Ib Biology Topic 4 Notes

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4.1.1 State that eukaryotic chromosomes are made of DNA and proteins 4.1.2 Define gene, allele and genome
Gene:| Heritable factors that control specific characteristics | Allele:| One specific form of a gene (differing form other alleles by one or few bases, occupying the same gene locus as other alleles of that gene)| Genome:| Whole genetic information of the organism|

Chromosomes are made of DNA and protein
4.1.3 Define gene mutation
* Gene mutation is the change in the base sequence of an allele * Will change the mRNA during transcription
* Will change the translation of the mRNA in a protein * The changed base sequence may produce different AA sequence in protein translated * Expression of mutated gene may/may not be beneficial to the organism * Substances that cause mutation are called mutagens (include chemicals/radiation) 4.1.4 Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia * Sickle cell anemia – genetic disease affecting the red blood cells * Gene loci for the normal beta chain of haemoglobin is on chromosome 11 * GAG is mutated to GTG (base codon) in the normal Hb gene (on mRNA) * The mutation changes a single base (T replaces A) – transcribes and translates into the AA Valine instead of Glutamic acid

4.2.1 State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei 4.2.2 Define homologous chromosomes

4.2.3 Outline the process of meiosis, including pairing of homologous chromosomes and crossing over, followed by two divisions, which results in four haploid cells. 4.2.4 Explain that non-disjunction can lead to changes in chromosome number, illustrated by reference to Down syndrome (trisomy 21)

4.2.5 State that, in karyotyping, chromosomes are arranged in pairs according to their size and structure 4.2.6 State that karyotyping is performed using cells...
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