Gene Interaction Flashcards
How do chromosomes pair up during meiosis in tetraploids?
Two bivalents or one quadrivalent
Define recombination frequency
a measure of genetic linkage and is used in the creation of a genetic linkage map. Recombination frequency (θ) is the frequency with which a single chromosomal crossover will take place between two genes during meiosis
Define
Barr body
the inactive X chromosome in female somatic cells
True or False:
The chromosomal complement of autotriploids is balanced
True
Why are autosomal aneuploids higher in older mothers?
In human females, meiosis begins in the foetus but arrests at the diplotene stage of prophase I.
Meiosis only recommences when the egg is released at ovulation
As egg ages up to 45 year, chance of nondisjunction increases potentially due to spindles being less efficient with age of the cell
How do you calculate genotype frequency?
Number of individuals with genotype divided by total population number multiplied by 100
Why is it useful to generate genetic maps?
To determine whether mutations affect different genes or not To clone genes using their map position To enhance our ability to predict inheritance patterns Very useful for genome sequencing projects
A Drosophila has the sex complement XXY. What is it’s sex? Is it viable? Is it fertile?
Female
Viable
Infertile
Definition
a genetic condition in which a male has an extra Y chromosome. Symptoms are usually few. They may include being taller than average, acne, and an increased risk of learning problems
Double Y syndrome
Define coupling phase
a phase in which the dominant alleles of two or more genes present in the same chromosome and hence linked together. Dominant alleles are contributed by the same parents.
True or False:
Most trisomy 21 babies do not live to term
True
80% do not successfully come to term
Define acrocentric
A chromosome in which the centromere is located quite near one end of the chromosome
Definition
the first step in X inactivation where the X inactivation centre (Xic) of one of the X chromosome is initiated by the expression of the gene XIST
Initiation
How do you calculate recombination frequency?
RF = Number of recombinants / Total progeny x 100
Definition
the final step in X inactivation where the inactivation is maintained by continued XIST expression in the Barr body in interphase
Maintenance
Definition
a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology
Population genetics
Definition
a branch of genetics that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis
Cytogenetics
If an individual is homologous for an inversion, what happens during meiosis?
Meiosis proceeds as normal
What is this an example of?
Nonreciprocal translocation
What is an example of a biochemical polymorphism?
Alcohol dehydrogenase allozyme
Define positive interference
the phenomenon that the occurrence of a crossover reduces the probability of another crossover in its vicinity
What is the effect of mitotic nondisjunction?
A permanent change in all descendant cells leading to a mosaic
Define
Copy number variation
a phenomenon in which sections of the genome are repeated and the number of repeats in the genome varies between individuals in the human population
Define
Giemsa stain
a stain that labels the phosphate groups of DNA and attaches itself to regions of DNA where there are high amounts of adenine-thymine bonding. Giemsa stain is used in Giemsa banding, commonly called G-banding, to stain chromosomes and often used to create a karyogram
Definition
The chromosomal variation in the normal complete set of chromosomes in a cell or an organism resulting in a multiple of the haploid or basic number of chromosomes
Euploid
Definition
a chromosome formed by three homologous chromosomes that lie close together or appear to join completely during meiosis
Trivalent
What are the male and female sex chromosome system in Drosophila ?
F: XX
M: XY
What is a somatic cell hybrid?
Somatic cell hybrids are formed through fusion of different somatic cells of the same or different species. Somatic cell hybrids contain the nucleus of both cells and in addition all cytoplasmic organelles from both parents
Define
Population
a group of organisms of a species that interbreed and live in the same place at a same time
Roughly how many crossovers occur in an average human chromosome at each meiosis?
2-3 crossovers
When there is no gain or loss of genetic material, what type of rearrangement is it?
Balanced
Very small numbers in the size of a population (bottlenecks) can lead to:
a) all individuals migrating to a new environment
b) natural selection against unfit individuals
c) mutation of A to a, and of a to A
d) genetic drift
d) genetic drift
What is this an example of?
Duplication
A Drosophila has the sex complement X. What is it’s sex? Is it viable? Is it fertile?
Male
Viable
Infertile
Define
Trisomy
a condition in which an extra copy of a chromosome is present in the cell nuclei, causing developmental abnormalities
True or False:
Autotriploids are viable but not fertile
True
(due to unbalanced gametes)
Definition
a congenital disorder arising from a chromosome defect, causing intellectual impairment and physical abnormalities including short stature and a broad facial profile. It arises from a defect involving chromosome 21, usually an extra copy (trisomy-21)
Down syndrome
What gametes are produced in nondisjunction II in males?
Define short tandem repeat (STR)
another name for a microsatellite
Definition
regions on the X and Y chromosomes where crossing over occurs exhibiting autosomal, rather than sex-linked, pattern of inheritance
Pseudo-autosomal
Definition
variant forms of an enzyme which differs structurally but not functionally from other versions coded for by different alleles at the same locus
Allozymes
Define loci
a fixed position on a chromosome, like the position of a gene or a marker
Define
Euploid
The chromosomal variation in the normal complete set of chromosomes in a cell or an organism resulting in a multiple of the haploid or basic number of chromosomes
What are the possible gametes for a paracentric inversion with a crossovers within the inverted region?
Definition
the conformation of pairing up of homologous chromosomes in meiosis that are heterozygous for inversions
Inversion loop
Define interference
the term used to refer to the non-random placement of crossovers with respect to each other during meiosis
Define
Oogenesis
the production or development of an ovum
What are the possible gametes of a pericentric inversion with no crossover within the inverted region?
Definition
the existence of two different forms (as of color or size) of a species especially in the same population
Phenotypic dimorphism
How does false exclusion occur in DNA profiling?
- Technical problems such as ‘allele drop-out’
- Contamination or mixed source of DNA
- Human error
Definition
a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13
Patau syndrome
Definition
the condition of having a diploid chromosome complement in which one chromosome lacks its homologous partner
Monosomy
Definition
a technique used in cytogenetics to produce a visible karyotype by staining condensed chromosomes. It is useful for identifying genetic diseases through the photographic representation of the entire chromosome complement. Also known as Giemsa banding
G-banding
Which gene determines maleness?
SRY
How do ring chromosomes form?
Why might autotriploids be desirable in plants?
They are sterile so they do not produce seeds (i.e. bananas)
Define
Robertsonian translocation
the most common form of chromosomal rearrangement where the participating chromosomes break at their centromeres and the long arms fuse to form a single, large chromosome with a single centromere
Define
Hardy-Weinberg principle
a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors
Definition
a type of natural selection in which the population mean stabilizes on a particular non-extreme trait value
Stabilising selection
Definition
an event that drastically reduces the size of a population producing a decrease in the gene pool of the population because many alleles, or gene variants, that were present in the original population are lost
Bottle neck
Define
Polyploidy
the state of a cell or organism having more than two paired (homologous) sets of chromosomes
What type of dominance allows us to determine genotype from phenotype?
Incomplete and co-dominance
True or False:
Once produced, a autotetraploid is an instant new species
True
(they are reproductively isolated from its diploid ancestor)
A Drosophila has the sex complement Y. What is it’s sex? Is it viable? Is it fertile?
Not viable
True or False:
The Hardy-Weinberg Principle describes a gene pool of a population that is evolving
False
Describes gene pool of a population that is no evolving
What would the recombinant frequency be if crossovers never occur between two gene loci?
0
What are the consequences of balanced translocations?
- Breakpoints can disrupt important genes
- Individuals heterozygous for a translocation have a variable risk of producing unbalanced gametes
Define
G-banding
a technique used in cytogenetics to produce a visible karyotype by staining condensed chromosomes. It is useful for identifying genetic diseases through the photographic representation of the entire chromosome complement. Also known as Giemsa banding
How do you calculate the degree of interference?
1 - coefficient of confidence (c)
Definition
a group of organisms of a species that interbreed and live in the same place at a same time
Population
Define
Phenotypic dimorphism
the existence of two different forms (as of color or size) of a species especially in the same population
Definition
a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors
Hardy-Weinberg principle
Why are 3 point crosses more accurate than 2 point crosses?
3 point crosses are able to include double crossovers
Definition
an unbalanced structural abnormality in which the arms of the chromosome are mirror images of each other.
Iso-chromosome
Define
Edwards syndrome
a genetic disorder caused by a third copy of all or part of chromosome 18
The simplest variant of a DNA sequence is called what?
Single nucleotide polymorphisms (SNPs)
What is it called when two genes are on a single pair of homologs and no exchange occurs? What is the F2 ratio?
Complete linkage 3:1
Definition
having the centromere situated so that one chromosome arm is somewhat shorter than the other
Submetacentric
True or False:
Unequal crossing over can occur between non-sister chromatids in both meiosis and mitosis
False
Unequal crossing over can occur between non-sister chromatids in meiosis but it only occurs between sister chromatids during mitosis
A RF of more than what requires a chi squared test to see if the genes are linked?
25
Define metacentric
having the centromere medially situated so that the two chromosomal arms are of roughly equal length
Define
Allodiploid
having two complete sets of chromosomes derived from two different species
Definition
a phenomenon in which sections of the genome are repeated and the number of repeats in the genome varies between individuals in the human population
Copy number variation
Define
Cytogenetics
a branch of genetics that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis
Define
Morphological
relating to the form or structure of things
If crossing over occurs during mitosis early in development, what will happen?
It will give rise to a patch of tissue different to the rest called a mitotic clone
True or False:
All genes on inactivated X chromosome are inactivated
False
~15% are not
Which of the following techniques allows the visualisation of initially smalle amounts o a particular stretch of DNA? a) Southern Blotting b) Cloning into bacteria c) PCR d) Combination of above
d) Combination of above
If the observed number of crossovers is more than expected what has occurred?
Negative interference
Define
Monosomy
the condition of having a diploid chromosome complement in which one chromosome lacks its homologous partner
Define
Maintenance
the final step in X inactivation where the inactivation is maintained by continued XIST expression in the Barr body in interphase
Where is gene B localised?
Chromosome 3
What are the problems with DNA fingerprinting?
- Southern blots require large amounts of DNA (several micrograms)
- The DNA must be intact (can’t reliably use degraded samples)
- Can be hard to interpret - are similar bands really the same allele from the same locus?
What are the phenotypic characteristics of allopolyploids?
Resembles a blend of the parent species
What type of phase is this? Ab/aB
Repulsion phase
What is an inactivated X chromosome called?
Barr body
Definition
a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone
Balancing selection
Definition
an evolutionary process by which the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population
Frequency-dependent selection
A human recessive disorder albinism occurs in 1/10,000 births.
What is the expected frequency of carriers?
What is the gene that regulates X inactivation?
XIST
Definition
evolutionary change within a species or small group of organisms, especially over a short period.
Microevolution
Definition
an individual or strain whose chromosome complement consists of more than two complete copies of the genome of a single ancestral species
Autopolyploid
Definition
a multinucleate cell that contains genetically different nuclei
Heterokaryon
When there is a gain or loss of genetic material, what type of rearrangement is it?
Unbalanced
What is the maximum proportion of the genome that can be deleted without it being lethal?
2%
Definition
a sex-determining gene on the Y chromosome in mammals that determines maleness and is essential for development of the testes
SRY
What is somatic polyploidy?
Normal variation in euploidy in certain tissues
What are the phenotypic characteristics of autopolyploids?
Resembles parent species, larger and slower growing
What are duplications caused by?
Mostly caused by abnormal crossing over of chromosome mispair due to presence of repeated sequences in genome
What is the difference between DNA fingerprinting and DNA profiling?
Define
Chromosome painting
The use of fluorescent-tagged chromosome-specific dispersed repeat DNA sequences to visualize specific chromosomes or chromosome segments by in situ DNA hybridization and fluorescence microscopy
SRY was located through rare abnormal cases of XX males and XY females. What happens to the SRY in these cases?
SRY gene is now on the X in 46, XX males
SRY gene is not on the Y in 46, XY females
- Arises by rare crossovers below the SRY gene at meiosis
How many chromosomes do humans have?
46
Define
Fluorescent in situ hybridisation (FISH)
a molecular cytogenetic technique that uses fluorescent probes that bind to only those parts of the chromosome with a high degree of sequence complementarity
Define restriction enzymes
an enzyme produced chiefly by certain bacteria, that has the property of cleaving DNA molecules at or near a specific sequence of bases
True or False:
Allodiploids are fertile
False
True or False:
Allopolyploid mammals are not usually viable
True
(there are exceptions i.e. mule)
Define
Pseudo-autosomal
regions on the X and Y chromosomes where crossing over occurs exhibiting autosomal, rather than sex-linked, pattern of inheritance
Define
Pericentric inversion
a reversal of the normal order of genes in a chromosome segment involving parts of a chromosome at both sides of the centromere
Define
Trivalent
a chromosome formed by three homologous chromosomes that lie close together or appear to join completely during meiosis
Definition
A region on the long (q) arm of chromosome 21 thought to be responsible for some, if not all, of the features of Down syndrome
Down syndrome critical region (DSCR)
Define
Dosage compensation
the process by which organisms equalize the expression of genes between members of different biological sexes
Define
Polymorphism
the presence of genetic variation within a population, upon which natural selection can operate
The distance between two loci that will generate 1% recombination between them is…
1 map unit
What are the defects caused by deletions the result of?
Haplo-insufficiency
Define
Dicentric chromosome
an abnormal chromosome with two centromeres. It is formed through the fusion of two chromosome segments, each with a centromere, resulting in the loss of acentric fragments (lacking a centromere) and the formation of dicentric fragments
What do you need to consider if the map distance between the outer loci is less than the sum of the teo internal regions?
Double recombination evens
Definition
an abnormal chromosome with two centromeres. It is formed through the fusion of two chromosome segments, each with a centromere, resulting in the loss of acentric fragments (lacking a centromere) and the formation of dicentric fragments
Dicentric chromosome
Definition
a product of reciprocal translocation that occurs at anaphase I that results in all gametes being unbalanced. The centromeres from the homologous chromosomes are separated
Adjacent I orientation
Define
Submetacentric
having the centromere situated so that one chromosome arm is somewhat shorter than the other
Define
Balancing selection
a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone
Define gel electrophoresis
a laboratory method used to separate mixtures of DNA, RNA, or proteins according to molecular size. In gel electrophoresis, the molecules to be separated are pushed by an electrical field through a gel that contains small pores
Definition
A type of chromosome rearrangement involving the exchange of chromosome segments between two chromosomes that do not belong to the same pair of chromosomes
Reciprocal translocation
What is the maximum recombinant frequency between two loci?
50
Define southern blotting
a procedure for identifying specific sequences of DNA, in which fragments separated on a gel are transferred directly to a second medium on which assay by hybridization may be carried out
What circumstances can increase the effect of genetic drift?
Bottleneck
Founder effects
Definition
a condition characterised by the presence of an extra X chromosome in each cell of a female
Triple X syndrome
Is Adjacent I balanced or unbalanced?
Unbalanced
If a population size is not very large, what causes changes to genotype and allele frequency?
Genetic drift
Define
Double Y syndrome
a genetic condition in which a male has an extra Y chromosome. Symptoms are usually few. They may include being taller than average, acne, and an increased risk of learning problems
True or False:
Many small duplications have no phenotypic effect
True
Which part of the human sex chromosomes always has one crossover?
The paired pseudoautosomal region (1) at the end of the short arm
What are the different applications of DNA fingerprinting and profiling?
Clinical
Forensic
Legal
Conservation biology
What is this an image of?
Balanced reciprocal translocation
What percentage of an individual heterozygous for reciprocal translations gametes are unbalanced?
~50%
Define
Klinefelter’s syndrome
a genetic condition that results when a boy is born with an extra copy of the X chromosome
Define crossover event
the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes during sexual reproduction
Which three autosomal trisomies survive to term?
21 (Down syndrome)
13 (Patau syndrome)
18 (Edwards syndrome)
Define
Non-disjunction
the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei
Definition
A chromosome pair with some homology but differing in size, shape, or staining properties. Homologous chromosome pair which are not morphologically identical (eg the sex chromosomes)
Heteromorphic chromosome
What type of dominance is seen for DNA markers?
Co-dominance
Define
Paracentric inversion
a reversal of the normal order of genes in a chromosome segment involving only the part of a chromosome at one side of the centromere
What are the three possible patterns that homologous chromosomes in a translocation cross can segregate into?
Alternate orientation
Adjacent I orientation
Adjacent II orientation
Definition
having the centromere terminally situated so that there is only one chromosomal arm
Telocentric
How many alleles do RFLP markers have?
Usually 2 (4 theoretically possible)
What are the two types of balancing selection?
Heterozygote advantage
Frequency-dependent selection
When much higher proportions of the parental gamete types occur than expected what is the suspected cause?
Linkage
A Drosophila has the sex complement XY. What is it’s sex? Is it viable? Is it fertile?
Male
Viable
Fertile
Define genetic map
A graphic representation of the arrangement of a gene or a DNA sequence on a chromosome. A genetic map is used to locate and identify the gene or group of genes that determines a particular inherited trait
Define
Telocentric
having the centromere terminally situated so that there is only one chromosomal arm
What are the possible gametes for a paracentric inversion with no crossovers within the inverted region?
True or False:
Autotetraploids are fertile
True
What would the recombinant frequency be if a crossover always occured between two gene loci?
50
Why can DNA profiling be used when the DNA sample is partially degraded?
The PCR will only amplify the intact DNA, degraded DNA will simply not amplify
Definition
an alteration in a gene that is present for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents or in the fertilized egg itself
De novo mutation
What type of dominance does RFLP alleles display?
Co-dominance
How do you describe the position of a gene on a chromosome using the correct nomenclature?
- Chromosome number
- Chromosome arm (p/q)
- Region of arm sub-divided by landmark G-bands
- Position within region
Define microsatellite
a tract of repetitive DNA in which certain DNA motifs (ranging in length from 1–6 or more base pairs) are repeated, typically 5–50 times
Small duplications retained in the genome lead to what?
Copy number variation
What is this an example of?
Reciprocal translocation
How many Barr bodies does X have?
0
Define repulsion phase
A linkage between dominant alleles of one or more genes and the recessive alleles of another (several genes) in such a case one parent involved in cross contributes the dominant allele of one gene while second parents provides the dominant allele of other genes
Why is the sickle cell anaemia allele retained in some African populations, despite the severity of the disease of the sickle cell homozygote?
Heterozygote advantage - individuals heterozygous for this allele are resistant to malaria
Define
Acentric
describes a chromosome without a centromere
Define
Reciprocal translocation
A type of chromosome rearrangement involving the exchange of chromosome segments between two chromosomes that do not belong to the same pair of chromosomes
How is it decided which X will be inactivated?
Random
Definition
The use of fluorescent-tagged chromosome-specific dispersed repeat DNA sequences to visualize specific chromosomes or chromosome segments by in situ DNA hybridization and fluorescence microscopy
Chromosome painting
True or False:
In interspecies hybrids, chromosomes of one or the other parent are progressively and random lost
True
What are two reasons why monosomy of autosomes is inviable?
- Recessive disease alleles
- Haploinsufficiency (50% not enough)
Define map unit
the distance between chromosome positions (also termed loci or markers) for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01. Also known as a centiMorga
What is the evolutionary advantage of inversions?D
True or False:
Monosomy is more abnormal than trisomy
True
Definition
the stock of different genes in an interbreeding population.
Gene pool
Definition
an aberrant chromosome whose ends have fused together to form a ring
Ring chromosome
Definition
the production or development of an ovum
Oogenesis
Definition
a reversal of the normal order of genes in a chromosome segment involving parts of a chromosome at both sides of the centromere
Pericentric inversion
Definition
the presence of genetic variation within a population, upon which natural selection can operate
Polymorphism
If the allele frequency of p is 0.8 what is the allele frequency of q?
0.2
What DNA marker does DNA fingerprinting target?
Minisatellite
Definition
the state of a cell or organism having more than two paired (homologous) sets of chromosomes
Polyploidy
How do we detect SNPs?
- Detect RFLP by restriction enzyme digestion of genomic DNA and Southern Blotting 2. Detect RFLP using PCR from genomic DNA follwed by restriction enzyme digestion
Define
Population genetics
a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology
Definition
describes a chromosome without a centromere
Acentric
The genotype for closely liked genes on a single chromosome or gamete is called what?
Haplotype
What are the benefits of genetic mapping?
- Tells you whether a disorder is caused by one gene or by different genes
- Genes whose DNA sequence is not yet known can be cloned from their map position
- Nearby markers can be used as a tag of a desired gene in plant and animal breeding
- Closely liked DNA markers are useful in genetic counseling
Define DNA fingerprinting
a technique used especially for identification (as for forensic purposes) by extracting and identifying the base-pair pattern of an individual’s DNA
Define
Adjacent II orientation
a product of reciprocal translocation that occurs at anaphase I that results in all gametes being unbalanced. The centromeres from homologous chromosomes end up in the same gametes making this vary rare
Definition
the process by which organisms equalize the expression of genes between members of different biological sexes
Dosage compensation
Define founder effects
the reduced genetic diversity which results when a population is descended from a small number of colonizing ancestors
How do you calculate the coefficient of confidence (C)?
Observed double crossovers / Expected double crossovers
Define
Aneuploidy
the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46
In mitosis, homologous chromosomes do/don’t pair to form bivalents
Don’t
Which of the common human sex chromosome aneuploids are fertile?
Triple X
Double Y
Define probe
A single-stranded DNA or RNA fragment used in genetic engineering to search for a particular gene or other DNA sequence. The probe has a base sequence complementary to the target sequence and will thus attach to it by base pairing
How many pairs of chromosomes do humans have?
23
An inversion with the centromere inside the inverted region is called what?
Pericentric
What effect does the size of pericentric inversions have on fertility?
The larger the inversion, the more likely crossovers will occur, increasing the chance of unbalanced gametes, further reducing fertility
What does an inversion or translocation arising and spreading through a population promote? How?
Speciation
Definition
a product of reciprocal translocation that occurs at anaphase I that results in half the gametes being normal and the other half being unbalanced
Alternative orientation
True or False:
The ratio of males to females is 1:1
False
Female slightly favoured
Define negative interference
the phenomenon that the occurrence of a crossover increases the probability of another crossover in its vicinity
Define multiplex PCR
the use of polymerase chain reaction to amplify several different DNA sequences simultaneously (as if performing many separate PCR reactions all together in one reaction)
Define
Turner’s syndrome
a genetic defect in which affected women have only one X chromosome, causing developmental abnormalities and infertility
Abnormal chromosomes only survive mitosis/meiosis is it still has ___ centromere and ____ telomeres
1 centromere and 2 telomeres
How do autotriploids form?
Arises if a diploid gamete (2n) joins with a haploid gamete (1n)
Robertsonian translocations occur only in what type of chromsome?
Acrocentric
What are the potential consequences of a balanced inversion?
- Breakpoints can disrupt important genes
- Individuals heterozygous for an inversion have a variable risk (depending on inversion size) or producing unbalanced gametes
Definition
having two complete sets of chromosomes derived from two different species
Allodiploid
Fusion of which chromosomes via Robertsonian translocation often results in Down syndrome?
14 and 21
Definition
the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46
Aneuploidy
What are the five assumptions of the HW principle?
- The population is very large
- There is no gene flow
- There is no natural selection
- There is no mutation
- There is random mating
What gametes are produced in nondisjunction I in females?
Define allele specific oligonucleotide hybridisation
a procedure for detection of alleles of known composition, by measuring hybridization of a labeled DNA sample with oligonucleotide probes of known sequence, differing from each other by a single nucleotide, under conditions stringent enough that only perfectly matched sequences hybridize
Define DNA profiling
the process where a specific DNA pattern, called a profile, is obtained from a person or sample of bodily tissue
Define
Fragile X syndrome
an inherited condition characterized by an X chromosome that is abnormally susceptible to damage, especially by folic acid deficiency. Affected individuals tend to have limited intellectual functions
Define
Directional selection
a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype
When nondisjunction occurs in meiosis II what happens?
Failure of a pair of sister chromatids to separate - two chromatids got to one pole and note to other
Define
De novo mutation
an alteration in a gene that is present for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents or in the fertilized egg itself
What are the resulting gametes when nondisjunction occurs at meiosis II?
True or False:
Polyploid occurs in mammals
False
It never occurs in mammals
What are the male and female sex chromosome system in birds?
F: ZW
M: ZZ
Definition
an inherited condition characterized by an X chromosome that is abnormally susceptible to damage, especially by folic acid deficiency. Affected individuals tend to have limited intellectual functions
Fragile X syndrome
Definition
composed of four homologous chromosomes synapsed in meiotic prophase
Quadrivalent
What causes female mammals to be natural mosaics?
X inactivation
Why are normal gametes produced by 47, XXX and 47, XYY?
- During early development of the germ line the normal karyotype is restored, so oocytes are 46, XX and spermatogonia are 46, XY
- Achieved as one sex chromosome is lost (e.g. by nondisjunction or lagging) during early mitosis. Only cells in which this has occurred can lead to the germ line
What happens once a gene duplicates?
When nondisjunction occurs in meiosis I what happens?
Failure of separation of a pair of homologous chromosomes - two homologues go to one pole and none to other
Define
Triple X syndrome
a condition characterised by the presence of an extra X chromosome in each cell of a female
How do homologous chromosomes behave at meiosis when they are heterozygous for a Robertsonian translocation?
How many Barr bodies does XX have?
1
Definition
a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype
Directional selection
Definition
an individual or strain whose chromosome complement consists of four copies of a single genome due to doubling of an ancestral chromosome complement
Autotetraploid
Define intragenic recombination
recombination occurring within a gene
Which of the following chromosome types segregates normally during cell division?
a) dicentric
b) acentric
c) ring
d) iso
d) iso
Define variable number of tandem repeats (VNTR)
another name for a minisatellite
Definition
a genetic condition that results when a boy is born with an extra copy of the X chromosome
Klinefelter’s syndrome
Define genetic chimera
a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction
What does unequal crossing over cause?
Both duplications and deletions
Define
Stabilising selection
a type of natural selection in which the population mean stabilizes on a particular non-extreme trait value
Definition
having or existing in only one form
Monomorphic
Define
Patau syndrome
a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13
Definition
a stain that labels the phosphate groups of DNA and attaches itself to regions of DNA where there are high amounts of adenine-thymine bonding. Giemsa stain is used in Giemsa banding, commonly called G-banding, to stain chromosomes and often used to create a karyogram
Giemsa stain
Human genes can be mapped using somatic cell hybrids as long as what requirements are met?
- Human gene product identifiable in cell culture
- Products of human and other species genes can be distinguished
Define
Reproductive isolation
the situation where different species may live in the same area, but properties of individuals prevent them from interbreeding
What are the three possible ways chromosomes in a trivalent can segregate?
Normal, balanced or unbalanced
How is DNA profiling performed?
PCR is used to detect and amplify DNA at one locus
What effects does the size of a paracentric inversion have on fertility?
The larger the inversion, the more likely crossovers will occur leading to more abnormal gametes and less fertility
What can high resolution genetic maps tell you?
Whether the markers are linked as well as generating a genetic map
If the chromosome number is double during meiosis to form a allotetraploid, what can occur?
All the chromosomes can form bivalents at meiosis and balanced diploid gametes will be produced making it fertile
What are the advantages of DNA profiling?
- PCR is extremely sensitive, requires very little starting material
- Can genotype partially degraded DNA samples
What is this showing?
Unequal crossing over
Definition
a genetic defect in which affected women have only one X chromosome, causing developmental abnormalities and infertility
Turner’s syndrome
What are the male and female sex chromosome system in mammals?
F: XX
M: XY
Define minisatellite
a tract of repetitive DNA in which certain DNA motifs (ranging in length from 10–60 base pairs) are typically repeated 5-50 times
What are the male and female sex chromosome system in many turtles?
F: high temp
M: low temp
Definition
a product of reciprocal translocation that occurs at anaphase I that results in all gametes being unbalanced. The centromeres from homologous chromosomes end up in the same gametes making this vary rare
Adjacent II orientation
True or False:
Autotriploids are fertile
False
Define centiMorgan
a map unit used to express the distance between two gene loci on a chromosome. A spacing of one centimorgan indicates a one per cent chance that two genes will be separated by crossing over
True or False:
Somatic polyploidy occurs in humans
True
True or False:
The silenced X chromosome reactivates in oogenesis
Definition
an individual or strain whose chromosomes are composed of more than two genomes each of which has been derived more or less complete but possibly modified from one of two or more species
Allopolyploid
Define PCR
a technique in molecular genetics that permits the analysis of any short sequence of DNA (or RNA) even in samples containing only minute quantities of DNA or RNA
Define bivalent
a pair of homologous chromosomes
Define
Monomorphic
having or existing in only one form
True or False:
Monosomies never survive
True
Define haplotype
a group of alleles in an organism that are inherited together from a single parent
What are the possible gametes of a pericentric inversion with a crossover within the inverted region?
What are the four common human sex chromosome aneuploids?
Triple X
Turner
Double Y
Klinefelter
Define
Iso-chromosome
an unbalanced structural abnormality in which the arms of the chromosome are mirror images of each other.
Drosophila also has XX females and XY males. Is the mechanism the same as in mammals?
No
2 or more X = female
Only 1 X = male
Y needed for functional sperm
Genes A; B; C; D are found on which chromosome?
A: Chromosome 5
B: Chromosome 3
C: Chromosome 8
D: Chromosome 1
Define
Heteromorphic chromosome
A chromosome pair with some homology but differing in size, shape, or staining properties. Homologous chromosome pair which are not morphologically identical (eg the sex chromosomes)
True or False:
In plants, if two 2n gametes join the 4n zygote will be viable but not fertile
False
It will be both viable and fertile
How are micro deletion syndromes detected?
High-resolution karyotyping or FISH
What is this an example of?
Inversion
Define
Allozymes
variant forms of an enzyme which differs structurally but not functionally from other versions coded for by different alleles at the same locus
Label these chromosomes based on centromere position
Define genomic DNA
chromosomal DNA
Define
Inversion loop
the conformation of pairing up of homologous chromosomes in meiosis that are heterozygous for inversions
How many Barr bodies does XY have?
0
Define coefficient of coincidence
a measure of interference in the formation of chromosomal crossovers during meiosis
True or False:
Allopolyploids arise from inter-species hybrids
What are the two types of inversions?
Fill in the gaps with either SNPs or Satellites
Definition
the inactive X chromosome in female somatic cells
Barr body
Define
Down syndrome
a congenital disorder arising from a chromosome defect, causing intellectual impairment and physical abnormalities including short stature and a broad facial profile. It arises from a defect involving chromosome 21, usually an extra copy (trisomy-21)
Definition
the situation where different species may live in the same area, but properties of individuals prevent them from interbreeding
Reproductive isolation
Why do trisomy 13, 18 and 21 have milder phenotypes than other autosomal trisomies?
They are smaller chromosomes with fewer essential genes
Define
Uniparental disomy
the situation in which 2 copies of a chromosome come from the same parent, instead of 1 copy coming from the mother, and 1 copy coming from the father
Which of the common human sex chromosome aneuploids are infertile?
Turner
Klinefelter
True or False:
Autosomal aneuploid rates are not affected by maternal age
False
Autosomal aneuploid are more frequent among offspring of older mothers
An inversion with the centromere outside the inverted region is called what?
Paracentric
Females have twice the amount of genes on their X chromosome than males. How is this dosage imbalance corrected?
Dosage compensation
Definition
a genetic disorder caused by a third copy of all or part of chromosome 18
Edwards syndrome
What gametes are produced in nondisjunction I in males?
What is an example of a method to detect SNPs that does not cause restriction site changes?
Allele specific oligonucleotide (ASO) hybridisation
During a Robertsonian translocation, which arm of the chromosome is lost?
P arm
True or False:
Centromeres are basically never completely centred so one arm will always be longer than the other
True
What are the categories fo chromosomal rearrangements?
Deletion
Duplication
Inversion
Translocation
Define restriction fragment length polymorphism (RFLP)
any variation in DNA between individuals revealed by restriction enzymes that cut DNA into fragments of different lengths in consequence of such variations
Define
SRY
a sex-determining gene on the Y chromosome in mammals that determines maleness and is essential for development of the testes
What is the method for chromosome painting?
- Make a probe that contains many sequences from an individual chromosome (isolate the chromosome cytologically, or obtain DNA from library of clones from that chromosome)
- Label probe chemically with fluorescent dye
- Hybridise probe to chromosome spreads in situ
- Results in only one chromosome type fluorescing (at many different sites along its length)
True or False:
FISH can be used to detect inversions
True
Define
Down syndrome critical region (DSCR)
A region on the long (q) arm of chromosome 21 thought to be responsible for some, if not all, of the features of Down syndrome
Define
Allotetraploid
a hybrid that has a chromosome set 4 times that of a haploid organism. They are created as a result of both chromosome sets of each parents being present in gametes
True or False:
Aneuploidy for sex chromosomes is more severe than for autosomes
False
Aneuploidy for autosomes is more severe than for sex chromosomes
On which population does genetic drift have a larger effect: 20 or 2000?
20
Define twin spots
two genetically different clones of neighboring cells in a background of normal cells
True or False: There is no recombination in Drosophila females
False There is none in males
What are the three steps of X inactivation?
Initiation
Spreading
Maintenance
What gametes are produced in nondisjunction II in females?
True or False:
All mammals share the same mechanism of sex determination
How does the mutation in Fragile X syndrome affect the FMR1 gene?
The full repeat expansion reduced the expression of the gene
What are the resulting gametes when nondisjunction occurs at meiosis I?
Definition
the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei
Non-disjunction
What is an example of a morphological polymorphism?
Labrador coat colour
Define single nucleotide polymorphism (SNPs)
a variation at a single position in a DNA sequence among individuals
Define
Autopolyploid
an individual or strain whose chromosome complement consists of more than two complete copies of the genome of a single ancestral species
Define
Genetic drift
variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce
What is the difference between a microsatellite and a minosatellite?
The length: micro = 2-10bp mini = 10-100bp
Can HW principle still be used to calculate the allele frequency of complete dominance traits?
Yes
Define
Frequency-dependent selection
an evolutionary process by which the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population
Definition
variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce
Genetic drift
Define chiasmata
a point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands
Definition
relating to the form or structure of things
Morphological
What is the term used to describe the transfer of genetic material between non-homologous chromosomes?
Translocation
Definition
the most common form of chromosomal rearrangement where the participating chromosomes break at their centromeres and the long arms fuse to form a single, large chromosome with a single centromere
Robertsonian translocation
Define
Dicentric chromosome
an abnormal chromosome with two centromeres. It is formed through the fusion of two chromosome segments, each with a centromere, resulting in the loss of acentric fragments (lacking a centromere) and the formation of dicentric fragments
True or False:
Ring chromosomes are very stable and are often retained
False
They are very unstable and are often lost during meiosis
Why are dicentric chromosomes lost during meiosis?
They form a dicentric bridge during meiosis, when chromosomes separate it will randomly break, resulting in variable deletion
Definition
the situation in which 2 copies of a chromosome come from the same parent, instead of 1 copy coming from the mother, and 1 copy coming from the father
Uniparental disomy
Define
Autotetraploid
an individual or strain whose chromosome complement consists of four copies of a single genome due to doubling of an ancestral chromosome complement
Define
Adjacent I orientation
a product of reciprocal translocation that occurs at anaphase I that results in all gametes being unbalanced. The centromeres from the homologous chromosomes are separated
What type or phase is this? AB/ab
Coupling phase
Definition
a hybrid that has a chromosome set 4 times that of a haploid organism. They are created as a result of both chromosome sets of each parents being present in gametes
Allotetraploid
Definition
an abnormal chromosome with two centromeres. It is formed through the fusion of two chromosome segments, each with a centromere, resulting in the loss of acentric fragments (lacking a centromere) and the formation of dicentric fragments
Dicentric chromosome
How does autotetraploidy occur?
Arises due to an accident during mitosis:
(chromosomes replicate but cell division does not occur)
Define
Allopolyploid
an individual or strain whose chromosomes are composed of more than two genomes each of which has been derived more or less complete but possibly modified from one of two or more species
Define
Alternative orientation
a product of reciprocal translocation that occurs at anaphase I that results in half the gametes being normal and the other half being unbalanced
Define
Ring chromosome
an aberrant chromosome whose ends have fused together to form a ring
What is the expected genotype frequency of a population in HW equilibrium?
p2 + 2pq + q2 = 1
Definition
a condition in which an extra copy of a chromosome is present in the cell nuclei, causing developmental abnormalities
Trisomy
How is DNA fingerprinting performed?
- Digest genomic DNA with a restriction enzyme and perform a Southen blot
- Use a probe complementary to the repeat to detect ALL the repeat loci at once
This will give you a specific ‘fingerprint’ of bands
Define
Gene pool
the stock of different genes in an interbreeding population.
Define
Bottle neck
an event that drastically reduces the size of a population producing a decrease in the gene pool of the population because many alleles, or gene variants, that were present in the original population are lost
How do the homologous chromosomes pair when a heterozygous reciprocal translocation has occurred?
What are some examples of causes of directional selection?
Selective predation, pesticide resistance in insects etc.
How was it determined that the presence of Y determines maleness?
Abnormal human karyotypes
Female: X, XX, XXX
Male: XY, XYY, XXY
Define
Heterokaryon
a multinucleate cell that contains genetically different nuclei
How many chromosomes would be found in somatic cells of an allotetraploid plant if its parent species had diploid number 4 and 6 respectively?
5
Definition
a molecular cytogenetic technique that uses fluorescent probes that bind to only those parts of the chromosome with a high degree of sequence complementarity
Fluorescent in situ hybridisation (FISH)
How many Barr bodies does XXXY have?
2
Why are most interspecies hybrids that survive sterile?
Either meiosis does not occur, or the two sets of chromosomes do not pair (all univalents, no balanced gametes)
Definition
the second step in X inactivation where the XIST RNA is not translated but spreads out and coats the inactivate X, ensuring most genes are inactivated
Spreading
Define autonomous
having the freedom to act independently
What are the different types of natural selection?
- Directional selection
- Stabilising selection
- Balancing selection
- Heterozygote advantage
- Frequency-dependent selection
What are the disadvantages of DNA profiling?
- Contaminating DNA can be easily amplified
- Multiplex PCR must be carefully optimised so that PCR are one locus does not interfere with another
Define
Quadrivalent
composed of four homologous chromosomes synapsed in meiotic prophase
How do you describe human karyotypes using the appropriate nomenclature?
- Number of chromosomes per cell
- Complement of sex chromosomes
- Any abnormal chromosomes
e. g. 47, XY, +21
What type of DNA marker does DNA profiling target?
Microsatellite
True or False:
Nondisjunction can occur during mitosis
True
How does false inclusion occur in DNA profiling?
- Relatives are likely to share alleles
- Some alleles more frequent in specific populations (Founder effect)
- Some markers show racial differences in allele frequency
If the observed number of crossovers is less than expected what has occurred?
Positive interference
When one chromosome arm is lost and the remaining arm is then duplicated, what is the result?
Iso chromosome
Why are acentric chromosomes lost during meiosis?
They cannot attach to the spindle
What are the causes of reciprocal translocations?
- Chromosome breaks
- Broken ends lack telomeres and are reactive, DNA repair enzymes may re-join incorrectly
- Abnormal crossing over between non-homologous chromosomes
The probability of mutation to a different allele per gene per generation is referred to as what?
Mutation rate (µ)
True or False
Sex chromosome aneuploidy is more common than autosome aneuploidy
True
What is this an example of?
Deletion
A Drosophila has the sex complement XX. What is it’s sex? Is it viable? Is it fertile?
Female
Viable
Fertile
If an individual is heterozygous for an inversion, how do homologous chromosomes pair?
Inversion loop
Define
Microevolution
evolutionary change within a species or small group of organisms, especially over a short period.
Definition
a reversal of the normal order of genes in a chromosome segment involving only the part of a chromosome at one side of the centromere
Paracentric inversion
Define
Spreading
the second step in X inactivation where the XIST RNA is not translated but spreads out and coats the inactivate X, ensuring most genes are inactivated
Define
Initiation
the first step in X inactivation where the X inactivation centre (Xic) of one of the X chromosome is initiated by the expression of the gene XIST
