difference between gene and allele
gene:
- a heritable factor that consists of a length of DNA and influences a specific characteristic
- a gene is a sequence of DNA that encodes for a specific trait (traits may also be influenced by multiple genes)
- a gene occupies a specific position on a chromosome(locus-singular, loci-plural)
alleles:
- alleles are alternative forms of a gene that code fro the different variations of a specific gene
- alleles posses very similar gene sequences and only differ from each other by one or a few bases
how are new alleles formed?
new alleles are formed by mutation.
gene
is a sequence of DNA that codes for a specific trait
alleles
are alternative forms of a gene that code for the different variations of a specific trait
locus
position of gene on a particular chromosome
(plural - loci)
gene mutation
is a change in the nucleotide sequence of a section of DNA coding for a specific trait
how are new alleles formed
through gene mutation
gene mutation can be ________ (3 and effect?)
- Beneficial mutations change the gene sequence (missense mutations) to create new variations of a trait
- Detrimental mutations truncate the gene sequence (nonsense mutations) to abrogate the normal function of a trait
- Neutral mutations have no effect on the functioning of the specific feature (silent mutations)
types of gene mutation (3)
- silent - no effect on protein synthesised
- missense - results in the synthesis of another protein
- nonsense - results in a stop codon
cause and effects of sickle cell anemia
- Sickle cell anaemia results from a change to the 6th codon for the beta chain of haemoglobin
- DNA: The DNA sequence changes from GAG to GTG on the non-transcribed strand (CTC to CAC on the template strand)
- mRNA: The mRNA sequence changes from GAG to GUG at the 6th codon position
- Polypeptide: The sixth amino acid for the beta chain of haemoglobin is changed from glutamic acid to valine (Glu to Val)
Consequence of Sickle Cell Anaemia
- The amino acid change (Glu → Val) alters the structure of haemoglobin, causing it to form insoluble fibrous strands
- The insoluble haemoglobin cannot carry oxygen as effectively, causing the individual to feel constantly tired
- The formation of fibrous haemoglobin strands changes the shape of the red blood cell to a sickle shape
- The sickle cells may form clots within the capillaries, blocking blood supply to vital organs and causing myriad health issues
- The sickle cells are also destroyed more rapidly than normal cells, leading to a low red blood cell count (anaemia)
significance of human genome project
the HGP showed that humans share the majority of their sequence, with short nucleotide polymorphisms contributing diversity
positive outcomes of human genome project
- Mapping – The number, location, size and sequence of human genes is now established
- Screening – This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic diseases
- Medicine – The discovery of new proteins have lead to improved treatments (pharmacogenetics and rational drug design)
- Ancestry – Comparisons with other genomes have provided insight into the origins, evolution and migratory patterns of man
genome
totality of genetic information of a cell, organism, or organelle.
includes all genes, as well as non-coding DNA sequences
human genome consists of
46 chromosomes (barring aneuploidy)
~3 billion base pairs
~21,000 genes
Gene sequences from different species can be identified and then compared using two online resources:
GenBank – a genetic database that serves as an annotated collection of DNA sequences
Clustal Omega – an alignment program that compares multiple sequences of DNA
