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Ch 14 & 15 - Coggle Diagram
Ch 14 & 15
Ch 14
Mendel’s Experimental, Quantitative Approach
Mendel’s fresh approach to the study of heredity allowed him to deduce principles that had remained elusive to others
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Trait
Each variant for a character, such as purple or
white color for flowers, is called a trait
advantages of using peas
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– Mating could be controlled; plants could be allowed to self-pollinate or could be cross-pollinated
True Breeding
He also started with varieties that were true- breeding (plants that produce offspring of the same variety when they self-pollinate)
hybridization
In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization
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F2 generation
When F1 individuals self-pollinate or cross-pollinate with other F1 hybrids, the F2 generation is produced
The Law of Segregation
In the 1800s, the explanation of heredity was the “blending” hypothesis
When Mendel crossed contrasting, true-breeding white- and purple-flowered pea plants, all of the F1 hybrids were purple
When Mendel crossed the F1 hybrids, many of the
F2 plants had purple flowers, but some had white
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The Testcross
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To determine the genotype we can carry out a testcross: breeding the mystery individual with a homozygous recessive individual
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Degrees of Dominance
Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical
• In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties
• In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways
Tay-Sachs disease
disease is a fatal inherited disorder; a dysfunctional enzyme causes an accumulation of lipids in the brain
– At the organismal level, the allele is recessive
– At the biochemical level, the phenotype (that is, the enzyme activity level) is incompletely dominant
– At the molecular level, the alleles are codominant
Pleiotropy
Most genes have multiple phenotypic effects, a
property called pleiotropy
Epistasis
In epistasis, expression of a gene at one locus alters the phenotypic expression of a gene at a second locus
Polygenic Inheritance
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Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype
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Cystic Fibrosis
Cystic fibrosis is the most common lethal genetic disease in the United States, striking one out of every 2,500 people of European descent
Ch 15
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Genomic Imprinting
For a few mammalian traits, the phenotype depends on which parent passed along the alleles for those traits
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