5.1: Modes Of Inheritance Flashcards
(34 cards)
What does dominance refer to?
Phenotype
How is a characteristic dominant?
- if it manifests in a heterozygote (2 alleles in a locus)
Why are brown eyes dominant?
-OCA-2 gene responsible
-Active OCA-2 = BROWN EYES
-Inactive OCA-2 = BLUE EYES
What are the 5 characteristics of dominant autosomal disorders?
- Single gene disease
- Multiple generations affected
- Affected person normally has an affected parent
- 1/2 chance of offspring having disease
- Males and females are equally affected
What happens if you are homozygous for dominant autosomal disease (RR)?
Usually lethal disease
What is the pedigree pattern for dominant autosomal disorders?
Vertical pedigree pattern
What are the 3 ways that diseases can be dominant?
- Gain of function
- Dominant negative effect
- Insufficient
What is Gain-of-Function?
Genes makes a protein with a new function
-e.g/ constitutively active; protein aggregation (toxic)
What is the dominant negative effect?
Mutated form of gene interferes with the activity of proteins
-e.g/ binding of dimers/multimers which reduces activity
What is Insufficient?
Mutant in one gene results in 1/2 amount of protein made that is not enough for function
Rare - usually affects collagen
What is the mutation that causes Huntington’s disease?
Results from expansion CAG (glutamine) repeat - produces protein huntingtin
What is the result of the mutation that causes Huntington’s disease?
Abnormal intracellular Huntington protein aggregate —> gains pathological function —> toxic to neurones = cell death
What mutations causes Brittle Bone disease?
- Type I = insufficient quantities of collagen
- Type 2,3,4 = abnormal protein with altered structure that interferes with the function of the normal protein
What is the result of the mutation that causes Brittle Bone disease?
Wearing of connective tissue - especially bone
What is a carrier of a autosomal recessive disorder?
-They have lost a single copy of gene
- BUT normal one is sufficient to maintain normal function
What are autosomal recessive disorders?
- 2 copes of abnormal gene must be present in order for disease/trait to be develop
- Tend to be ‘loss of function’ mutations (e.g/deletions)
What are the 4 characteristics of autosomal recessive disorders?
- Parents and children of affected people are NORMALLY unaffected
- One of more siblings affected
- Offspring has 1/4 chance of being affected (compared to affected sibling)
- Males and females equally affected
What is the pedigree pattern for autosomal recessive disorders?
Horizontal pedigree pattern
What can increase the chance of being affected by a recessive disorder?
Consanguineous marriage (cousin marriages)
What are the characteristics of cystic fibrosis?
- failure to thrive
- defective chloride ion channel
- results in impaired airway defence
-prone to respiratory infections
-digestive issues
What mutation causes cystic fibrosis?
Various mutation in a gene encoding chloride ion channel (CFTR gene on chromosome 7)
What is the result of the mutation that causes Cystic fibrosis?
- Defective chloride ion channel - Cl does not move out of cell = mucus builds up outside
- Loss of function; work less well; degraded faster; present inadequate amounts
- recessive as gene for single channel is sufficient to maintain activity
What are the sex chromosomes?
-consists of X and Y chromosome
- determines the sex
- X = 1000-1300 genes (850 protein coding)
- Y = 150 genes (50-70 protein coding)
Who do the X-linked disorders (recessive) affect?
Mainly males (effectively dominant)
- females can be carriers and affected males are linked through females
- affected boys may have affected uncles
- homozygous females have the disorder
-parents and children of affected NORMALLY unaffected
