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Chapter 14
- 1. Chapter 14 Notes Mendeland the gene idea
- 2. Concept 14.1 In 1857,Gregor Mendel began breeding peas to study inheritance Geneticists use the term character to describe a heritable feature - ex. flower color Each variant for a character is called a trait - ex purple flowers or white flowers
- 3. Concept 14.1 Mendel beganhis experiment using true- breeding plants - when the plants self-pollinate, all offspring are of the same variety Mendel would cross 2 true-breeding plants. This crossing is called hybridization.
- 4. Concept 14.1 - thetrue-breeding parents are the P generation (parental generation) and their hybrid offspring are referred to as the F1 generation (First filial). - when the F1 generation is allowed to self-pollinate, their offspring become the F2 generation (second filial).
- 5. Concept 14.1 By thelaw of segregation, the two alleles for a character are packaged into separate gametes. - P generation: purple x white - F1 generation: all purple - F2 generation: ¾ purple, ¼ white Mendel saw this in 6 other varieties
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- 7. Gregor Mendel’s Discoveries 1.Alternative versions of genes (different alleles) account for variations in inherited characters. - the alternative forms of a gene are called alleles. ex. gene: flower color alleles: white, purple
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- 9. Concept 14.1 2. Foreach character, an organism inherits two alleles, one from each parent. 3. If the two alleles differ, than one, the dominant allele, is fully expressed in the organisms appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance.
- 10. Concept 14.1 4. Thetwo alleles segregate (separate) during gamete production Punnett squares are used to predict the results of a genetic cross between individuals of known genotypes.
- 13. Concept 14.1 Homozygous: whenthe alleles for a gene are identical Heterozygous: when the alleles for a gene are different Phenotype: physical appearance Genotype: genetic makeup
- 14. Concept 14.1 A testcrosscan be used to determine the genotype of an organism that displays a dominant trait. - ex. Is the purple flower homozygous or heterozygous? Cross it with a recessive (white) flower. The results will tell the genotype.
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- 16. Concept 14.1 A crossin which only one character is discussed is a monohybrid cross. ex. flower color If two characters are discussed, the cross is a dihybrid cross ex. flower color, seed color
- 17. Concept 14.1 Independent lawof assortment: each pair of alleles will segregate independently during gamete formation.
- 18. Concept 14.3 Incomplete dominance -when the F1 hybrids have an appearance somewhere in between the phenotypes of the parents. - white + red = pink
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- 20. Concept 14.3 Codominance/Multiple Alleles -the two alleles affect the phenotype in separate distinguishable ways. - ex. A, B, AB, and O blood types
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- 22. Concept 14.3 Pleiotropy - theability of a gene to affect an organism in many ways - ex. the alleles for sickle-cell disease cause multiple symptoms
- 23. Concept 14.3 Epistasis - agene at one locus alters the phenotypic expression of a gene at a second locus - ex. coat color in mice
- 24. Concept 14.3 Polygenic inheritance -the additive effect of two or more genes on a single character; not an “either or” situation - converse of pleiotropy where a single gene affects several phenotypic characters - skin color
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- 26. Extending Mendelian Genetics Naturevs. Nurture: The environmental Impact on Phenotype - the environment plays an important role on one’s phenotype - ex. nutrition influences height, sun- tanning darkens the skin
- 27. Concept 14.3 Norm ofreaction: the product of a genotype is not generally a rigidly defined phenotype, but a range of phenotypic possibilities which may be due to environmental influences. Characters are multifactorial when both genetic and environmental factors influence phenotype
- 28. Concept 14.4 Pedigree: afamily tree that describes the relationships between generations for a particular trait - pedigrees are used to map out specific phenotypic traits
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- 30. Many human disordersfollow Mendelian patterns of inheritance Recessively Inherited Diseases - if someone is heterozygous for a trait they are termed a carrier. Carriers do not display the trait but can pass on the allele to offspring Concept 14.4
- 31. Common recessive geneticdisorders - Cystic fibrosis: 1/2500 people of European decent; 1/25(4%) are carriers - Tay-Sachs disease: - sickle-cell disease: 1/400 African- Americans Concept 14.4
- 32. Common dominant geneticdisorders - Anchondroplasia: form of dwarfism - Huntington’s disease: no obvious phenotypic effect until 35 to 45 yrs. old Concept 14.4