Chapter 8 Changes In Chromosome Structure

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Genetic variation

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genetic differences among members of the same species or between different

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Allelic variation

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genetic variation in a population that involves the occurrence of two or more different alleles for a particular gene.

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Metacentric

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describes a chromosome with the centromere in the middle.

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Submetacentric

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describes a chromosome in whichthe centromere is slightly off center

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Acrocentric

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a chromosome with the centromere significantly off center, but not at the very end.

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Telocentric

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describes a chromosome with itscentromere at one end.

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Karyotype

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a photographic representation of all the chromosomes within a cell. It reveals how many chromosomes are found within an actively dividing somatic cell.

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G banding

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the chromosomal banding pattern thatis observed when the chromosomes have beentreated with the chemical dye Giemsa.

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Deletion

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condition in which a segment of DNA is missing.

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Deficiency

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condition in which a segment ofchromosomal material is missing.

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Duplication

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a segment of DNA that is repeated more than once within a genome.

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Inversion

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a change in the orientation of geneticmaterial along a chromosome such that asegment is flipped in the reverse direction.

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Translocation

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(1) when one segment of a chromosome breaks off and becomes attached to a different chromosome; (2) when a ribosome moves from one codon in an mRNA to the next codon

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Simple translocation

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when one piece of a chromosome becomes attached to a different chromosome.

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Reciprocal translocation

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when two different chromosomes exchange pieces

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Terminal deletion

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when a segment is lost fromthe end of a linear chromosome.

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Repetitive sequences

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DNA sequences that are present in many copies in the genome.

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Gene duplication

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an increase in the copy number of a gene. Can lead to the evolution of gene families.

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Gene family

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two or more different genes within a single species that are homologous to each other because they were derived from the same ancestral gene.

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Homologous

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in the case of genes, this termdescribes two genes that are derived from the same ancestral gene. Homologous genes have similar DNA sequences. In the case of chromosomes, the two homologs of a chromosome pair are said to be homologous to each other.

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Paralogs

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homologous genes within a single species that constitute a gene family.

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Copynumber variation (CNV)

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a type of structural variation in which a segment of DNA that is 1000 bp or more in length commonly exhibits copy number differences among members of the same species.

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Telomeres

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specialized DNA sequences found at the ends of linear eukaryotic chromosomes

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Unbalanced translocation

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a translocation inwhich a cell has too much genetic materialcompared with a normal cell.

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Robertsonian translocation

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the structure produced when two telocentric chromosomes fuse at their short arms.

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Euploid

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describes an organism in which the chromosome number is an exact multiple of a chromosome set.

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Triploid

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an organism or cell that contains three sets of chromosomes

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Tetraploid

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having four sets of chromosomes (i.e., 4n).

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Polyploid

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an organism or cell with three or more sets of chromosomes.

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Trisomic

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a diploid cell with one extra chromosome (i.e., 2n + 1)

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Monosomic

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a diploid cell that is missing achromosome (i.e., 2n − 1).

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Nondisjunction

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event in which chromosomes do not segregate properly during mitosis or meiosis.

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Polytene chromosome

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chromosomes that arefound in certain cells, such as Drosophila salivary cells, in which the chromosomes have replicated many times and the copies lie side by side.

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Meiotic nondisjunction

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the event in which chromosomes do not segregate equally during meiosis.

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Mosaicism

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when the cells of part of an organism differ genetically from the rest of the organism.motif the name given to a domain or amino acid sequence that functions in a similar manner in many different proteins.