1. Fundamentals of Genetics
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2. Patterns of Inheritance
The History of Genetics
Genetics - scientific study of heredity
Trait - characteristic that can be passed from parents to offspring
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3. Once accepted hypothesis
Blending of Traits
Once accepted hypothesis
did not explain appearance of unexpected traits in offspring
Oops…blond baby boy. Where did that come from?
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4. Gregor Mendel ’s
self-fertilization - cross of the same plant; offspring receives genetic information from one parent only
cross-fertilization - cross of 2 different plants; offspring receives different forms of genetic trait from each parent
Studied pea plants
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5. Hybrid - organism receives different forms of a genetic trait
Purebred - organism receives the same genetic traits from both of its parents
Hybrid - organism receives different forms of a genetic trait
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6. Mendel’s Observations
Crossed two different purebreds (P generation = parent generation)
resulting offspring is F1 (1st filial) -offspring
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7. crossed these, resulting in F2 (2nd filial) generation
Found that there were always two types of traits - Dominant and Recessive
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8. Mendel’s Conclusions:
Disproved blending hypothesis
offspring receives one of two “factors” from each parent - “factors” are genes
genes - sections of a chromosome that code for a trait
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9. Allele - distinct form of a gene
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10. dominant allele - expressed when two different alleles are present; represented with a capital letter: A
recessive allele - form of a gene that is not expressed when paired with a dominant allele; represented with a lower case letter: a
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11. Mendel is the Father of Modern Genetics
Gregor Mendel
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12. Cellular Basis of Inheritance
Chromosome Theory of Heredity states that the material of inheritance is carried by the genes in the chromosomes
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13. Genes represent traits
Genotype - genes that make up an organism
includes both genes in a homologous pair
Phenotype - outward expression of the trait
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14. homozygous - two alleles are identical (AA or aa)
also known as purebred organism
heterozygous - two alleles are different (Aa)
also known as a hybrid organism
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15. Mendel’s Laws
Law of Segregation - gene pairs separate when gametes form
one gamete carries one gene and the other carries the other gene
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16. Law of Independent Assortment - gene pairs segregate into gametes randomly and independently of each other
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17. Law of Dominance - dominant allele is expressed, recessive allele will be hidden unless in homozygous form
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18. Genetics and Prediction
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19. Predictions for One Trait
Probability - predict likelihood of an event or outcome
“tails”
“heads”
“Heads” is one possible outcome out of a total of 2 possible outcomes.
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20. Punnett square - grid for organizing genetic information
can be used to make predictions about a cross between two organisms
monohybrid cross - cross between two parents involving one trait P p
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21. AA x aa (A = normal, a = albino)
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22. Genotypic ratio = AA 0/4 or 0% Aa 4/4 or 100% aa 0/4 or 0%
Phenotypic ratio = Normal 4/4 or 100%
Albino 0/4 or 0%
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23. Predictions for Two Traits
Two trait cross – cross between two parents and two traits
Dihybrid cross - cross between two heterozygous parents
use a 4 X 4 punnett square
sixteen possible outcomes
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24. HhTt x hhtt (H = long hair, h = short hair; T = tail, t = no tail)
FOIL! Ht hT ht HT ht
HhTt
Hhtt
hhTt
hhtt
Hhtt
hhTt
hhtt ht
HhTt ht
HhTt
Hhtt
hhTt
hhtt ht
HhTt
Hhtt
hhTt
hhtt
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25. Genotypic ratio = HHTT 0/16 or 0% HHTt 0/16 or 0% HHtt 0/16 or 0%
HhTt 4/16 or ¼ or 25%
Hhtt /16 or ¼ or 25%
hhTT 0/16 or 0%
hhTt 4/16 or ¼ or 25%
hhtt 4/16 or ¼ or 25%
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26. Phenotypic ratio: 25% Long hair, tail 25% Long hair, no tail
25% short hair, tail
25% short hair, no tail
JK!
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27. Test Cross G?
GG or Gg
Test cross - breed an organism whose genotype is questionable with a homozygous recessive organism
results determine genotype of questionable organism
then it’s Gg
If all offspring gg X G?
then it’s probably GG
If any offspring
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28. Incomplete Dominance
color in snapdragons, hypercholestolemia, instead of white or red – color is pink
heterozygous offspring show a phenotype that is in-between the phenotypes of the two homozygous parents
blending of traits X
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29. r w r rr rw w rw ww
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30. Codominance HA = normal HS = sickle Both alleles are expressed equally
both are dominant and equally expressed – both normal red blood cells and sickle-shaped blood cells present in heterozygote
Both alleles are expressed equally
Ex. Sickle Cell Disease
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31. Polygenic Trait (Epistasis)
Trait controlled by more than one gene
ex. Eye color
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32. Multiple Alleles
Three or more alleles for a trait in a human population
ex. Blood types: IA, IB, i (type O)
Karl Landsteiner discovered antigens which are responsible for different blood types
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33. Multiple Alleles - Blood Types
IA - contains antigen A
IB - contains antigen B
IAIB - contains antigens for both A & B
i - contains neither A nor B
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34. Blood Groups
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35. Universal recipient: AB Dominant Trait in Blood Groups
Universal donor: O
Universal recipient: AB
Dominant Trait in Blood Groups
Rh antigen = named after Rhesus Monkey
people who have the Rh antigen = Rh+ (positive)
people who do not have it = Rh- (negative)
Rh-, Rh+ person = positive
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36. Pleiotropy Single gene affects more than one trait
ex. Sickle cell anemia - effects include blood cell shape, anemia, weakness, brain damage, spleen damage, & heart damage
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37. Environmental Effects
Phenotype is a combination of genetic and environmental influences, epigenetics
Ex. Identical twins share the same DNA but may look and act differently
ex. Himalayan rabbit - fur color depends on body temperature – dark where cooler, white where warmer
Yes, they are identical!
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38. Issues in Biology
Up to a 3 inch height difference observed in studies where twins were raised in two different countries/environments
“Nature vs. Nurture” Issue
studies have been done on identical twins that have been separated at birth VS
Twins raised in different adoptive homes showed similar interests and careers when they reconnected as adults
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