10. (a) (i) What is meant by genetic engineering? (ii) State two applications of genetic engineering, one involving a micro-organism and one involving a plant - Leaving Cert Biology - Question 10 - 2005

1. Involving a micro-organism: Genetic engineering in bacteria to produce insulin for diabetes treatment.
2. Involving a plant: Engineering crops, such as tomatoes, to be herbicide-resistant, allowing farmers to control weeds without harming the plants.

Recessive: This term refers to an allele that is masked by the presence of a dominant allele when both are present. The expression of a recessive allele occurs only when an individual is homozygous for that trait.

Allele: An allele is a variant form of a gene that can exist in different versions, affecting the phenotype of an individual.

Dominant allele: This is an allele that expresses its trait even when only one copy is present, masking the effect of the recessive allele.

A person with a heterozygous allele pair has one dominant allele and one recessive allele. Because the dominant allele masks the expression of the recessive allele, the individual will not exhibit symptoms of the condition associated with the recessive allele.

The chance of one child inheriting the condition from two heterozygous parents can be calculated using a Punnett square. The possible genotypes are: 1 homozygous dominant (NN), 2 heterozygous (Nn), and 1 homozygous recessive (nn).

Therefore, the probability of a child inheriting the recessive condition (nn) is rac{1}{4} or 25%.

Genetic screening refers to testing individuals for the presence of specific genes or genetic conditions. This process can help identify carriers of genetic disorders before they pass these genes to their offspring.

After in-vitro fertilisation, genetic screening can be used to test embryos for genetic disorders before implantation. This can help in selecting embryos that do not carry serious genetic conditions, thereby reducing the risk of hereditary diseases in the child.

Linkage refers to the tendency of genes that are located close to each other on a chromosome to be inherited together during meiosis. Sex linkage is a genetic phenomenon where genes are located on sex chromosomes, leading to different inheritance patterns based on gender.

Linked genes do not assort independently because they are located on the same chromosome and are physically connected. During meiosis, they are more likely to be inherited together rather than segregating independently, which violates Mendel's second law of independent assortment.

Mother: XcX (one allele for colour blindness; one normal). Father: XY (normal vision).

Mother: XcX (one allele for colour blindness; one normal allele). Father: XY (normal vision).