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PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 14
Chapter 14
Mendel and the Gene Idea
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PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 14 Chapter 14
Mendel and the Gene Idea
- (^) Overview: Drawing from the Deck of Genes
- (^) What genetic principles account for the transmission of traits from parents to offspring?
- (^) An alternative to the blending model is the “particulate” hypothesis of inheritance: the gene idea - (^) Parents pass on discrete heritable units, genes
- (^) Gregor Mendel
- (^) Documented a particulate mechanism of inheritance through his experiments with garden peas
Figure 14.
Mendel’s Experimental, Quantitative Approach
- (^) Mendel chose to work with peas
- (^) Because they are available in many varieties
- (^) Because he could strictly control which plants mated with which
- (^) Crossing pea plants
Figure 14.
1 5 4 3 2 Removed stamens from purple flower Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower Parental generation (P) Pollinated carpel matured into pod Carpel (female) Stamens (male) Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F 1 ) APPLICATION By crossing (mating) two true-breeding varieties of an organism, scientists can study patterns of inheritance. In this example, Mendel crossed pea plants that varied in flower color. TECHNIQUETECHNIQUE When pollen from a white flower fertilizes eggs of a purple flower, the first-generation hybrids all have purple flowers. The result is the same for the reciprocal cross, the transfer of pollen from purple flowers to white flowers.
TECHNIQUERESULTS
- (^) Mendel chose to track
- (^) Only those characters that varied in an “either- or” manner
- (^) Mendel also made sure that
- (^) He started his experiments with varieties that were “true-breeding”
- (^) In a typical breeding experiment
- (^) Mendel mated two contrasting, true-breeding varieties, a process called hybridization
- (^) The true-breeding parents
- (^) Are called the P generation
The Law of Segregation
- (^) When Mendel crossed contrasting, true- breeding white and purple flowered pea plants - (^) All of the offspring were purple
- (^) When Mendel crossed the F 1 plants - (^) Many of the plants had purple flowers, but some had white flowers
- (^) Mendel discovered
- (^) A ratio of about three to one, purple to white flowers, in the F 2 generation
Figure 14.
P Generation (true-breeding parents) (^) Purple flowers White flowers
F 1 Generation (hybrids) All plants had purple flowers F 2 Generation EXPERIMENT True-breeding purple-flowered pea plants and white-flowered pea plants were crossed (symbolized by ). The resulting F 1 hybrids were allowed to self-pollinate or were cross- pollinated with other F 1 hybrids. Flower color was then observed in the F 2 generation. RESULTS Both purple-flowered plants and white- flowered plants appeared in the F 2 generation. In Mendel’s experiment, 705 plants had purple flowers, and 224 had white flowers, a ratio of about 3 purple : 1 white.
- (^) Mendel observed the same pattern
- (^) In many other pea plant characters
Table 14.
Mendel’s Model
- (^) Mendel developed a hypothesis
- (^) To explain the 3:1 inheritance pattern that he observed among the F 2 offspring
- (^) Four related concepts make up this model
- (^) Second, for each character
- (^) An organism inherits two alleles, one from each parent
- (^) A genetic locus is actually represented twice
- (^) Third, if the two alleles at a locus differ
- (^) Then one, the dominant allele, determines the organism’s appearance
- (^) The other allele, the recessive allele, has no noticeable effect on the organism’s appearance