Describe DNA (structure, location, function).
- Deoxyribonucleic acid
- blueprint for controlling the characteristics of an organism.
- located in the nucleus.
- double helix structure.
Describe the structure of a nucleotide.
- Consists of:
- a phosphate
- pentose sugar
- nitrogenous base
Describe nitrogenous bases.
- Each base will only bond with one other specific base.
- Known as complementary base pairing.
- Guanine –> Cytosine
- Adenine –> Thymine
Describe the significance of the sequence of nitrogen bases.
The sequence of nitrogen bases along a strand of DNA is the basis of all inherited traits.
Define chromosomes (structure and number).
- an organised length of DNA found in the nucleus of cells.
- thread-like structure
- different organisms have different number of chromosomes. Humans cells have 23 pairs of chromosomes.
Describe autosomes.
- Any chromosome (numbered 1-22 in humans) that is not a sex cell.
- Control the inheritance of all non-sex linked characteristics.
Describe sex chromosomes.
- chromosomes that determine the biological sex of an organism.
- females XX
- males XY
Describe somatic cells.
- all body cells that are not sex cells
- diploid: contain two sets sets of cells (2h) one from each parent.
- 46 chromosomes.
Describe sex cells.
- gametes/sexual reproduction cells.
- sprem + egg
- haploid: contain single set of chromosomes (n).
- 23 chromosomes.
Describe homologous chromosomes + criteria.
chromosomes occur as homologous pairs in body cells.
criteria for homologous pairs:
- same size and length
- same centromere position
- same genes at same gene loci.
Describe the purpose of a karyotype.
- a karyotype is an image of all chromosomes organised in their homologous pairs.
- numbered by size from largest to smallest.
- help determine genetic disorders and the biological sex of an organism.
Describe fertilisation.
- fertilisation is the fusion of the nuclei of male and female gametes.
- produces a zygote which matures into an embryo.
Describe the process of meiosis.
- the process of cell division to produce gametes.
- a single diploid parent cell divides twice to produce four haploid gamete cells.
- genetic information is passed on to offspring via haploid gametes.
Describe dominant/recessive inheritance.
- inherited on an autosome
- two possible alleles
- dominant alleles (GG)
- recessive alleles (gg)
- homozygous dominant and heterozygous individuals will always display dominant phenotype.
- recessive phenotype can only be observed in homozygous recessive individuals.
What is a carrier?
Heterozygous individuals that have an allele but does not display it.
Define Genotype.
The alleles carried by an organism. E.g., gg,
Define Phenotype.
The observable characteristics of an individual. E.g., brown fur.
Describe punnet squares.
Show possible offspring based off parents genotypes.
Describe co-dominance inheritance.
- inherited on an autosome
- both alleles are dominant (GH)
- no carriers
- both phenotypes are displayed.
- e.g. a white bunny (WW) and a black bunny (BB) produce a bunny with black and white spots (WB).
Describe incomplete dominance inheritance.
- inherited on an autosome
- both alleles dominant
- no carriers
- a mixture or intermediate between two phenotypes is displayed.
- e.g a white bunny (WW) and a black bunny (BB) produce a grey bunny (WB).
Describe a pedigree chart.
- Shows the inheritance and appearance of traits.
- A trait that skips a generation must be recessive.
- a trait that appears in every generation is most likely dominant.
Define Gene.
A sequence of DNA organised into short sections on chromosomes which codes for a particular trait.
Define Allele.
Different variations of a gene that occupy the same locus on a gene.
