C23 - Patterns of Inheritance Flashcards
What’s a genotype?
Genetic composition of an organism, which describes all the alleles it contains.
Genotypes for a particular locus can be heterozygous or homozygous.
What’s a phenotype?
An organisms observable characteristics. It results from the interaction of genotype and environment.
What’s a gene?
A length/section of DNA that codes for the production of a particular polypeptide.
What’s a locus?
The position in a chromosome of a particular gene
What’s an allele?
A gene variant. A gene can have many different variants and they all occupy the same locus.
What does dominant and recessive mean?
Dominant - allele is expressed and affects an organisms phenotype, even when with a recessive allele.
Recessive - allele only expressed when the dominant is absent.
What’s codominance?
When two alleles both contribute to the organism’s phenotype to an equal extent.
When 2 codominant alleles are present, both are transcribed and translated to produce polypeptides.
What’s cystic fibrosis?
A genetic disease caused by (2) recessive alleles.
Homozygous recessive genotype leads to a faulty transport protein, producing sticky mucus, infertility, poor growth and salty skin.
Normally, the CTFR mRNA is translated to produce a transmembrane protein controlling the movement of Cl- ions. In CF, this protein doesn’t function. (Affected gene locus is on chromosome 7).
What are the 3 types of mutation?
Substitution / point mutation - a nucleotide is exchanged for a different one.
Insertion - an extra nucleotide or nucleotides are placed into the DNA sequence.
Deletion - a nucleotide or nucleotides are removed
What’s a frameshift?
When insertion or deletion mutations alter all subsequent triplet codes in the DNA sequence, and not only the triplet where the mutation occurs.
This usually produces a non-functioning polypeptide.
What are the types of substitution mutation?
Silent - the same amino acid is still coded for due to the code being degenerate
Nonsense - stop codon produced
Missense - a different amino acid is coded for
What’s phenylketonuria (PKU)?
A genetic disease caused by inheriting 2 recessive alleles. (Affected gene locus is on chromosome 12).
It prevents the enzyme phenylalanine from being made which can accumulate in babies and cause brain damage.
What’s Huntington’s disease?
A genetic disease caused by an insertion mutation in a gene on chromosome 4 / an accumulation of protein fragments in brain neurones.
The (CAG) triplet is repeated over 40 times in the gene
It’s a result of a dominant allele.
What’s sickle cell anaemia?
A genetic disease as a result of a substitution mutation in the gene coding for beta polypeptides in haemoglobin.
(Affected gene locus is on chromosome 11).
This mutation causes valine to be added to the polypeptide’s primary sequence instead of glutamic acid.
What happens in a silent mutation?
A base in a DNA triplet is substituted for another, however the same amino acid is produced.
What happens a nonsense mutation?
A base in a DNA triplet is substituted for another, which results in a stop codon being produced (on the mRNA).
What happens in a missense mutation?
A base in a DNA triplet is substituted for another, which codes for a different amino acid.
What chromosome locus is affected by cystic fibrosis?
Chromosome 7
What chromosome locus is affected by phenylketonuria (PKU)?
Chromosome 12
