Lecture 20 The effects of Mutations II
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Define the term Aneuploid
A diploid chromosome set that is missing one chromosome.
Define a carrier
An individual who has one normal and one defective allele for a gene responsible for an inherited disease, but does not suffer from the disease because the effect of the defective allele is masked by the presence of the unmutated gene.
Define haploinsufficiency
Situation where inactivation of one of a pair of gene results in a change in the phenotype of the mutant organism.
Define monosomy
2n-1 , where one chromosome is missing from a pair in a diplpoid set.
Explain what the Philadelphia Chromosome is
An abnormal chromosome resulting from a translocation between human chromosomes 9 and 22, a common cause of chronic myeloid leukemia.
Define trisomy
This is where there are 3 copies of a chromosome in an otherwise diploid nucleus (2n+1)
Explain the concept of haploinsufficiency (google definition)
The situation that occurs when one copy of a gene is inactivated and the remaining functional copy of the gene is not adequate to produce the normal phenotype. (so there is a change in the phenotype)
How many genes are inactivated in haploinsufficiency
One copy out of the pair of alleles is inactivated.
Explain how the Philadelphia chromosome arises
Occurs when chromosomes 9 and 22 break and exchange portions. This creates abnormally small chromosome 22.
What do we mean by a diploid organism
• 2 copies of each chromosome - 2 copies of each gene
Which factor influences the shape of peas
Sucrose content. Low sucrose causes the mature pea to stay round. High sucrose causes mature peas to be wrinkled. Sucrose content is controlled by the SBE1 gene.
Which gene converts sucrose into starch
SBE1 gene.
Explain how wrinkled peas arise
• Pea shape depends on sucrose content • SBE1 gene controls conversion of sucrose into starch. • wrinkled peas have a defective SBE1 allele therefore cannot convert sucrose into starch. • Results in high sucrose content, depletes water, results in wrinkly seeds.
How many chromosomes in Pea cell
14 chromosomes (diploid number. Arises from 2 sets of 7.
What are alternative forms of a gene called
Alleles
Wrinkled peas is which type of inheritance
Recessive, as it requires two non functional copies of SBE1 alleles to produce the wrinkled phenotype.
One functional and one non functional copy of SBE1 will result in which phenotype
Round pea phenotype.
is cystic fibrosis recessive or dominant
Recessive
What happens in haploinsufficient individuals
A mutation in just one gene/allele will cause disease.
Give an example of a disease that shows haploinsufficiency
Alagille syndrome is an example of haploinsufficiency
What does Alagille syndrome result in
Results in heart abnormalities and liver problems from abnormal bile ducts. Arises in deformed allele for the CD339 protein (JAG1) .
What is the CD339 JAG1 protein involved in
it is inovolved in cell to cell signalling during embryo development.
What arises when there is haploinsufficiency for the CD339 Jag 1 gene.
there is insufficient signalling protein (JAG 1)
What is retinoblastoma
Cancer of the retina.