AQA Biology Variation and Inheritance

Annotations:

• 23 pairs of chromosomes and 46 all together 

Annotations:

• Genes are a small lengths of chromosomes and contain the instructions to make new proteins and therefore control characteristics of an organism 

Annotations:

• Every cell has a nucleus which contains chromosomes. Chromosomes are long molecules of DNA(deoxyribonucleic acid discovered by Watson and Crick in 1953) containing regions called genes which carry information to influence the characteristics of an organism

Annotations:

• 4- C, G, A and T These are the genetic code that makes a protein. The DNA tells us the order the amino acids (bases) come in  

Annotations:

• Variation is the differences between organisms.  Some characteristics are affected by more than one gene and show continuous variation like height. Height is controlled by environment and genes. Although, variation caused by only one gene like eye color shows discontinuous variation and is categorical.   

1. What affects variation?

   Annotations:

   • Genes Environment Mixture of both

Annotations:

• In plants: Ovules act as the egg (female) and Pollen acts as the sperm (male) In animals: Eggs are the female reproductive cells and Sperms are the male reproductive cells  

Annotations:

• The reproductive cells in an organism

Annotations:

• Sexual reproduction is where there are two parents and gametes fuse to create an offspring. The offspring will have half its genes from the father and half from the mother and therefore a mixture  of characteristics. It is highly unlikely that any two gametes will contain the same variation of genes. The offspring will be different even if they come from the same parents unless they are identical twins are come from the same fertilised cell   

Annotations:

• They are called clones because they are genetically identical individuals to their parent as they only receive genes from one parent and are produced by   

Annotations:

• Asexual reproduction is from one parent by cell division and no fusion of gametes. It happens much more quickly than sexual reproduction and animals like aphids can do this to reproduce quickly. Plants also do this. They can reproduce underground stems called runners that help it to spread quickly and outcompete other plants. Plants like potatoes form underground storage organs that can form a new plant in the next season   

Annotations:

• We can copy asexual reproduction and take a potato from an old plant and plant it separately We can take cuttings of a plant which will grow roots and form a new plant. This is quicker than sexual reproduction and therefore cheaper   

Annotations:

• It is mainly used in gardening and cells are taken from the tip of a shoot and placed onto sterile agar. The cells then divide and form a callus ( a small ball of cells). The callus and split into different calluses and are put on different agar with different nutrients and chemicals that make it grow roots and shoot. When it is large enough it is put into compost.  

Annotations:

• An egg and sperm are fertilised. The embryo starts to divide and is taken before it starts to specialise and the cells are separated to start making new embryos and are  then transplanted into the womb of host mothers. The host mother then give birth to identical offspring. This means farmers can get more offspring from their best animals

Annotations:

• Adult cell cloning is another popular technique.  A nucleus of an unfertilised cell is removed and is replaced by an adult body cell. The cell is given an electric shock to divide like a normal embryo.  The embryo is placed in the womb of an animal to develop

1. What is the problem with this sort of cloning?

   Annotations:

   • This was first done with Dolly the sheep and has been successfully repeated. However, many people are scared that this could be done with humans, but it is being used to help problems like spinal cord damage by making a replacement of cells.