Sexual vs Asexual Reproduction

Think of reproduction as nature's way of creating the next generation - but there are two completely different approaches. Sexual reproduction involves two parents whose gametes (sex cells) fuse together, creating offspring with loads of variation. This is brilliant for survival because it's unlikely an entire species will be wiped out by disease, though it does require finding a mate and takes more time.

Asexual reproduction is like nature's copy machine - only one parent needed, and it's super quick and energy efficient. However, there's no variation, which means if a disease strikes, it could potentially wipe out the whole population. Bacteria and some plants use this method.

When fertilisation happens, an egg (23 chromosomes) meets a sperm (23 chromosomes) to create a cell with the full set of 46 chromosomes. This fertilised egg contains genetic material from both parents, which is why you might have your mum's eyes and your dad's nose.

Quick Tip: Remember that gametes are haploid (half the chromosomes), whilst normal body cells are diploid (full set).

Genetic Disorders and Screening

Some genetic conditions get passed down through families, but they work in very different ways. Cystic fibrosis is caused by a recessive gene, meaning you need two copies of the faulty gene to actually have the condition. It affects cell membranes, causing thick mucus in lungs and digestive system, leading to chest infections.

Polydactyly (extra fingers or toes) works oppositely - it's caused by a dominant gene. This means you only need one copy of the gene to have extra digits. There's no such thing as being a "carrier" for polydactyly because if you have the gene, you have the condition.

Embryo screening allows doctors to test for genetic disorders before birth using two main methods. Amniocentesis $15-16 weeks$ removes amniotic fluid, whilst chronic villus sampling $10-12 weeks$ takes cells from the placenta. Both carry a 0.5-1% miscarriage risk.

The screening debate is complex - it helps families prepare and make informed decisions, but raises ethical questions about abortion rates and the lack of cures for many conditions.

Remember: Dominant conditions need just one faulty gene, whilst recessive conditions need two copies.