1. AP BIOLOGY Mendel and the Gene Idea

2. Gregor Mendel: The Father Of Genetics

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5. TRUE BREEDING VS. HYBRID  True breeding organisms produce offspring of the same variety when they self-pollinate.  Hybridization is the crossing of two true-breeding varieties.

6. MONOHYBRID CROSSES  Track the inheritance of a single characteristic such as flower color.  P1 generation- original parents  F1 generation- hybrid offspring of the P1 generation.  F2 generation- offspring resulting from interbreeding of the hybrid F1 generation.

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9. MENDEL’S IDEAS  Different alleles of a gene account for variations in inherited characteristics.  For each trait, an organism inherits two alleles, one from each parent.  If the two alleles differ, the dominant allele will be expressed in the organism’s appearance.  The two alleles for each characteristic segregate during gamete production, with the egg or sperm each getting one of the two alleles.

10. DOMINANT AND RECESSIVE ALLELES  Alleles are alternate versions of a gene  Dominant alleles are expressed in the organism’s appearance, while the recessive allele is masked.  An organism must receive a recessive allele from each parent for the trait to be expressed.

11. HOMOZYGOUS VS. HETEROZYGOUS  An organism is said to be homozygous when it has two identical alleles for a trait. Ex) TT, tt  Heterozygous means having two different alleles for a given trait Ex) Tt

12. PHENOTYPE VS. GENOTYPE  Phenotype is the physical and physiological expression of an organism’s traits.  Phenotype can be expressed in how an organism look, behaves, or functions.  Genotype is the actual genetic makeup an organism has; the genes it has for the trait

14. TESTCROSS  A test cross involves the breeding of an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype.  The ratio of resulting phenotypes gives clues to the unknown genotype.

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16. DIHYBRID AND TRIHYBRID CROSSES  A dihybrid cross is a cross between parents that have two different traits.  A trihybrid cross is between parents differing in three traits.

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18. MENDEL’S LAWS  Law of Segregation- Allele pairs separate during gamete formation, and then randomly reform pairs during fertilization.  Law of Independent Assortment- Each allele pair segregates independently during gamete formation; applies when genes for two traits are located on the same chromosome.

19. GENETICS AND PROBABILITY  Mendelian inheritance reflects the rules of probability.  Rule of multiplication- used to determine the chance that two or more independent events will occur together in a specific combination. Multiply the probability of one event by the probability of the other happening.  Rule of addition- the probability of an event that can occur in two or more different ways is the sum of the separate probabilities of those ways.

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21. INCOMPLETE DOMINANCE  Incomplete dominance is a type of inheritance in which the F1 hybrids have an appearance that is intermediate between the phenotypes of the parents.  Example: Red flowers crossed with white flowers results in pink offspring

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23. Incomplete Dominance

24. CODOMINANCE  Codominance is a phenotypic situation in which both alleles are expressed in a heterozygous organism.  Example: Cross of white chickens and black chickens results in speckled offspring

25. CODOMINANCE

27. TAY-SACHS DISEASE  In Tay-Sachs disease, brain cells lack an enzyme to metabolize gangliosides. Lipids accumulate in the brain causing damage and eventually death.  Although it is considered to be caused by a recessive allele, individuals that are heterozygous for Tay-Sachs have an enzyme-activity level between normal and those with the disease even though they lack outward symptoms of the disease.

29. ACHONDROPLASIA  Achondroplasia is a disorder caused by a dominant allele.  Individuals affected by this disorder have short stature, a form of dwarfism.  Heterozygotes have the dwarf phenotype.  The condition affects 1/10,000 individuals in the general population.  The majority of people are homozygous for the recessive allele.

30. HUNTINGTON’S DISEASE  Huntington’s disease is a degenerative disease of the nervous system that does not become apparent until the person reaches adulthood. It is possible that they would have had children before they were aware that they had the disease.  Offspring could find out if they inherited the disease by DNA analysis.

31. IS A DOMINANT ALLELE ALWAYS MORE COMMON IN A POPULATION?  For example, the allele for polydactly (having extra fingers or toes) is dominant, but occurs in only 1/400 babies born.  The recessive allele is more common (399/400 have the normal number of digits)  No, a dominant allele does not always occur more frequently in a population than the recessive allele.

32. MULTIPLE ALLELES  Multiple alleles are more than two alleles that represent a gene.  Different phenotypes result from different combinations of the alleles.  Example: ABO blood groups Phenotypes include type A, B, AB, and O blood  The genes coding for the glycoproteins (antigens) on the surface of red blood cells, which determine blood type, are inherited from parents

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34. PLEIOTROPY  Most genes have multiple phenotypic effects, a property called pleiotrophy.  Pleiotropic alleles are responsible for the multiple symptoms associated with certain hereditary diseases in humans, such as cystic fibrosis and sickle-cell disease.

35. WHAT IS EPISTASIS?  Epistasis is the situation where one gene alters the expression of another gene that is independently inherited.  Example: Fur color in mice  BB,Bb = black bb= brown  CC, Cc = pigment is deposited cc= no pigment  Any animal with cc will be white, no matter what color fur was coded for

36. Epistasis In Mice

37. POLYGENIC INHERITANCE  Polygenic inheritance is an additive effect of two or more genes on a single phenotypic character.  Skin color is a result of polygenic inheritance.  Three separately inherited genes affect the darkness of skin. Dark is dominant over light.

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40. ENVIRONMENTAL IMPACT ON HUMAN PHENOTYPE  Human phenotypes can be influenced by environmental factors.  For example: nutrition influences growth and height, exercise alters physical build, sun exposure darkens the skin, and experience improves performance on intelligence tests.

41. NORM OF REACTION  The “norm of reaction” for a genotype is the range of phenotypic possibilities for a single genotype, as influenced by the environment.  Generally, norms of reaction are broadest for polygenic characters.  Polygenic characteristics are“multifactorial” because many factors, both genetic and environmental, collectively influence phenotype.

42.  Environmental effect on Phenotype

43. FAMILY PEDIGREES  Pedigrees are family trees describing the interrelationships of parents and children across generations.  Pedigrees can be used to trace the inheritance of characteristics.

45. CARRIERS  Some human disorders are recessive traits.  A person heterozygous for the trait does not have the disease, but are considered to be “carriers” because they can pass the recessive allele to their offspring.

46. CYSTIC FIBROSIS  Cystic fibrosis affects 1/2500 whites of European descent. 1/25 is a carrier.  The disease is caused by a defect in a gene that codes for a membrane protein functioning in chlorine ion transport between cells and extracellular fluid.  Symptoms include high extracellular Cl- conc., thick mucus build up in the pancreas, lungs, digestive tract, and other organs, bacterial infection, and eventually death.

47. SICKLE-CELL DISEASE  Sickle-cell disease affects 1/400 African- Americans.  It is caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells, causing them to have a “sickle” shape.  1/10 African-Americans are heterozygous for the sickle-cell allele.  Individuals with the sickle-cell trait (carriers) have an increased resistance to malaria.

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49. LETHAL ALLELES  Lethal dominant alleles are much less common than lethal recessive alleles.  Lethal dominant alleles are not masked in heterozygotes. Individuals often do not survive to reproduce.  A person who is a carrier for a lethal recessive allele may not know it until they have children.

50. MULTIFACTORIAL DISEASES  Multifactorial diseases are those that have both a genetic as well as an environmental influence.  Examples include heart disease, diabetes, cancer, alcoholism, and mental illnesses such as schizophrenia and manic- depressive disorder.

51. PKU  PKU is phenylketonuria, a condition caused by lack of enzymes to metabolize the amino acid phenylalanine.  Buildup of phenylalanine and phenylpyruvate accumulate in the blood, causing mental retardation.  Problems can be prevented by early identification, and a special diet low in phenylalanine

52. CARRIER RECOGNITION  Carrier recognition is the process of determining if an individual is a carrier of a particular genetic disorder.  PRO: allows people with family histories of the disorder to make informed decisions about having children  CON: carriers could be discriminated against if the info is used in the wrong way