genetics ch 10

Chromosome break point

Location where both DNA strands are severed during chromosome breakage

Terminal deletion

Loss of the end of a chromosome arm including a telomere

Acentric fragment

Chromosome fragment lacking a centromere that is usually lost during cell division

Partial deletion heterozygote

Organism with one normal chromosome and one chromosome missing a segment

Cri-du-chat syndrome

Disorder caused by deletion on chromosome 5 producing a cat-like cry in infants

Interstitial deletion

Loss of an internal segment of a chromosome due to two breaks

Unequal crossover

Misaligned recombination resulting in duplication on one chromosome and deletion on the other

Partial duplication heterozygote

Organism with one normal chromosome and one chromosome containing duplicated segments

FISH (fluorescent in situ hybridization)

Molecular technique using fluorescent probes to detect DNA sequences

Deletion mapping

Technique used to locate genes based on deletions that reveal recessive alleles

Pseudodominance

Expression of a recessive allele due to deletion of the dominant allele

Chromosome inversion

Rearrangement where a chromosome segment is reversed in orientation

Paracentric inversion

Inversion that does not include the centromere

Pericentric inversion

Inversion that includes the centromere

Inversion heterozygote

Individual with one normal chromosome and one inverted chromosome

Inversion loop

Structure formed during pairing of inverted and normal homologs

Dicentric chromosome

Chromosome with two centromeres formed during crossing over in paracentric inversion

Acentric fragment (in inversion)

Fragment lacking centromere lost during cell division

Crossover suppression

Reduction in recombination within inverted regions

Chromosome translocation

Movement of chromosome segments to nonhomologous chromosomes

Nonreciprocal translocation

Transfer of a segment without exchange

Reciprocal translocation

Exchange of segments between two nonhomologous chromosomes

Robertsonian translocation

Fusion of two chromosomes reducing chromosome number

Translocation heterozygote

Individual with one normal and one translocated chromosome set

Alternate segregation

Separation pattern producing balanced gametes

Adjacent-1 segregation

Separation producing duplicated and deleted gene regions

Adjacent-2 segregation

Rare segregation where homologous centromeres move together

Semisterility

Reduced fertility due to abnormal gamete formation

Chromatin

Complex of DNA and protein that makes up chromosomes

Histone proteins

Basic proteins that bind DNA and help package it

Nonhistone proteins

Diverse proteins involved in chromosome structure and function

Nucleosome

Fundamental unit of chromatin consisting of DNA wrapped around histone proteins

Histone octamer

Complex of eight histone proteins forming nucleosome core

Linker DNA

DNA between nucleosomes

10-nm fiber

“Beads-on-a-string” chromatin structure

30-nm fiber

Coiled chromatin structure forming a solenoid

Chromosome scaffold

Protein framework that organizes chromatin loops

Matrix attachment regions (MARs)

Sites where chromatin loops attach to scaffold

Chromatin condensation

Process of compacting DNA for cell division

Position effect variegation (PEV)

Variation in gene expression due to chromatin position

Heterochromatin

Highly condensed chromatin with low gene expression

Euchromatin

Less condensed chromatin with active gene expression

Chromosome territories

Distinct regions occupied by chromosomes in the nucleus

Interchromosomal domains

Spaces between chromosome territories for molecular movement

Karyotype

Organized display of chromosomes used to detect abnormalities

Centromere

Region dividing chromosome into arms and attaching to spindle

p arm

Short arm of a chromosome

q arm

Long arm of a chromosome

Metacentric chromosome

Chromosome with centromere near the middle

Submetacentric chromosome

Chromosome with centromere slightly off center

Acrocentric chromosome

Chromosome with centromere near one end

Telocentric chromosome

Chromosome with centromere at the tip

Chromosome banding

Technique using stains to identify chromosomes by patterns

G-banding

Standard staining method using Giemsa dye

Fluorescent probes

Molecules that emit light to identify DNA sequences

Polyploidy

Condition of having more than two sets of chromosomes

Autopolyploidy

Polyploidy from duplication within a species

Allopolyploidy

Polyploidy from combining chromosomes of different species

Meiotic nondisjunction

Failure of chromosomes to separate during meiosis

Mitotic nondisjunction

Failure of chromosomes to separate during mitosis

Hybrid vigor

Increased growth and productivity in hybrids

Reproductive isolation

Inability to interbreed due to genetic differences

Nondisjunction

Failure of chromosomes or chromatids to separate properly

Aneuploidy

Abnormal number of chromosomes not equal to a full set

Euploid

Having complete sets of chromosomes

Trisomy

Condition with one extra chromosome (2n + 1)

Monosomy

Condition with one missing chromosome (2n − 1)

Gene dosage

Number of copies of a gene

Gene balance

Proper proportion of gene products for normal function

Down syndrome

Trisomy 21 causing developmental and physical abnormalities

Patau syndrome

Trisomy 13 with severe abnormalities

Edwards syndrome

Trisomy 18 causing developmental defects

Klinefelter syndrome

XXY condition in males

Turner syndrome

XO condition in females

Triple X syndrome

XXX condition in females

Jacob syndrome

XYY condition in males

Down syndrome critical region (DSCR)

Region on chromosome 21 linked to Down syndrome traits

DYRK gene

Gene associated with cognitive defects in Down syndrome

DSCAM gene

Gene involved in nervous system and heart development

Mosaicism

Presence of genetically different cell populations in one individual

Uniparental disomy

Inheritance of both chromosomes from one parent

Trisomy rescue

Loss of one chromosome from a trisomic zygote