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GENETICS Unit 7 1
GENETICSUnit 7
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allele
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How we inherit our genesEach human offspring inherits one maternal
set of 23 chromosomes and one paternal set.
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Unlucky catch A baby inheriting two copies of the defective FMO3 gene will develop fish odor syndrome.
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Homozygous vs. Heterozygous
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Homozygous
Heterozygous
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Family resemblance:
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• Offspring resemble their parents because they inherit alleles from their parents.
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Hereditythe passing on from one generation to another
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HEREDITY
I AM the family face;Flesh perishes, I live on,Projecting trait and traceThrough time to times anon,And leaping from place to placeOver oblivion.
The ears-heired feature that canIn curve and voice and eyeDespise the human spanOf durance—that is I;The eternal think in man,That heeds no call to die. —Thomas Hardy, Moments of Vision and Miscellaneous Verses,
1917
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Some traits are controlledby a single gene
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• One gene gives one trait most of the time
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HISTORY
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History of Genetics Timeline
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Older Ideas
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blending of their two parents’ traits via the blood
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Charles Darwin pangenesis
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LamarckInheritance of Acquired
Characteristics
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Mendel didn’t do anything radically new, but simply applied methodical
experimentation and scientific thinking
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Mendel chose a good organism to study: the garden pea.
• relatively easy to fertilize manually by “pollen dusting”
• easy to collect dozens or even hundreds of offspring from a single cross
• pea plants are fast enough breeders that Mendel could conduct experiments that lasted for multiple generations
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Mendel chose to focus on seven easily categorized traits
a. flower color is purple or white b. seed color is yellow or green c. flower position is axial or terminald. pod shape is inflated or
constrictede. stem length is long or shortf. pod color is yellow or greeng. seed shape is round or wrinkled
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Mendel began his studies by first repeatedly breeding together similar plants until he had many distinct populations, each of which was unvarying
for a particular trait
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• In the mid-1800s, Gregor Mendel - how traits are inherited.
• experimentation and hypothesis testing, -easily observed and categorized traits in garden peas.
• Why was the pea plant a good organism with which to study heredity?
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Punnett Squares: Give Genotypes and Phenotype Ratios
TtRr X TtRr
Ttrr X ttrr
ttRr X Ttrr
TTrr X ttRR
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Mendel’s conclusions:• that the inheritance of each trait
is determined by "units" or "factors" that are passed on to descendants unchanged - now called genes
• that an individual inherits one such unit from each parent for each trait
• that a trait may not show up in an individual but can still be passed on to the next generation 31
Mendel's observations from these experiments can be summarized in two principles:
• the principle of segregation • the principle of independent
assortment
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Principle (Law) of Segregation:
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Principle (Law) of Independent Assortment:
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But wait…there’s more!
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Phenotype vs. Genotype
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Phenotype
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Genotype
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Chance is important• consequence of segregation
• fertilization is a chance event
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Test Cross
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Test cross
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• In this test-cross, a homozygous white female alligator is bred with a normally colored male of unknown genotype.
• The color of their offspring will help identify whether the male is homozygous dominant or heterozygous.
Test CrossYou mate a pigmented male alligator to a female albino alligator. The clutch of baby alligators includes both pigmented and albino individuals. What is the genotype of the father?
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• In a test-cross, an individual with a dominant phenotype and an unknown genotype is mated with a homozygous recessive individual.
• The phenotypes of the offspring reveal the unknown genotype.
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Pedigrees• In cross-pollinating plants that either produce
yellow or green pea seeds exclusively, Mendel found that the first offspring generation (f1) always has yellow seeds. However, the following generation (f2) consistently has a 3:1 ratio of yellow to green.
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Pedigrees• This 3:1 ratio occurs in later generations as well.
Mendel realized that this was the key to understanding the basic mechanisms of inheritance.
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What is the genotype of the paternal grandmother?
1. Homozygous recessive
2. Heterozygous3. Homozygous
dominant4. Cannot be
determined
What is the probability that you (“Me” in the diagram) will be a carrier for this disease?1. 1/42. 1/33. 1/24. 2/35. 3/4
Sometimes it’s hard to figure out the pattern…
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Exceptions to the Rule…
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Incomplete dominance: the heterozygote appears to be intermediate between the two homozygotes
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Codominance: the heterozygote displays characteristics of both homozygotes
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Multiple Alleles:Gene that has three or more alleles
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ABO Blood Groups
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The gene for aldehyde dehydrogenase (ADH) is incompletely dominant. A woman who is heterozygous for this gene (ADH+/ADH) marries a man who is homozygous for the normal allele (ADH+/ ADH+). What is the probability that they will have heterozygous children?
An individual with type O blood marries an individual with type AB blood. Which of the following would not be a possible offspring blood type?1. A2. B3. O4. All of the above are
possible.
Pleiotropy One Gene Many Effects
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Sex-Linked Genes
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Polygenic TraitsControlled by two or more than two
genes
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Genes & the Environment• Drinking diet soda can
be deadly if you carry a single bad gene
• Ice pack on the back of rabbits & cats
• Alcoholism• Weight
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