3.) Topic 3 DNA And Inheritance Flashcards
What is DNA?
DNA is a double-stranded polymer of nucleotides, wound to form a double helix. It is made up of 2 long strands of alternating sugar and phosphate molecules connected by bases
What is the function of DNA?
DNA is genetic information an organism needs to develop.
DNA is a code and it codes for amino acids.
It also controls characteristics or your appearance
What is a gene?
A gene is a section of DNA that codes for a specific protein.
What are chromosomes?
The structure made of DNA that codes for all the characteristics of an organism. They are strands of DNA
Where is DNA found?
Nucleus, in the cells
What does each strand of DNA consist of?
Alternating sugar and phosphate molecules
How are these 2 strands joint together?
By bases
What are the 4 bases and which one pairs with which?
A - Adenine
T - Thymine
C - Cytosine
G - Guanine
A pairs with T
C pairs with G
What does the order of the bases in a gene determine?
The order of the amino acids they code for
What is the triplet code?
Order of 3 bases
What does each triplet code for?
An amino acid
What does the order of amino acids determine?
Order of amino acids determines the structure and function of the protein formed
How many different amino acids are there?
64
What is genetic profiling?
Analysing DNA and a method of comparing DNA
How is a genetic profile created?
4 steps
- Sample of cells collected
- DNA extracted from cells
- DNA sample cut into fragments using enzymes. This ends up with fragments of different size
- Fragments separated into bands. A pattern develops creating a genetic profile
Name some things genetic profiling can be used for
Paternity testing Prison systems Trace down family trees Identification of genes which can link to diseases Classification
Name the advantages and disadvantages of genetic profiling
advantages:
Crime scene use
Discovery of genetic disorder
Determine paternity
Disadvantages:
Invasion of privacy some believe
Theft of DNA profiles
What is an allele
Different form of the same gene
What is a genotype
Letters that show the pairs of genes (genetic make-up of an individual)
What is a phenotype
What you see as a result of a genotype e.g. blue eyes
They are the physical characteristics of an organism
What is the dominant allele
The allele that shows in the phenotype whenever it is present. It is represented by a capital letter
What is the recessive allele
This is the hidden allele when the dominant allele is present. It is represented by a lower case
What is a gamete
A sex cell.
Male gametes are sperm
Female gametes are egg
What does it mean by homozygous
This is 2 identical alleles for the gene concerned (genes are the same)
What does it mean by heterozygous
2 different alleles for the gene concerned (genes are different)
What is F1
First generation - the offspring produced when two organisms interbreed
What is F2
Second generation - the offspring produced when two
organisms from the F1 generation are bred together
What is selfing?
A technique where which pollen from a plant is used to fertilise ovules in flowers of the same plant
What are the different ways to produce a DNA fingerprint and what are the meanings?
Isolation – separate the DNA from other tissues.
Fragmentation – use an enzyme to break the DNA into short lengths.
Separation – pass an electric current across a layer of gel which has the DNA fragments at one end. The fragments will move different distances across the gel. This is called gel electrophoresis.
Comparison – match the pattern of fragments on the gel with other samples of DNA.
How can genetic crosses of single gene combinations (monohybrid inheritance) be examined?
By punnett squares
The allele for brown eyes is dominant (B) where as the as the allele for blue eyes is recessive (b). A women who is heterozygous is crossed with man who is homozygous recessive. What is the probability that the offspring will have blue eyes?
B b
b Bb bb
b Bb bb
50% chance of the offspring having blue eyes
The allele for cystic fibrosis is recessive (f)
A mother who is heterozygous is crossed with a man who is who is also heterozygous. Complete a Punnett square for this. What is the chance that the child will have cystic fibrosis, be healthy or be a carrier of the disease
F f
F FF Ff
f Ff ff
25% have the disease
50% be a carrier of the disease
25% be healthy
Flower colour in pea plants is inherited genetically. The white allele is recessive, and the pink allele is dominant. A plant that is homozygous recessive is bred with a plant that is heterozygous.
If 48 seeds are produced, calculate an estimate for how many will have pink flowers.
a a
A Aa Aa
a aa aa
48/2 = 24
= 24
Overall, how does DNA work?
A gene is a section of DNA that codes for a particular protein. DNA consists of 2 strands of alternating sugar and phosphate molecules and each of these strands are joint by bases. There are 4 different bases A, G, C and T. A pairs with T and C pairs with G. The order of these bases determine the order of amino acids which they code for. 3 bases in a row is called a codon and these form a triplet code. This triplet code will determine the order of amino acids (64 different amino acids). This will form a particular pattern and proteins will be made.
How many pairs of chromosomes do humans have?
23 pairs (46 altogether)
What are the first 22 pairs known as in a human body
autosomes or homologous chromosomes
What does the final 23rd pair of chromosome determine
Determines sex. Whether the offspring will be male or female
What are males sex chromosomes
X and Y (XY)
What are females sex chromosomes
X and X (XX)
What do the cells in the testes divide to produce
Sperm and each sex chromosome goes into each sperm
What do the cells in the ovaries divide to produce
Egg and each sex chromosome goes into each egg
Which one is the large and small chromosome?
X is the large
Y is the small
What is a zygote
Fertilised egg
What is the diploid number
Full number of chromosomes in a cell
What is the haploid number
Half the number of chromosomes in a cell
What is genetic engineering or genetic modification
The artificial transfer of taking genes from one organism and placing them into the genome of another
What is a transgenic organism
An organism that contains foreign DNA
What are herbicides?
Chemicals that farmers use to kill plants that compete with crops
How have herbicide resistant soya plants been produced?
3 steps
- Genes from resistant plants are ‘cut out’ using enzymes
- They are transferred into the chromosomes of Soya bean plant cells
- The modified cells are cloned to produce GM plants resistant to herbicide
What are advantages of GM crops?
Plants that are resistant to herbicide can be sprayed with herbicide to kill weeds leaving the plants unaffected
Fewer chemicals need to be introduced into the environment to kill insects and plants
Increased in yield
Food will last longer and taste better
Useful in medicine e.g. insulin-producing bacteria, anti-thrombin in goat milk.
GM crops can produce oils which can be used as biofuels, an alternative to fossil fuels.
What are disadvantages of GM crops?
There are concerns about the health effect of eating them
Long term effects are unknown
Negative environmental impacts e.g. reduction in biodiversity, impact on food chain, contamination of non-GM crops forming ‘superweeds’.
Expensive
GM plants could become a pest themselves e.g. due to herbicide-resistance.
What are some issues of GM crops
GM crops could reduce a developed countries reliance on crops from developing countries. This could result in loss of trade and severe economic damage for the developing countries
Difficult to stop the pollen from GM crops grown in fields from pollinating other nearby crops. People who do not want GM crops may still end up with genetically modified genes having them
What is fertilisation
When the male and female gametes fuse restoring the full number of chromosomes
