Inheritance160-page3 - expressed is recessive. Note: These...

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Inheritance Patterns - 3 Mendel's research led to the following conclusions, two of which are presented as Mendel's Principles: Mendel's Statements about Inheritance 1. There are alternative forms (or variations) of genes, the "units" that determine inherited traits. The alternative forms of a gene are now called alleles. To relate this to what we know about homologous chromosomes, the alleles are located at the same locus on homologous chromosomes. (Specifically, we inherit the alleles for a gene, not the gene). 2. An individual will have 2 alleles for each inherited trait. The 2 alleles may be the same, or they may be different. If the two alleles are the same, the individual will be homozygous for that trait. If the two alleles are different, the individual will be heterozygous for the trait. When the two alleles for a gene pair are different from each other, one will be expressed, and the second will not affect the organism's appearance. The allele always expressed is said to be dominant, and the one that may not be
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Unformatted text preview: expressed is recessive. Note: These statements are true for the traits tested in Mendel's peas and for many genes, but are not universally true. Many genes have alleles that are equally expressed, as we shall see, and there are genes that have more than 2 alleles within the population. 3. Gametes have just one allele for each trait, because the allele (gene) pairs are separated (or segregated) during meiosis I when homologous chromosomes pair and then separate. 50% of the gametes receive one allele and 50% of the gametes receive the alternative allele when the alleles are heterozygous. (And as Mendel proposed, fertilization results in restoring the pairs of alleles for the next generation). This statement ultimately resulted in Mendel's Principle of Segregation: Pairs of genes segregate during the formation of gametes (Meiosis), so that each gamete has one of each gene pair (one allele) but not both. Fertilization restores the gene pairs (on the homologous chromosomes)....
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This note was uploaded on 12/29/2011 for the course BIO 151 taught by Professor Edwards during the Spring '10 term at SUNY Stony Brook.

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