Chap 14 PPT - CHAPTER FOURTEEN Mendel And the Gene Idea...

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CHAPTER FOURTEEN Mendel And the Gene Idea
What hypothesis accounts for the passing of traits from parents to offspring?
Mendel used the scientific approach to identify two laws of inheritance Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments Mendel chose to track only those characters that varied in an either-or manner He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate)
Advantages of pea plants for genetic study: There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits Mating of plants can be controlled Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels) Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another
TECHNIQUE RESULTS Parental generation (P) Stamens Carpel 1 2 3 4 First filial gener- ation offspring (F 1 ) 5
In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization The true-breeding parents are the P generation The hybrid offspring of the P generation are called the F 1 generation When F 1 individuals self-pollinate, the F 2 generation is produced
The Law of Segregation When Mendel crossed contrasting, true- breeding white and purple flowered pea plants, all of the F 1 hybrids were purple When Mendel crossed the F 1 hybrids, many of the F 2 plants had purple flowers, but some had white Mendel discovered a ratio of about three to one (3:1), purple to white flowers, in the F 2 generation
EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers × F 1 Generation (hybrids) All plants had purple flowers F 2 Generation 705 purple-flowered plants 224 white-flowered plants
Mendel reasoned that only the purple flower factor was affecting flower color in the F 1 hybrids Mendel called the purple flower color a dominant trait and the white flower color a recessive trait Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits What Mendel called a “heritable factor” is what we now call a gene
Mendel’s Model Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F 2 offspring Four related concepts make up this model These concepts can be related to what we now know about genes and chromosomes
Concepts 1. Alternative versions of genes account for variations in inherited characters 2. Each character an organism inherits two alleles, one from each parent 3.

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