Genetic Diseases - Genetic Inheritance Flashcards
What is a genetic disease?
Disease that is caused by an abnormality in an individual’s DNA
About genetic diseases:
- Most genetic disorders are quite rare
- Genetic disorders may or may not be inherited (passed down from the parents to offspring)
- In non-heritable genetic disorders, defects may be caused by somatic mutations - changes to the DNA of somatic cells after the birth
- The defect can only be heritable if genetic disorder occurs in the germ line
Types of genetic disorders
- Single gene defects
- Chromosome abnormalities
- Multifactorial disorders
- Cancer (progressive accumulation of mutations in different genes and different chromosomes abnormalities, usually in somatic cells)
RECAP DNA to proteins:
- DNA sequence transcribed into RNA
- Mature mRNA is translated into proteins.
RNA sequence is read consecutively in groups of three consecutive nucleotides (codons), from the start codons
- Codons are nonoverlapping and the message has no gaps
- There are stop codons that block the translation
Gene (unit of heredity)
encodes the synthesis of a gene product, usually a protein (or RNA), according to its nucleotide sequences, following the genetic code
Single gene disorders
Group of over 10,000 diseases caused by changes or mutations that occur in the DNA sequence of a single gene, producing either an altered protein or no protein at all
Mutations can lead to…
a) a gain-of-function but also to a loss-of-function (conferring abnormal or enhanced protein activities)
b) The resulting protein alteration/deficiency is responsible for the disease symptoms
c) A condition that is present from birth (congenital
The gene mutation may be passed between generations:
If present at birth or arise in germ cells of a parent
Different mechanism of inheritance:
- autosomal dominant
- autosomal recessive
- X-linked recessive or dominant
autosomal dominant
if a single mutated allele is sufficient to cause the disease (heterozygosis)
autosomal recessive
- if both mutated allele must be inherited to be affected (homozygosis)
X-linked recessive or dominant
mutated gene is present on the X chromosome
Mutations alter the coding information of genes, in different ways:
- Missense mutations
- Nonsense mutations
Missense mutations
These are base changes that alter the codon for an amino acid resulting in its replacement with a different amino acid
Nonsense mutations
Base changes that convert an amino acid codon to a stop codon, resulting in a premature termination of translation and the production of a shortened protein
Silent mutations-
do not cause any change in an amino acid
Frameshift mutations
These mutations result from the insertion or deletion of one or more bases causing the alteration of the reading frame of the gene and a different set of codons, leading to an altered protein
Promoter mutations or mutations on other regulatory sequences
Affect the way gene transcription is regulated, often abnormally reducing or enhancing the expression of certain genes
Promoter mutations or mutations on other regulatory sequences
Affect the way gene transcription is regulated, often abnormally reducing or enhancing the expression of certain genes
Sickle cell Anaemia
Autosomal recessive
Caused by homozygosity (sickle cell Anemia)
both alleles - for a point mutation in the beta-globin gene within the chromosome 11
Normal Red Blood Cell
- Red blood cells shaped like a disk
- Haemoglobin (protein) carries oxygen to all parts of the body
Sickle Red Blood Cell
- Red blood cells form an abnormal crescent shape
- Haemoglobin (protein) is abnormally shaped
- Don’t move easily through your blood vessels
-Form clumps and get stuck in the blood vessels
What does sickle cell Anaemia cause?
Blockage in blood vessel by blood cells preventing flow
Cystic fibrosis
autosomal recessive
