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)
What is the genome?
The genome is the totality of genetic information of a cell, organism or organelle
What does the genome include?
This includes all genes as well as non-coding DNA sequences (e.g. introns, promoters, short tandem repeats, etc.)
What was the Human Genome Project?
The Human Genome Project (HGP) was an international cooperative venture established to sequence the human genome
What did the HGP show?
The HGP showed that humans share the majority of their sequence, with short nucleotide polymorphisms contributing diversity
What were the 4 (general) outcomes of the HGP?
mapping
screening
medicine
ancestry
What was the outcome of the HGP in terms of mapping?
The number, location, size and sequence of human genes is now established
What was the outcome of the HGP in terms of screening?
This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic diseases
What was the outcome of the HGP in terms of medicine?
The discovery of new proteins have lead to improved treatments (pharmacogenetics and rational drug design)
What was the outcome of the HGP in terms of ancestry?
Comparisons with other genomes have provided insight into the origins, evolution and migratory patterns of man
Will the number of genes present differ between species?
YES!!!
The number of genes present in an organism will differ between species and is not a valid indicator of biological complexity
How is the number of genes in a genome predicted?
The number of genes in a genome is usually predicted by identifying sequences common to genes
What may the identifying regions be include?
These identifying regions may include expressed sequence tags (ESTs) or sequences that are homologous to known genes
What makes the counts of unique gene numbers difficult?
The presence of pseudogenes and transposons make accurate counts of unique gene numbers very difficult
Why may gene estimations greatly vary?
As scientists may use different approaches to predicting gene numbers, final estimations can vary significantly
For instance, the number of genes in rice (Oryza sativa) is estimated as being between 32,000 – 50,000
The number of genes in humans is estimated as being between 19,000 – 25,000
What can be used to compare gene sequences from two different species?
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
https://ib.bioninja.com.au/standard-level/topic-3-genetics/31-genes/gene-comparisons.html
