Lecture 30. Mapping Mendelian Traits Flashcards
Talk about dominant inheritance.
The affected individual usually has at least one affected parent. The disease can be transmitted by either parent. Usually 50% of siblings have the disease
Talk about recessive inheritance ?
Affected people are usually born to unaffected parents who are both carriers. Children from these matings have a 25% chance of being affected
Talk about x-linked inheritance.
Usually males are affected. The mother is an unaffected carrier. 50% of male children are affected and there is no male to male transmission.
How many versions of each autosome do we have ?
2
What is female deactivation ?
Rendering transcriptionally silent one of the x-chromosomes by highly condensing it
What is the law of segregation ?
Alternative forms of the same genes at the same position/locus on homologous chromosomes
What is mitosis ?
Somatic cell division
By what stage have all 46 chromosomes replicated ?
Late prophase
What are replicated chromosomes held together by ?
The centromere
What has occurred by metaphase ?
The nuclear membrane has disappeared and all 46 chromatids are drawn to opposite poles of the cell, and two daughter cells are generated
What does the formation of germ cells require ?
Reductive division or meiosis
How are chromosomes prepared ?
- A small blood sample is removed.
- White cells are recovered and place in a culture
- An agent is added which arrests cell replication
- The cells are lysed and chromosomes are stained
What is the agent that is often added to prepare chromosomes ?
Colchicine
What are metacentric chromosomes ?
Centromere divides chromosome into equal halves
What are sub-metacentric ?
P arm is shorter than q arm
What is acrocentric chromosomes ?
No short arm
What does SRY stand for ?
Sex determining gene
What does the SRY encode ?
A transcription factor which controls the expression of testis determining genes
What does chronic myeloid leukaemia display on an ideogram ?
A chromosomal translocation - small pieces of chromosome 9 and 22 exchange places
What is the chromosomal translocation in chronic myeloid leukaemia called ?
The Philadelphia translocation
What is a treatment option for a chronic myeloid leukaemia which is not caused by translocation ?
Gleevac
What is a method of chromosome analysis ?
Multi-colour special karyotyping (SKY)
What tissue has the highest oxygen consumption per unit gram in the human body ?
Retina
What are cones required for in eyes ?
Day time vision
Where are cones found ?
Foveal pit
What are rods required for ?
Night time vision
What are some clinical manifestations of renitis pigmentosa ?
- Night blindness
- Loss of rod photoreceptors
- Tunnel vision
- Eventual complete vision loss
Where is the mutation that forms the disease retinitis pigmentosa ?
Chromosome 3
What does the mutated gene for retinitis pigmentosa encode ?
Rhodopsin
What is rhodopsin ?
A light sensitive pigment of rod photoreceptor cells
What is the mutation of rhodopsin for retinitis pigmentosa ?
A single point mutation within one allele of the gene, proline is changed to histidine at position 23 of the polypeptide.
What is the coefficient of relationship ?
The proportion of alleles shared by 2 people as a result of a common genetic descent
What is leber congenital amaurosis ?
The most prevalent form of congenial blindness. Photoreceptors are non-functional but remain alive within the retina
Signs and symptoms of Alzheimer’s ?
- Memory loss for recent events - progresses into dementia
- Inability to converse, loss of language ability
- Affective/personality disturbance - hostile
- Death from opportunistic infections
How can you confirm Alzheimer’s disease ?
- Neuronal (amyloid, beta amyloid, Abeta amyloid) plaques
- Neurofibrillary tangles
- Bain atrophy
How can you classify Alzheimer’s disease ?
- Familial verses sporadic
2. Early verses late onset
Which locus segregates with familial alzheimer’s disease ?
Chromosome 21
What is the linkage analysis test statistic ?
The LOD score
What is the LOD score ?
Based on the log of the ration of the probability of a segregation occurring under the assumption of linkage and the probability of it occurring under the assumption of independent segregation
What is linkage ?
The relationship between two or more loci
What is association ?
The relationship between the alleles of two or more loci
What is association mapping ?
The coincidence of trait and marker allele in populations
Why is association mapping a good technique for candidate gene testing ?
Resolution is high but coverage is low
