Outline a possible cause of Down syndrome.

Outline the processes involved in oogenesis within the human ovary.

Discuss the ethical issues surrounding IVF.

non-disjunction (can cause Down syndrome);
occurs when pair of homologous chromosomes fails to separate during meiosis;
one gamete/daughter cell receives two chromosomes / diagram showing this;
occurs in anaphase I/II of meiosis;
fertilization involving this gamete leads to change in chromosome number/47 chromosomes;
most common form of Down is trisomy 21/extra chromosome 21;
increase risk of Down syndrome with increased age of mother;

oogenesis is process by which female gametes/eggs are produced;
begins during fetal development; oogonia/large number of cells formed by mitosis;
oogonia/cells enlarge/undergo cell growth/become primary oocytes;
begin first meiotic division but stop in Prophase I;
until puberty;
(at puberty) some follicles develop each month in response to FSH;
(primary oocyte) completes first meiotic division;
forms two cells of different/unequal sizes / unequal distribution of cytoplasm;
(creating a) polar body;
polar body eventually degenerates;
larger cell/secondary oocyte proceeds to meiosis II;
stops at prophase II;
meiosis II completed if cell is fertilized;
ovum and second polar body formed;

To award full marks, discussion must contain both pro and con considerations.

pros/positive considerations: [3 max]
chance for infertile couples to have children;
decision to have children is clearly a conscious one due to difficulty of becoming pregnant;
genetic screening of embryos could decrease suffering from genetic diseases;
spare embryos can safely be stored for future pregnancies/used for stem cell research;

cons/negative considerations: [3 max]
IVF is expensive and might not be equally accessible;
success rate is low therefore it is stressful for the couple;
it is not natural/cultural/religious objections;
could lead to eugenics/gender choice;
could lead to (unwanted) multiple pregnancies with associated risks;
production and storage of unused embryos / associated legal issues / extra embryos may be used for (stem cell) research;
inherited forms of infertility might be passed on to children;
Accept any other reasonable answers.

Most of the candidates gave trisomy 21 and non-disjunction, but fewer were able to accurately describe how it comes about. Confusion between genetic mutation and chromosome mutation was common especially when discussing causes.

Quite a few candidates described the process of ovulation in detail, gaining no marks. Most candidates did refer to the formation of the polar body in oogenesis, but missed out on many of the changes given in the mark scheme. Detailed discussions of the menstrual cycle were common. Some obviously understood it but could not write clearly and logically/a general lack of detail.

Most candidates gained a fair number of marks, but often limited their score by focusing on the negatives of IVF rather than the positives. But then again, the mark scheme only listed 4 pros vs 7 cons.