SL Biology - Topic 3: Genetics

gene

heritable factors that influence specific characteristics via a length of DNA that codes for a polypeptide

allele

alternative forms of a gene

homologous pairs

cells that have two copies of every gene

gene mutation

is a change in the sequence of base pairs in a DNA molecule which may result in a new allele

substitution mutation

a mutation that occurs when a base in the DNA sequence is randomly swapped for a different base

sickle cell anemia

when the base gene thymine (T) is replaced by the base adenine (A) within the hemoglobin gene causing the distortion in the shape of red blood cells

genome

the total of all genetic information in an organism

plasmids

very small circular DNA molecules that usually only contain a few genes.

histones

the main positively charged globular proteins in eukaryotic chromosomes

haploid cells

contain one complete set of chromosomes, meaning they have half the number of chromosomes compared to normal body cells

diploid cells

a pair of homologous chromosomes containing a full set

mitosis

gives rise to genetically identical cells and is the type of division used for growth, repair and replacement of cells

meiosis

gives rise to cells that are genetically different from each other and is used to produce gametes

meiosis I

the stage of meiosis when homologous pairs of chromosomes are split up, two produce two haploid (n) nuclei

meiosis II

The stage of meiosis when the chromatids that make up each chromosomes separate to produce four haploid (n) nuclei

gametes

the sex cells of an organism, which fuse during fertilization to form a zygote

dominant alleles

an allele which only needs to be inherited from one parent to be expressed

recessive alleles

an allele which needs to be inherited from both parents in order to expressed

gel electrophoresis

used to separate proteins or fragments of DNA according to size

cystic fibrosis

a genetic disorder of cell membranes caused by a recessive allele leading to the production of non-functional channels resulting in the body producing large amounts of mucus in the air passages

huntington’s disease

a genetic condition that develops as a person ages, with individuals experiencing neurological degeneration with it ultimately being fatal.

red-green color blindness

caused by a recessive allele found on the x chromosome responsible for the synthesis of of the photoreceptor proteins