Lecture 17: Modes Of Inheritance Flashcards
What is meant by homozygous?
Someone with 2 identical copies of an allele
What is meant by heterozygous?
Someone with 2 different alleles for a particular gene is heterozygous
What is a single position on a gene/chromosome called?
A locus
How many chromosomes do humans have?
46 chromosomes (23 pairs)
- 22 autosomal pairs
- sex chromosomes XX and XY
What is meant by dominant autosomal?
A characteristic is dominant if it manifests in a heterozygote (i.e. 2 diff alleles at a locus)
Describe the characteristics of dominant 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 equally affected and equally likely to pass on condition
- vertical pedigree pattern
What is meant by a vertical pedigree pattern?
Disease transferred from parent to child
Multiple generations affected
Name some examples of a dominant autosomal disorder?
Huntington’s disease
Osteogenesis imperfecta - Brittle Bone Disease
What is the mutation in Huntington’s disease?
DNA expansion of a CAG repeat on chromosome 4
What is the result of the Huntington’s disease mutation?
Abnormal intracellular Huntington protein aggregate gains a pathological function and is toxic to neurons resulting in cell death
Dominant autosomal disorders tend to be either…?
- Gain of function: gene now makes a protein with a new function e.g. longer lifespan/new location thus increasing their effect
- Dominant negative effect: mutated form interferes w/activity of proteins it binds to
- Insufficient: results in 1/2 amount of protein that’s not enough for normal function
What is meant by autosomal recessive disorders?
2 copies of abnormal gene must be present in order for the disease or trait to develop
What do autosomal recessive disorders tend to be?
loss of function mutations
What is the chance of each subsequent sibling of a child affected by an autosomal recessive disorder also being affected?
1 in 4
What pedigree pattern is observed in autosomal recessive disorders?
horizontal pedigree pattern
What is an example of an autosomal recessive disorder?
Cystic fibrosis
What is the mutation that causes cystic fibrosis?
Various mutations in gene encoding chloride ion channel (CFTR gene on chromosome 7)
What is the result of mutations in cystic fibrosis?
- defective chloride ion channel
- loss of function, work less well, degraded faster or present in inadequate amounts
- impair airway defense, digestive issues
What are the sex chromosomes?
X and Y
XX = female
XY = male
What determines the sex of the progeny?
Sperm
What sex is more affected by an alteration on a gene on the X chromosome and why?
Males since they only have one copy of X chromosome
Who do X-linked recessive disorders mainly affect?
Males
Affected boys may have affected uncles
What is the risk of a brother of a son affected by X-linked recessive disorder also having the disorder?
1 in 2 risk
What are some examples of X-linked recessive disorders?
Haemophilia
Fabry’s disease
