Biology (NCEA Level 2)
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Segregation of Alleles
Each organism inherits two versions of every gene called alleles, one from each parent. these two alleles are found on separate chromosomes and separate from each other when gametes are formed during meiosis, with one allele ending up in each gamete.
Genetic Variation: increases genetic variation as half the gametes get one version of the gene and half get the other version. The offspring produced from each type of gamete will be genetically different.
During meiosis the pairs of homologous chromosomes line up on the equator. The chromosome are pulled to opposite side of the nucleus by spindle fibres and end up in different gametes. Each homologous pair separate independently from one another when gamtes are formed, creating a huge variety of combinations and increasing genetic variation.
When the homologous chromosomes pair up on the equator during meiosis, sections of genetic material can be exchanged between the inner chromatids of the chromosomes. This results in a reshuffling of alleles.
genetic variation: creating new combinations of alleles not found in the parents.
A sudden change in the genetic material (DNA) of an organism that is permanent.
When neither allele in a heterozygous organism is dominant resulting in it showing an intermediate/blend between the two homozygous phenotypes.
When both alleles are independently and fully expressed in the phenotype of the heterozygous organism.
When two different genes are found on the same chromosome and usually get inherited together.
Alleles which cause premature death of an organism. They are usually dominant but may be recessive.
Sex Linked genes
When a gene is carried on one of the sex chromosomes but not the other. Usually the X chromosome, as it is bigger than the Y and has a non-homologous section.
When only one copy of an allele (dominant) is needed to show the phenotype. The recessive phenotype will only show in the absence of the dominant allele (homozygous recessive).
Multiple alleles occur when more than two different alleles can occupy the same gene locus on a chromosome. Only 2 alleles of the gene can occur in any one individual, but in the population there can be more than two different forms of the allele.
Some individuals in a population are better adapted to the environment in which they live, and are more likely to survive and reproduce, passing on the alleles increasing in frequency witihng the gene pool creating genetic change.
When individuals may randomly enter or leave a population.
When random changes in allele frequencies occur in a population due to chance events causing genentic change.
Net movement of molecules (or ions) from a region of high concentration to a region of low concentration across a semi-permeable membrane.
Facilitated diffusion is the movement of large, polar or water-soluble particles that are unable to diffuse directly through the phospolibid layer of the cell membrane. It is down a concentration gradient and therefore a passive process.
Net movement of water molecules from a region of higher water concentration to a region of lower water concentration across a semi-permeable membrane.
Movement of molecules and ions across a plasma membrance from a low concentration to a high concentration.
The engulfing of material by the plasma membrane to form a small sac or 'endocytotic vacuole'.
Transporting substances out of a cell.
Enzymes are biological catalysts. This means that they change the rae of chemical reactions (usually speed them up) but remain unchanged and can be used again.
- Series of chemical reactions which releases energy (in the form of ATP) in living cells.
- Oxygen + Glucose --> Energy (ATP) + Carbon dioxide + Water
- The conversion of light energy into chemical potential energy in the form of glucose, using CO2 and H2O in the presence of chlorophyll.
- Carbon Dioxide + Water --> Oxygen + Glucose
- catalysed by light energy and chlorophyll.
Process of DNA Replication
- 1. The double stranded helix unwinds.
- 2. The hydrogen bonds between the bases break and the two strands separate.
- 3. This exposes the bases of the nucleotides.
- 4. As the bases are exposed, new nucleotides containing the complementary bases attach.
- 5. New hydrogen bonds form between the bases and the strands recoil.
- 6. The process produces two identical molecules of DNA from the original molecule.
3 adjacent bases (nucleotides) on DNA that code for a codon.
Sequence of the three nucleotides on m-RNA that codes for a particular amino acid.
An exposed group of three bases on t-RNA that recognises and pairs with a codon on m-RNA.
As there are 64 different codons and only 20 amino acids, most amino acids are coded for by more than 1 codon. This redundancy in the code is called degeneracy. It buffers the effect of mutations because if only one base changes, in the 3rd position, this does not necessarily change the amino acid that is picked up. i.e. the same amino acid is coded for.
Transcription occurs in the nucleus. It begins when a section of DNA unwinds and the template strand acts as a template for the production of an mRNA strand. This process is catalysed by the enzyme RNA polymerase. The enzyme transcribes only a gene length of DNA at a time and therefore recognises start (promoter) and stop (termination sequence) codes at the beginning and end of the gene.
- 1. The mRNA molecule passes through a slot between the large and small units of the ribosome, where the message on the mRNA is translated into a polypeptide chain from the 5' end to the 3' end.
- 2. tRNA molecules are present in the cytoplasm. One end of each tRNA molecule is attached to a specific amino acid, one of 20 present in the body. The other end has an anticodon corresponding to that amino acid.
- 3. At any one time, two mRNA codons are bound to the ribosome. The anticodon on a tRNA molecule bonds to the codon on the mRNA strand.
- 4. The amino acids on the tRNA molecules that are sitting side by side on the ribosome, then bind together with a peptide bond. This starts the formation of a polypeptide chain.
- 5. As each new amino acid is joined onto the growing polypeptide chain, the ribosome nudges the mRNA strand along one codon and the next tRNA falls into place.
- 6. the tRNA molecule separates from its amino acid and leaves the ribosome to 'reload'
- 7. When a stop codon is reached on the mRNA, there is no corresponding tRNA peptide so synthesis stops.
Physical or hemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level.
Point mutation/ Gene mutation
Point mutations affect only a single gene - this type if mutation alters one nucleotide on the DNA.
Metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyzse these reactions.
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