Lecture 2 Flashcards
What are telomeres and what are their function?
They are repeated sequences of DNA bases at the end of chromosomes that serve to protect the chromosome.
What is a centromere?
Repetitive sequence that links sister chromatids.
What happens at each stage of mitosis?
G2- loosely coiled chromosomes that have been replicated
Prophase- spindle fibres appear and chromosomes condense
Prometaphase- spindle fibres attach and chromosomes condense
Metaphase- chromosomes align on metaphase plate
Anaphase- sister chromatids pulled to opposite ends of cell
Telophase- nuclear membrane reforms and spindle fibres break down. Chromosomes decondense.
Cytokinesis- cytoplasm divides and two identical daughter cells are obtained
What are homologous chromosomes?
Two chromosomes that have the same DNA sequence and the same genes in the same locations but may be different variants which are called alleles. Eg alleles for eye colour.
Sister chromatids on the other hand have identical genes and the same alleles.
What is recombination in meiosis?
Crossing over of genetic material between non sister chromatids eg the chromatids of the other chromosome.
Crossing over sites called chiasmata.
What is a tetrad?
Two sets of two sister chromatids. The two sets are known as bivalent forms as they come from the same chromosome pair.
Can you describe meiosis?
Go back to lecture if not.
What are the consequences of meiosis?
Maintain constant chromosome number
Generation of genetic diversity through random assortment and crossing over
Why is it more likely that you will get problems with offspring if you have them when you are older?
Meiosis 2 for example only happens upon fertilisation by the egg. If this happens later in life there is a higher chance that mistakes will occur.
Can you describe the processes of oogenesis and spermatogenesis?
Yes/no
When in mitosis do the homologous pairs of chromosomes line up?
They don’t, this only occurs in meiosis
Which phase of cell cycle or chromosomes replicated?
S phase
What is the function of the sry gene on the Y chromosome?
It determines sex
What is non disjunction?
Failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis
What is a metaphase spread?
When cycle stopped in metaphase and chromosomes looked at to see banding patterns etc
What is a karyotype?
Number and type of chromosomes in a cell. Total number of chromosomes in a species
What is trisomy 21?
3 number 21 chromosomes which will result in Down’s syndrome
What is G0
Time in cell when nothing mitosis related is happening
What is aneuploidy
Abnormal chromosomes number
What is mosaicism?
Presence of two or more different cell lines in the body.
If non disjunction occurs at first post zygotes cell division then more cells will be affected if it happens later down the line. This is because later you would have a line of normal cells and a line of affected cells.
