Genetics Flashcards
What are some essential features of cell division
- Faithfully replicate genetic material
- Accurately segregate into daughter cells
How long does it take to replicate the human genome?
8 hours
How long does it take to segregate the replicated genome?
2 hours
How long does it take to segregate the replicated genome?
2 hours
How is the cell division cycle controlled?
Cyclin dependent kinases
What is down syndrome?
A genetic disorder that involves having 3 copies of chromosome 21
What happens if there is a promotor or splice site sequence change?
Stop transcription or cause abnormal splicing
What could happen if there is a base change within a gene?
- Change in protein sequence
- Not every base change causes disease
- May or may not reduce protein function
- Some missense mutations make a protein work faster
- May cause a premature stop codon
What could happen if there is an insertion or deletion of bases in a gene?
Frame shifts possible so mutations can be in frame or out of frame
Describe disorders with mendelian inheritance
A change in a single gene, sufficient to cause clinical disease, is inherited in a fashion predicted by Mendel’s law
What shape represents males in inheritance diagrams?
Square
What shape represents females in inheritance diagrams?
Circle
What is nonpenetrance?
Failure of a genotype to manifest
Describe mitochondrial DNA
- 16,559 base pairs
- Many copies in a cell (because of many mitochondria)
- Contains important genes for mitochondrial metabolic pathways and ribosomal RNAs
- Inherited almost exclusively maternally
- Point mutations and deletions occur
What are some different types of growth?
- Multiplicative/replicative growth - cell replication
- Auxetic growth - cell size increase
- Accretionary growth - extracellular space increases
- Combined pattern of growth
Define hyperplasia
Increase in number of cells
Define hypertrophy
Increased cell size
What term is used to describe decreased/regressed growth?
Atrophy
What factors can be underlying causes for systemic growth disorders?
- Hormones and growth factors
- Genetics
- Nutrition
- Environmental factors
- Secondary effects of disease
Describe turner’s syndrome
- 45 chromosomes
- Missing X chromosome
- Female
- Very short
Describe Beckwith-Wiedemann syndrome
- Inheriting two copies of a chromosome from one (paternal) parent and none from the other is bad news
- Increased expression of IGF-II
- Decreased expression of H19
- Overgrowth in early childhood
What factors influence differentiation?
- Location
- Growth factors
- Hormones
- Adjacent cells
- Autocrine factors
What is metaplasia?
- Change of differentiated cell type
- Response altered cellular environment
- Often epithelial or mesenchymal cells
Describe dysplasia
- Increased cell proliferation
- Atypical morphology
- Decreased differentiation
- Often premalignant
Describe neoplasia
- Abnormal uncoordinated excessive cell proliferation
- Persists after initiating stimulus withdrawn
What is agenesis?
Failure to develop an organ or structure
What is atresia?
Failure to develop a lumen
What is hypoplasia?
Failure of an organ to develop to a normal size - may only apply to a segment of an organ
What is ectopia/heterotopia?
Small areas of mature tissue from one organ present in another
What is maldifferentiation?
- Failure of normal differentiation
- Persistence of primitive embryological features
How is a chromosome recognised?
- Banding pattern with specific stains
- Length
- Position of centromere
What is a key feature of acrocentric chromosomes?
The short arm doesn’t really matter
Which chromosomes are acrocentric?
13, 14, 15, 21, 22
What are aneuploidies?
Whole extra or missing chromosomes
What are translocations?
Rearrangement of chromosomes
What is another name for down syndrome?
Trisomy 21
What is another name for Edward syndrome?
Trisomy 18
What is another name for Patau syndrome?
Trisomy 13
What is robertsonian translocation?
Two acrocentric chromosomes stuck end to end
What are the reproductive risks involved in reciprocal translocations?
- For most translocations, ~50% of conceptions will have either normal chromosomes or the balanced translocation
- Unbalanced products result in: miscarriage (large segments) or dysmorphic delayed child (small segments)
Which chromosomes are involved in the production of a philadelphia chromosome?
9 and 22
What are the 3 single chromosome mutations?
- Deletion
- Duplication
- Inversion
What is quantitative inheritance?
Complex disorder & continuous traits are influenced by multiple genes and multiple environmental factors
Describe the threshold model
For a discontinuous phenotype with an underlying continuous distribution, a threshold exists above which the abnormal phenotype is expressed. Population incidence is the proportion beyond the threshold in the general population. Among relatives, the proportion beyond the threshold is the familial incidence
Describe heritability
- Heritability of a trait or disease is the proportion of the total variance that is genetic
- The overall variance of the phenotype is the sum of the environmental and genetic variance
- Heritability provides information on the importance of genetic factors in the causation of the disease
Describe disease causing mutations
A gene change that causes a genetic disorder
What is synonymous polymorphism?
Changes DNA sequence but not the amino acid or subsequent protein produced
What is non-synonymous missense polymorphism?
Changes DNA sequence and the amino acid and protein produced
What is non-synonymous nonsense polymorphism?
Changes DNA sequence to code a premature stop codon
What are two possible definitions of polymorphism?
- Any variation in the human genome that has a population frequency of greater than 1%
- Any variation in the human genome that does not cause a disease in its own right. It may however, predispose to a common disease
What percentage of genes do different types of twins share?
Monozygotic - 100%
Dizygotic - 50%
