Summary Notes designed for the International Baccalaureate Diploma Programme. These notes are detailed yet concise, with all the information to achieve a 7 in IB Biology HL or SL. These notes were made using information from the IB syllabus, Oxford IB Diploma HL Biology Textbook, Bioninja and the B...
Unit 3.1
• A gene is a heritable factor that consists of a length of DNA and influences a specific
characteristic.
• The entire base sequence of human genes was sequenced in the Human Genome Project. The
genome is the whole of the genetic information of an organism
• A gene occupies a specific position on a chromosome known as the gene locus.
• Alleles are different forms of a specific gene such
as having brown or blonde hair. They differ from
each other by only 1 or 2 bases. New alleles are
formed by a mutation.
• Sickle cell anaemia is caused by base substitution
mutation where a thymine is replaced with alanine.
• This causes the haemoglobin to be unable to carry
oxygen properly so the cell develops a sickle
shape.
• Rice has more genes than humans, E. Coli has less. Humans have around 21,000.
Unit 3.2
• Prokaryotes have one chromosome consisting of a circular DNA molecule. They may also have
extra DNA in the form of plasmids.
• Bacterial cells may exchange plasmids via their sex pili, in a process known as bacterial
conjugation.
• Eukaryotic chromosomes are linear DNA molecules associated with histone proteins.
• In humans there are 22 pairs of autosomal chromosomes and one pair of sex chromosomes.
• On a eukaryotic chromosome the p arm is short and the q arm is long. Gene loci are named
based on their chromosome number, arm and band location e.g 7p20.
• Homologous chromosomes (one from each parent) carry the same sequence of genes but not
necessarily the same alleles of those genes.
• Diploid nuclei (2n) have pairs of homologous chromosomes whereas haploid nuclei (n) have one
chromosome of each pair.
• A karyogram shows the chromosomes of an organism in homologous pairs of decreasing
length. They can be used to determine the sex or to identify trisomy (Down’s Syndrome is
trisomy 21).
• The chromosome number does not give an indication of how complex a species is:
Unit 3.3
• During meiosis one diploid nucleus divides to produce four haploid nuclei.
• DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids.
• See Unit 10.1 for stages of meiosis.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller tiyadevinamistry. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.49. You're not tied to anything after your purchase.
