By Laura Kuenssberg
BBC political correspondent
The embryo bill is seen as a question of conscience
Questions of morality will dominate the House of Commons at the beginning of this week.
As the Human Fertilisation and Embryology Bill returns to be debated by MPs, the government is preparing itself for Labour backbenchers to vote against parts of its own programme.
Debate about hybrid embryos will begin sometime after 3.30pm in the House of Commons on Monday.
The proposal to allow the mixing of DNA from human cells with animal eggs, which would then be used for research, is seen as an attack on the dignity of life by some MPs from all of the political parties, a group which includes some ministers.
The government's belief though is that permitting and regulating the creation of animal-human embryos is essential.
Labour MPs will be allowed a free vote at this stage of the bill on these issues, seen as questions of conscience.
An amendment being suggested by the Conservative shadow health secretary, Andrew Lansley, would remove the permissibility of "50-50" hybrids, which combine either animal egg and human sperm, or human egg and animal sperm.
Some MPs believe this amendment gives them the best chance of defeating the government.
Permission to create these types of "pure hybrids" was not in the government's original legislation.
As legislation stands, clinics must take account of the welfare of the unborn child, including the need for a male parent
And this would not impact on the regulation of the kind of hybrids which have already been created during some scientific research in the UK.
These are created by transferring DNA from human cells, such as skin cells, into animal eggs that have had virtually all their genetic information removed.
The resulting embryos are more than 99% human, with a small animal component of around 0.1%.
Fewer MPs object to this than to the so-called pure hybrids - and some MPs are confident that this amendment will garner a good deal of support.
On Monday evening MPs will also vote on the creation of so called saviour siblings, children created through fertility treatment, so that their cells can be used to help a sick brother or sister.
Then on Tuesday afternoon, MPs turn to the controversial issue of the need for a father.
As legislation stands, clinics must take account of the welfare of the unborn child, including the need for a male parent.
Andrew Lansley is against combining human and animal matter
But the government bill would remove this, to try to end discrimination against single women or lesbian couples, who may be turned away by some fertility clinics.
As with the hybrid embryos this is one of the parts of the debate where strong views are held - and where Labour MPs have been given a free vote.
Then, later on Tuesday evening, will come perhaps the most controversial and heated issue of all.
The Conservative MP, Nadine Dorries, is leading attempts to amend the bill so that it reduces the upper time limit for abortion to 20 weeks.
She has on several occasions attempted to force the House of Commons to debate the issue but has been defeated.
Tuesday night represents a major opportunity for her case to be heard. With medical advances in recent years, many MPs believe that the current abortion limit of 24 weeks it too high.
Yet, an equally fervent group of MPs believe that women's right to choose up to that stage of pregnancy must be maintained.
Again, it is not likely that the government will lose on this. Gordon Brown, his health secretary and other ministers have all reaffirmed that they will not vote for a change.
But then again abortion law is, as convention dictates, a matter of conscience, and as such, MPs are left to vote as they wish.
That means, as health minister Dawn Primarolo illustrated on Sunday when pressed on the issue, it is not possible to predict the result of the vote in advance.