MT2 Flashcards
linkage
the association of two genes on the same chromosome
coupling configuration
arrangement of linked alleles in a dihybrid such that the two dominant
alleles are on a chromosome, the two recessive alleles are on the other chromosome (AB/ab)
repulsion configuration
arrangement of linked alleles in a dihybrid such that a dominant and a
recessive allele are together on each chromsome (Ab/aB)
cis dihybrid
a dihybrid in which the alleles are coupled (AB/ab)
trans dihybrid
a dihybrid in which the alleles are in repulsion (Ab/aB)
tetrad
(2) The four haploid product cells from a single meiosis (see the alternate definition provided
in Chapter 2)
octad
an ascus containing eight ascospores, produced in species in which the tetrad normally
undergoes a postmeiotic mitotic division
first division segregation
different alleles go into different nuclei at the first meiotic division
producing an MI division pattern of ascospores
second division segregation
different alleles go into different nuclei at the second meiotic division
producing an MII division pattern of ascospores
molecular marker
a site of DNA heterozgosity (difference), not necessarily associated with
phenotypic variation, used as a tag for a particular chromosomal locus
single nucleotide polymorphism (SNP)
change in a single nucleotide that can be located within a gene or intergenic regions
restriction enzyme
(restriction endonuclease) – an enzyme that will recognize specific target
nucleotide sequences in DNA and break the DNA chain at those points
simple sequence length polymorphism (SSLP)
the presence of different numbers of short or simple
repetitive elements at one particular locus in different homologous chromosomes
haplotype
a genetic class described by a sequence of DNA or of genes that are together on the same
physical chromosome (a chromosomal segment defined by the array of markers it carries)
complete dominance
alleles which, when combined in the heterozygote show a phenotype
indistinguishable from one of the homozygotes
haplosufficiency
one copy of the normal gene is able to confer a normal phenotype
haploinsufficiency
one copy of the normal gene is unable to confer the normal phenotype
codominance
alleles which, when combined in the heterozygote show phenotypic characteristics of
both homozygotes
incomplete dominance
alleles which, when combined in the heterozygote show a phenotype
intermediate between the homozygotes
lethal allele
an allele whose expression results in the death of the individual expressing it (may be
recessive or dominant)
pleiotropic mutation
a mutation that affects several different phenotypic characteristics
prototroph
an organism that will survive on minimal medium (carbon source, inorganic salts, water)
auxotroph
an organism that will not survive on minimal medium, but whose growth depends on
supplementation of medium with a specific substance
complementation test
a test for determining whether two mutations are in different genes (they
complement) or the same gene (they fail to complement)
heterokaryon
cell with 2 nuclei in a common cytoplasm (results from fusing two haploid cells)
epistasis
the phenotype of a mutant allele at one gene overrides the phenotype of a mutant allele at
another gene, such that the double mutant has the same phenotype as the first mutant
suppression
a mutation in one gene can cancel the effect of a mutation in a second gene, resulting in
a wild type phenotype
genetic redundancy
(duplicate genes) – Two independent genes that produce the same phenotypic
effect when present individually or when present together
penetrance
the proportion of individuals with a specific genotype who show that genotype phenotypically
expressivity
the degree to which a particular genotype is expressed in the phenotype
chromosomes break and re-join during pairing, what is the visual evidence of that?
chiasmata
crossing over occurs where?
chromatids (genes on the same chromosome)
