Flashcards reviewing the objectives of IB Biology Topic 10, genetics.
Describe the behavior of the chromosomes in the phases of meiosis:
Chromosomes replicate and pair up to allow for: crossing over, and independent assortment. Starts as one diploid cell, by the end of meiosis, it is four haploid cells.
Outline the formation of chiasmata in the process of crossing over:
In Prophase I, the chromosomes pair up into a tetrad, crossing over occurs, the site of the crossing over and exchange of sections is called the chiasmata. There are 1-3 chiasmata per chromosome pair.
Meiosis results in an effectively genetic variety in gametes, due to crossing over in Prophase I and independent assortment in Metaphase 1
State Mendel's Law of Independent Assortment:
The alleles of two genes pass into gametes without influencing each other.
Explain the relationship between Mendel's Law of Independent Assortment and Meiosis:
Meiosis divides the chromosomes into groups of four. Each allele for one trait has a 50% chance of being passed on. But the two alleles combined make four different options, which makes the chances for these being passed on 25%.
Distinguish between autosomes and sex chromosomes:
Autosomes are chromosomes not directly involved in determining sex, however sex chromosomes are directly involved in this.
Explain how crossing over between non-sister chromatids of a homologous pair in Prophase 1 can result in an exchange of alleles:
There are four recombinant gametes, cross over at chiasmata in Metaphase 1 and break into four different chromosomes.
Define: Linkage Group
A linkage group is any pair of genes that are located on the same chromosome and do not assort independently.
Explain an example of a cross between two linked genes, and identify recombinants in a cross:
Alleles in linkage crosses G W ------- g w Recombinants=Gw, and Wg