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You and Your Genes Revision Lesson 1

You and Your Genes Revision Lesson 1. What are Genes?. All living organisms are made of cells Most cells have a nucleus In the nucleus are chromosomes, made from DNA. To write: DNA makes up chromosomes in the nucleus of cells. Chromosomes contain thousands of genes

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You and Your Genes Revision Lesson 1

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  1. You and Your GenesRevision Lesson 1

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

  3. Chromosomes contain thousands of genes • 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. • To write: 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. • 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. • 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. • 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 • Characteristics are also determined by environmental factors.

  6. To write: 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. • 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.

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

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