Genetics Flashcards
Where is DNA found in humans?
in chromosomes in the nucleus of cells
What do chromosomes contain?
1000s of genes
Why are chromosomes found in pairs?
one is maternal and the other is paternal
How many pairs of chromosomes do humans have?
23
What is DNA made of?
A polymer of nucleotides
What does each nucleotide contain?
a phosphate, a sugar and 1 of 4 bases
What are the four bases?
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
What codes for proteins?
The sequence of bases
What type of structure is the double stranded DNA molecule found in?
Double helix structure
What is the human genome?
The entire genetic material of a human
How many genes are present in the human genome?
30,000
Why is knowledge of the human genome important?
- to search for genes linked to diseases
- to understand and treat hereditary disorders
- to trace human migration
What does each gene code for?
A protein
How many bases of DNA strand code for 1 of the 20 amino acids in a protein?
3
What does the sequence of the base determine?
The sequence of the amino acids
Is the double stranded structure stable or unstable?
Stable
Why does DNA have two strands?
One strand of DNA codes for genes, the other is complementary to it to give it strength
What are the pairs of bases in genes?
A binds with T
C binds with G
What are loacted either sides of genes?
Control regions which tell the body how often a gene needs to be expressed (used)
Describe the process of protein synthesis:
- An enzyme will make a copy of the gene in a molecule called mRNA (messenger) which travels out the nucleus to a ribosome in the cytoplasm.
- Here, each triplet (three bases), is paried with a tRNA(transfer) molecule with a specific amino acid attached.
- The amino acids are joined together in a specific sequence to form a protein chain
- This chain will fold in a specific way to make a protein with a specific shape e.g. enzyme
What is a DNA mutation?
Any change to the base sequence in DNA
What are the possible affects of a DNA mutation?
- The amino acid sequence can be changed and the function of the protein can be thus affected e.g. changing the shape of an enzyme’s active site
- The regulation of the gene can be affected, making it switch on more or less often than required
When do mutations occur?
Randomly during cell division
What factors increase the rate of mutations?
Radiation and carcinogens
What is the function of the cell cycle?
To control the replication of organelles and DNA so that cell division can occur
Describe the basic cell cycle:
- Growth 1: replication of organelles
- Synthesis: DNA replication
- Growth 2: Replication of organelles and cell growth
- Nuclear division: mitosis/meiosis
Describe the stages of mitosis:
- DNA becomes visible in the nucleus
- Nucleus disappears and chromosomes pair up
- chromosomes line up down the middle of the cell
- spindle fibres connect to the chromosomes
- spindle fibres pull the chromosomes apart
- nucleii form around the separated chromosomes
- cell divides into two identical cells
What is the product of mitosis?
2 daughter cells that are identical to the parent cell are formed which are diploid
What does diploid mean?
They have 2 copies of each chromosome (ie. 23 pairs)
What is mitosis used for?
growth, repair and asexual reproduction
What is the product of meiosis?
4 non-identical haploid gametes
Describe the stages of meiosis:
- The DNA in the cell replicates
- The nucleus disappears and the chromosomes pair up together
- The chromosomes line up in pairs down the middle of the cell. Spindle fibres attach to them and pull them apart
- the first division creates two non-identical cells
- the second division creates 4 haploid cells
- 4 gametes are formed
Compare mitosis and meiosis:
- 1 division vs 2 divisions
- 2 daughter cells vs 4 daughter cells
- identical cells vs non-identical cells
- diploid vs haploid
- growth,repair, aseual reproduction vs sexual reproduction
How is the diploid number of chromosomes maintained during fertilisation?
each gamete has 23 chromosomes so 23 (sperm) + 23 (egg) = 46 (zygote-fertilised egg)
What are the advantages of sexual reproduction?
- introduces variation into offspring.
- can lead to natural selection and evolution over time
- artificial selection can be used to selectively breed desired traits
What are the advantages of asexual reproduction?
- faster and more energy efficient
- doesn’t require another parent/mate
- lots of clones can be made if the environment is favourable
What organisms use both asexual and sexual reproduction?
malrial parasite, fungi and some plants
How do malarial parasties use both sexual and asexual reproduction?
- asexual reproduction in humans
- sexual reproduction in mosquitos
How do fungi use both sexual and asexual reproduction?
- asexual reproduction in spores
- sexual reproduction when required (ie. limited resources)
How do some plants use both sexual and asexual reproduction?
- asexually with cuttings/runners
- sexually with seeds
What determines sex in an embryo and when?
The sex chromosomes (pair 23) at about 6 weeks after fertilisation
What chromsomes do females possess?
XX
What chromosomes do males possess?
XY
What type of chromsome does an egg have?
X
What type of chromsomes do sperm have?
50% X and 50% Y
How many copies of each gene do we have? Why?
Two copies of each gene as we have two copies of each chromosome
What is an allele?
A different version of a gene
How many genes control fur colour in mice?
1
What are the two mice fur alleles and which is dominant and which is recessive?
Black fur (dominant) and brown fur (recessive)
What are the symbols for black fur and brown fur?
B and b
What is the genotype of an organism?
The combination of dominant and/or recessive genes which an organism receives from their parents (e.g. BB for mice fur)
What is the phenotype of a mouse?
The fur colour
What is a mouse with a genotype BB called? WHat colour fur does it have?
A homozygous dominant - black
What is a mouse with a genotype Bb called? What colour fur does it have?
A heterozygous - black
What is a mouse with a genotype bb called? What colour fur does it have?
A homozygous recessive - brown
What is a carrier?
An organism which carries a recessive gene in one of their two chromosomes so can pass it on to their offspring but display the dominant gene
What does polygenic mean?
Means a characteristic is defined by many genes
What type of diseases are cystic fibrosis and polydactyl?
Monogenic hereditary diseases
What is cystic fibrosis?
- living condition where a patient produces very thick sticky mucus which builds up in lungs, digestive system, reproductive system
- it is recessive so 2 carries have a 1/4 chance of their child having cystic fibrosis
What is polydactyly?
- where someone grows extra fingers or toes
- it is dominant so a patient cannot be a carrier of it as the heterzygous individual will be a sufferer
What are the disadvantages of sexual reproduction?
- takes time and energy to find a mate or spread gametes so is less efficient
- often slower than asexual reproduction
WHat are the disadvantages of asexual reproduction?
- if the environment changes, all offspring are at risk since they are genetically identical and may not survive
Compare asexual and sexual reproduction:
- Asexual requires one parent whereas sexual requires 2
- fertilisation is used in sexual reproduction and mitosis in asexual reproduction
- offspring from sexual reproduction are genetically different to one another and their parents whereas asexually reproduced offspring are genetically identical to their parent
What does sexual reproduction in plants involve?
The joining of pollen and an ovule in fertilisation
How do plants reproduce asexually?
runners form at the ends of exisiting stems by mitosis
How will the genome project help identify which rare diseases are inherited?
- the genome of a person with a rare disease can be compared to the genome of a relative
- if the relative has the disease, DNA sequences that are similar can be looked for
- if the relative does not have the diesease, scientists can look for DNA sequences that are different
- these genes may be linked to the disease and mean it is inherited
How will the genome project help to develop treatments for rare diseases?
- if genes that are linked to diseases are identified, treatments can be developed
- this could be genetic engineering to change a gene
What is non-coding DNA?
- DNA around a gene which switches the gene on and off but doesn’t actually code for a protein
What is gene expression?
when a protein, coded for by a gene, is synthesised in a cell
What can be used to show genetic crosses?
Punnett squares and family trees
What is an allele?
A different version of a gene
What does dominant mean?
That gene is always expressed if it is present
What is a genotype?
The combination of alleles in an organism
What is a gene?
A part of DNA made up of a specific sequence of nucleotides which code for a protein
What is meiosis?
The process of cell division in sexual reproduction ehich produces 4 non-identical, haploid gametes
What is a phenotype?
The expressed physical feature associated with a genotype
When did Gregor Mendel publish his work?
1866
Why was Mendel’s work originally rejected?
Most scientists believed in blended inheritance in which all characteristics are passed on
When was the behaviour of chromosomes during cell division obeserved?
The late 19th century
What was observed in the early 20th century?
That chromosomes and Mendel’s units behaved in similar ways. Led to idea that units (genes) were located on chromosomes
What was discovered in the mid 20th century?
The structure of DNA and thus the mechanism of gene function
What are stem cells?
Undifferentiated cells capable of dividing to produce more stem cells or specialising to make many different types of specialised cells.
Where are stem cells located in animals?
- in the embryo
- in bone marrow
What is the difference between stem cells in bone marrow and embryos?
The stem cells in bone marrow can differentiate into a limited number of specialised cells like blood cells whereas those in embryos can differentiate into most human cells
Where are stem cells located in plants?
In meristem tissue which is found behind the root and shoot tips and between xylem and phloem cells
What is special about stem cells in plants?
They can differentiate into any plant cell throughout the life of the plant
What are the two methods of cloning plants?
- tissue culture
- cuttings
What does cloning with cuttings involve?
- removing a small part of a plant and using it to grow a new cloned plant via asexual reproduction
What does tissue culture cloning involve?
where colned whole plants are grown from just a few cells from the parent plant
What is the use of tissue culture and cuttings?
Useful for culturing economically and comercially important plants such as crops with disease resistance and preserving rare or endangered plants
What is the therapeutic cloning of animals?
- cloning of an organism so it has the same genes as another, meaning it can be used for replacement organs without the risk of immune system rejection
What are the disadvantages with therapeutic cloning and organ replacement?
there is a risk of viral infection and many people are ethically opposed to it
What are the two methods of making clones in animals?
- embryo splitting
- adult cell cloning
Describe the embryo splitting cloning process:
- when an embryo is at the 16 cell stage it is split into either 2 or 4 new embryos
- each of these is transferred into a surrogate mother’s uterus and the resulting young are all clones of one another
Describe the adult cell cloning process:
- nucleus from an adult cell is taken
- nucleus from an egg cell is taken
- the adult’s nuclues is put into the egg cell
- this cell is then given an electric shock and culture medium, allowing the embryo to form
- this is transferred to a surrogate and a cloned baby will grow
Why is the egg cell with the adult nucleus given an electric shock?
To stimulate mitosis
What is genetic engineering?
It is where a gene is taken from an organism, transferred into the genome of another organism of a different species, to provide desireable characteristics
Describe the genetic engineering process:
- gene is removed from the original species, using enzymes called Restriction Endonucleases
- this gene is inserted into a vector, typically a virus or a plasmid
- this is then used to insert the gene into the host organism
What happens if animal or plant cells are engineered early in development?
The characteristics of the whole organism can be changed
How have plants already been genetically engineered?
- to grow better with higher yield in unfavourable conditions (e.g. drought or pest infested)
- to be more nutritious
How have bacteria been engineered to help diabetics?
They have been engineered to make human insulin
What is the advantage of using bacteria making human insulin?
It makes the insulin more readily available, cheaper and more widely accepted by society
What is the grounding for fears about GM crops?
The fact that long term effects have not been studied
Describe how bacteria are used to produce human insulin:
- functioning insulin gene is extracted from a human chromosome
- a plasmid is taken from a bacterium and cut open with enzymes
- gene is joined with the plasmid with enzymes
- the new plasmid is taken up by the bacterium
- gene is switched on to make bacteria produce insulin
What features can be given to GM crops?
- Pest Résistance
- increased fruit size
- increased nutrition
- disease resistance
- herbicide resistance
- pesticide resistance
What is the advantage of using tissue culture rather than taking cuttings?
Can create thousands of clones from one small piece of tissue which can’t be done with cuttings
What is the disadvantage of tissue culture compared to cuttings?
Needs to be carried out using specialist equipment in a laboratory whereas cuttings requires none
What is the advantage of adult cell cloning for producing animals with certain traits compared to embryo cell cloning ?
- embryo cells cloning clones mixed DNA from a mother and father so possess a mixture of traits
- Adult cell cloning means all the animals get the one set of DNA from the one animal known to have the good traits
What is the name of the process where genetic engineering is used to cure illness?
Gene therapy
Describe how gene therapy can be used to cure type one diabetes
- healthy gene producing insulin can be cut out of Humans DNA and transferred into a vector like a virus
- this can infect the persons cells and the healthy insulin gene is thus inserted into their DNA
