Sub lesson - Chromosomal variation Flashcards
Inversion explanation:
- A section of chromosome may break odd, turn through 180 degrees and then join again.
Deletion explanation:
A part of a chromosome, containing genes and regulatory sequences, is lost.
Translocation explanation:
A piece of one chromosome breaks off and then becomes attached to another chromosome
Non-disjunction
One pair of chromosomes or chromatids fail to separate
Phases of Mitosis:
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Duplication
A piece of a chromosome may be duplicated.
What occurs in the interphase?
Chromosomes invisible and DNA replicates
What occurs in prophase?
Chromosomes appear and nucleus disappears
What occurs in metaphase?
Chromosomes at equator and spindle forms
What occurs at anaphase?
Chromatids pulled to poles
What occurs in telophase?
Chromatids at poles and nucleus reforms
What occurs in cytokinesis?
Cytoplasmic division
What is the role of meiosis for variation?
Produces gametes which fuse in sexual reproduction to form offspring.
Produces haploid cells.
Increases variation.
Homologous chromosomes in diploid cells?
Contain paternal chromosome and maternal chromosome.
- Similar length and contain same genes at the same loci, they contain different alleles.
Structure of homologous chromosomes when they replicate?
- Sister-chromatids
- Linked to homologous chromosomes by centromere.
Independent Segregation Assortment
- Happens in metaphase I, when the chromosomes line up on the equator.
- In humans, this means 23 homologous pairs of chromosomes lying side by side.
- Arrange themselves randomly.
- One of each pair will pass to each daughter cell.
- Each chromatid goes in the direction of the pole they are facing (random).
Prophase I?
- Chromosomes shorten and thicken (condense)
- Pairs of homologous chromosomes line up closely together.
- One centriole from each pair moves towards the opposite poles of the cell
- Nuclear membrane break down.
- Unique to meiosis I, chromosomes cross over and exchange genetic material.
Crossing over:
During crossing over, a chiasma randomly forms and creates a point of contact between chromatids. This allows for the exchange of genetic material.
The chiasma forms between non-sister chromatids as there are not identical and therefore the exchange of genetic material can lead to new combinations of alleles that were not seen in the parents.
Why is does crossing over increase variation?
The formation of the chiasma is completely random event and can form at any point along the length between the two non-sister chromatids.
