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Unformatted text preview: 58 Chapter 2 Patterns of Inheritance At the gene level, what is the explanation for the patterns by which phenotypic variants are inherited? We have seen that many cases of discontinuous variation are caused by variant alleles of a single gene: one allele causes one phenotype, and another allele of that same gene causes a different phenotype. The inheritance of such a pair of variants is governed by rules laid down by Mendel: genes come in pairs; the pairs segregate equally during gamete formation; gametes therefore carry one member of each pair; and zygotes are formed by random fusion of male and female gametes. These simple rules govern the production of the standard ratios. Which ratio is observed depends on which genotypes are mated. Is the pattern of inheritance influenced by the location of the relevant gene or genes in the genome? We have seen that this indeed is the case. Three broad genomic locations can be delineated: on autosomal chro- mosomes, on sex chromosomes, and on organelle chro- mosomes. These chromosomal locations all produce distinct patterns of inheritance. Autosomal position pro- duces inheritance patterns identical in each sex of prog- eny, sex chromosome position can produce different patterns in the two sexes, and organelle chromosome position produces patterns dependent only on the or- ganelle genotype of the maternal parent....
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.
- Spring '08