1 4 chapter 14~ mendel & the gene idea. 2 mendel’s discoveries 4 blending- hereditary material...
TRANSCRIPT
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Chapter 14~Mendel & The Gene Idea
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Mendel’s Discoveries
Blending- Hereditary Material– Both parents
contribute genetic material
Inheritable factors– Genes - passed
from generation to generation
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Mendelian genetics
Character
– (heritable feature, i.e., fur color) Trait
– (variant for a character, i.e., brown) True-bred
– (all offspring of same variety) Hybridization
– (crossing of 2 different true-breds) P generation- (parents) F1 generation-
– (first filial generation, first offspring)
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Leading to the Law of Segregation
Alternative versions of genes (alleles) account for variations in inherited characteristics
For each character, an organism inherits 2 alleles, one from each parent
If the two alleles differ, then one, the dominant allele, is fully expressed in the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance
The alleles for each character segregate (separate) during gamete production (meiosis).
Mendel’s Law of Segregation
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Genetic vocabulary…….
Punnett square: predicts the results of a genetic cross between individuals of known genotype
Homozygous: pair of identical alleles for a character
Heterozygous: two different alleles for a gene
Phenotype: an organism’s traits
Genotype: an organism’s genetic makeup
Testcross: breeding an unknown dominate phenotype with a homozygous recessive phenotype
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Monohybrid Cross
Cross between 2 parents that are both heterozygous for 1 trait
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The Law of Independent Assortment
Law of Segregation involves 1 character. What about 2 (or more) characters?
Monohybrid cross vs. dihybrid cross
The two pairs of alleles segregate independently of each other.
Mendel’s Law of Independent Assortment
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Non-single gene genetics, I Incomplete dominance:
appearance between the phenotypes of the 2 parents. Ex: snapdragons
Codominance: two alleles affect the phenotype in separate, distinguishable ways. Ex: Tay-Sachs disease Ex: Roan cattle
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Non-single gene genetics, II Multiple alleles: more than 2 possible alleles for a gene.
– Ex: human blood types
– (A and B alleles are both dominant = codominant / O allele is recessive)
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Non-single gene genetics, III
Pleiotropy: genes with multiple phenotypic effect.
– Ex: sickle-cell anemia
• causes problems with blood which causes other problems
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Non-single gene genetics, IV
Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus.
– Ex: mice coat
• C leads to deposition of color while B or b leads to the color.
• BBcc would be white even though the genes code for black
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Non-single gene genetics, V
Polygenic Inheritance:
– an additive effect of two or more genes on a single phenotypic character
– Ex: human skin pigmentation and height
– - i.e. the more dominant the alleles the more color
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Human disorders
The family pedigreeMale = SquareFemale = CircleIf phenotypic trait is present it is shown by shading the symbol
Dominant = widow’s peak Dominant = Free earlobe
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Human disorders
Recessive disorders:
– Cystic fibrosis
– Tay-Sachs
– Sickle-cell - blood disorder
– Hemophelia- blood disorder
Dominant disorders:
– Huntington’s
– Acondroplasia (dwarfism)
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How do they stay in population?
Carriers- individuals not exhibiting phenotype, but can pass the gene to offspring)
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Recessive Disorders
Cystic fibrosis
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Recessive Disorders
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Test is available - will determine if individual has Huntington’sNo cure - Do you find out?How does it stay? Affects show up after reproductive years.
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TESTING FOR DISORDERS
Testing in womb:
– •amniocentesis
– •chorionic villus sampling (CVS)
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