Genes Flashcards
Define a gene
A gene is a heritable factor that influences a specific character. By ‘character’ we mean some feature of an organism like ‘height’ in the garden pea plant or ‘blood group’ in humans.
(A gene is a sequence of DNA that encodes for a specific trait)
Define plasmids
Smaller extra loops of DNA
Define DNA
DNA is the genetic blueprint which codes for, and determines, the characteristics of an organism
Define a Gene locus (plural = loci)
The position of a gene on a particular chromosome is
Define Alleles
Alleles are alternative forms of a gene that code for the different variations of a specific trait. (An allele is a specific form of a gene). Alleles only differ from each other by one or a few bases
Example: a gene may code for eye color, an allele may code for brown eye color
Define a chromose
A structure composed of DNA and protein
Distinguish between homologous & Homozquous
Explain how DNA becomes a chromosome
DNA, a double strand of anti-parallel nuclei acids, coils in a double helix structure held together by hydrogen bonds. The double helix will then wrap around 8 histone protein twice to form a nucleosome. Nucleosomes will supercoil once to form chromatin. The chromatin will then supercoil into a chromosome structure which enables examine genes.
Define a gene mutation
A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait. New alleles are formed by mutation
Explain the relationship between Dominant and recessive traits
Dominant traits occur more often/frequently than recessive traits
Recessive traits occur less frequently/often than dominant traits
Describe the 3 types of gene mutations
Gene mutations can be beneficial, detrimental or neutral
1) Beneficial mutations change the gene sequence (missense mutations) to create new variations of a trait (In humans, scientists have uncovered a recent mutation in the receptor proteins of the cell membrane. People possessing this mutation (though few in number) have shown a resistance to HIV. This is due to the inability of the virus to bind correctly to the host cell. )
2) Detrimental mutations truncate the gene sequence (nonsense mutations) to abrogate the normal function of a trait
( A human example is cystic fibrosis. A mutation in a single gene causes the body to produce thick, sticky mucus that clogs the lungs and blocks ducts in digestive organs)
3) Neutral mutations have no effect on the functioning of the specific feature (silent mutations) (Example: The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival.)
Define genome
A genome is the whole of the genetic information of an organism.
State the genome size of a human, fruit fly, Paris japonica and E. Coli bacteria in basepairs (bp) units
1) Human (Homo sapiens) = 3,000
2) Fruit fly (D. Melanogaster) = 140
3) E. Coli bacteria (Eschericha coil) = 5
4) Paris Japonica (A rare Japanese flower) = 150,000
Keynote; there is no correlation between the number of chromosomes or genes and the complexity and specialization of a particular species
