Animal taxonomy, evolution and genomics
What is a mutation?
A mutation is a change in DNA that affects genetic information.
How do spontaneous mutations occur?
Spontaneous mutations occur naturally at a low rate during normal cell cycles due to DNA breaks, incorrect DNA repair and replication errors
What is the base mutation rate?
The base mutation rate is the speed at which spontaneous mutations occur in DNA
What are mutagens?
Mutagens are natural physical or chemical agents that increase the mutation eate by altering DNA structure or sequence
What are chemical mutagens?
Chemical mutagens are substances that cause DNA mutations by altering bases or structure
Examples of chemical mutagens and their function:
Base analogues-substitube normal bases
nitrojs acid alters structrue and pairing
How does radiation act as a mutagen?
Radiation from the electromagnetic spectrum, especially ionizing radiation, damages DNA
What is the effect of mutations in somatic cells?
Mutations cannot be passed to offspring but may cause diseases such as cancer.
What are germline mutations?
Germline mutations are mutations in sex cells that can be passed onto offspring.
What size of genome mutations can occur?
Genome mutations can affect a single base or large segments of chromosomes.
What are small scale mutations?
small scale mutations are mutations involving only one or a few nucleotides, such as Single and Multi nucleotides polymorphisms
What are large scale mutations?
large scale mutations are mutations that affect large DNA segmenrs
What are gene mutations?
Mutations that affect a single gene
What is a point mutation?
A point mutation is a mutation involving a single base change in DNA (SNP).
What are the types of point mutations?
the types of point mutations single, missense, and nonsense mutations
What are insertion and deletion mutations?
They are mutations involving in the addition and removal or one or more nucleotides.
What is a frameshift mutation?
A frameshift mutation is a mutation that shifts the reading frame of a gene due to insertions or deletions.
What is an allele?
An allele is a variant form of a gene.
Where are alleles located on a chromosome?
Alleles are located at the same position, called a genetic locus, on a chromosome.
Why are humans described as diploid organisms?
They are described as diploid organisms because they have pairs of each type of chromosome and therefore two alleles at each genetic locus in somatic cells.
Where do the two alleles in somatic cells come from?
One allele is inherited from each parent.
Why do gametes contain only one allele of each gene?
Because gametes are haploid, so they carry one allele per genetic locus.
What does autosmal recessive inheritance mean?
Autosmal recessive inheritance refers to traits controlled by recessive alleles located on autosomes.
What is a carrier of an autosmal recessive allele?
A carrier has one normal allele and one altered recessive allele but does not show the trait.
Why do carriers usually not show symptoms of recessive conditions?
As the dominant normal allele produces enough functional protein.
Why is inheritance sometimes described as more complex than dominant and recessive?
As not all alleles show simple dominance, some are co-dominant or show incomplete dominance.
What is co-dominance?
Co-dominance occurs when both alleles in a heterozygote are fully expressed
What is meant by "degrees of dominance"?
Some alleles are particularly dominant over others rather than completely dominant.
How does fur colour in mammals demonstrate complex inheritance?
Black > brown
brown > light brown.
What does it mean when a gene has multiple alleles?
More than two alleles for a gene exist in the population.
What are quantitative characters?
Quantitative characters are traits that vary continuously within a population
What causes variation in quantitative characters?
Polygenic inheritance
Example of a quantitative character in humans?
Human skin colour
What is epistasis?
Epistasis is a genetic interaction where one gene alters how another gene is expressed.
How does epistasis affecy coat colour in mammals?
One gene determines pigment colour, while another controls whether pigment is deposited in hair.
Why doesnt population growth remain exponential?
Because resources become limited as population size increases.
Why is variation important for evolution?
It provides differences that natural selection can act upon.
What is natural selection?
The process by which better-adapted individuals reproduce more successfully.
What is genetic drift?
Random changes in allele frequencies, especially in small populations.
What is speciation?
The formation of species overtime
What type of inheritance do most human gene disorders show?
Autosmal recessive inheritance.
What is the common molecular cause of gene disorders?
Loss of function of an important protein.
What causes sickle cell anemia at a molecular level?
A missense mutation in the ẞ-globin gene replacing glutamate with valine
How do sickle red blood cells differ from normal ones?
They form a crescent shape and clump in red blood vessels
What is phenylketonuria (PKU)
An autosmal recessive disorder caused bu deficiency of phenylalanine hydroxylase (PAH).
What causes cystic fibrosis?
A defective chloride (salt) channel protein in cell membranes.
Why is cystic fibrosis life threatening?
Thick mucus traps bacteria, causing chronic lung infections.
What is meant by heterozygous advantage in cystic fibrosis?
Carriers may have protection against severe diarrhoeal diseases like cholera.
What is huntingtons disease?
An autosmal dominant, degenerative brain disorder.
Why does huntingtons disease often appear?
Typically between 30-50 years
Why are X-linked recessive disorders more common in males?
Males have only one X-chromsome.
Why are Y-linked disorders rare?
The Y chromosome carries very few genes.
How are mitochondrial disorders inherited?
Through the maternal line only.
What are complex disorders?
Diseases influenced by many genes and environmental factors.
Why are some complex disorders quantitative traits?
They show continuous variation influenced by many genes
Why is pieiotropy?
When one gene affects multiple traits.