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Genetics Chapter 6
Chromosome variation
| Term | Definition |
|---|---|
| chromosome mutations | difference from the wild type in the number or structure of one or more chromosomes; often affects many genes and has large phenotypic effects |
| metacentric | the centromere is located approximately in the middle, and so the chromosome has two arms of equal length |
| submetacentric | the centromere is displaced toward one end, creating a long arm and a short arm |
| acrocentric | the centromere is near one end, producing a long arm and a knob, or satellite, at the other end |
| telocentric | the centromere is at or very near the end of the chromosome |
| the complete set of chromosomes possessed by an organism is called it ________ | karyotype |
| chromosome mutations can by frouped into three basic categories: | chromosome rearrangements, aneuploids, and polyploids |
| chromosome rearrangements alter the ________ of chromosomes; | structure |
| aneuploidy | the number of chromosomes is altered: one or more individual chromosomes are added or deletered |
| polyploidy | one or more complete sets of chromosomes are added |
| chromosome rearrangements | mutations that change the structure of individual chromosomes |
| what are the four basic types of rearrangements? | duplications, deletions, inversions, and translocations |
| chromosome duplication | a mutation in which part of the chromosome has been doubled |
| tandem duplication | duplicated region is immediately adjacent to the original segment (ABCDEFG to ABCDEFEFG) |
| displaced duplication | if the duplicated segment is located some distance from the original segment, either on the same chromosome or on a different one (ABCDEFG to ABCDEFGEF) |
| reverse duplication | when the duplication is inverted (ABCDEFG to ABCDEFFEG) |
| paracentric inversion | inversion that does not include the centromere in the inverted region |
| pericentric inversion | inversion that includes the centromere in the inverted region |
| in individuals heterozygous for a duplication, the duplicated region will form a ______ when homologous chromosomes pair in meiosis | loop |
| deletions often have pronounced effects on the phenotype owing to unbalanced ____ _______ | gene dosage |
| segmental duplication | duplications greater than 1000 base pairs in length |
| chromosomal deletion | loss of a chromsome segment |
| pseudodominance | the expression of a normally recessive mutation |
| haploinsufficient gene | when a single copy of a gene is not sufficient to produce a wile-type phenotype |
| chromosome inversion | a chromosome segment is inverted-turned 180 degrees (ABCDEFG to ABCFEDG) |
| position effect | dependence of the expression of a gen on the gene's location in the genome |
| dicentric chromatid | a chromatid that has two centromeres |
| acentric chromatid | a chromatid that lacks a centromere |
| dicentric bridge | structure produced when the two centromeres of a dicentric chromatid are pulled toward opposite poles, stretching the dicentric chromosome across the center of the nucleus. eventually the bridge breaks as the two centromeres are pulled apart |
| translocation | the movement of genetic material between nonhomologous chromosomes or within the same chromosome |
| nonreciprocal translocation | genetic material moves from one chromosome to another without any reciprocal exchange |
| reciprocal translatino | two-way exchange of segments between the chromosomes |
| Robertsonian translocation | the longs arms of two acrocentric chromosomes become joined to a common centromere through a translocation, generating a metacentric chromosome with two long arms and another chromsome with two very short arms |
| chromosomes of cells grown in culture sometimes develop constrictions or gaps at particular locations called _______ ______ | fragile sites |
| fragile-X syndrome | a disorder that includes intellectual disability |
| copy-number variation (CNV) | difference among individual organisms in the number of copies of any large DNA sequence (larger than 1000bp) |
| aneuploidy | change in number of individual chromosomes |
| polyploidy | change in the number of chromosome sets |
| nondisjunction | the failure of homologous chromosomes or sister chromatids to separate in meiosis or mitosis |
| nondisjunction leads to what? | some gametes or cells that contain an extra chromosome and other gametes or cells that are missing a chromosome |
| what are four types of common aneuploid conditions in diploid individuals? | nullisomy, monosomy, trisomy, and tetrasomy |
| nullisomy | the loss of both members of a homologous pair of chromosomes. 2n-2, n= haploid |
| monosomy | the loss of a single chromosome. 2n-1 |
| trisomy | the gain of a single chromosome, 2n+1 |
| tetrasomy | the gain of two homologous chromosomes, 2n+2 |
| effects of aneuploidy | disrupts gene dosage and often has severe phenotypic effects |
| what two syndromes result from sex-chromosome aneuploids? | Turner syndrome and Klinefelter syndrome |
| primary Down syndrome is caused by what? | the presence of three full copies of chromosome 21 |
| familial Down syndrome is caused by what? | the presence of two normal copies of chromosome 21 and a third copy that is attached to another chromosome through a translocation |
| translocation carriers | persons with the translocation (do not have Down syndrome) |
| all the chromosomes in an ___________ derive from one species | autopolyploid |
| all the chromosomes in an ___________ come from two or more species | allopolyploid |
| autoploidy is due to what? | accidents of meiosis or mitosis that produce extra sets of chromosomes, all derived from a single species |
| autoploidy: because all the chromosome sets in autopolyploids are from the same species, they are __________ and attempt to align in prophase I of meiosis, which usually results in sterility | homologous |
| autoploidy: no matter how the three homologous chromosomes align, their random segregation will create ________ ______- | unbalanced gametes (with various numbers of chromosomes) |
| when an unbalanced gamete fuses with a normal gamete, the resulting zygote has different numbers of chromosomes. This difference creates unbalanced _____ ________ in the zygote, which is often lethal | gene dosage |
| allopolyploidy arises from what? | hybridization between two species; the resulting polyploid carries chromosomes sets derived from two or more species |
| allopolyploidy: amphidiploid | type of allopolyploid, consisting of two combined diploid genomes |
| allopolyploidy: although the chromosome number for amphidiploids has doubled, it is functionally diploid: every chromosome has one and only one homologous partner, which is exactly what meiosis requires for proper segregation. now what? | the amphidiploid can now undergo normal meiosis to produce balanced gametes having six chromosomes |
Created by:
cmccartney2
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