Topic 9 - Inheritance, variation and evolution

Definition of sexual reproduction

The fusion of male and female gametes, where the offspring has a mixture of their parents’ genes and are genetically different to their parents.

Definition of asexual reproduction

No fusion of gametes, only one parent therefore no mixing of genes, resulting in offspring genetically identical to the parent, clone.

Definition of DNA

A polymer made up of two strands where the genetic information of the cell is.

Definition of gene

A small section of DNA on a chromosome which codes for a particular sequence of amino acids to make a specific protein

Definition of Genome

The entire set of genetic material in an organism

How is the Human Genome project helped scientists?

• Mapped out the genes that make up human chromosomes

1. Allows scientists to identify genes in the genome that are linked to different types of disease

2. Knowing which genes are linked to inherited diseases which helps us understand them better and could help scientists to develop treatments for them

3. Scientists can trace migration of certain populations from the common ancestor from Africa

How are proteins made in protein synthesis

1. mRNA is made by copying code from DNA, the complementary pair, acting as a messenger between the DNA and ribosome

2. In the ribosome, correct amino acids are brought to the ribosomes by carrier molecules which have the complementary base pair of the mRNA, which is the same as the bases on the DNA.

3. Amino acids are attached to each carrier molecule, attaching to the mRNA in the right pair and order to form a protein

What are the functions of protein

Enzymes - acts as biological catalysts to speed chemical reactions in body

Hormones - used to carry messages around the body

Structural proteins - are physically strong, e.g. collagen

What do the long strands of DNA consist of

alternating sugar and phosphate sections, and attached to each sugar is one of the 4 bases

How might a mutation seriously affect a protein

• A mutation changes the sequence of DNA bases in a gene, producing a genetic variant

• Therefore, as the sequence of DNA bases codes for particular sequences of amino acids, a change in the sequence of amino acids could change the protein it makes

• So the mutation may code for an altered protein with a change in its shape

• Hindering its ability to perform its function

What are the three types of mutation?

1. INSERTIONS - Where a new base is inserted into the DNA base sequence where it shouldn’t be, having a knock on effect on all other amino acids that the bases code for as they are shifted.

2. DELETIONS - Where a random base is deleted from the DNA base sequence, again shifting the bases that code for specific amino acids, a knock on effect

3. SUBSTITUTIONS - Where a random base in the DNA sequence is changed to a different base

What is fertilisation?

The fusion of male and female gametes

Describe the process of meiosis

1. DNA replicates forming two armed chromosomes with each arm being the same. The chromosomes then arrange into pairs

2. Chromosomes lineup in the centre of the cell

3. The pairs are pulled apart in the first division so each new cell only has one copy of each chromosome pair. Random chromosome pairs end up in of two cells

4. In the 2nd division, the chromosomes line up again at the centre of the cell and the arms are pulled apart

5. 4 genetically unique gametes are formed