Mutation and Meiosis Flashcards
Define gene mutation.
A change in the base sequence.
Why can a mutation have a positive effect?
Mutation can change the sequence of amino acids, making a protein (e.g. enzyme) that may be more efficient at its function. Organism more likely to continue coding for better protein.
Why can a mutation have no effect?
Because of degenerate nature of genetic code, the triplet may still code for the same amino acid despite the change in base/s. Same polypeptide chain made.
Why can a mutation have a negative effect?
Mutation may change the sequence of amino acids, making a protein that cannot perform its function. For example, a change in the active site of an enzyme may no longer be complementary to substrate.
What are the two most common types of gene mutations?
- Base Substitution
- Base Deletion.
What effect does Base Substitution have?
Nucleotide in DNA replaced with a nucleotide with a different base. Different amino acid may be produced, may have no effect on degenerate code or changes tertiary structure of proteins.
What effect does Base Deletion have?
Nucleotide is lost from normal DNA sequence. Causes frame shift as different amino acids are formed past that point. Polypeptide unlikely to function correctly.
Define chromosomal mutation.
Change in gene or quantity of DNA.
What are two types of chromosomal mutations?
- Polyploidy
- Non-Disjunction
Describe polyploidy.
Changes occur in number of sets of chromosomes. Organism may have three or more sets of chromosomes. Common in modern wheats.
Describe Non-Disjunction.
Chromosomes fail to seperate correctly in meiosis. Gametes or zygotes formed from that will have one more or less chromosome than they should.
What are the stages of meiosis?
- Homologous chromosomes pair up. Cell divides to form two daughter cells with one chromosome from each homologous pair.
- Chromatids from each chromosome split up and cells seperate to produce 4 haploid daughter cells.
What is the purpose of meiosis?
Produce 4 haploid gamete (daughter) cells.
Describe Independent Assortment.
Homologous pairs of chromosomes line up along the equator of the cell in a random arrangement. When cell divides, the number of maternal and paternal chromosomes are random inside each cell.
Describe Crossing-Over.
One chromosome may swap places with the same part of its homologous pair leading to a combination of different alleles on the gene. Happens when chromosomes are lined up (chiasmata) and exchange genetic material.
