IB Biology Topic 3

What is a gene

A sequence of DNA which codes for a specific trait (traits also may be influenced by multiple genes)

What is a locus

The position of a gene of a particular chromosome

What are alleles

Alternate forms of a gene which code for different variations of a specific trait.

What are missense mutations

Beneficial mutations which change the gene sequence to create new variations of a trait.

What are nonsense mutations

Detrimental mutations which change the gene sequence the alter the normal function of the trait

What are silent mutations

Neutral mutations with no effect on the trait

What are the causes of sickle cell anemia

Results from a change to the 6th codon in the beta chain in haemoglobin

The mRNA strand changes from GAG to GUG

The amino acid changes from glutamic acid to valine

What are the consequences of sickle cell anemia

The amino acid change alters the structure of haemoglobin, making it carry oxygen less efficiently.

It changes shape to a sickled shape, which can cause them to clot. They also are destroyed more rapidly, causing anaemia.

What is the genome

The totality of genetic information of a cell, organism or organelle.

What is the genome made up of

46 chromosomes

Around 3 million base pairs

Around 21,000 genes

What is the Human Genome Project

A venture aimed to sequence the entire human genome.

What did the Human Genome Project lead to

The mapping including location, size and sequence of human genes is established.

Comparisons with other genomes has provided insight into origin, evolutionary and migratory patterns of humans

The discovery of new proteins has allowed improved medical treatments.

Where is genetic material found in prokaryotes

Free in the cytoplasm in an area called the nucleoid

They also may have additional circular DNA called plasmids.

What is bacterial conjugation

What bacterial cells exchange plasmids through their sex pilli. The exchange allows bacteria to evolve new features within a generation.

Where is the genetic material in eukaryotes found

DNA is associated with 8 histone proteins to form a nucleosome.

Nucleosomes are linked by an additional histone protein to form a strain of chromatosomes

This supercoils to form chromosomes

What is the centromere

The constriction point which joins the 2 arms of the chromosome.

What are homologous chromosomes

Chromosomes with the same structural features and the same genes at the same loci

One is from each parent

What is the difference between diploid and haploid

Nuclei possessing pairs of homologous chromosomes are diploid (2n) (body cells)

Nuclei possessing only one set of chromosomes are haploid (n) (sex cells)

What are autosomes

All chromosomes in an organism which are not sex determining (X and Y)

What is a karyogram

A visual profile made from organising and staining chromosomes. The chromosomes of an organism are arranged into homologous pairs according to size.

What is autoradiography

Chromosomes are labelled and fixed to a photographic surface where they are immersed in a radioactive substance. Allows us to view the chromosomal DNA

Why do organisms with different diploid numbers not produce fertile offspring

They cannot form homologous pairs in zygotes. For instance, a horse (diploid = 64) and a donkey (diploid = 62) may produce an infertile mule (non-diploid = 63)

What are heterosomes

All the chromosomes which are not sex determining

What does meiosis 1 produce

2 haploid cells where the homologous chromosomes are split, however the haploid cells still have 2 chromatids.

What does meiosis 2 produce

2 haploid cells where the chromatids are split.

How is amniocentesis performed

Amniocentesis involves the extraction of a small amount of amniotic fluid (contains foetal cells) with a needle

• It is usually conducted later than CVS (~16 weeks of pregnancy) with a slightly lower risk of miscarriage

• 
  

How does gel electrophoresis work

1. Gel electrophoresis is typically performed using a gel made from a porous substance like agarose. The gel is put in a mould with buffer, allowing electrical conductivity

2. The DNA, RNA, or protein samples are mixed with a loading dye and loaded into wells at one end of the gel.

3. An electric current is applied across the gel. Because DNA, RNA, and proteins are negatively charged, they move towards the positively charged electrode (anode).

4. Molecules within the sample move through the gel matrix at different rates based on their size and charge. Smaller molecules move more quickly through the gel, while larger molecules move more slowly. Therefore, the molecules become separated into bands based on their size.

What is the process of gene transfer

1. Isolation of gene and vector (by PCR)

2. Digestion of gene and vector (by restriction endonuclease)

3. Ligation of gene and vector (by DNA ligase)

4. Selection and expression of transgenic construct

How is CVS performed

Chorionic villi sampling involves removing a sample of the chorionic villus (placental tissue) via a tube inserted through the cervix

• It can be done at ~11 weeks of pregnancy with a slight risk of inducing miscarriage (~1%)