Genetics - Knowledge and Understanding 2
In the lac operon of Escherichia coli:
A null mutation in Lac I prevents expression of beta-galactosidase
Mutations in Lac O result in constitutive expression of beta-galactosidase
Lac O encodes a trans-acting factor
The Lac I gene is constitutively expressed
The Lac I gene is induced by allolactose
The analysis of morphogenesis in bacteriophage T4 showed that:
Capsid assembly is a linear pathway
Phage tails have to be made before phage heads
Tail fibres are the last components to be added
Heads are assembled before DNA is inserted into them
Gene products are involved that are not included in the structure of the capsid
Gene therapy for the treatment of inherited disorders
Involves correction of mutant genes in human eggs, prior to fertilization.
Involves delivery of DNA to humans by inhalation of genetically engineered viruses
Has been used to treat haemophilia
Has been used to treat cystic fibrosis
Has been used to treat adenosine deaminase deficiency
In studies of human ancestry:
Genetic markers on the Y-chromosome enable paternal descent to be inferred
Genetic variation in mitochondrial genomes enables paternal descent to be inferred
Genetic variation on the Y chromosome is more frequently the result of mutation than recombination
Genetic variation on autosomes is more frequently the result of recombination than mutation
Genetic markers on the X-chromosome were used to identify the descendants of Genghis Khan
In the early development of a zygote of Drosophila melanogaster:
The anterior/posterior axis is set up without maternal inputs
The genome of the zygote is not initially important
The dorsal/ventral axis is determined by gravity
The egg is asymmetrical before it is fertilised
Maternal information is needed to set up the left-right axis
Transposons:
Are found in human genomes
Are mobile genetic elements
Do not contribute to evolutionary change
Cause mutant phenotypes that are always stably inherited
Do not occur in bacterial genomes
The transcription of protein-coding genes in eukaryotes:
Is inhibited by cycloheximide
Is inhibited by alpha-amanitin
Is carried out by RNA polymerase II
Occurs only in the cell nucleus
Can be analysed using promoter-reporter fusions
The Lac operon of Escherichia coli is regulated:
By altering the copy number of the lacZ gene
By monitoring the availability of alternative sources of carbon
At the level of translation
By monitoring the concentration of allolactose
By monitoring the availability of oxygen
Gene expression in eukaryotes may be regulated by:
Changes in the number of copies of a gene contained in a cell
Alteration of the structure of DNA/protein complexes in chromosomes
Transcription factors
Post-translational modification of proteins
Mutation
Concerning 18S, 5.8S and 28S ribosomal RNA in eukaryotes:
They are transcribed separately
They are encoded by genes in long tandem arrays
They are co-translated
They are produced by post-transcriptional cleavage
They are encoded by genes located at centromeres
In autosomal recessive conditions, there is:
A greater chance that females will be affected.
A 50% chance that a carrier will pass on the affected allele to a child.
A 50% chance that the unaffected sib of an affected child will be a carrier.
A 25% chance that a child of two carrier parents will be affected by the condition.
A 50% chance that an affected parent will pass on the condition to a child.
RNA splicing:
Involves the removal of introns
Requires the action of DNA ligase
Involves the formation of 3'-5' phosphodiester bonds
Involves the formation of 2'-5' phosphodiester bonds
Occurs in the formation of ribosomal RNA
In the plant Arabidopsis thaliana:
Floral organ development has been studied using homoeotic mutations
Floral organ development is regulated by 4 genes, each expressed exclusively in the 4 whorls of the flower
Mutant plants deficient in the "B-function" have flowers that lack sepals
Mutant plants deficient in the "C-function" have flowers that produce additional whorls of petals
Complementation tests have been used to determine the numbers of genes that regulate floral organ development
Cystic fibrosis is a severe inherited disease caused by an autosomal recessive mutation on chromosome 7. In Caucasian populations, approximately 1 in 23 will be a heterozygous carrier:
The likelihood of a (Caucasian) newborn infant having CF is approximately 1 in 500
The likelihood of a (Caucasian) newborn infant having CF is approximately 1 in 2000
The likelihood of a (Caucasian) newborn infant having CF is approximately 1 in 50
Carriers of the defective CF allele can be identified by PCR analysis
A standard approach to the control of CF is to sterilise carriers of the mutant allele
Concerning X-linked inheritance in humans:
Males have two X chromosome
There is no crossing over in males on any chromosome
Females are hemizygous for genes on the X chromosome
X-linked conditions are commoner in males than in females
Charcot-Marie-Tooth disorder is a sex-linked recessive condition
In the fruit fly Drosophila melanogaster:
A fly carrying two mutant alleles of the bicoid gene does not show normal anterior-posterior development
A fly whose father carried two mutant alleles of the bicoid gene does not show normal anterior-posterior development
A fly whose mother carried two mutant alleles of the bicoid gene does not show normal anterior-posterior development
A fly carrying two mutant alleles of the Antennipedia gene has legs in place of antennae
A fly whose mother carries two copies of the Antennipedia gene has legs in place of antennae
Concentration gradients of morphogenetic proteins:
Regulate cell fate in Caenorhabditis elegans
Determine polarity in Drosophila melanogaster
Determine polarity in Caenorhabditis elegans
Regulate head assembly of bacteriophage T4
Are set up by asymmetric distribution of mRNA in Drosophila embryos
Concerning human inherited conditions:
Red-green colour blindness is a sex-linked condition
Male pattern baldness is a sex-linked condition
All male offspring of females who carry the defective allele responsible for haemophilia will be haemophiliacs
Heterozygotes carrying a single mutant allele of the gene associated with Huntington's disease will suffer from the disease
Severe combined immune deficiency can be treated by "gene therapy"
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