Flashcards in PA20293 gene transcription and DNA Deck (149)
What is the difference between genetics and genomics?
Genomics is the study of all the genes in an organism, how genes and proteins work together and interact.
Genetics is the study of inheritance of genes, mutations and inherited diseases.
What determines expression rate?
How often genes get transcribed into proteins
Are all Polymorphisms harmful?
No, some are harmless, and are found in the non coding regions of genes (introns)
Polymorphisms are changes in gene sequence.
What does polygenic mean?
A disease caused by more than one gene being mutated.
These are very common
An example of a disease that isn't polygenic ie is caused by a single gene mutation: cystic fibrosis.
What is an autosomal disease?
The gene causing the disease is not present on the sex chromosome.
Ie not X linked (XX, XY)
Autosomal dominant and autosomal recessive
Two copies of each gene are inherited by a child, one maternal one paternal. If a mutation occurs, when will a disease show up in a child? Think about dominant and recessive genes...
If the allele is dominant, only one copy of the mutated gene needs to be inherited. The disease will show up if the child inherits one mutated copy from one parent and it's on a dominant gene.
If the child inherits two copies of a recessive mutated gene, one from each parent, the disease will show up. For a recessive linked disease to show up both copies need to be mutated.
What happens if a disease is X-linked, and in a male, there is a mutation on the X chromosome?
They will express the disease, males don't have another copy to back it up as their chromosome is XY unlike females which are XX.
What happens if a disease is X linked, and In a female a gene is mutated on one of her X chromosomes?
She won't express the disease as she has an back up healthy copy of the gene on her other X chromosome. She will be a carrier of the disease however. Females: XX
Does the sex of the child determine whether they inherit a disease or not with autosomal dominant/ recessive diseases?
Only with X linked inheritance pathways
If a disease is autosomal recessive, and a child inherits one dominant copy and one mutated recessive copy from their parents, will they express the disease in their phenotype?
They will be a carrier
For a recessive linked disease to show in the phenotype, 2 recessive genes must be present; homozygous recessive
Examples of diseases caused by X linked alleles?
Heamophilia and colour blindness
X linked diseases most often in males, most often X linked recessive
What are the three most common modes of inheritance?
Autosomal dominant, autosomal recessive, X linked recessive.
The 4th mode is X linked dominant but this is rare
What are molecular markers of disease?
Identifying molecular markers located along DNA which are inherited with disease, can help to locate the region of the gene causing the disease.
Molecular markers; map disease loci, they're based on Polymorphisms
Polymorphisms act as convenient markers for studying inheritance
If you've inherited a polymorphism it's likely you've inherited the genes around it
What are RFLP's and what are they used for?
Restriction fragment length Polymorphisms.
Changes in sequences of restriction site of enzymes
Enzymes won't cut at usual places,
Results in different sized fragments to usual
Inheritance of a polymorphism could indicate the likely presence of a linked allele for the inherited disease.
What are SSRs?
Simple sequence repeats
Repeat of 2-8 bases
Due to slippage of template
Can map disease loci, Map what's maternal and paternally inherited
These random repeated sequences make an individuals gene profile unique
You're looking for Polymorphisms and repeats when studying loci
Why do we want to map out/ locate genes that cause disease?
If we find out what the gene is we can target it for therapy, we can get an idea of what protein is involved, we can use the protein as a molecular target for treatment
What is gene mapping?
The process of determining the locus for a particular biological trait (phenotype) eg a disease.
Locus/ loci: the specific location of a gene / DNA sequence on a chromosome
Individuals get mapped at several different loci ie you're usually looking at about 14 different loci: and you're looking for different Polymorphisms and repeats.
Links are made between inheriting particular Polymorphisms and whether a disease is present or not.
You're looking for mutations in genes near to inherited markers, these markers may be Polymorphisms, SSRs, RFLPs
What's the problem with gene mapping?
It doesn't narrow the search for our gene down that much, only to about 10 genes. We need to use techniques such as northern blotting to search for our effected gene more thoroughly.
Also gene mapping has no success with polygenic diseases.
True or false: a loss of heterozygosity can lead to cancer
Polymorphic, heterozygous regions may be lost where it results in the loss of a functional tumour suppressor gene. If the person suffers a point mutation in the back up gene copy too a loss of heterozygosity has occurred.
What is the concept of heterozygosity of genes?
The fact we have "back up" copies of genes in case a mutation occurs
When genomic copies from each parent have different bases in polymorphic regions due to SNPs, the region is heterozygous
You loose heterozygosity if there is a mutation in both a gene and the back up
What is contact inhibition?
Receptors on a cell surface touch another cell surface ligand, which results in cell growth inhibition, ie this is a stop signal. This is lost in cancer cells
True or false: It only takes one mutated gene to cause cancer
Multiple changes in DNA are needed to convert a normal cell into a cancer tumour cell.
usually at least 3 diff genes need to be mutated
Eg Loss of : apoptosis pathway, kinase pathway and repair mechanisms.
What do single base mutations and sequence mutations lead to?
Single base: one different amino acid; could lead to loss of protein function but not definate.
Sequence: deletions/ mutations may scramble encoded mRNA: leads to complete loss of function protein.
Cancer requires 3-7 hits on relevant genes for it to occur. What does this mean?
3-7 mutations need to occur on relevant genes which are those regulating cell growth and division, DNA repair, and cell death.
Proto oncogenes are the mutated, cancerous form of oncogenes. True or false?
False. Oncogenes are the mutated form of the normal cellular genes Proto-oncogenes
This mutation is usually dominant
Receptors on cell surfaces receive growth signals. What can increase numbers of receptors/ increase their activity?
If more receptors are made; due to gene number being amplified, or translocation of receptors gene to an area of high transcription rate.
Confrontational change in receptor; the receptor is always activated even without a Ligand
Constitutive dimerisation (dimerisation does not need a signalling molecule)
In breast cancer,what does the her 2 receptor suffer, and what does this lead to?
Results in neu oncoprotein
Ligand independent, therefore constitutively active
In cancer, what does the EGF receptor suffer and what does this lead to?
Leads to the Erb B oncoprotein
This is a constitutively active protein tyrosine kinase