Human Intervention in Evolution

Chapter 16 – Part 2

Transferring genes between species

The universal nature of DNA allows scientists to be able to manipulate DNA between species.

As a result scientists can transfer genes from one organism into another organism.

Gene transfer between species

As a result of DNA being universal among all living things, it has allowed scientists to transfer whole genes between species.

Genetic engineering has allowed genes to be transferred between different species.

Any organism that has a foreign gene, or foreign piece of DNA is said to be a transgenic organism (TGO).

If the cell that is receiving the foreign DNA is a prokaryotic cell, then it is said the gene is transformed.

If the cell that is receiving the foreign DNA is a eukaryotic cell, then it is said the gene is transfected.

Techniques for gene transfer

There are different techniques that can be used to introduce genes into a cell.DNA can be micro-injected into a host cellThe DNA can be carried to the target cell in a

retrovirus or adenovirus.An electric pulse can be used.Using a ‘gene gun’

Cloned transgenic animalsOnce a desired gene is taken up by the embryo

of a particular organism, it is then cloned to produce a number of identical copies of the embryo.

This is done through the method of embryo splitting.

Gene TherapyGene therapy is a technique which may be used to replace a

faulty gene, or to introduce a new gene whose function is to cure or to favourably modify the clinical course of another gene.

The vector used to do this is usually a virus.There are considerable challenges when developing successful

gene therapy for specific conditions. For example: The condition being treated must be well understood. The underlying faulty gene must be identified and a working copy

of the gene must be available. The specific cells in the body requiring treatment must be

identified and accessible. A means of efficiently delivering working copies of the gene to

these cells must be available.There are also a number of ethical issues to consider.

Stem Cells: A New Approach

Stem cells are another way in which we can alter evolutionary processes.

Stem cells can be used to replace cells which have been lost or damaged in some way.

For example:Alzheimer’s diseaseType 1 DiabetesParkinson’s DiseaseSpinal Cord Injuries

Stem CellsStem cells are cells which can differentiate into

any other cell in the body.There are different types of stem cells. For

example:Embryonic stem cells – these are from early

embryos.Adult stem cells (somatic stem cells) – obtained

from bone marrow, skin and umbilical cord blood.

Stem CellsEmbryonic stem cells come from a four to seven-

day-old blastocyst (early embryo). They have the ability to form virtually any type of cell found in the human body, but are not capable of developing into a whole new organism.

Embryonic germ cells are derived from the part of a human embryo or fetus that will ultimately produce eggs or sperm (gametes).This called the gonadal ridge found at 6 to 9 weeks of gestation when the embryo is developing into a fetus. Little research is now performed using this type of cells because they do not appear to be as versatile as embryonic stem cells.

Stem CellsAdult stem cells are more specialised than

embryonic stem cells. They are found in the majority of tissues and organs in our body and generate the mature cell types within that tissue or organ. They have a restricted ability to produce different cell types and to self-renew.

Umbilical cord blood stem cells are collected from umbilical cords at birth. They are capable of producing all of the blood cell types in the body. Cord blood stem cells are currently being used to treat patients who have undergone chemotherapy.

Stem CellsStem cells that have the potential to develop into any of the cell types found in an adult organism are called pluripotent. Embryonic stem cells and embryonic germ cells are pluripotent.Stem cells that only have the potential to make a few cell types in the body are called multipotent.Cells that are capable of forming a completely new embryo that can develop into a new organism are called totipotent. A fertilised egg is totipotent as it has the potential to develop into a new organism.

Therapeutic cloning for stem cell therapy

Therapeutic cloning refers to cloning for the purpose of treatment.

Therapeutic cloning involves the creation of an embryo through the nuclear transfer technique.

The cell used in the nuclear transfer is a healthy cell from the patient, allowing the use of a perfect genetic match.

Ethical IssuesThe use of stem cells from early embryonic cells has

caused a lot of ethical debate.It has been argued that it should be illegal as it is

destroying an embryo which could potentially develop full term.

There are many laws and acts which researchers are legally bound by.Researchers can only use ‘excess’ embryos.They must have written permission by each individual

responsible for the embryo.Researchers must have a special license to carry out

research on embryos.Embryos cannot be created for research purposes.

Genetic ScreeningGenetic screening involves the analysis of a DNA

sample in order to determine the presence of one or more alleles associated with inherited disorders.

There are many reasons why genetic screening may be carried out:an adult may be screened to determine if they carry a

particular alleleAn embryo can be screened to see if they are affected

by any inherited diseases (e.g.: Down Syndrome)Pre-natal tests may be carried out to confirm if an

unborn fetus is affected by a genetic disorder.Predictive testing may also be carried out in order to

identify the risk of developing a late-onset disease.

Human ReproductionThere are many ways in which human

reproduction can be altered.

Stopping Conception

Overcoming InfertilityThere are many different ways in which

infertility can be overcome, in order to allow couples to conceive.

Some examples are:Donor insemination IVFDonation of eggsSurrogacyGamete intrafallopian transfer Intracytoplasmic sperm injection

Donor InseminationThis involves the fertilisation of the woman by

donor sperm.This is used widely by infertile couples where

the problem lies with male being unable to produce viable sperm.

It is also widely used by lesbian couples wanting to conceive.

IVF – In-Vitro FertilisationIVF is used by couples who produce normal viable

gametes, but are unable to conceive for other reasons, such as damaged fallopian tubes.

In IVF, eggs are collected from the female, and sperm is collected from the male, and these gametes are fertilised external to the females body.

One, or several of the successful embryos are the implanted into the female.

Any excess embryos may be stored in liquid nitrogen for future use.

Donation of EggsSome females have difficulties producing eggs.In this case, an infertile woman may use eggs

from another female.The sperm to fertilise the egg is collected from

the woman’s partner.

SurrogacySurrogacy is the process where one female

carries the child of another female, who for some reason or another cannot carry her own baby.

This procedure is also used by gay dads wanting to conceive.

One of the major issues surrounding surrogacy is the fact that the woman acting as the incubator can become attached to the child they’ve been carrying for 9 months.

Gamete Intrafallopian Transfer

This is used by couples who can both produce viable gametes, but for some reason these gametes are physically prevented from meeting.

In this technique, the gametes are collected from both individuals and then introduced into the fallopian tube of the female. The gametes then have a chance to fertilise.

Intracytoplasmic Sperm Injection

This is a technique used when the male cannot produce a high enough sperm count to achieve normal conception.

An embryologist chooses a single sperm which is more motile and this is then injected into the egg cell.

This is then implanted into the female through the IVF procedure.