Begegnungen mit der Natur 8, Arbeitsheft

18 Vererbung und Humangenetik How about using English – The units of heredity Fill in the correct words: In the nuclei of body cells there are long threads made of and protein, called chromosomes. The chromosomes contain , units which determine all sorts of things about us – the colour of our hair or eyes, our height or whether we have a genetic disease for example. Humans have got 23 pairs of inside each cell. The two chromosomes of a pair are the same size and shape. They are called . They have genes for the same characteristic in the same position. So we have two copies from each gene, one from the mother, the other from the father. There are different varieties of DNA codes of a gene, called . If the two alleles (from father and mother) are identical, we call this . If the alleles are different, we call this . The genes that we have are our , the features we have are called . Alleles can be dominant, recessive or codominant. If you have got one allele for brown eyes and one allele for blue eyes, the colour of your eyes will be brown, because the allele for brown eyes is while the allele for blue eyes is . Is neither of the alleles dominant or recessive, both alleles have an effect on the phenotype. We call this . The last pair of our chromosomes makes us male or female. They are called . In the picture you can see that the man’s sex chromosomes are not alike. The bigger one is the , the smaller one, the . Men have the genotype XY while women have the genotype XX. Eggs and sperm are made by . Therefore there are only 23 chromosomes in the nuclei of – one allele for any characteristic. Because the sex chromosomes in the body cells of a woman are both X, all her eggs have . In the body cells of a man the- re are X- and Y-chromosomes. Therefore one half of a man’s sperm contain , the other half . If a sperm cell with X-chromosome fertilises an egg, the baby will be a . In the other case, when a fertili- ses an egg, the baby will be a boy. Schulbuch Seite 19, 40, 48-53, 55 O 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 X Y alleles – chromosomes – codominance – DNA – dominant – gametes – genes – genotype – girl – heterozygous – homologous chromosomes – homozygous – meiosis, phenotype – recessive – sex chromosomes – sperm cell with Y-chromosome – X-chromosome – X-chromosomes – X-chromosomes – Y-chromosome – Y-chromosomes Nur zu Prüfzwecken – Eigentum des Verlags öbv