Week 2: Genetic diseases Flashcards
What is the Boveri-Sutton chromosome theory?
Shows that chromosomes are the basis of all genetic information
Each gene is found on a specific loci on a specific chromosome
The behaviour of chromosomes in meiosis undermines Mendels law of inheritance
What are Mendels Law?
Law of dominance
Law of segregation (chromosomes exist in pairs that seperate during gamete formation - each gamete will only contain one copy of each chromosome)
Law of independent assortment (Different pairs of chromosomes seperate independently of each other)
What two processes do chromosomes undergo in meiosis?
- Segregation
- Independent assortment
What is a reciprocal cross?
Genetic testing to identify the importance of parental sex in inheritance
Uses two crosses of pure breed parents
1. Affected female x unaffected male
2. Affected male x unaffected female
Compare the proportion of affected offspring
What is a pattern of inheritance?
How genetic variant are distributed and passed on in families
Define autosomal dominany
One copy needed for trait to be expressed and person affected.
Either inherited or mutated
Give an example of an autosomal dominant condition?
Huntington disease
Achondroplasia
Define autosomal recessive
Both copies of gene must have the mutated allele in order to be expressed and the person affected.
Typically skip generations
Give examples of autosomal recessive conditions
Hurler syndrome
Cystic fibrosis
Sickle cell disease
Define X-linked dominant
Gene loci on x-chromosome, one mutated version sufficient to express trait and person be affected
Give an example of an X linked dominant condition?
Fragile X syndrome
Define X-linked recessive
Gene carried on X-chromosome, all copies of allele must be mutated allele is needed to express the trait and person be affected.
More common in males
Give some examples of x linked recessive conditions
Colour vision deficiency
Duchennes Muscular Dystrophy
Hemophilia
Hunter syndrome
What is a Y-linked genetic condition?
Gene carried on Y chromosome
Passed from father to son
Give an example of a Y linked condition?
Y chromosome infertilltiy
What is meant by co-dominance?
Both alleles of a gene are apparent in the phenotype
(Striped flower)
What is meant by incomplete dominance?
Pink flower
An allele has a partial effect over the other allele
What is an example of a codominant condition?
ABO blood group
What is meant by mitochondrial inheritance?
Also known as maternal inheritance
Genes in mitochondrial DNA, only eggs contribute to zygote mitochondrial DNA.
Only passed through maternal lines but can affect daughters and sons
What is an example of a mitochondrial inherited condition?
Leber hereditary optic neuropathy
What is huntington disease?
Autosomal dominant
Brain disorder causing uncontrolled movement, emotional problems and loss of cognition.
Characterised by progressive breakdown of nerves and atrophy of cortex
What is cystic fibrosis?
Autosomal recessive
Thick sticky mucus build up in the lungs and other organs
Mutation affects the ability to regulate chloride and water movement across the cell membrane
What is fragile X syndrome?
X-linked dominant
Causes a range of development problems including learning disabilities and cognitive impairment
What type of genetic disease is an example of non-medelian pattern of inheritance?
Mitochondrial DNA diseases
Affected mother - all children will be affected
Affected father - no children will be affected
Only one copy of gene, always inherited from mother
What is meant by genomic imprinting?
Occurs in gametogenesis before fertilisation
When the ability of a gene to be expressed depends on the sex of the parent who passed on the gene.
The imprinting is erased with each meiotic division, although is maintained by mitosis
New imprinting pattern forms by epigenetics - CpG hypermethylation and histone hypoacetylation.
Typically the same pattern of genes are imprinted in each human
The imprinted gene is silenced and the other allele expressed
What is epigenetics?
Heritable changes in gene expression, without altering the base sequence of DNA.
Caused by changes in the envrionment
Mainly includes DNA methylation and histone tail acetylation
WHat are some examples of epigenetic changes?
DNA packing - folding of DNA into compact structure to fit within the nucleus
DNa methylation
Dietary impacts
Environmental impacts
Transposable elements - DNA sequences that move from one area to another
Regulatory genes
Individual lifestyle
What are some disorders related to epigenetics?
Cancers
Mental retardation associated disorders
Immune disorders
Pediatric disorders
Neuropsychiatric disorders
What are the enzymes associated with different blood groups?
Type A: gene codes for GTA glycotransferase that adds N-acetylgalactosamine
Type B: gene encodes GTB: glycotransferase that adds galactose
Type O: no enzyme
Note the two enzymes are almost identical with only four different amino acid changes
Describe the patterns of inheritance of blood groups
Rhesus independent of ABO, RhD antigen is dominant
AB dominant over O
A and B are co-dominant
Gives a total of eight different possible blood groups
How common are the different types of blood groups?
O - 47%
A - 42%
B - 8%
AB - 3%
Draw a table to show the antigens expressed on the rbcs and the antibody made in each blood group?
What is the physiological state of chemical alteration of DNA?
DNA is subject to many chemical alteration, these changes must be corrected to ensure the genetic information encoded is not corrupted.
A failure to repair DNA results in a amutation
What is a transition mutation?
A type of substitution mutation that replaces a pyrimidine with a pyrimide and a purine to purine.
What is a transversion mutation?
A type of substition mutation with changes the base from a pyrimidine to a purine and vice versa