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recesive genes
regarding conditions like cystic fibrosis inherited via both parents carrying the recessive gene. does this mean...
we only have 1 of these particular genes or do we have lots of resesive genes and only 1 of them is affected?so we have dominant and recessive genes but how many of each do we all have both or just either or? do both people have 1 affected res gene or do they both have resecive or dominant genes?
we only have 1 of these particular genes or do we have lots of resesive genes and only 1 of them is affected?so we have dominant and recessive genes but how many of each do we all have both or just either or? do both people have 1 affected res gene or do they both have resecive or dominant genes?
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Ok, I'm not entirely sure this is going to answer the question correctly but I'll try. no doubt theprof will post a much more comprehensive answer :)
Genes contain sections known as alleles and it is these alleles that cause the variation between us all. Some alleles are dominant and some are recessive. Many genetic conditions are caused by recessive alleles meaning that a person may be a carrier for the condition but never suffer any symptoms as they have a dominant allele making sure that the gene still functions properly. Lets say the dominant gene is A and the recessive one is a, so, if you are a carrier, the alleles on your gene will look like this Aa. The allele combination will repeat on the gene in every nucleus in every cell of your body.
Sexual reprodution involves the combination of 2 haploid cells i.e. an egg or sperm only carries half the DNA of the parent cell. This means that every egg or sperm of a carrier will contain either the healthy A allele or the deffective a. There are various combinations that can occur and it is a totally random process. I'll try to show this in a diagram: -
Parent A or a A or a
Offspring AA Aa Aa aa
Healthy Carrier Carrier Affected
So if you are both carriers, there is a 1 in 4 chance that the offspring will be affeted by the condition.
Not sure that got to the point :S I can explain it much better but I didn't want to ramble too much
Genes contain sections known as alleles and it is these alleles that cause the variation between us all. Some alleles are dominant and some are recessive. Many genetic conditions are caused by recessive alleles meaning that a person may be a carrier for the condition but never suffer any symptoms as they have a dominant allele making sure that the gene still functions properly. Lets say the dominant gene is A and the recessive one is a, so, if you are a carrier, the alleles on your gene will look like this Aa. The allele combination will repeat on the gene in every nucleus in every cell of your body.
Sexual reprodution involves the combination of 2 haploid cells i.e. an egg or sperm only carries half the DNA of the parent cell. This means that every egg or sperm of a carrier will contain either the healthy A allele or the deffective a. There are various combinations that can occur and it is a totally random process. I'll try to show this in a diagram: -
Parent A or a A or a
Offspring AA Aa Aa aa
Healthy Carrier Carrier Affected
So if you are both carriers, there is a 1 in 4 chance that the offspring will be affeted by the condition.
Not sure that got to the point :S I can explain it much better but I didn't want to ramble too much
StudentGal, that was a good answer and there�s not much I�d like to add. So if you�ll allow me, I�ll ramble on in general terms instead.
Let�s go back to basics for a moment. All our genes are carried on 23 pairs of chromosomes. Of those 23 pairs, 22 pairs are the same in males and females and are called autosomes. The 23rd pair determines if an individual is male or female and these chromosomes are called the sex chromosomes. A female has two X chromosomes whilst a male has an X and a Y (XY). There are over 30000 pairs of genes on the 46 chromosomes in cells, and in each pair, one gene copy is inherited from the mother, whilst the other is inherited from the father. Genes can are prone to intramolecular reorganization for various reasons and these changes are called mutations.
Cystic fibrosis is an autosomal recessive disorder. The genes from such traits and diseases are carried on the autosomes and autosomal recessive inheritance is a pattern of single-gene transmission by which traits, conditions and diseases are passed from a parent to a child.
Now for autosomal recessive conditions to occur, both genes in a gene pair must be mutated. The phrase autosomal recessive means that males and females are likely to inherit a given condition and that two non-working copies of the gene (one from each parent) are required for an individual to have the condition. Anyone with one non-working gene is called a carrier or heterozygote. In general, carriers do not have any physical symptoms of the condition, as their working copy is dominant and compensatory.
(continued)
Let�s go back to basics for a moment. All our genes are carried on 23 pairs of chromosomes. Of those 23 pairs, 22 pairs are the same in males and females and are called autosomes. The 23rd pair determines if an individual is male or female and these chromosomes are called the sex chromosomes. A female has two X chromosomes whilst a male has an X and a Y (XY). There are over 30000 pairs of genes on the 46 chromosomes in cells, and in each pair, one gene copy is inherited from the mother, whilst the other is inherited from the father. Genes can are prone to intramolecular reorganization for various reasons and these changes are called mutations.
Cystic fibrosis is an autosomal recessive disorder. The genes from such traits and diseases are carried on the autosomes and autosomal recessive inheritance is a pattern of single-gene transmission by which traits, conditions and diseases are passed from a parent to a child.
Now for autosomal recessive conditions to occur, both genes in a gene pair must be mutated. The phrase autosomal recessive means that males and females are likely to inherit a given condition and that two non-working copies of the gene (one from each parent) are required for an individual to have the condition. Anyone with one non-working gene is called a carrier or heterozygote. In general, carriers do not have any physical symptoms of the condition, as their working copy is dominant and compensatory.
(continued)
Heterozygotes will pass the defective gene from one generation to the next. However, if carriers marry, the offspring will have a 1 in 4 chance of being affected and homozygous, a 1 in 2 chance of being a carrier and a 1in 4 chance of being genetically normal. Consanguinity (relationship by blood) increases the risk � in first-cousin marriages for example, there is a 3% theoretical increased risk of having an abnormal child.
In northern Europe, somewhere between 1in 22 and 1in 25 of us are carriers for cystic fibrosis with a sufferer in about 1 in 2000 live births.
Cystic fibrosis is caused by (hold on, it�s going to be very technical here!) a malfunctioning gene called the Cystic Fibrosis Transmembrane Conductance Regulator, usually abbreviated to CFTR (Thank, God!), which is 1480 amino acids long. This protein is a chloride channel protein and has a major role in maintaining secretions in airways and ducts in the body. It does this by hindering sodium uptake whilst excreting chloride ions. All organs that rely on mucus are affected by CFTR malfunction including the lungs, skin, pancreas and liver etc.
One of the problems with Cystic fibrosis is that allelic heterogeneity occurs. This is where different forms of mutation occur within the same gene. At the last count, there were over a 1250 such mutations. These different mutations result in different clinical presentations of patients, which is why doctors never see cystic fibrosis patients with identical symptoms.
In northern Europe, somewhere between 1in 22 and 1in 25 of us are carriers for cystic fibrosis with a sufferer in about 1 in 2000 live births.
Cystic fibrosis is caused by (hold on, it�s going to be very technical here!) a malfunctioning gene called the Cystic Fibrosis Transmembrane Conductance Regulator, usually abbreviated to CFTR (Thank, God!), which is 1480 amino acids long. This protein is a chloride channel protein and has a major role in maintaining secretions in airways and ducts in the body. It does this by hindering sodium uptake whilst excreting chloride ions. All organs that rely on mucus are affected by CFTR malfunction including the lungs, skin, pancreas and liver etc.
One of the problems with Cystic fibrosis is that allelic heterogeneity occurs. This is where different forms of mutation occur within the same gene. At the last count, there were over a 1250 such mutations. These different mutations result in different clinical presentations of patients, which is why doctors never see cystic fibrosis patients with identical symptoms.
And just to confuse you even more, recessive genes are not always autosomal. When a mutation is carried on the sex chromosomes it is called a sex-linked recessive mutation. Many disorders in humans are of this type. Hemophilia and blue eyes being a couple of common ones.
In order for a mutation of this type to become active it needs to be inherited from both parents by a daughter. Males having only one active sex chomosome only need to inherit it from their mother and they will show the mutation, dispite it being recessive.
Males can not be carriers for this type of mutation - they either show it, or do not have it. But women can carry and often are without their knowledge.
In order for a mutation of this type to become active it needs to be inherited from both parents by a daughter. Males having only one active sex chomosome only need to inherit it from their mother and they will show the mutation, dispite it being recessive.
Males can not be carriers for this type of mutation - they either show it, or do not have it. But women can carry and often are without their knowledge.
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