CB3a Meiosis
1. Gametes are produced by meiosis
o Meiosis is a type of cell division that creates gametes (sperm and egg cells).
o It reduces the chromosome number by half, producing haploid cells (23
chromosomes in humans).
2. What happens in meiosis (overview)
o One diploid cell divides twice to form four haploid cells.
o Each gamete is genetically unique due to crossing over and independent
assortment.
3. Why haploid gametes are needed
o During fertilisation, two gametes fuse to form a zygote.
o If gametes weren’t haploid, the zygote would have double the
chromosomes.
4. What is an organism’s genome?
o The genome is the complete set of DNA, including all genes, in an organism.
o It contains instructions for building and maintaining the organism.
5. Function of genes
o Genes code for proteins, which carry out functions and determine traits.
o Each gene has a specific role, like eye colour or enzyme production.
6. Where genes are found
Genes are located on chromosomes inside the nucleus of eukaryotic cells.
CB3b DNA
1. Where DNA is found
o DNA is found in the nucleus of eukaryotic cells, tightly coiled into
chromosomes.
2. Name the bases in DNA
o The four bases are:
o Adenine (A)
o Thymine (T)
o Cytosine (C)
o Guanine (G)
3. Base pairing rules
o A pairs with T
o C pairs with G
o These pairs are held together by hydrogen bonds.
4. How DNA strands are held together
o The bases form pairs in the middle, and the sugar-phosphate backbone runs
along the sides.
o Hydrogen bonds between base pairs keep the strands together.
5. Structure of DNA
o DNA is a double helix—two strands twisted like a ladder.
o The sides are made of sugar and phosphate; the rungs are base pairs.
6. Extracting DNA from fruit
Steps:
Mash fruit to break cells
Add detergent and salt to dissolve membranes
Filter the mixture
Add cold alcohol—DNA appears as white strands
1. Gametes are produced by meiosis
o Meiosis is a type of cell division that creates gametes (sperm and egg cells).
o It reduces the chromosome number by half, producing haploid cells (23
chromosomes in humans).
2. What happens in meiosis (overview)
o One diploid cell divides twice to form four haploid cells.
o Each gamete is genetically unique due to crossing over and independent
assortment.
3. Why haploid gametes are needed
o During fertilisation, two gametes fuse to form a zygote.
o If gametes weren’t haploid, the zygote would have double the
chromosomes.
4. What is an organism’s genome?
o The genome is the complete set of DNA, including all genes, in an organism.
o It contains instructions for building and maintaining the organism.
5. Function of genes
o Genes code for proteins, which carry out functions and determine traits.
o Each gene has a specific role, like eye colour or enzyme production.
6. Where genes are found
Genes are located on chromosomes inside the nucleus of eukaryotic cells.
CB3b DNA
1. Where DNA is found
o DNA is found in the nucleus of eukaryotic cells, tightly coiled into
chromosomes.
2. Name the bases in DNA
o The four bases are:
o Adenine (A)
o Thymine (T)
o Cytosine (C)
o Guanine (G)
3. Base pairing rules
o A pairs with T
o C pairs with G
o These pairs are held together by hydrogen bonds.
4. How DNA strands are held together
o The bases form pairs in the middle, and the sugar-phosphate backbone runs
along the sides.
o Hydrogen bonds between base pairs keep the strands together.
5. Structure of DNA
o DNA is a double helix—two strands twisted like a ladder.
o The sides are made of sugar and phosphate; the rungs are base pairs.
6. Extracting DNA from fruit
Steps:
Mash fruit to break cells
Add detergent and salt to dissolve membranes
Filter the mixture
Add cold alcohol—DNA appears as white strands
