Theme 2D Flashcards
What are mutations?
- Changes to nucleic acid sequence (DNA and RNA)
- Changes can be small (gene level) or large (chromosomal level)
- Altered gene sequence can change amino acid sequence of polypeptide resulting in phenotype variation
- Evolutions primary force: favouring beneficial mutations
What mutations can be inherited and which ones can’t?
Germline (gamete) cell mutations can be inherited. Somatic cell mutations cannot be inherited.
What are somatic cells expressed as?
Sectors (size depends on when they occurred in development). Mutation occur in a progeniter cell and all the daughter cells of it will express the mutation
What are some small mutations?
- Base substitution: single nucleotide change
- Insertion: one or more base pairs added in sequence during DNA replication, can result in frameshift mutation
- Deletion: one or more base pairs skipped during DNA replication, can also result in frameshift mutation
What are spontaneous mutations?
Naturally occurring mutations caused by DNA replication errors
- Chemical alterations to bases occur naturally in cells, but are usually repaired by DNA repair mechanisms
What are induced mutations?
Mutagens (can be either natural or artificial). Causes mutations at a much higher rate.
- Induce mutations by replacing a base, altering base so that it mis-pairs with another base, or damaging the base so that it can no longer pair correctly
What are the effects of mutations on the amino acid sequence of polypeptides?
- Missence/nonsynonymous mutations: codon change causes change in amino acid
- Nonsense: premature stop, sense codon changes into a stop codon
- Silent/synonymous: codon change does not change the amino acid due to degeneracy of the genetic code
- Frame shift: insertion or deletion of a small number of base pairs that alter the reading frame
What are some large scale mutations?
- Deletion: loss of genes
- Duplication/amplification: increasing dosage of genes
- Translocation: interchange of genetic parts from non-homologous chromosomes
- Inversion: reversing orientation of a segment of a chromosome
What is a loss of function allele?
Mutations that reduce/eliminate gene function/expression
What are gain of function alleles?
Mutations that enhance gene function/expression
What are the phases of the cell cycle?
- G1 and G2: synthesis of proteins, RNA, things other than DNA
- S phase: DNA replication
- M phase: mitosis, nuclear division
- Cytokinesis: cell division
- G0: resting phase (most adult human cells are in this phase)
What are homologous chromosomes?
Maternal and paternal pair of chromosomes. Same number and order of genes, but different alleles
What are sister chromatids?
Identical copies of a chromosome, created during DNA replication, joined at the centromere
What happens during the S phase?
- DNA replication
- Centriole duplication
What happens before prophase?
- Duplicated chromosomes condense and become sister chromatids
- Duplicated centrioles move further apart and form mitotic spindles
- Nuclear envelope breaks down
What happens in prometaphase?
- Each kinetochore of sister chromatid is attached to a spindle
- Chromosomes move to equator of the cell
What happens in metaphase?
- All chromosomes are aligned at the equator of the cell
- Chromosomes are attached to opposite poles and are under tension
What happens during anaphase?
- Cohesins are degraded
- Sister chromatids and centromere separate to opposite poles
- Centrosomes move further apart
What happens during telophase?
- Chromosomes clustered at opposite poles and decondensing
- Nuclear envelope reforms around chromosomes
- Cytoplasm begins to divide by furrowing (cytokinesis)
How are tetrads attached in meiosis?
A protein structure called the synaptonemal complex
What is different about meiosis in the first phase from mitosis?
- sister chromatids and centromeres do not split
- sister chromatids are no longer identical after recombination in prophase 1
What is different between meiosis 1 and 2?
- There is no additional DNA replication in Meiosis 2
- Centromeres and sister chromatids separate in anaphase 2
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