Chapter 6 - Genetic Linkage and Mapping in Eukaryotes Flashcards
How is the law of independent assortment violated?
Transmission of genes close to each other on the same chromosome
When two or more genes are located on the same chromosome and physically linked
Synteny
When genes close together on a chromosome are transmitted as a unit
Genetic linkage
Chromosomes are called…
Linkage groups
Study of linkage between two genes
Two-factor cross
Study of linkage between three genes
Three-factor cross
Genes that are far apart on the same chromosome can independently assort due to…
Crossing over
Suggested that the transmission of two traits from parents could be somewhat coupled
Bateson and Punnett
Replicated sister chromatid homologues associate as
Bivalents
Crossing over may produce
Recombinant genotypes
Haploid cells that contain a combination of alleles NOT found in the original chromosomes
Recombinant cells
Produced during the exchange of DNA between two homologous chromosomes during meiosis in one or both parents to create a novel combination of genetic material
Recombinant offspring
First direct evidence of linkage came from studies by
Thomas Hunt Morgan
Conducted experiments involving two linked genes to obtain evidence that genetic recombination comes from crossing over
Creighton, McClintock and Stern
The specific location a gene is on a chromosome
Locus
Used to determine that linear order of linked genes along the same chromosome
Genetic mapping
Uses of genetic mapping
Understanding complexity, cloning, understanding of evolution, diagnosis of disease, odds of having children with a disease, and improvement of agriculturally important strains
What is the relative distance between linked genes based on
The likelihood that a crossover would occur
Percentage of recombinant offspring is correlated to
The distance between the two genes
Genes that are far apart result in
Many recombinant offspring
Close genes result in
Few recombinant offspring
Map distance equals
Percentage of recombinant offspring out of total offspring
Units of map distance
Map units, centiMorgans
A testcross is expected to yield a maximum of…
50% recombinant offspring
Separates the gene in the middle from the other two genes at either end
Double crossover
When a first crossover decreases the probability that a second will occur nearby
Interference
Equation for interference
I = 1-C
What does C represent
Coefficient of coincidence
Equation for C
Observed number of double crossovers / expected number of double crossovers
Haploid cells reproduce…
Asexually
In Ascomycetes, meiosis produces four haploid cells called…
Spores
A group of 4 spores is a…
Tetrad
The spores are enclosed in a sac called an…
Ascus
Tetrad may contain four haploid cells with nonrecombinant arrangements of alleles
Parental ditype
An ascus may have two nonrecombinant cells and two recombinant cells
Tetratype
An ascus with a nonparental ditype contains…
Four cells with recombinant genotypes
If the two genes assort independently…
50% recombinant spores are produced
If the two genes are linked…
The type of crossover between them determines what type of ascus is produced
The nonparental ditype can only be produced from…
Double crossover
Crossing over in mitosis is expected to be much less likely than during meiosis, producing a new combination of alleles
Mitotic recombination
If mitotic recombination occurs during an early stage of embryonic development…
Daughter cells containing recombinant chromosomes continue to divide which can result in a patch of tissue with different characteristics than the rest of the organism
Who discovered changes from mitotic recombination?
Curt Stern
