Lecture_9_-_Variation_in_Chromosome_Number-1

Lecture_9_-_Variation_in_Chromosome_Number-1 - Lecture 9...

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Lecture 9 Lecture 9 Chromosome Mutations: Chromosome Mutations: Variation in Chromosome Variation in Chromosome Number & Arrangement Number & Arrangement
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Modifications of Chromosome Modifications of Chromosome Numbers Numbers Members of diploid species normally contain exactly two haploid sets of homologous chromosome An individual “gene” is a location or segment of DNA on a pair of homologous chromosomes An “allele” is a specific nucleotide sequence found at a specific location on one chromosome Each individual diploid plant or animal can carry either one or two alleles of a specific gene Each individual passes on only one of these alleles to each of its gametes and therefore to each of its offspring These individual alleles are responsible for the genetic variation that occurs among individuals for a gene This genetic variation is partially responsible for the phenotypic variation that occurs among individuals in a population for a particular trait
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Modifications of Chromosome Modifications of Chromosome Numbers Numbers Although members of diploid species normally contain exactly two haploid chromosome sets, many known cases vary from this pattern Modifications can include changes in the total number of chromosomes, the deletion or duplication of genes or segments of a chromosome, and rearrangements of the genetic material within or among chromosomes Such changes are called chromosome aberrations or chromosome mutations
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Modifications of Chromosome Modifications of Chromosome Numbers Numbers Since chromosomes are the units of genetic transmission, chromosome aberrations may be passed on to the offspring in a manner predictable by Mendelian laws The genome of most species is delicately balanced, even minor changes in the genetic makeup in an individual can produce unique phenotypes . The addition or deletion of individual alleles thru abnormal chromosome numbers may have no effect on an individual; minor effects or even major effects. Substantial changes in the genome or genetic makeup in an individual can be lethal, particularly in animal species
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Terminology Describing Variation in Terminology Describing Variation in Chromosome Number Chromosome Number Euploidy is a term which means an individual has a complete, or normal, set of diploid chromosomes. Aneuploidy is a condition where an individual gains or loses one or more chromosomes, but not a complete haploid set. The loss of one chromosome from a haploid set is called a monosomy (2n-1) and the addition of one chromosome to a diploid set is called a trisomy (2n+1).
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Terminology Describing Variation in Terminology Describing Variation in Chromosome Number Chromosome Number Polyploidy occurs when more than two complete haploid sets of chromosomes are present in an individual. For example, individuals with three
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This note was uploaded on 05/07/2011 for the course DARY 2072 taught by Professor Hay during the Spring '09 term at LSU.

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Lecture_9_-_Variation_in_Chromosome_Number-1 - Lecture 9...

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