Genetics Test 2 Flashcards
Social sex determination
Many fish undergo sex reversal, depends on the mating system
Temperature dependent sex determination (TSD)
Controls sex determination in reptiles, crocodiles most turtles and some lizards: incubation temperature of egg drying embryonic development determines sex
Modifications at chromosome level
Phenotype variations (often substantial) result from changes of individual genes
Chromosome level mutations and aberrations
Total number of chromosomes vary, deletions, duplications, rearrangements
Aneuploidy
Organism gains or loses one or more chromosomes but not the entire set
Euploidy
Complete haploid sets of chromosomes beyond two are present (polyploidy more than 2, triploidy 3)
Nondisjunction
Gives rise to chromosome variation when paired homologs fail to disjoin during segregation (meisosis 1 or 2)
Monosomy
Loss of one chromosome producing 2n-1 complement, although a copy remains if one copy is lethal the organism is not viable
Haploinsufficiency
When one copy is not sufficient for an organism to survive
Trisomy
2n+1 chromosomes, addition produces more viable organisms, trisomes for autosomes are often lethal, plant trisomes are viable but the phenotype is altered
Trivalent
Three copies of chromosome are synapsed
Bivalent and univalent
Prior to first Miotic division, one bivalent and one univalent (an unpaired chromosome) may be present instead of a trivalent
Down syndrome
Trisomy of chromosome 21, has 12-14 defining characteristics (of which those affected experience 6-8)
Down syndrome critical region (DSCR)
Critical region of chromosome 21, genes in this region are dosage sensitive, responsible for many phenotypic associated syndromes
Origin of extra 21st chromosome
Nondisjunction of chromosome 21 during meiosis, homologs do not disjoin in anaphase 1 or 2, leads to n+1 gametes, ovum is source of 95% of trisomy cases, risk increases rapidly with maternal age
Diagnostic testing
Amniocentesis or chorionic villus (CVS) fetal cells are obtained from amniotic fluid or chorionic of placenta OR NIPGD fetal cells and DNA obtained from maternal circulation
Trisomics
Often found in spontaneously aborted fetuses
Polyploidy
More than two multiples of haploid chromosomes found
Autopolyploidy
Addition of one or more sets of chromosomes identical to haploid complement of same species
Allopolyploidy
Combination of chromosome sets from different species as consequence of hybridization
Allotetraploid
Polyploid contains equivalent of four haploid genomes derived from separate species
Amphidiploid
Allotetraploid with full diploid genome of each parent species
Endopolyploidy
Condition where any certain cells in diploid organism are polyploid, set of chromosomes replicates repeatedly without nuclear division
Chromosome rearrangements
Deletions, duplications, inversions, nonreciprocal trans locations, reciprocal trans locations
Alteration of chromosomes
Deletions and duplications (total amount of chromosomes changes)/inversions and translocations (same but rearranged)
Deletions
Missing region of chromosome
Completion loop
Synapsis between chromosome with large intercalary deletion and normal complete homolog, requires unparallel region of of normal homologous to loop out of linear structure into deletion or compensation loop
Cri-du-chat
Deletions of small terminal portion of chromosome 5p, segmented deletion, infants exhibit anatomical malformations
Duplication
Replicated segment of chromosome, single locus is present more than once in genome, can produce compensation loop, arise from unequal crossing over between synapsed chromosomes during meiosis
Gene redundancy
Ex. rRNA, multiple copies of genes encode for ribosomal RNA genes
Gene amplification
Another mechanism that increases rRNA, oocytes store nutrients including ribosomes, used by embryo in early development for rRNA synthesis
Gene duplication
Hypothesized to be major source of new genes, hypothesis supported by discovery of genes with substantial amount of DNA sequence in common, but distinct gene product
Copy number variants (CNVs)
Represent quantitative differences in number of large DNA sequences, found in coding and noncoding regions of genome, play crucial role in expression of traits
Inversion
Rearrangement of linear gene sequence, no loss of genetic information, segment of chromosome turned 180° within chromosome, requires two breaks in chromosomes and reinsertion inverted segment, may arise from chromosomal looping
Types of inversions
Paracentric (does not change the length of the two arms of the chromosome, centromere NOT part of inverted segment
Pericentric (centromere IS part of inverted segment)
Inversion loop
Inverted and noninverted chromosomes in meiosis paired only if they form inversion loop
Translocation
Movement of chromosomal segment to new location in genome
Reciprocal translation
Involved exchange of segments between two nonhomologous chromosomes, genetic mutation is lot or gained, has unusual synapsis configuration during meiosis
Segregation patterns
Alternate segregation (pattern at first meiotic division, complete set of genetic information) adjacent segregation (leads to gametes containing duplications and deficiencies)
Robertsonian translocation
Involves breaks at extreme ends of the short arms of two nonhomologous chromosomes, small segments are lost, large submetacentric chromosome produced
Fragile sites
More susceptible to chromosome breakers when cultured in a sense of folic acid or other chemicals, sites imdicate regions of non-rightly coiled chromatin
Fragile X syndrome (Martin bell syndrome)
Folate sensitive site on X chromosome exhibits FXS, most common form of inherited mental retardation; dominant trait
Semi conservative DNA replication
Each replicated DNA molecule consists of one old strand and one new strand
Conservative DNA replication
Two newly synthesized strands come together, original helix is conserved
Dispersive DNA replication
Parental strands are dispersed into two new double helices
Meselson and Stahl
Provided strong evidence that DNA is semiconservative in prokaryotes