Biology Forums - Study Force

1) A onion root tip and the whole onion root tip has 200 cells in total. of these 200 cells, 120 are in interphase, 34 are in prophase, 20 are in metaphase, 12 are in anaphase and 14 are in telophase. If a cell undergoes mitosis in 24 hours, then how long does the average growing onion cell spend in metaphase and interphase. 2 marks

2) compare and contrast phenomena that occur in prophase of mitosis and meiosis. 3 marks

3) in molecular genetics, a deletion, substitution, or mutation of a single nucleotide can have adverse effects on an organism. Explain two effects if a whole chromosome is lost in the process of meiosis. 4 marks

In mitosis the homologous chromosomes do not pair up. In meiosis the homologous chromosomes pair up to form tetrads and genetic exchange takes place between non - sister chromatids in a process called crossing over.

Monosomies (when instead of inheriting one chromosome from your mom, and one from your dad, you only inherit one total) are pretty much all lethal, unless it's a sex chromosome. Having a trisomy (three copies, instead of two) is barely better. Down's is the mildest trisomy you can have (of non-sex chromosomes, having 3 X's is mild, having XYY is even milder), there are about 2 more survivable trisomies, the rest are lethal.

It's called "gene dosage". Bad things happen if you don't have the same gene dosage across your genome. Duplicating your whole genome, as some plants sometimes do, is different.

While a cell might live, a multicellular organism would be unlikely to develop unless there were very few developmental genes on the chromosome. Some tumor cells are missing a number of chromosomes, especially those which have genes that slow cell proliferation. Those same genes can tell cells when to stop proliferating in normal development. Of the human chromosomes, only a absence of a second sex chromosome of compatible with life. Partial deletions produce specific patterns of abnormality, with severity following the extent of the deletion.