Genetics and Evolution III

Frage	Antworten
What can you use to identify genes responsible for a trait?	Recombination The closer 2 genes are on a chromosome the less likely they are to be separated by recombination and the more likely these alleles are to be co-inherited Recombination mapping narrows down the region to help find the gene
Draw a diagram used to explain finding yfg	parental chromosomes marker mutants for regions Red chromosome has wild type alleles homologous to the mutant alleles. Blue chromosome is allowed to recombine with the red chromosome, producing a female that's heterozygous, with each egg produced from that female potentially having a recombination event
What do you force the parents to do you sexually depraved git?	Sexy types wild type with all mutants, see whether the offsprings chromosomes each has a copy of these mutations or not Use the markers to tell whether a specific region has come from the blue or red chromosome.
What does SNP stand for?	Molecular marker known as a single nucleotide polymorphism The chromsomes being studied have a nucleotide at a specific position in the genome e.g. GATTTAGAATTC GATTTAGAAGTC
What is RFLP?	Restriction Fragmentation Length Polymorphism (e.g. using EcoR1 restriction site). GAATTC is a recog site for EcoR1 to exise the DNA at that site, it won't recognise allele 2 as the sequence has been altered.
Describe the banding this would cause	If DNA that was homozygous for allele 1 was taken,amplified, then cut with EcoR1, 2 bands would be produced, being 2kb an 1kb Look at the lecture for this again
Name one more example of a marker	Variable repeat lengths PCR using flanking primers can be used to amplify the variable length region These regions are highly variable and so are present as multiple different alleles in the population. Basis for genetic finger printing. (Diagram).
Why are chromosome deletions not so bad?	(a) Most wild type alleles are dominant to loss of function alleles (b) Therefore mutations or complete removal of one copy of the gene isn't detrimental to survival (c) Chromosome deletions can remove just a tiny bit of DNA or remove large regions, there is a maximum size deletion that is tolerated.
What is the basis of identifying actively expressed DNA?	Actively transcribed DNA has to be more open in structure and less compact, as a result it stains less darkly with dye. As some genes are active and some aren't you'll get variable bands of lighter/darker DNA.
How can this staining be used to find chromosome deletions?	If there's chromosomal deletion in one copy of the DNA and not in the homologue, pairs of chromosomes will loop out during synapses as there's nothing to bind to. We can then study these loops to see if the gene is in the missing bit or not by mapping the deletions.
What will occur if mfg is part of the deletion?	Investigating whether mfg is in the chromosomal deletion represented in red If mfg is part of the deletion then no functional copy of the gene will exist as the mutant will have no functional copy as the gene is recessive, and that will show as the phenotype of interest (male sterility) will occur.
What will occur if mfg isn't part of the deletion?	Normal fertile flies will be produced We'll know that it's not in the overlapping region with vir130 a the offspring wouldn't be sterile if it were.
What is the region defined by?	Physical break boxes, this then has to be mapped back to the genome and can be found by comparing to proximal genes to the gene of interest.
What is Holoprosencephaly	Holoprosencephaly causes neural and facial ventral midline defects cyclopia, close eyes, incomplete forebrain separation single central incisor
What can cause HPE?	At least 12 different loci first 3: SHH at 7q36 HP34 is mapped to a haplo-insufficient region in 18p11
What does haplo-insufficient mean?	Phenotype present only in one functional copy of a locus.
Why was HPE4 easy to find?	As the mutation is dominant (haplo-insufficient). Deletions of a region of Chromosome 15 are visible cytologically in some patients. TGIF, a gene important in the formation of the ventral midline was already identified in that region
How do you map recessive mutations in family?	Do a pedigree analysis to look at those inbred dirty fuckers
Describe infantile-onset symptomatic epilepsy syndrome	caused by a homozygous loss-of-function mutation of GM3 synthase. Autosomal recessive found cos inbred asf amish family
Honing in on the gene	"We carried out a genome-wide screen for linkage and identified a single region of homozygosity on chromosome 2p12 - p11.2 spanning 5.1 cM Molecular markers were used to see which bits of the genome were homozygous in all affected individuals and in more of the unaffected individuals. Marker is so close to the gene of interest that it hasn't recombined in any of the meiosis events Lots of variable length repeat PCRs (In a high thoroughput system.) Makers distributed over the whole genome
How will an individual who is homozygous for mfg be for a marker that's extremely close to it?	mfg will be homozygous for it, and not homozygous to distant markers.
Why do most marker alleles segregate independently of the disease status?	As they're on different chromosomes or far away on the same chromosome specific alleles of

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Genetics and Evolution III

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