| What is DNA? | DNA is a large and complex polymer, which is made up of two strands forming a double helix DNA determines the characteristics of a living organism |
| What is an allele? | Alleles are different versions of the same gene. For any gene, a person may have the same two alleles, known as homozygous or two different ones, known as heterozygous. |
| What is a genotype? | the collection of alleles that determine characteristics and can be expressed as a phenotype. |
| Describe a dominant allele? | A dominant allele is always expressed, even if one copy is present. Dominant alleles are represented by a capital letter, for example, A. The allele for brown eyes is dominant. You only need one copy of this allele to have brown eyes. Two copies will still give you brown eyes. |
| What is a recesive allele? | A recessive allele is only expressed if the individual has two copies and does not have the dominant allele of that gene. Recessive alleles are represented by a lower case letter, for example, a. The allele for blue eyes is recessive. You need two copies of this allele to have blue eyes. |
| What is a homosygous? | Homozygous alleles are both identical for the same characteristic, for example AA or aa. |
| What is heterozygous? | Heterozygous alleles are both different for the same characteristic, for example Aa. |
| What is are monohybrid crosses? | Genetic crosses of single gene combinations examined using punnet squares:
Dominant: Upper case T
Recessive: Lower case t |
| Describe the chromosomes interms of what they control? | Twenty two pairs are known as autosomes, and control characteristics, but one pair carries genes that determine sex - whether offspring are male or female |
| Show male and female chromosomes? | male: XY (Xx)
Female: XX (XX)
the larger chromosome (X) is the X the smaller chromosome (x) is the y |
| What is cystic fibrosis? | Cystic fibrosis is an inherited disorder of cell membranes that mainly affects the lungs and digestive system.
Problems:
1)Lungs can become clogged with lots of thick, sticky mucus as too much is produced.
2)Over many years, the lungs become increasingly damaged and may eventually stop working properly. |
| How is cystic fybrosis inherited? | 1)It is caused by a faulty recessive allele on chromosome 7
2)To be born with cystic fibrosis, a child has to inherit two copies of this faulty gene - one from each of their parents.
3)Their parents will not usually have the condition themselves, because they will only carry one faulty gene and one that works normally. |
| Describe the chance of inheriting cystic fybrosis? | 1)An individual who is homozygous (ff) with the recessive allele will develop cystic fibrosis.
2)Someone who is heterozygous (Ff) will be a carrier of the recessive allele, but will not develop cystic fibrosis and have no symptoms.
3)Someone who is homozygous with the dominant allele (FF) will not develop cystic fibrosis, as you need two faulty alleles (ff) for the condition. In this combination, no faulty alleles are present. |
| What is Polydactyly? | -an inherited condition in which a person has extra fingers or toes.
-It is caused by a dominant allele of a gene. This means it can be passed on by just one allele from one parent if they have the disorder.
-Someone who is homozygous (PP) or heterozygous (Pp) for the dominant allele will develop polydactyly. |
| Describe 3 tests for genetic disorders. | 1)Antenatal testing is used to analyse an individual's DNA or chromosomes before they are born. This testing is offered to couples who may have an increased risk of producing a baby with an inherited disorder, but it can't detect all the risks of inherited disorders.
2)Neonatal testing (new born blood spot test) involves analysing a sample of blood from pricking a baby's heel. It detects genetic disorders in order to treat them early.
3)Pre-implantation genetic diagnosis (PGD) is used on embryos before implantation. Fertility drugs stimulate the release of several eggs.The eggs are collected and fertilised in a Petri dish. This is known as in vitro fertilisation (IVF). Once the embryos have reached the eight-cell stage, one cell is removed.
The cells are tested for the disorder causing alleles. Embryos that don't contain the disorder allele are implanted into the uterus. |
| What is the main limitation of genetic testing? | False positives (think their child has disease)
False negatives (think child wont have disease, cant plan level of care needed) |
| Describe the process of gene therapy. | Used to decrease chance of getting genetic disorder :
1)dentify the gene involved in the genetic disorder
2)restriction enzymes cut out the normal allele
3)many copies of the allele are made
4)copies of the normal working allele are put into the cells of a person who has the genetic disorder due to a mutated or faulty copy of an allele |
| What are the problems with gene therapy? | 1)the alleles may not go into every target cell, which are cells that need the new non-faulty cell
2)the alleles may be inserted into the chromosomes in random places, rather than in the required position, so they do not work properly
3)some treated cells may be replaced naturally by the patient's own untreated cells, as cells are frequently replaced through the process of mitosis during growth and repair |
| Give 3 alternative options of gene therapy. | 1)using nose sprays, which allow a patient to introduce the working allele up their nose and it will be taken into their body and incorporated
2)using cold viruses that are modified to carry the allele - the viruses go into the cells and infect them
3)the direct injection of DNA |
| What pedigree analysis? | Use family tree to predict chance of getting disorder. |
| Descaribe the discovery of ingeritence | Gregor Mendel (1822-1884) studied the inheritance of different characteristics in pea plants.
1)He found that when he bred red-flowered plants with white-flowered plants, most of the offspring had red flowers, but some had white, because the allele for red flowers is dominant, and the allele for white flowers is recessive.
2)One of Mendel's observations was that the inheritance of each characteristic is determined by 'units' that are passed on to descendants unchanged.
3)His work wasnt accepted:
-(1)when he presented his work to other scientists he did not communicate it well so they did not really understand it
-(2)it was published in a scientific journal that was not well known so not many people read it
-(3)he could not explain the science behind why characteristics were inherited
4)He was accepted in early 20th centuries when microscopes were developed.
5)James Watson & Francis Crick worked out the structure of DNA. By using data from other scientists Rosalind Franklin & Maurice Wilkins, they were able to build a model of DNA. They showed that bases occurred in pairs, and x-ray data showed that there were two chains wound into a double helix. |
