1. You and Your Genes Revision Lesson 1

2. What are Genes? All living organisms are made of cells All living organisms are made of cells Most cells have a nucleus Most cells have a nucleus In the nucleus are chromosomes, made from DNA. In the nucleus are chromosomes, made from DNA. To write: To write: DNA makes up chromosomes in the nucleus of cells. DNA makes up chromosomes in the nucleus of cells.

3. Chromosomes contain thousands of genes Chromosomes contain thousands of genes Genes carry the information that controls what an organism is like, with each gene determining one characteristic. Genes carry the information that controls what an organism is like, with each gene determining one characteristic. Each gene codes for a protein e.g. structural proteins and enzymes. Each gene codes for a protein e.g. structural proteins and enzymes. To write: To write: Sections of chromosomes are called genes, which control cells and code for proteins. Sections of chromosomes are called genes, which control cells and code for proteins.

4. Why do we look similar but not the same as our parents? Human cells, except gametes, contain 46 chromosomes in 23 pairs. Human cells, except gametes, contain 46 chromosomes in 23 pairs. One chromosome in each pair came from the father, and one from the mother. One chromosome in each pair came from the father, and one from the mother. In each chromosome, the same genes are in the same place. In each chromosome, the same genes are in the same place. Different versions of the same gene are called alleles Different versions of the same gene are called alleles

5. For each gene, a person has 2 identical or 2 different alleles. They have inherited one from the mother and one from the father. For each gene, a person has 2 identical or 2 different alleles. They have inherited one from the mother and one from the father. We are therefore a mix of alleles from both of our parents, so we are not the same. Siblings have a different mix (apart from identical twins). We are therefore a mix of alleles from both of our parents, so we are not the same. Siblings have a different mix (apart from identical twins). Some characteristics are determined by one gene but most depend on many genes Some characteristics are determined by one gene but most depend on many genes Characteristics are also determined by environmental factors. Characteristics are also determined by environmental factors.

6. To write: To write: Most human cells have 46 chromosomes (23 pairs – one from each parent). Most human cells have 46 chromosomes (23 pairs – one from each parent). Different versions of genes are called alleles. Our mix of alleles determines what we are like. Most characteristics are due to a number of genes. Some are due to only one gene, and some are affected by environment.

7. What makes us male or female? Humans have one pair of sex chromosomes in each body cell. Females have XX, males XY. Humans have one pair of sex chromosomes in each body cell. Females have XX, males XY. Sex cells (sperm or egg) contain only 23 chromosomes. Every egg has an X, half of sperm have X, half Y. The Y chromosome has the instructions to make a male. Sex cells (sperm or egg) contain only 23 chromosomes. Every egg has an X, half of sperm have X, half Y. The Y chromosome has the instructions to make a male. At fertilisation, if a Y sperm fertilises an egg, a male will develop. If an X sperm fertilises an egg a female will develop. At fertilisation, if a Y sperm fertilises an egg, a male will develop. If an X sperm fertilises an egg a female will develop.

8. To write: There are 1 pair of sex chromosomes in each human cell, XX or XY. There are 1 pair of sex chromosomes in each human cell, XX or XY. Sex cells contain half the number of chromosomes (23) Sex cells contain half the number of chromosomes (23) A pair of XX alleles makes a female. XY makes a male. A pair of XX alleles makes a female. XY makes a male.