Chapters 4, 5, 18 Flashcards
Recombination map
A chromosome map in which the positions of loci shown are based on recombinant frequencies.
Linked genes
The situation in which two genes are on the same chromosome as deduced by recombinant frequencies less than 50 percent.
Thomas Hunt Morgan’s experiment with ____ led to linkage hypothesis
Fruit flies
When two genes are close together on the same chromosome pair (that is, when they are linked), they do not ______
Assort independently
a recombinant frequency of _____ percent is a diagnostic for linkage.
Less than 50
During meiosis, when duplicated homologous chromosomes pair with each other, a cross-shaped structure called a ____ often forms between two nonsister chromatids.
Chiasma
For linked genes, recombinants are produced by crossovers between _____ chromatids during meiosis.
nonsister
cis formation
In a heterozygote having two mutant sites within a gene or within a gene cluster, the arrangement A1A2/a1a2.
trans formation
In a heterozygote with two mutant sites within a gene or gene cluster, the arrangement a1 +/+ a2.
A ____ is the breakage of two DNA molecules at the same position and their rejoining in two reciprocal recombinant combinations.
crossover
To study double crossovers, we need ___ linked genes
3
Crossovers between sister chromatids are ____
Rare
A chromosome map; an abstract map of chromosomal loci that is based on recombinant frequencies.
Linkage map
A distance on the chromosome map corresponding to 1 percent recombinant frequency
genetic map unit (aka centimorgan)
Three point testcross
A testcross in which one parent has three heterozygous gene pairs.
larger RF value indicates 2 loci are
further apart
Typically, for linked genes, we have the eight genotypes at the following frequencies:
two at high frequency
two at intermediate frequency
two at a different intermediate frequency
two rare
Interference
A measure of the independence of crossovers from each other, calculated by subtracting the coefficient of coincidence from 1.
a crossover does ____ the probability of a crossover in an adjacent region.
reduce
coefficient of coincidence (c.o.c.)
The ratio of the observed number of double recombinants to the expected number.
Interference = (give equation)
1 - (observed double recombinant frequency / expected double recombinant frequency)
when there are not any observed double recombinants, what is c.o.c.?
zero
Longer regions have ___ crossovers and thus _____ recombinant frequencies
more; higher
Molecular marker
a locus of heterozygosity due to changes in DNA sequences (e.g. nucleotide substitution, insertion , deletion etc.)
2 types of molecular markers
Single nucleotide polymorphisms (SNPs)
Simple sequence length polymorphism (SSLPs)
Advantage of using molecular markers:
(name 2)
Abundant
Mostly neutral (directly measure genotype)
haplosufficient
a single normal allele provides enough function, so A+A− individuals are healthy
Haploinsufficient
one wild type allele can not produce enough product
Dominant negative
Mutant allele acts as a spoiler
Incomplete Dominance
The heterozygote does not resemble either parents, it has an intermediate phenotype
(i.e. pink flowers with red and white parentals)
Codominance
Both alleles in a heterozygote express their phenotypes
(i.e. blood type AB)
hypostatic gene
one whose phenotype is altered by the expression of an allele at a separate locus, in an epistasis event.
one gene–one enzyme hypothesis
the idea that genes act through the production of enzymes, with each gene responsible for producing a single enzyme that in turn affects a single step in a metabolic pathway.
epistasis
the interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another.
auxotroph
a mutant organism (especially a bacterium or fungus) that requires a particular additional nutrient which the normal strain does not.
In dominant epistasis, only a single copy of an allele is required to inhibit the expression of an allele at a different locus, which gives rise to the ____ ratio of the F2 generation.
12:3:1
leaky mutation
some function
null mutation
all function lost
An individual will lack essential function and die if there are null mutations in how many duplicate systems?
Both
3 colors of lab retrievers ratio
9:3:4
Yellow labs are the result of
recessive epistasis
Complementation
a relationship between two different strains of an organism which both have homozygous recessive mutations that produce the same phenotype
pleiotropy
the production by a single gene of two or more apparently unrelated effects.
haplotype
a unique combination of variants that reside near each other on a chromosome
Which organism can benefit from inbreeding?
Plants
If the association between the alleles at two loci is random, then the two loci are said to be at
linkage equilibrium.
Noncoding SNPs (ncSNPs) are found in
introns
mutation rate
the probability that a copy of an allele changes to some other allelic form in one generation.
Inbreeding can lead to a reduction in vigor and reproductive success called
inbreeding depression
Other than mutation, the only other means for new variation to enter a population is through
migration / gene flow
microsatellite
a tract of repetitive DNA in which certain DNA motifs are repeated, typically 5–50 times
flanking sequence
A DNA sequence located adjacent to a gene, either upstream from its 5’-end or downstream from its 3’-end.
