Genetic terms

Genotype is the genetic composition of an organism.
Phenotype is the set of characteristic manifested by an organism.
An individual has a heterozygous condition if he has 2 different alleles of the same gene
An individual has a homozygous condition if he has 2 identical alleles of the same gene.
Codominance is a genetic interaction where the codominant alleles of a gene express themselves equally in the phenotype
Dominance is a genetic interaction where 1 allele of a gene masks the expression of another allele in the heterozygote.
Locus is the position of a gene in a DNA molecule of a chromosome
A gene is the functional unit of inheritance
An allele is an alternative form of a gene.

Chromosomal Aberration

Chromosomal aberration refers to a change in number of chromosomes, can occur on one, or several, or all of the chromosomes within a nucleus. This is cause by the failure of sister chromatids to separate during anaphase of mitosis or the failure of homologous chromosomes to separate during anaphase I and/or II of mitosis. Aneuploidy refers to the loss or gain of single chromosomes but polyploidy refers to the increase in entire haploid sets of chromosomes. Structural aberrations are the result of chromosomal breaks that occur during meiosis or mitosis. This often leads to reshuffling of alleles on the chromosome. This is often caused by the deletion, duplication, translocation, inversion of several gene loci within chromosomes.

Q: Explain why mutations for antibiotic resistance spread so rapidly among bacteria

Frequent use of antibiotic kills many bacteria, creating a selection pressure. As a result, bacteria with mutations that give them resistance to a particular antibiotic have an advantage over the other bacteria that do not. They survive to reproduce more than the other types, and pass on this advantageous allele in greater numbers. The frequency of this allele therefore increases in subsequent generations, leading to an increase in frequency of resistant types in subsequent generations. As bacteria have a haploid genome, this alleles will be expressed and there will be no masking of any recessive alleles. In addition, bacteria multiply rapidly as they reproduce asexually by forming clones.