Topic 10 Flashcards
When do chromosomes replicate?
During interphase
What phase of interphase does DNA replication occur?
S phase
What is produced from DNA replication?
Two sister chromatids that are held together by a centromere
Which meiosis do sister chromatids separate?
Meiosis 2
Which meiosis do sister chromatids separate?
Meiosis 2
Outline the stages of meiosis
P1 M1 A1 T1 P2 M2 A2 T2
What happens during prophase 1?
Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
What happens during metapahse 1?
M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
What happens during Anaphase 1?
A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
What happens during Teleophase 1?
Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
What happens during Prophase 2?
Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
What happens during Metaphase 2?
M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
What happens during Anaphase 2?
A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
What happens during teleophase 2?
T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
Why is there an independent assortment of genes?
Due to random orientation of pairs of homologus chromosomes
What is the orientation of each pair of chromosome?
The orientation of each homologous pair is random and is not affected by the orientation of any other homologous pair
When will independent assortment not occur?
When genes are located on the same chromosome ( linked genes)
What chromatids do a chiasmata form between?
Non sister chromatids
Synapsis
- During prophase I of meiosis, homologous chromosomes become connected in a process known as synapsis
- The connected homologues are known as a bivalent
- While autosomes always undergo synapsis during meiosis, sex chromosomes often remain unpaired
Chiasmata
While in synapsis, non-sister chromatids may break and recombine with their homologous partner (crossing over)
These non-sister chromatids remain physically connected at these points of exchange – regions called chiasmata
Chiasmata (singular = chiasma) hold the homologous chromosomes together as a bivalent until anaphase I
Chiasmata formation between non-sister chromatids can result in the exchange of alleles
Draw a diagram to show chiasmata formation
What does crossing over produce?
-Crossing over produces new combinations of alleles on the chromosomes of the haploid cells
What is crossing over?
The exchange of DNA between non sister chromatids
What are recombinant chromosomes
The chromosomes that consist of genetic material of both homologues
