of a genetic cross between individuals of known genotype.
PP x pp
All Pp
Purple
Purple
White
F1
Pp x Pp
F2Predicts 75% purple: 25% white
Or 3:1 ratio
Call the dominant allele “P”Call the recessive allele “p”
1. Law of segregation
p
P p
P
Dihybrid Cross • Experimental cross between individuals
that are homozygous for different versions of two traits
AABB aabbx
AaBb
AB AB ab ab
TRUE-BREEDING PARENTS:
GAMETES:
F1 HYBRID OFFSPRING:
purple flowers, tall
white flowers,dwarf
All purple-flowered, tall
Phenotypic Ratios in F2
Four Phenotypes:– Tall, purple-flowered (9/16)
– Tall, white-flowered (3/16)
– Dwarf, purple-flowered (3/16)
– Dwarf, white-flowered (1/16)
AaBb X AaBb
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
aB
AB
AB
abAb
Ab
aB
ab
1/4
1/4
1/4
1/4
1/4 1/4 1/4 1/4
AaBb aabbAabb aaBb
AABB AABb AaBB AaBb
AABb AAbb AaBb Aabb
AaBb aaBB aaBbAaBB
1/161/161/161/16
1/161/161/161/16
1/161/161/161/16
1/16 1/16 1/16 1/16
Metaphase I
Metaphase II:
Gametes:
1/4 AB 1/4 ab 1/4 Ab 1/4 aB
A A A A
A A A A
AAAA
B B
B B
BB
B B
BBBB
a a a a
aa aa
aaaa
bb b b
bb b b
b b b b
OR
Law of independent assortment
•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 ________________
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.
Examples of recessive disorders
Flower Color in Snapdragons:
Pink-flowered plant X Pink-flowered plant
White-, pink-, and red-flowered plants in a 1:2:1 ratio
(heterozygote) (heterozygote)
Pink flowers have one normal and one ____________allele
__________________ Dominance
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
Codominance
• 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
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
Describing Continuous Variation
Range of values for the trait
Nu
mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e t
rait
(line of bell-shaped curve indicates continuous variation in population)
Range of values for the trait
Nu
mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e t
rait