The Genome, Chromosomes, DNA and Genetics Flashcards
Chromosomes definition
Genetic structures occurring in functional pairs in the nucleus of cells, except gametes and bacteria
What are genes?
A short length of DNA which codes for amino acids, a protein or a characteristic
What are chromosomes and their genes made of ?
DNA
What does DNA stand for?
Deoxyribonucleic acid
What do DNA molecules do?
They carry the code that controls what cells are made of and what they do
What makes up DNA?
Deoxyribose sugar backbone, phosphate and a base
What are the 3 units of deoxyribose sugar, phosphate and base joined together to form?
A nucleotide
Name the two base pairs
AT
GC
The code uses groups of 3 singular bases to code for a single amino acid. What are these called?
Base triplets
Mitosis definition
The exact duplication of chromosomes producing daughter cells that are genetically identical to parent cells
Cells with pairs of chromosomes are referred to as …
Diploid cells
Describe the process of mitosis (5)
- a cell containing a single chromosome replicates its DNA
- two identical copies of chromosomes are made and the cell starts to divide. Chromosomes are arranged in the middle of the cell.
- The two stranded chromosome thicken and centrioles make spindle fibres to pull the chromosomes apart
- A new nuclear membrane forms around each set of the separated chromosomes
- The cell splits into two as the cytoplasm is divided evenly and each new cell receives a copy of the original chromosome - creating two identical daughter cells
What is meiosis for ?
This type of cell division is responsible for the production of the sex cells (gametes). This occurs in the testes and ovaries of mammals and results in the formation of sperm and egg cells that contain the haploid number of chromosomes.
What is meiosis referred to as?
Reduction division ( one cell producing four genetically different, haploid daughter cells)
Why is meiosis necessary?
To ensure that chromosome number is kept constant from generation to generation
Name another important feature of meiosis
The cells produced are genetically different to the parent cells
What is independent assortment?
The chromosomes are divided randomly when being divided into the daughter cells. Gametes will contain some chromosomes obtained from your mother and some from your father
What do phosphate and sugar deoxyribose backbone with interlinking bases form?
A double helix
What does mitosis allow organisms to do? (3)
- grow
- replace work out cells
- repair damaged tissue
Cells with pairs of chromosomes are referred to as ..
Diploid cells
Stages of Meiosis (4)
- DNA replication
- Separation of the chromosomes
- Division of the cytoplasm (we now have formed 2 cells with 46 chromosomes from one cell with 46 chromosomes)
- These 2 cells then have their chromosome pairs separated into chromatids to form a total of 4 cells each with 23 chromosomes (haploid cells)
Definition of DNA
Deoxyribonucleic acid built up from nucleotides found in chromosomes
Who first studied inheritance
Gregor Mendel
Genotype
The genes an individual possesses
Phenotype
The physical characteristics that are visible depending on the organisms genotype
What are sex linked characteristics ?
When X and Y chromosomes carry other genes that control other characteristics like red green colour blindness and haemophilia
Recessive meaning
An allele that is overruled by a dominant allele of that characteristic
Give two ways cells produced by meiosis would differ from those produced by mitosis
- Cells produced by meiosis would be gametes
- Meiosis forms 4 cells instead of 2 in mitosis
What is cancer ?
Uncontrollable cell division of abnormal cells
Describe the process of the back cross (4)
- Cross the organism of unknown genotype with a homozygous recessive individual using a back cross.
- Observe the phenotype of the offspring
- If the offspring of the cross show any of the recessive characteristics then the parent of unknown genotype MUST have been heterozygous
- If the offspring only show the dominant characteristics then the parent MUST have been a homozygous dominant
What is cystic fibrosis caused by ?
A recessive allele. People with the disease need to be homozygous recessive to suffer from the symptoms.
What is Haemophilia ? (2)
- a condition that affects the clotting of blood, due to the defective gene preventing the manufacture of a key protein involved in blood clotting.
- It is caused by a recessive allele on the X chromosome
What is Huntington’s Disease?
This condition affects nerve cells in the brain leading to brain damage. It is caused by a dominant allele
What is Down’s Syndrome caused by ? (2)
- The inheritance of an extra chromosome.
- This is due to some of the eggs produced by the mother having 2 copies of chromosome 21 due to an error in chromosome segregation during meiosis
Describe the steps during genetic engineering : (4)
- Extract the DNA from the human cells using the restriction enzyme to isolate the gene of interest
- Small rings of DNA called plasmids are removed from bacterial cells and opened using the same restriction enzyme.
- The isolated gene is inserted into the plasmid using another enzyme and taken into a bacterial cell.
- The bacteria multiply, producing the protein coded for by the inserted gene
Why is it important to use the same enzyme to cut out the insulin gene and cut open the plasmid ? (3)
- to ensure that the shape of the human insulin gene is complementary to the plasmid
- They will cut the same sequence of bases to produce sticky ends
- This allows base pairing to occur
What is the genome?
The entire genetic material of an organism
What do built up amino acids in the correct sequence form?
Proteins
What is genetic screening ?
Biotechnology that allows samples from amniotic fluid to be tested for genetic abnormalities in chromosomes or alleles
What is genetic engineering ?
A process that modifies the genome of an organism to introduce desirable characteristics
Why are bacteria used in genetic engineering ?
- Due to their high reproductive rate which means that a large number of copies of the desired gene will be made in a short space of time
- They also contain plasmids that can be transferred from 1 cell to another quite easily
What are plasmids referred to as?
Vectors
What does the process of genetic engineering require?
- The donor DNA (section coding for human insulin)
- Host DNA (bacterial plasmid)
To be cut with the same enzyme
What do restriction enzymes produce and why are they useful?
They produce sticky ends with short sequences of free bases that can be used to stick different pieces of DNA together because they are available for complementary base pairing
What are the negatives of genetic screening? (3)
- the amniocentesis test carries a 1% risk of miscarriage
- Carriers of genetic conditions face a dilemma after a test that diagnoses abnormalities whether to abort
- It makes genetic information available to wider society, e.g insurance companies
Three steps of downstream processing :
- Extraction: the insulin has to be removed from the fermenter
- Purification: contaminants and impurities must be removed
- Packaging: the insulin must be packaged in a way that allows for easy distribution to the patient
Explain the importance of the fermenter system having a controlled:
Nutrient supply
Temperature
pH
- Nutrient supply allows the bacteria to grow and reproduce and work at an optimum rate
- If the temperature is too hot then the enzymes may become denatured and too cold means the enzymes will become dormant
- pH affects the enzymes in the bacteria as they will have an optimum pH to grow and reproduce at
Why must air be added to the fermenter ?
Air contains oxygen for respiration. Respiration releases energy for growth
Why is a gas outlet required for the fermenter ?
Any gases that build up can be released to prevent high pressures and explosions
Disadvantages of producing non-human insulin: (3)
- it differs in structure to human insulin and is therefore not as effective for humans
- Slow to produce
- Diabetics can begin to recognise animal insulin as foreign and their white blood cells will attack it
Advantages of using genetically engineered human insulin (3)
- No harm comes to animals
- Reliable supply
- There is no allergic reaction to human insulin
Explain why large numbers of offspring are needed to ensure conclusions of the back cross are valid (2)
- Ratios will only be accurate when large numbers of offspring are produced
- This is because it is totally random which gametes, and therefore alleles, will fuse during fertilisation
