Biology G12 Topic 2 - Genetics

gene

sections of dna that code for a specific trait
eg. hair colour

allele

different forms of the same gene
eg. blonde, brunette

genome

a complete set of DNA - all the genetic information needed to build and maintain an organism

female sex chromosome

XX

male sex chromosome

XY

sex chromosomes

carry the genes which determine a person’s sex

autosomal chromsomes

chromosomes which are not sex linked

no of chromosomes in humans

46 (2 of each kind)
- 23 from mother
- 23 from father

2 chromosomes of a pair = homologous chromosomes

gross structure of DNA molecule

double helix with bases (Adenine, Cytosine, Guanine, and Thymine) and their complimentary pairs

Adenine + Thymine

Cytosine + Guanine

base sequence within a gene

the code for a sepcific protein

mutations

spontaneous genetic change - how new alleles are formed

source of genetic vartiation

mutations can either be

• genetic

• chromosomal

genetic mutation

involves a change in the base/structure of the DNA

small changes in the genetic material can have great impact on an organism

slight changes in the base sequence of DNA will change the instructions on how to form proteins, creating a change in the final protein produced

Thalassemia

genetic mutation in haemoglobin gene.

The body is not able to make enough haemoglobin, this causes the body to not carry enough oxygen resulting in weakness and fatigue

Haemophilia

genetic mutation in the genes that make proteins with the role of blood clotting

this mutation keeps cloths from forming where there is an injury, causing too much bleeding that can be difficult to stop.

some types of cancers

cancers are due to a mutation that causes certain cells to stop working properly leading them to become cancerous and divide and grown uncontrollably,

eg. breast cancer, skin cancer

down’s syndrome

a form of mental and physical disability resulting from a chromosomal mutation

during the process of meiosis , one of the chromosomes fails to separate from its homologous partner. as a result the ovum carries 24 instead of 23 chromosomes. the resulting zygote has 47 instead of 46 chromosomes

chromosomal mutation

occurs when the normal number of chromosomes is changed, a chromosome is either added or removed.

mutations bring about…

allelic variation, which is the basis of natural selection

in rare circumstances, mutations produce an adaptation that makes an organism better suited to its environment and gives it an advantage in case of environmental change

rate of mutations may be increased by

mutagenic agents

examples of mutagenic agents

• uv radiation

• x rays

• nuclear radiation

• chemicals

haploid cells

• ½ the full number of chromosomes

• one set of chromosomes represented as n

  • in humans n=23

• formed by meiosis

• gametes

  • eg. egg cell

diploid cells

• full number of chromosomes

• 2 sets of chromosomes = 2n

  • in humans 2n=46

• formed by mitosis

• somatic cells

  • eg. skin cell

haploid cells have ½ the number of the original chromosomes

so that once they fuse to form a zygote, the original diploid number of chromosomes is restored

process of mitosis

The DNA of the parent cell is doubles and then divided into 2 genetically indentical daughter cells.