Lecture 7

Question 1

What is unique about neurospora crassa?

Answer 1

One of the first model organisms used by beadle and tatum
exists as a haploid fungi (n=7)
reproduces both sexually and asexually
when different mating types come into contact their nuclei fuse to form diploid nuclei which then undergo meiosis and mitosis in order to from unique ascospores

Question 2

What is the process of ascospore formation?

Answer 2

2n meiocyte undergoes meiosis I and II in order to form a tetrad with four haploid nuclei, this then undergoes a mitotic division so each haploid nuclei duplicates to from an octad ascospore

Question 3

How can centromeres be mapped in neurospora crassa?

Answer 3

The distance from a locus to a centromere can be mapped by observing the frequencies of patterns spore types arriving after secondary and primary division in the ascus
We then divide the number of 2nd divisions by two, divide this by the total number of ascis and then multiply by 100 to find the map distance from the centromere to the gene

Question 4

What is the physical basis for recombination?

Answer 4

Barbara McClintock and Harriet Creighton found a single chromosome with abnormalities (a kink and a knob) at each end
They found that some of the offspring had one of these abnormalities on one chromosome and the other abnormality on its pair showing that the two had recombined, this also was confirmed by genetic markers in each abnormality

Question 5

What is chiasmata?

Answer 5

The crossing over point between two chromosomes

Question 6

Can crossovers involve more than one chromatid?

Answer 6

Yes, but any single cross over can only occur between two chromatids