questions Flashcards
describe a method that the student could use to calculate the magnification accurately
use an (eye piece) graticule to measure the diameter
take several measurements and calculate the mean (for each cell)
calibrate the (eye piece) graticule
when does the crossing over first take place ?
prophase I
explain why crossing over between two different genes results in a maximum of 50 % of gametes with the recombinant alleles
- crossing over occurs between chromatids (between the same
homologous chromosomes) - therefore (only) half the chromosomes (produced by anaphase II)
will be recombinant chromosomes (so maximum of 50 %) - crossing over does not always take place (so can be less than 50 %)
explain the importance of this lower change in mean temperature to organisms that live in the oceans such as fish
if the temperature is increased - there is less oxygen for fish in water
- need appropriate body temperature for enzyme activity
explain the role of the centrioles in sperm cells following fertilisation
- to be the source of centrioles in the zygote
- so that the spindle (fibres) can be synthesised (in the zygote /
embryo) - so that the (fertilised egg cell /zygote) can divide by mitosis (to
form the embryo)
comment on how each of these five factors would results in male infertility
- low sperm count
- structural defect of sperm cells
- absence of an acrosome
- mutations in the mitochondria DNA
- chromosome mutations
- low sperm count- fewer sperm arriving at the egg cell, reducing the likelihood of fertilisation
- structural defect of sperm cells - sperm will not be able to digest through (the outer membrane of egg cell)
- absence of an acrosome - less energy available for flagellum
- mutations in the mitochondria DNA - cell division may be affected
- chromosome mutations - effects in flagellum could prevent motility - two flagella may get tangled up together
