Genetics

Question 1

Describe the structure and function of DNA, RNA, genes and chromosomes

Answer 1

-DNA, deoxyribose nucleic acid (sugar, nucleotides, phosphate). It is the key genetic material for every living organism. Carries information allowing living cells to produce all the proteins required for life. It is double stranded, made up of 2 chains of nucleotides. Which have 4 bases: A, T, G and C. Double helix.
-RNA, ribose nucleic acid, it is present in all living cells. Normally single stranded. Backbone made up of alternating phosphate groups and the sugar ribose. Four bases: A, U, C and G
-A gene is a length of DNA carrying a code to make a specific protein
-Genes: genetic code is based on 3 base groupings known as codons. Each code codes for a protein. Decoded by transcription then translated into a protein.
-A chromosome is a tightly coiled strand of DNA around a hi stone. Most cells in the body contain 46 chromosomes and these are paired together. These are diploid cells

Question 2

Define the terms: allele, locus, genotype, phenotype, homozygous, heterozygous, dominance, co-dominance, recessive, homologous chromosomes, mutation, autosomes and sex chromosomes

Answer 2

An allele is one of two (or more) versions of DNA sequence, an individual inherits two alleles, one from each parent
Homozygous: if the 2 alleles are identical
Heterozygous: if the 2 alleles are different
Genotype: the combination of alleles that they possess for a specific gene
Phenotype: the combination of their observable characteristics/traits
Dominant allele: an allele that is preferentially expressed over another
Recessive allele: an allele that is not preferentially expressed over another
Co-dominance: for some traits there can be more than 2 alleles that code for it, and more than 1 allele can be dominant.
Homologous chromosome: chromosomes belonging to the same pair
Mutation: a hereditable alteration in the base sequence of a gene
Sex chromosome: they determine the individual biological sex. XX FEMALE, XY MALE
Autosomal chromosomes: pairs 1-22 ie. Not the sex chromosome

Question 3

Differentiate between chromosomes, single genes, polygenic and multi factorial disorders

Answer 3

Single gene e.g. Huntingtons: not sex linked, so only need one copy of a faulty gene to inherit
Polygenic: several genes responsible for any given trait e.g. eye/hair colour, multiple faulty genes are needed
Multi factorial: complex interactions of genes with the environment e.g. smoking and sunlight

Question 4

Differentiate between mitosis and meiosis

Answer 4

Mitosis is a process where a single cell divides into 2 identical daughter cells
Meiosis is a process where a single gene divides twice to produce 4 cells containing half the amount of genetic information