Genetic variation Flashcards
What is a gene?
A section of DNA that contains the coded information for making polypeptides and functional RNA
What does a universal code mean?
Every sequence of the bases codes for the same amino acids
What does a degenerate code mean?
More than one different triplet can code for the same amino acid
What is an intron?
Non-coding DNA
What is an exon?
Coding DNA
Describe tRNA
a small single stranded molecule folded into a clover leaf shape, with one end of the chain extending beyond the other.
Describe mRNA
Single stranded molecule small enough to pass through nuclear pores to enter the cytoplasm where the codons are translated to synthesise a protein.
Describe the process of protein synthesis
Transcription- production of mRNA by using DNA as a template. A length of DNA is transcribed into a mRNA molecule
DNA helicase acts on a specific region of the dna causing 2 strands.
Translation- after DNA is transcribed to mRNA, the codons then must be translated into a sequence of amino acids to make a polypeptide using tRNA
Once mRNA is outside the nuclear pore and tRNA is now bound to amino acids, must associate with a ribosome on the RER.
What is a mutation?
A change to the dna base sequence causing a change to the phenotype of an organism
Define a gene mutation by deletion
Arises when a nucleotide is lost from the normal dna sequence- the removal of a single base will cause a frame shift resulting in an entirely different polypeptide
Define a gene mutation by base substitution
The polypeptide will differ in a single amino acid, the significance of this depends upon the precise role of the amino acid
What is a chromosome mutation?
Changes in the structure or number of whole chromosomes
Define polypoidy
Changes in whole sets of chromosomes occur when organisms have three or more sets of chromosomes
Define non-disjunction
The failure of homologous chromosomes to separate properly during cell division
What is the purpose of mitosis
To produce 2 genetically identical diploid daughter cells
What is the purpose of meiosis
To produce 4 genetically different haploid daughter cells
What happens in prophase 1
The chromosomes condense and the nuclear envelope breaks down. Crossing-over occurs.
What happens in metaphase 1
Pairs of homologous chromosomes move to the equator of the cell
What happens in anaphase 1
Homologous chromosomes move to the opposite poles of the cell
What happens in telophase 1 and cytokinesis
Chromosomes gather at the poles of the cells and the cytoplasm divides
What happens in prophase 2
A new spindle forms around the chromosomes
What happens in metaphase 2
Chromosomes line up at the equator
What happens in anaphase 2
Centromeres divide. Chromatically move to the opposite poles of the cells.
What happens in telophase 2 and cytokinesis
A nuclear envelope forms around each set of chromosomes. The cytoplasm divides.
When does independent segregation occur
Metaphase 1 and metaphase 2
What happens during independent segregation
Each chromosome lines up alongside its homologous partner
Describe the process of crossing over
During prophase 1, chromatids of each pair become twisted around one another, during this twisting process tensions are created and portions of chromatids breaks off and rejoin
Define genetic diversity
Variety of different alleles within a population
Define gene pool
Total collection of genes and their alleles present in a population of a particular species
Define genotype
All of the alleles that an organism carries on its chromosomes
Define Phenotype
Physical and behavioural traits of an organism
What is natural selection
The process where advantageous traits increase in frequency within a population over time e
What are the three types of natural selection?
-directional selection
-stabilising selection
-disruptive selection
What is directional selection
Favours one extreme phenotype, causing a shift in the populations traits
Define stabilising selection
Favours intermediate phenotypes and selects against extreme traits
What is disruptive selection?
Favours extreme phenotypes at both ends of the spectrum and selects against intermediate phenotypes
Define genetic diversity
Variety of different alleles in a population
Define population
A group of organisms of the same species, living in the same area at the same time
Define community
A group of populations living and interacting with each other in an area
Define habitat
The environment in which a species normally lives
Define ecosystem
A community and its abiotic environment
What are the different groups in classification
Domain, kingdom, phylum, class, order, family, genus, species
What are the different forms of classification?
Artificial classification, natural classification and phylogenetic classification
What are the different domains?
Bacteria, archaea, eukarya
What are the 4 kingdoms?
Protocista, fungi, plantae, animalia
