Biology Unit 2
- Created by: Ali
- Created on: 20-05-12 12:15
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Variation
Investigating Variation
Interspecific variation - variation between different species
Intraspecific variation - variation between the same species
Causes of variation
- Mutations - sudden changes to genes which may or may not be passed onto the next generation
- Meiosis - nuclear division forming the gametes
- Fusion of gametes - random fusion at fertilisation
Environmental Influences
- climate
- pH
- food availability
- soil conditions
In most cases, variation is due to both genetic and environmental factors
Standard Deviation
- Mean - measurement at the maximum height
- Standard deviation - range of values around the mean
DNA and Meiosis
Structure of DNA
- a nucleotide is made up of a phosphate, a deoxyribose sugar and an organic base
- DNA is made up of two strands of nucleotides which are very long, held together by hydrogen bonds
- the bases contain nitrogen
- adenine and guanine are double ring bases
- thymine and cytosine are single ring bases
- adenine and thymine join by two hydrogen bonds
- guanine and cytosine join by three hydrogen bonds
Double Helix
- phosphate and deoxyribose sugar wind around one another to form a double helix
- each complete turn contains 10 base pairings
Function
- hereditary material responsible for passing genetic material
- infinite sequences of bases causing immense inter/intraspecific diversity
The Triplet Code
Genes
- sections of DNA that code for making polypeptides and proteins
Triplet Code
- 3 bases code for an amino acid
- each amino acid has it's own code of bases
- introns are sections of DNA that don't code for amino acids
Chromosomes
Structure
- centromere in the middle surrounded by chromatids
- proteins hold the DNA in place in chromosomes
Homologous proteins
- chromosomes come in pairs because one comes from the egg and the other from the sperm
- total number of homologous pairs is the diploid number
Alleles
- different forms of a gene
- differences in the base sequences of an allele may result in a different amino acid being coded for
- lead to the production of a different polypeptide
- protein formed from polypeptide will have different tertiary structure so not complementary of substrate
Meiosis
Process
- homologous chromosomes pair with their chromatids and wrap around each other
- chromatids can cross over and recombine
- homologous pairs separate and one chromosome from each pair goes to one of the two daughter cells
- chromatids move apart making 4 daughter cells
Independent Segregation
- chromosomes randomly segregate and assort resulting genetically unique gametes
Crossing over
- chromatids become twister around each other
- portions of the chromatids break off
- broken portions rejoin with the chromatids of its homologous partner
Genetic Diversity
Selective Breeding
- deciding who should breed with who depending on the desired characteristics
Founder Effect
- a few members of a population colonise a new region
- when they breed there won't be much variation due to a small range of alleles
Genetic Bottlenecks
- population can suffer massive drop in numbers
- survivors don't have wide range of alleles
The Variety of Life
Haemoglobin
Structure
- primary - 4 polypeptide chains
- secondary - each chain is coiled into a helix
- tertiary - each chain is folded into a precise shape to carry oxgyen
- quaternary -…
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