Chapter 6 - Eukaryotic Linkage Flashcards
The transmission of genes close to one another on the same chromosome violates this Mendelian law
Law of independent assortment
This term refers to two or more genes that are physically linked on the same chromosome
Synteny
Genes located close together on a chromosome tend to be transmitted as a unit, influencing inheritance patterns in this phenomenon
Genetic linkage
Chromosomes are called this, as they contain a group of genes that are linked together
Linkage groups
How many linkage groups do humans have?
24 (22 autosomal, 1 X, 1 Y)
This type of cross studies linkage between two genes
Two-factor cross
This type of cross studies linkages between three genes
Three-factor cross
Genes that are far apart on the same chromosome may independently assort from each other due to this
Crossing over
What are three types of crossing over?
Single, double, multiple
In 1905, these two scientists conducted a cross in sweet peas involving two different traits
William Bateson and Reginald Punnett
What two sweet pea traits did Bateson and Punnett study?
Flower color and pollen shape
Did Bateson and Punnett obtain the expected 9:3:3:1 phenotypic ratio in the F2 generation for their two-factor sweet pea crosses?
No
During which phase of meiosis does crossing over occur?
Prophase I
Replicated sister chromatid homologs associate as these
Bivalents
Crossing over may produce these genotypes
Recombinant genotypes
These are haploid cells that contain a combination of alleles not found in the original chromosomes
Nonparental or recombinant cells
These offspring are produced by the exchange of DNA between two homologous chromosomes during meiosis in one or both parents, leading to a novel combination of genetic material
Recombinant offspring
The first direct evidence of linkage came from studies conducted by this scientist
Thomas Hunt Morgan
Thomas Hunt Morgan studied body color, eye color and wing length inheritance patterns in this organism
Drosophila
Thomas Hunt Morgan considered the previous studies of this cytologist to explain his data
F. A. Janssens
Janssens microscopically observed these and proposed that crossing over involves a physical exchange between homologous chromosomes
Chiasmata
Morgan realized that crossing over between these chromosomes was consistent with his data
Homologous X chromosomes
These three scientists performed crosses involving two linked genes to obtain direct evidence that genetic recombination is due to crossing over
Harriet Creighton and Barbara McClintock and Curt Stern
This is performed to determine the linear order of linked genes along the same chromosome
Genetic mapping
The relative distance between linked genes is based on this
The likelihood that a crossover will occur between them
Experimentally, the percentage of these is correlated with the distance between the two genes
Recombinant offspring
What is the equation for gene map distance?
Map distance = # of recombinant offspring/Total # of offspring x 100
What are the units of distance in genetic maps?
Map units (mu) [or centiMorgans (cM)]
One mu is equivalent to this
1% recombination frequency
Genetic mapping experiments are typically accomplished by conducting this
Testcross
Multiple crossovers set a quantitative limit on these as the physical distance increases
Measurable recombination frequencies
Data from this type of cross can also yield additional information about map distance and gene order
Three-factor cross
In the offspring of crosses involving linked genes, these phenotypes occur most frequently
Nonrecombinant phenotypes
In the offspring of crosses involving linked genes, these phenotypes occur least frequently
Double crossover phenotypes
In the offspring of crosses involving linked genes, these phenotypes occur with intermediate frequency
Single crossover phenotypes
This crossover separates the gene in the middle from the other two genes at either end
Double crossover
This term refers to the decreased probability that a second crossover will occur near a first crossover
Positive interference
What is the expression for interference?
I = 1- C
What is C in the expression for interference?
Coefficient of coincidence
The coefficient of coincidence (C) is the observed number of double crossovers divided by this
Expected number of double crossovers
Much of our earliest understanding of genetic recombination comes from the genetic analysis of this group of organisms
Fungi
Are fungi typically haploid or diploid?
Haploid
Do haploid fungal cells reproduce sexually or asexually?
Asexually
These fungal cells have been particularly useful to geneticists because of their unique style of sexual reproduction
Sac fungi (ascomycetes)
Ascomycete meiosis produces four of these haploid cells
Spores
A group of 4 spores is this
Tetrad
This is a sac in which fungal spore tetrads are enclosed
Ascus
Some fungi species form this many spores following a mitotic division of a tetrad
Octad
What characteristic of asci makes them good for genetic researchers to study?
All the spores within one ascus are the product of a single meiotic division
If an ascus has a tetrad with nonrecombinant allele arrangements, it is said to have this
Parental ditype (PD)
If an ascus has two nonrecombinant and two recombinant cells, it is called this
Tetratype (T)
If an ascus has four recombinant cells, it is this
Nonparental ditype (NPD)
If two genes assort independently, the number of asci with a parental ditype is expected to equal the number of asci with this
Nonparental ditype
A nonparental ditype can only be produced from this
Double crossover
1/4 of all double crossovers are this
Nonparental ditypes
These two tetrad classifications are ambiguous and can be derived in two different ways
Parental ditype and tetratype
What is the formula for finding map distances from fungal tetrad analysis (without accounting for double crossovers)?
Map distance = Nonparental ditypes (NPD) + 1/2 * Tetratypes (T)
/
Total number of asci * 100
What is the more precise way to calculate map distance using fungal tetrads, accounting for double crossovers?
Map distance = Single crossover tetrads + 2 * Double crossover tetrads / Total number of asci * 0.5 * 100
