4 Genetic Information & variation- Mutations & meiosis Flashcards
What are mutations?
Changes to the base sequence of DNA
Almost always harmful- interrupt normal functioning of a protein
What causes mutations?
Addition,deletion and substitution of bases
What is an addition mutation?
Where one or more bases are added to the DNA sequence
e.g. ATCGTT—> ATCCGTT
What is a deletion mutation?
Where one or more bases are removed from the DNA sequence
e.g. ATCGTT—> ATCTT
What is a substitution mutation?
Where one or more bases are changed in the DNA sequence
e.g. ATCGTT—> ACCGTT
What processes cause gene mutations?
DNA replication
-Bases in DNA sequence are read & copied; can be errors in replication process, causing mutation, which are spontaneous
Mutagenic agents
-Increase rate of gene mutations. Include chemicals, e.g bromine, and exposure to ionising and ultraviolet radiation
Chromosome mutation
-Arise spontaneously during meiosis, affect number of chromosomes in developing zygote (aneuploidy) Non-disjunction= chromosomes don’t separate properlyi
What is meiosis and its role?
The process that produces haploid (half number of chromosomes) gamete cells from diploid (full amount of chromosomes) cells. It is necessary for sexual reproduction to take place; gametes fusing together to make a new diploid organism, one copy of chromosome from each parent
How is meiosis genetically diverse?
-Makes 4 genetically diverse daughter cells, which receive different combination of chromosomes
-Random fertilisation means that any 2 gametes can fuse together to produce a random combination of chromosomes
What happens in the first stages of meiosis?
-Chromosomes in cells replicate, produce identical copy of each other- chromatids. These condense to form a double-armed chromosomes; each arm made from one chromatid and joined by a centromere, called sister chromatids
-Chromosomes are found in homologous pairs (chromosomes w/ identical genes, different alleles). They’re arranged in the centre of a cell, moved by spindle fibres
-Homologous chromosomes separate, pulled to opposite ends of cell by spindle fibres; the separation from each pair is random, and they’re pulled to each side of cell
What happens during cell division (meiosis I)?
-As homologous chromosomes separate, cell divides into two cells
-One chromosome from each pair is separated into each cell
-This is meiosis I, and produces 2 genetically different daughter cells
-Sister chromatids separated randomly by spindle fibres, pulled to opposite ends of cell
What happens during the 2nd cell division (meiosis II)?
- As sister chromatids separate, cell divides into 2 new cells.
-One chromatid from a chromosomes is separated into each cell; this is meiosis II
-Produces four genetically different haploid cells
What are the 2 ways in which meiosis creates genetic variation?
Crossing over & independent segregation
What is crossing over?
-Chromosomes of a homologous pair are arranged down the middle of a cell before first division in meiosis I
-Sections of DNA are swapped between chromosomes in a pair; this is crossing over
-Produces new combinations of alleles; a key part of genetic recombination
-Increases genetic variation
What is independent segregation?
The process of separating chromosomes into random combinations
-Chromosomes in homologous pair are separated in meiosis I in random formation, producing 2 genetically different daughter cells
-Increases genetic variation
What is the difference between meiosis and mitosis?
Number of cells
-Meiosis; 4, mitosis; 2
Number of chromosomes
-Meiosis; haploid, 23 (half of parent cell), mitosis; diploid, 46
Genetic variation
-Meiosis; genetically different daughter cells, mitosis; genetically identical daughter cells
Products
-Meiosis; gametes only, Mitosis; replication of every body cell
