Modes of Inheritance Flashcards
Describe DNA in bacteria
- Bacteria usually have one DNA chromosome (unlike human cells which generally have 23 pairs of chromosomes)
- Asexual reproduction – one bacteria divides into two
- Their genomes encodes ~ 4000-6000 genes
- Each gene encodes for an mRNA
- Each mRNA encodes one protein
What is homozygous and heterozygous?
- Someone with two identical copes of an allele is homozygous for that gene
- Someone with two different alleles for a particular gene is heterozygous
What is a single position?
A locus
What doe each gene have?
alleles
How many genes, chromosomes, autosomal pairs do we each have?
- Human genetic material encoded on chromosomes
- 25000 genes
- 46 chromosomes (23 pairs)
- 22 autosomal pairs
What are sex chromosomes?
- Sex chromosomes XX and XY
* DNA obtained from the father and mother
What are human genetic disorders ?
- Sometimes a human has genes that are mutated or missing from their make-up altogether. In such cases, the missing or abnormal genes can cause a human genetic disorder
- Single gene Disorders (Focus of this lecture)
- 4000 different types
- Most common approximately 1/500 to very rare per disease
- BUT they affect a large number of people and affect all body systems and hence all specialties
- Chromosomal Disorders
- 1/150 babes
- Complex Disorders
- Inherited and environmental factors
What is dominant autosomal?
•A characteristic is dominant if it manifests in a heterozygote (ie two different alleles at a locus)
Describe dominate autosomal disorders
- Single gene/allele disease or trait
- Disease passed down to offspring with multiple generations affected
- Each affected person normally has one affected parent
- Each child of an affected person has a 1 in 2 chance of being affected
- Males and females are equally affected and equally likely to pass on the condition
- Vertical pedigree pattern
What is Huntington’s disease?
Huntington’s disease background: 1/20000 in UK
•Symptoms usually start 30-50 years of age
•Difficulty concentrating, depression, stumbling, involuntary jerking, problems swallowing
Mutation
•Results from a DNA expansion of a CAG repeat on chromosome 4
Result
•Abnormal intracellular Huntington protein aggregate gains a pathological function and is toxic to neurons resulting in cell death
What is Osteogenesis imperfecta?
Osteogenesis imperfecta – brittle bone disease: 1/15000
•Group of genetic disorders mainly affecting bones
•Bones break easily
•Mild to severe
•Hearing loss, breathing problems, short height, blue tinge to whites of eye
Mutations
•Type I – insufficient quantities of Collagen
•Type II, III and IV mutation of gene results in an abnormal protein has an altered structure and interferes with the function of the normal protein (expressed from the normal gene)
Result
•Weakening connective tissue particularly bone
What do dominant autosomal disorders tend to be?
- Gain-of-function- gene now makes a protein with a new function eg longer lifespan/new location thus increasing their effect
- Dominant negative effect- the mutated form interferes with the activity of proteins it binds eg dimers or multimers which reduces activity
- Insufficient- mutant in one gene results in ½ the amount of a protein that is not enough for normal function
What re carriers of autosomal recessive disorders?
•Carriers of recessive diseases have lost a single copy of a gene but the normal one is sufficient to maintain normal function
What are autosomal recessive disorders?
- Recessive means that two copies of the abnormal (non-working) gene must be present in order for the disease or trait to develop
- Tend to be ‘loss of function’ mutations (eg deletions)
- Parents and children of affected people are normally unaffected
- One of more siblings affected
- Each subsequent sibling of an affected child has a 1 in 4 chance of being affected
- Males and females equally affected
- A horizontal pedigree pattern
What is cystic fibrosis?
Cystic fibrosis 1/3000 newborns •Failure to thrive •Defective chloride ion channel •Results in impaired airway defense •Prone to respiratory infections •Digestive issues eg meconium ileus •Largest cohort of chronically infected patients Mutations •Various mutation in gene encoding chloride ion channel (CFTR gene on chromosome 7) Result •Defective chloride ion channel •Loss of function, work less well, degraded faster or present in inadequate amounts
