3.1 Genes Flashcards
What is DNA?
DNA is the genetic blueprint which codes for, and determines, the characteristics of an organism
What features does DNA code for (3)?
This includes the physical, behavioural and physiological features of the organism
What is DNA packaged into?
DNA is packaged and organised into discrete structures called chromosomes
What is a gene?
A gene is a sequence of DNA that encodes for a specific trait (traits may also be influenced by multiple genes)
What is a locus?
The position of a gene on a particular chromosome is called the locus (plural = loci)
What are alleles?
Alleles are alternative forms of a gene that code for the different variations of a specific trait
For example, the gene for eye colour has alleles that encode different shades / pigments
What similarities do alleles have?
As alleles are alternative forms of one gene, they possess very similar gene sequences
Alleles only differ from each other by one or a few bases
What is a gene mutation?
A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait
What does mutation form?
New alleles are formed by mutation
What three “types” of gene mutation can there be (in terms of how they affect the organism)?
Gene mutations can be beneficial, detrimental or neutral
What do beneficial mutations do?
Beneficial mutations change the gene sequence (missense mutations) to create new variations of a trait
What do detrimental mutations do?
Detrimental mutations truncate the gene sequence (nonsense mutations) to abrogate the normal function of a trait
What do neutral mutations do?
Neutral mutations have no effect on the functioning of the specific feature (silent mutations)
What is an example of a disorder caused by a gene mutation?
Sickle cell anaemia is an example of a disorder caused by a gene mutation
How did the mutation in sickle cell anaemia arise?
The disease allele arose from a base substitution mutation – where a single base was changed in the gene sequence
What is the cause of sickle cell anaemia? (in the DNA)
Sickle cell anaemia results from a change to the 6th codon for the beta chain of haemoglobin
How is the DNA sequence different in a person with sickle cell?
DNA: The DNA sequence changes from GAG to GTG on the non-transcribed strand (CTC to CAC on the template strand)
How is the mRNA sequence different in a person with sickle cell?
mRNA: The mRNA sequence changes from GAG to GUG at the 6th codon position
How is the polypeptide different in a person with sickle cell?
The sixth amino acid for the beta chain of haemoglobin is changed from glutamic acid to valine (Glu to Val)
What does the change in the polypeptide result in people with sickle cell?
The amino acid change (Glu → Val) alters the structure of haemoglobin, causing it to form insoluble fibrous strands
What does the insolubility of Hb lead to?
The insoluble haemoglobin cannot carry oxygen as effectively, causing the individual to feel constantly tired
What does the fibrous nature of the Hb lead to?
The formation of fibrous haemoglobin strands changes the shape of the red blood cell to a sickle shape
What may the sickle cells form?
The sickle cells may form clots within the capillaries, blocking blood supply to vital organs and causing myriad health issues
What is another disadvantage of sickle cells?
The sickle cells are also destroyed more rapidly than normal cells, leading to a low red blood cell count (anaemia)
