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F215: Control, Genome
and the Environment
OCR Biology


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F215: Control, Genome and the Environment

Module 1: Cellular Control and Variation
5.1.1: Cellular Control
(a) State that genes code for polypeptides, including enzymes

(b) Explain the meaning of the term `genetic code'
The genetic code is the sequence of base pairs on a length of DNA. It codes…

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- A second molecule of tRNA, with an anticodon complementary to the second codon on the
mRNA strand, also binds to its specific amino acid, and also binds to the mRNA strand.
- Ribosomal enzymes cause a peptide bond to form between the two amino acids.
- The first…

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Lactose present
Lactose is taken up by the bacterium, and then binds to the lac repressor, causing it to
change shape. This shape change causes the repressor protein to
dissociate from the operator region, which allows RNA polymerase to bind to the
promoter region, and hence transcribe the structural…

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5.1.2: Meiosis and Variation
(a) Describe, with the aid of diagrams and photographs, the behaviour of chromosomes during meiosis, and the associated behaviour of the nuclear
envelope, cell membrane and centrioles (names of the main stages are expected, but not the subdivisions of prophase)
Meiosis is the process by…

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3. Anaphase II
The spindle fibres contract.
Sister chromatids are separated at the centromere and pulled to opposite poles of the
The chromatids randomly segregate (any combination of chromatids is possible in
each of the daughter cells).
4. Telophase II
Nuclear envelopes form around the daughter cells.

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3. During metaphase II, the independent assortment and distribution of sister chromatids
means that any combination of chromatids could enter the daughter cells
4. Random mutations
1. Any female can mate with any male
2. Any sperm cell (male gamete) can fuse with any egg cell (female gamete)…

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Codominance: (e.g. blood group)
First Generation
Heterozygous Group `A' Female x Heterozygous Group `B' Father
Second Generation Male Gametes
Female Gametes B Bo
Group AB Group A
Bo BBB o B oB o
Group B Group O


First Generation
Homozygous Group `A'…

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(f) Describe the interactions between loci (epistasis)
Many different alleles can have an effect upon the same characteristic. These alleles
interact to produce the phenotype. Epistasis is the interaction of different gene loci so that the phenotypic
expression of one gene locus masks or suppresses the effect of another…

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(j) Explain the basis of continuous and discontinuous variation by reference to the number of genes which influence variation
Continuous variation:
Most continuous variation is controlled by multiple genes (known as `polygenic'). Multiple gene
loci interact together to form a large range of possible phenotypes. Different alleles at the…


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