2.3 DNA and Inheritance

Describe the structure of DNA.

* It is a polymer made of many nucleotide monomers.
* It is made of 2 long strands of alternating sugar and phosphate molecules in the shape of a double helix.

Why is the backbone described as 'alternating sugar phosphate'?

One side starts with phosphate, sugar the other will start with sugar, phosphate.

State the letters that represent the 4 bases in DNA.

A, T, C & G.

Describe pairing rules in DNA.

A pairs with T.
C pairs with G.

Name the 4 bases in DNA. (Higher)

Adenine (A), Thymine (T), Cytosine (C) & Guanine (G).

Why are the bases described as complimentary?

They bind together with hydrogen bonds.

How are proteins made? (Higher)

* DNA carries the code to make a protein which is called a gene.
* A group of 3 bases (a codon) codes for one amino acid, and binds with other amino acids to make one long chain.
* The order of the amino acids determines the structure and function of the protein formed.

What makes proteins different?

The order of amino acids.

How many bases code for an amino acid?

3- a group of three bases is a ‘codon.’

What is genetic profiling?

A method of comparing DNA by cutting it into fragments and comparing the fragments with each other.

How do you carry out genetic profiling?

1. Sample of cells collected
2. DNA extracted from cells
3. DNA sample cut into fragments using enzymes
4. Fragments separated into bands, creating a genetic profile

Give 3 uses of genetic profiling.

- Paternity testing (working out who is the biological parent of a child).
- Forensic identification (matching a criminal to DNA left at a crime scene).
- Matching an organism's DNA to classify it.

Give 2 benefits of genetic profiling.

- It can help to catch criminals.
- It can be used to identify the presence of disease-causing genes.

What are the ethical issues surrounding genetic profiling?

It could be used against people by insurance companies based on a person's predisposition to certain diseases.

What is a gene?

A section of DNA that codes for a protein.

What are alleles?

Different versions of the same gene.

What is a chromosome?

A long strand of DNA that contains genes.

What are gametes?

Gamete are sex cells (sperm or eggs).

What are the male sex chromosomes?

XY

What are the female sex chromosomes?

XX

How many chromosomes are in a gamete?

23 chromosomes.

What is a dominant allele?

A version of a gene that is always expressed when present.

What is a recessive allele?

A version of a gene that is ONLY expressed in the absence of a dominant allele.

What is meant when an organism is homozygous?

When an organism has two copies of the same allele (two recessive or two dominant).

What is meant when an organism is heterozygous?

When an organism has two different versions of the same gene (one dominant and one recessive).

What is the genotype?

The genes present for a trait.

What is the phenotype?

The visible characteristic.

What is the F1 generation?

The offspring produced when 2 organisms are bred together.

What is the F2 generation?

The offspring produced when two offspring (F1 generation organisms) are bred together.

How are dominant alleles represented in a punnett square?

They are represented using uppercase letters.

How are recessive alleles represented in a punnett square?

They use the lowercase version of the same letter as the dominant allele.

What is genetic engineering?

Altering the genome of an organism.

What is genetic modification?

Transferring desired genes artificially from one species to another.

Describe how genetic modification can be carried out.

1. DNA is taken from an organism
2. The useful / desired gene is cut out of the chromosome by enzymes
3. The useful / desired gene is inserted into the chromosome of the target plant
4. The new chromosome is inserted into the target plant
5. The target plant now has the new gene

Give 2 advantages of genetically modified crops.

- Better crop yields.
- Food will last longer and taste better.

Give 2 disadvantages of genetically modified crops.

- The new genes can easily spread to other plants in the environment.
- The long term effects genetically modified crops cause on health is still unknown.