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Lecture_10_Mendel (6 slides per page)

Lecture_10_Mendel (6 slides per page) - Mendel and the Gene...

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1 Mendel and the Gene Idea Mendel’s Law of Segregation Mendel’s Law of Independent Assortment Readings: Chapter 14 Topics of Ch. 14 not covered: Extending Mendelian genetics for two or more genes (epistasis and quantitative genetics); multiple alleles. Table 14.1 Results of crosses for seven characters Mendel developed a hypothesis to explain these results that consisted of four related ideas . Alternative version of genes (different alleles ) account for variations in inherited characters. The purple-flower allele and white-flower allele are two DNA variations at the flower-color locus . Alleles of the same locus (= the location of a gene) are located on different chromosomes of the homologous chromosome pair Recessive Dominant Fig. 14.4 2. For each character, an organism inherits two alleles, one from each parent. A diploid organism inherits one set of chromosomes from each parent. Each diploid organism has a pair of homologous chromosomes and therefore two copies of each locus. These homologous loci may be identical, as in the true-breeding plants of the P generation. Alternatively, the two alleles may differ; purple-flower allele from one parent and a white-flower allele from the other. One allele may be dominant to the other. The two alleles for each character segregate (separate) during gamete production. This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis. The separation of alleles into separate gametes is summarized as Mendel’s law of segregation . Mendel’s law of segregation: the two alleles for a character are packaged into separate gametes Fig. 14.5 Punnett square
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2 Some vocabulary of genetics : An organism with two identical alleles for a character is homozygous for that character. Organisms with two different alleles for a character is heterozygous for that character. A description of an organism’s traits is its phenotype . A description of its genetic makeup is its genotype . Two organisms can have the same phenotype but have different genotypes if one is homozygous dominant and the other is heterozygous. It is not possible to predict the genotype of an organism with a dominant phenotype. The organism must have one dominant allele, but it could be homozygous dominant or heterozygous. A test cross : breeding a homozygous recessive with dominant phenotype. The unknown genotype, can determine the identity of the unknown allele. Fig. 14.7 Mendel’s monohybrid crosses – led to formulation of law of segregation .
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