5.19 Describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep

The stages are as follows:

1. Remove a donor (diploid) cell with the full genetic information (contained in the nucleus)
2. A cell must be obtained, but one with the capacity to divide. Thus, an egg cell is taken from a sheep.
3. The egg cell nucleus is removed (it is enucleated)
4. Desired DNA is placed into the egg cell. They are fused together with an electric shock. 
5. This newly combined cell divides by mitosis to produce a sheep embryo.
6. The embryo is placed into the womb of another sheep (the surrogate mother)
7. As the cells continue to divide, it will grow into a fetus and eventually be born.

The cloned sheep will have the DNA of the cell donor.

Source: http://media1.shmoop.com/images/biology/biobook_biotechnology_graphik_18.png

5.20 Evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation.

As mentioned, one use of cloned, transgenic animals (meaning they have had another organism's DNA inserted into them) is to produce commercial quantities of human antibodies or organs for transplantation. Some examples include:

• Cows with medicine in their milk can be cloned
• Pigs with human hearts can be cloned for organ transplant

Animals can be given genes to produce human antibodies, which can be later injected into humans to help them face infection, rather than allow the immune system to find the appropriate antibody (which would likely take much longer). 

Sheep and cows can be modified to produce human proteins in their milk, which makes it more beneficial for us.

Animals with organs similar enough to human ones can be used for transplants, which would significantly reduce the problem of shortages. However, this may be a problem for ethical reasons (i.e. it can be considered inhumane to breed animals only to cut out their organs)

There are advantages and disadvantages of the process:

😃

• Cloning can happen at any time of year (out of breeding season)
• Infertile animals can be cloned
• Desired traits can be passed on with almost 100% certainty

😓

• Cloned animals may develop problems 
• Cloning is a relatively new technology, meaning that it may have negative consequences that we are not aware of 
• Low success rate (many animals will die horrible deaths)
• Difficult, time-consuming and expensive

3.17 Understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance

Homozygous: two same alleles of a gene on each chromosome on a homologous pair
Heterozygous: one of each allele of a gene on each chromosome on a homologous pair
Rescessive: an allele only expressed if the dominant allele is absent or if [the recessive gene] is homozygous.
Dominant: an allele that always express itself whether it is heterozygous or homozygous


Homologous pair: a chromosome containing a maternal and paternal chromatid joined together. (these have the same gene but may have different alleles)
Chromatid: each of the two threadlike strands that chromosomes divide into during mitosis.

3.16 Understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics

Genes exist in alternative forms called alleles. These control the differences in inherited characteristics. 

Extra information:
Alleles can be dominant or recessive, homozygous or heterozygous. They are written as big or small letters. Eg: Aa or AA or aa. This is known as a genotype. The physical characteristic it codes for is called a phenotype.

3.15 Describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)

Above, you can see an image of the structure of DNA. It is made up of two coiled strands, known as a sugar phosphate backbone. As the name suggests, it is made up of a sugar and a phosphate (alternating). The base pairs are the 'coding'. It is believed that every living thing has the same base pairs:

• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)

Adenine always pairs up with thymine, guanine always pairs up with cytosine. The order in which these are paired in is what makes up the 'coding' of an organism.

(Virtual flashcards on this topic can be found here, or click 'inheritance flashcards' on the right hand side menu)

3.14 Understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein

A gene is a length of DNA. This codes for a specific protein. These proteins join together to make a chain. 

Structure of DNA

3.13 Understand that the nucleus of a cell contains chromosomes on which genes are located

The nucleus of any cell will contain chromosomes in which genes are located. 

If you unwrapped a chromosome, you would see it is essentially just strands of DNA coiled around a protein. DNA stands for deoxyribonucleic acid (you don't need to know that).