Chapter 4: Variation & Mutation Flashcards
when is a gene expressed
when a gene is read, transcribed and translated into a protein
what is the phenotype
by coding for proteins, genes determkine important facts of biological structure and function. these observable traits are known as the phenotype
what is variation
the diversity of genetic and phenotypic traits within and between populations
what are the mechanisms behind variation
environmental factors, mutation, and sexual reproduction
what are the types of environmental factors
external = temperature, ph, avaliability of food.
internal = action of hormones
what is epigenetics
the study of inheritable (but reversable changes in gene expression without a change in DNA sequence.
epigenetics can also influence phenotype by controlling gene expression,, and can effect growth and developement of organisms
when can spontaneous mutations occur
during cell division or DNA replication
what are mutagens
physical or chemical environmental factors that induce mutations
when do spontaneous mutations occur
during the S phase of the cell cycle, when dna is exposed during replication is vulnerable to damage.
what are the main ideas scientists have formed about mutations
mutations arise spontaneously and are not directed by the environment. mutations are persistent. majority of mutations confer disadvantages on the organisms that inherit them.
how do mutations occur during meiosis
unequal corssing over, if non-sister chromatids misalign during crossing over, one gamete may gain extra nucleotides (leading to an insertion mutation), and one may lose some nucleotides (leading to a deletion mutation).
name three physical mutagens
x-rays, UV light, nuclear radiation
what do x-rays do
gene and chromosome aberrations
what does uv light do
stuctural distortion by cross-linking neighbouring nucleotides
what does nuclear radiation
breaks in DNA strands
give an example of a chemical mutagen
mustard gas , affects the base guanine , resulting in a substitution mutation
what are point mutations
the simplest form of a mutation, just a single nucleotide within the original DNA sequence is affected by a substitution, addition or deletion.
what is substitution
occurs when one nucleotide is replaced by another, they have number of affects on the translated protein, they are the source for new SNPs
what are SNPs
single nucleotide polymorphisms, if it occurs in a gene, the mutated gene sequence can be transcribed and translated into a protein that is the same as that encoded by the original form of the gene.
what are the types of point mutations
synonymous mutation, missense mutation, nonsense mutation
what are synonymous mutations
also called silent mutations, occurs when the substituted base results in a codon that codes for the same amino acid as the original codon. this happens because there is a level of redundancy in the genetic code.
what are missense mutations
when a SNP changes the amino acid.
what are nonsense mutations
occurs when a SNP creates a new stop codon within the original gene sequence, this leads to early termination of translation of the transcribed gene sequence. results in the production of an incomplete polypeptide
what is a frameshift mutation
the reading frame for the corresponding amino acid has been nudged away from the original, can be from a gene insertion or deletion, has a profound effect on the corresponding protein
what are the three effects of mutations on survival
neutral mutations, deleterious mutations, beneficial mutations.
what are neutral mutations
the protein product is unchanged compared to the original, organisms survival is unaffected. missense substitutions are sometimes also neutral mutations, if the amino acid is swapped with one with similar properties.
what are deleterious mutation
mutations may disrupt the function of an encoded protein, undermining the organism’s overall abilirty to carry out its basic processes and survive, nonsense mutations are typically deleterious.
what are beneficial mutation
gene mutation produce a new allele that benefits the survival of the organism. it could be a missense mutation that changes the function of the original protein, or a nonsense mutation that eliminates a protein that may have been harmful to the organism in some circumstances.
what are the types of chromosomal mutations
variations in chromosome number and variations in chromosome stucture
what is monoploidy
they are n, have more than one set of chromosomes
what is polyploidy
have many sets of chromosomes
what is aneuploidy
the condition in which there is an addition or loss of one chromosome from a cell (e.g. 2n + 1 or 2n - 1).
what are the types of variations in chromosome number
monoploidy, polyploidy, aneuploidy
what are the types of variation in chromosome structural
deletions, inversions, duplications, translocations
what are deletions
a region of a chromosome is lost, resulting in the absence of all the genes in that area.
what are inversions
one region of a chromosome is flipped and reinserted.
what are duplications
a region of a chromosome is repeated, resulting in an increase in copies of the genes in that region.
what are translocations
a region from one chromosome is aberrantly attached to another chromosome.
what is independent assortment
during meiosis, homologous chromosome pair and then randomly move to different daughter cells.
what are the causes of variation is sexual reproduction
crossing over, independent assortment and random segregation, crossing over, random fertilisation.
what is crossing over
the swapping of alleles that occurs in meiosis during prophase I only. during the formation of off and sperm cells in meiosis, paired maternal and paternal homologous chromosomes align so that corresponding DNA sequences from the paired chromosomes are able to cross over one another.
what is random segregation
during anaphase I, the randomly lined up maternal and paternal homologous chromosomes move to opposite poles of the cell
what is random fertilisation
the random union of gametes. because a male gamete can fertilise any of the females gametes, resulting in a unique combination of the maternal and paternal genes
what is non-disjunction
the two identical chromosomes do not separate, but go into the same cell. it results in the formation of two types of gametes in equal proportions, but one type has two copies of a particular chromosome, and the other has none.
define mutation
a mutation refers to a change in the base sequence of an organisms DNA.
causes of mutations
mutagens:
- chemicals
- radiation
- toxins
cellular error
- chromosomal
- point
when can a mutagen not arise
during cell divison
Explain why insertion and deletion mutations can have a profound effect on the protein produced by a gene.
- Insertion- additional bases added to sequence (1)
- Deletion- bases removed from sequence (1)
- May cause a FRAMESHIFT (1),
- the ‘reading frame’ has shifted/moved, every codon after the mutation is read incorrectly. (1)
identify three factors that increase genetic diversity and explain each one
Random Assortment (1)
During metaphase I, the homologous chromosomes line up in a random order at the equator of the cell (1)
therefore the chromosomes that sort into the new cells is a chance event (1).
Fertilisation (1)
Any two gametes combine to form a diploid zygote (1) so any egg or sperm has the same chance to be fertilised (1).
Crossing Over (1)
Non-sister chromosomes (of homologous pairs) tangle during Prophase I (1)
Two non-sister chromatids exchange DNA material (1)
and new allele combinations are created (1).
