5.3 Understanding Genes and Chromosomes

5.3 Understanding Genes and Chromosomes

Structure of ChromosomeChromosomes is made up of a long DNA (deoxyribonuclei acid) coiled around protein molecules (histones)DNA molecule contains thousands of genes.

Structure of DNAStructure of DNA nucleotideStructure of DNA molecule

DNA structureA DNA molecule consist of two polynucleotide strands coiled together to form a double helix

The nitrogenous base is linked by hydrogen bonds.

Application of Knowledge in Genetics to MankindSelective BreedingIs used to produce offspring that posses desirable characteristics of both parents.Genetic EngineeringAlso known as a recombinant DNA technology. Alter characteristics of an organism into its DNA. Modified DNA is known as recombinant DNA. Organism with the recombinant DNA is known as genetically modified organism (GMO)

cloningProduces exact copies of the cloned genesGenes replicate within the same speciesGenetic engineeringProduces a totally uniques set of genesGenes can be swapped across species

Gene therapyis the insertion, alteration, or removal ofgeneswithin an individual'scellsandbiological tissuesto treatdisease. It is a technique for correcting defective genes that are responsible for disease development.The most common form of gene therapy involves the insertion of functional genes into an unspecified genomic location in order to replace amutatedgene, but other forms involve directly correcting the mutation or modifying normal gene that enables a viral infection. Although the technology is still in its infancy, it has been used with some successDNA fingerprinting (DNA profiling)The chemical structure of everyone's DNA is the same. The only difference between people (or any animal) is the order of thebase pairs. There are so many millions of base pairs in each person's DNA thiouj at every person has a different sequence.Using these sequences, every person could be identified solely by the sequence of their base pairs. However, because there are so many millions of base pairs, the task would be very time-consuming. Instead, scientists are able to use a shorter method, because of repeating patterns in DNA.These patterns do not, however, give an individual "fingerprint," but they are able to determine whether two DNA samples are from the same person, related people, or non-related people. Scientists use a small number of sequences of DNA that are known to vary among individuals a great deal, and analyze those to get a certain probability of a match.

ExerciseDeoxyribonucleic acid (DNA) is made up of units called nucleotides. Every unit of nucleotide is formed from a chain of deoxyribose sugar, a nitrogenous base and a phosphate.

(a) Draw and label the structure of a nucleotide. Describe the structure of the DNA (b) there are four different types of nucleotides which have varied nitrogenous bases. State the four types of nitrogenous bases. (c) The DNA strands are held together by hydrogen bonds between the pairs of bases. State the pairing of bases between the DNA strands (d) What is meant by genetic engineering

(e) Genetic engineering is applied in the medical field and agriculture. State three application of genetic engineering in the medical fieldDiagram shows the pedigree of a family with a genetic trait. Haemophilia is caused by recessive allele on the chromosome. The haemophilia trait is controlled by the recessive allele.(a) What is meant by sex-linked ?(b) i. State the genotypes of J and P ii. State all the possible genotypes of the offspring of J and PWhat is the probability of J and P producing haemophiliac childrenT marries female who is heterozygous dominant for blood clotting. What is the probability of their children being.(i) haemophiliacs?(ii) carriers of the diseases?(iii) normal?(iv) Draw the Punnet square to show the genotype and phenotypes of their children(e) More males get haemophilia compared to females. Explain.

In a pea plant green pod (G) is dominant to yellow pod (g), while inflated pod (C) is dominant to constricted pod (c). Pure breeding plant with green and inflated pod is crossed with pure breeding plants with yellow and constricted pods.(a)(i) Explain the term pure breeding plants (ii) Draw a genetic diagram to show this cross(b) What is the phenotype shown by F1 plantsThe F1 plants self pollinated to produce the second filial generation (F2) (i) What is meant by self-pollination? (ii) What are the gametes of the F1 plants (iii) Draw a Punnett square to show the genotype of the F2 plants (iv) What is the phenotypic ratio of F2 plants