Chapter 17 Flashcards
Define acentric chromosome
- a chromosome having no centromere
Define acentric fragment
- a chromosome fragment having no centromere
Define adjacent-1 segregation
- in a reciprocal translocation, the passagr of a translocated and a normal chromosome to each of the pole
Define allopolyploid
- a polyploid formed from the union of 2 separate chromosome sets and their subsequent doubling
Define alternate segregation
- in a reciprocal translocation the passage of both normal chromosomes to one pole and both translocated chromosomes to the other pole
Define amphidiploid
- a polyploid formed from the union of 2 separate chromosome sets and their subsequent doubling
- an allopolyploid
Define anaphase bridge
- in a dicentric chromosome, the segment between the centromeres being drawn to opposite poles at nuclear division
Define aneuploid
- a genome having a chromosome number that differs from the normal chromosome number for the species by a small number of chromosomes
Define autopolyploid
- polyploid formed from the doubling of a single genome
Define balanced rearrangement
- a change in the chromosomal gene order that does not remove or duplicate any DNA
- the 2 classes of balanced rearrangement are inversions and reciprocal translocations
Define balancer
- a chromosome with multiple inversions, used to retain favourable allele combinations in the uninverted homolog
Define bivalent
- 2 homologous chromosomes paired at meiosis
Define chromosome mutation
- any type of change in chromosome structure or number
Define deletion
- the removal of a chromosomal segment from a chromosome set
Define deletion loop
- the loop formed at meiosis by the pairing of a normal chromosome and a deletion-containing chromosome
Define deletion mapping
- the use of a set of known deletions to map new recessive mutations by pseudodominance
Define dicentric bridge
- in a dicentric chromosome, the segment between the centromeres being drawn to opposite poles at nuclear division
Define dicentric chromosome
- a chromosome with 2 centromeres
Define disomic
- an abnormal haploid carrying 2 copies of one chromosome
Define dosage compensation
- the process in organisms using a chromosomal sex-determination mechanism (such as XX vs XY) that allows standard structural genes on the sex chromosome to be expressed at the same levels in females and males, regardless of the number of chromosomes
- in mammals, dosage compensation operates by maintaining only a single active X chromosome in each cell
- in Drosophoila, it operates by hyperactivating the male X chromosome
Define Down syndrome
- an abnormal human phenotype, including mental retardation, due to a trisomy on chromosome 21
- more common in babies born to older mothers
Define duplication
- more than one copy of a particular chromosomal segment in a chromosome set
Define embryoid
- a small dividing mass of monoploid cells, produced from a cell destined to become a pollen cell by exposing it to cold
Define euploid
- a cell having any number of complete chromosome sets or an individual organism composed of such cells
Define gene balance
- the idea that a normal phenotype requires a 1:1 relative proportion of genes in a genome
Define gene-dosage effect
1) proportionality of the expression of some biological function to the number of copies of an allele present in the cell
2) a change in phenotype caused by an abnormal number of wild-type alleles (observed in chromosomal mutations)
Define genetic load
- the total set of deleterious alleles in an individual genotype
Define hexaploid
- a cell having six chromosome sets or an organism composed of such cells
Define homeologous chromosome
- partly homologous chromosomes, usually indicating some original ancestral homology
Define insertional duplication
- a duplication in which the extra copy is not adjacent to the normal one
Define intragenic deletion
- a deletion within the gene
Define inversion
- a chromosomal mutation consisting of the removal of a chromosome segment, its rotation through 180*, and its reinsertion in the same location
Define inversion heterozygote
- s diploid with a normal and inverted homolog
Define inversion loop
- a loop formed by meiotic pairing of homologs in an inversion heterozygote
Define Klinefelter syndrome
- an abnormal human male phenotype due to an extra X chromosome (XXY)
Define monoploid
- a cell having only one chromosome set (usually as an aberration) or an organism composed of such cells
Define monosomic
- a cell or individual that is basically diploid but has only one copy of one particular chromosome type and thus has chromosome number 2n+1
Define multigenic deletion
- a deletion of several adjacent cells
Define nonallelic homologous recombination (NAHR)
- crossing over between short homologous units found at different chromosomal loci
Define nondisjunction
- the failure of homolog (at meiosis) or sister chromatids (at mitosis) to separate properly to opposite poles
Define nullisomic
- refers to a cell or an individual organism with one chromosomal type missing
- has a chromosome number like n-1 or 2n-1
Define paracentric inversion
- an inversion not including the centromere
Define parthenogenesis
- the production of offspring by a female with no genetic contribution from the male
Define pentaploid
- an individual organism with with 5 sets of chromosomes
Define pericentric inversion
- an inversion that includes the centromere
Define polyploid
- a cell having 3 or more chromosome sets pr an organism composed of such cells
Define polytene chromosome
- a giant chromosome in specific tissues of some insects, produced by an endomitotic process in which the multiple DNA sets remain bound in a haploid number of chromosomes
Define position-effect variegation
- PEV
- variegation caused bt the inactivation of a gene in some cells through its abnormal juxtaposition with heterochromatin
Define pseudodominance
- the sudden appearance of a recessive phenotype in a pedigree, sue to a deletion of a masking dominant gene
Define pseudolinkage
- the appearance of linkage from 2 genes on translocated chromosomes
Define rearrangement
- the production of abnormal chromosomes by the breakage and incorrect rejoining of chromosomal segments
- ex inversions, deletions and translocations
Define segmental duplication
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Define semisterility
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Define tandem duplication
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Define tetraploid
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Define translocation
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Define triploid
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Define trisomic
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Define trivalent
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Define Turner syndrome
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Define unbalanced rearrangement
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