Meiosis and Sex determination Flashcards
What are homologous chromosomes?
Chromosomes of the same size, same centromere position and the same sequence of genes at the same loci.
Where does chiasmata form?
At points of contact between the non-sister chromatids of a homologous pair.
What happens at a chiasmata?
Sections of DNA are exchanged.
What are linked genes?
Those on the same chromosome. Crossing over can result in new combinations of the alleles of these genes.
What does random crossing over of DNA produce?
Genetically different recombinant chromosomes.
What lines the homologous pairs up at the equator?
Spindle fibres.
How are homologous pairs arranged at the equator?
Randomly.
What is independent assortment?
Each pair of homologous chromosomes is positioned independently of the other pairs. irrespective of their maternal or paternal origin.
What occurs in Meiosis II?
Each of the two cells produced in Meiosis I undergo a further division where sister chromatids of each chromosome are separated.
What determines sex in birds, mammals and some insects?
Sex chromosomes.
In most mammals what determines the development of male characteristics?
The SRY gene on the Y chromosome.
What happens to on of the X chromosomes in females?
It is randomly inactivated at an early stage of development.
What does X chromosome inactivation prevent?
A double dose of gene products which could be harmful to cells.
What are hermaphrodites?
Species that have functioning male and female gametes and usually have a partner with which to exchange gametes.
What is the benefit of hermaphroditism?
If the chance of encountering a partner is an uncommon event, there is no requirement for the partner to be of the opposite sex.
