If a woman who is a known carrier for the gene of colour blindness marries a normal male, what percent of her male progeny are expected to be affected by the condition?
1. 0
2. 25
3. 50
4. 100
| Statement I: | Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome(s). |
| Statement II: | Failure of cytokinesis after telophase stage of cell division results in an increase in a whole set of chromosomes in an organism. |
| 1. | Yellow pod colour is a recessive trait in Pisum sativum. |
| 2. | Mendel applied statistical analysis and mathematical logic for the first time to problems in biology. |
| 3. | If a test cross results in progeny with two different phenotypes, the parent plant with dominant phenotype must be homozygous for the trait. |
| 4. | Although a gene can have more than two alleles, an individual can have only two alleles in somatic cells. |
| Complete dominance | Incomplete dominance | Co-dominance | ||
| I | F1 progeny | Resemble one of the parents | Do not resemble either of the parents | Resemble both parents |
| II | F2 phenotypic ratio | 3 : 1 | 1: 2 : 1 | 1: 2 : 1 |
| III | F2 genotypic ratio | 1: 2 : 1 | 1: 2 : 1 | 1: 2 : 1 |
| IV | Example | Height in garden pea | Flower colour in snapdragon | ABO blood group |
| V | Blending | Does not occur | Occurs | Occurs |
| Statement I | If two genes are located on heterologous chromosomes they will assort independently and a dihybrid cross will yield a F2 phenotypic ratio of 9: 3: 3: 1. |
| Statement II | If the two genes are linked the dihybrid F2 phenotypic ratio will vary significantly from 9: 3: 3: 1 with strength of linkage directly proportional to the distance between the genes. |
| Sickle Cell Anaemia | Thalassemia | ||
| I | Mode of inheritance | Autosomal recessive | Sex linked recessive |
| II | Cause | Substitution of valine by glutamic acid due to a single base substitution at the sixth codon of the beta globin chain | Mutation or deletion of genes located on chromosomes 11 or 16 |
| III | Effect on haemoglobin | Qualitative – incorrectly functioning globin | Quantitative – synthesis of too few haemoglobin molecules |
| I. | Down’s syndrome | Trisomy 21; Simian palmar crease, Furrowed tongue, Mental retardation |
| II. | Klinefelter’s syndrome | 47,XXY; Genetically female, gynaecomastia and sterility |
| III. | Turner’s syndrome | 45, XO; genetically male, Rudimentary ovaries, lack of secondary sexual characters |