Section 3- Genetics Flashcards
What are alleles
Different versions of the same gene. All genes exist in different versions
How are alleles represented in genetic diagrams
With letters
Homozygous allele
2 alleles for a gene that are the SAME
Heterozygous allele
2 alleles for a gene that are DIFFERENT
Dominant alleles
- shown with a capital letter
- overrule recessive alleles
- To display dominant allele, organism can have either 2 dominant alleles or 1 dominant and 1 recessive
Recessive alleles
- shown by a small letter
- if an organism has 1 dominant allele and 1 recessive, then the dominant allele would determine what characteristics the organism has
- for an organism to display recessive characteristics, both alleles must be recessive
Genotypes
Combination of alleles you have
Phenotype
Physical characteristics
Different combinations of alleles give rise to different phenotypes
Sexual reproduction
- where genetic information from 2 organisms (mother and father) is combined to produce offspring which are genetically different to either parent.
- Father and mother produce gametes, which are reproductive cells that only contain half the number of chromosomes making it haploid. In animal cells these gametes are sperm and egg cells
What happens in sexual reproduction
- At fertilisation, a male gamete fuses with a female gamete to produce a fertilised egg known as a zygote. The zygote then ends up with the full set of chromosomes making it diploid.
- The zygote then undergoes mitosis and develops into an embryo
Differences of meiosis and mitosis
MITOSIS:
- used for growth and repair
- creates diploid cells
- produces 2 genetically identical daughter cells
- one stage of cell division
- occurs in somatic cells
MEIOSIS:
- used for reproduction
- creates 4 non identical haploid sex cells or gametes
- occurs in testes and ovaries
Similarities of mitosis and meiosis
- takes place in the nuclei
- involves cell division
- stages are common
- synthesis of dna
Division 1 of meiosis
- Interphase - before the cell starts to divide it duplicated is DNA so that there is enough for each new cell. One arm of each x shaped chromosome is an exact copy of the other arm,
- Prophase – the membrane around the nucleus breaks down
- The chromosomes lineup in pairs in the centre of the cell this is known as metaphase. One chromosome in each pair came from the father. Any other pair came from the mother.
- The pairs of then pulled apart from the spindle fibres which is known as anaphase. This means that each new cell has one copy of each chromosome.
- Each new cell will have a mixture of the mothers and fathers chromosomes mixing up the genes like this is really important as it creates genetic variation.
Division 2 of meiosis
- The chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart by spindle fibres.
- You get for haploid daughter cells – these are gametes. Each gamete. Only has a single set of chromosomes does gametes are genetically different..
DNA
- DNA is made up of nucleotides
- DNA strands are polymers made up of lots of repeating units called nucleotides. Each nucleotide consists of one sugar molecules, one phosphate molecules and one base.
- The sugar molecules and phosphate molecule in the nucleotides form together to form a ‘backbone’ to the DNA strand. The phosphate and sugar molecules alternate.
- One of the 4 different bases join to each sugar, these are the bases:
- A- Adenine, T- thymine, C- cytosine, G- Guanine
- A DNA molecule has 2 strands coiled together in the shape of a double helix which is a double stranded spiral.
Complimentary base pairs
- Adenine
- Thymine
- Cytosine
- Guanine
1. Each base links to a base on the opposite strand in the helix
2. The complimentary base pairs are joined together by weak hydrogen bonds
How is DNA stored
DNA is stored as chromosomes and contains genes
What are chromosomes
Chromosomes are long, coiled up molecules of DNA. They’re found in the nucleus of eukaryotic cells.c
What are genes
A Gene is a section of DNA on a chromosome that codes for a particular protein. The sequence of bases in the genes determines what protein is produced
What makes the genome
All of the organisms DNA makes up its DNA
How to extract DNA from fruit cells
- Mesh some strawberries and put them into a beaker containing a solution of detergent and salt
- Filter the mixture to get froth and big insoluble bits of the cell out.
- Add some iced cold alcohol to the filter the mixture.
- The DNA will start to come out of the solution as it is not soluble in the cold alcohol. It will appear as a stringy white precipitate, which could be carefully fished out using a glass rod.
Why is it useful to use detergent when extracting DNA from fruit cells
Detergent will break down the cell membranes to release the DNA
Why is is useful to use salt when extracting DNA from fruit cells
Salt will make the DNA stick together
What is cystic fibrosis
an inherited condition that causes sticky mucus to build up in the lungs and digestive system. This causes lung infections and problems with digesting food.
What chromosomes do females have
XX - homozygous
What chromosomes do males have
XY- heterozygous
What alleles cause cystic fibrosis
- It is a recessive allele, f, which is carried by 1 person in 30.
- Because it is recessive, people with only 1 copy of the allele won’t have the disorder, they are known as carriers.
- Both parents must have the disorder themselves or be carriers for their child to inherit the disease.
Mutations
Mutations are changes to the base sequence of DNA. When they occur within a gene, they result in an allele of a different version of the gene. They don’t always have a big effect on the phenotype but some mutations have a small effect and they alter the individuals characteristics
What makes cystic fibrosis
- A mutation causes a protein that controls the movement of salt and water in and out of the cells to stop working properly.
- This leads to the production of thick and sticky mucus in the lungs and digestive system making it difficult to breathe and digest food
How are new phenotypes made
New combinations of alleles may interact with each other to produce new phenotypes
Human genome project
To find every single human gene and what they all do. They have huge benefits for medicine:
- prediction and prevention of diseases
- testing and treatments
- better and new medication
Prediction and prevention of diseases
- Many common diseases like cancer and heart diseases are caused by interaction of different genes as well as lifestyle factors.
- If doctors knew what teens predisposed people to what diseases we can all get individually, tailored advice on the best diet and lifestyle to avoid our likely problems
- Doctors could also check us regularly to ensure early treatment if we do develop the disease with suspectible to
What is genetic variation within a species caused?
- Is caused by organisms having different alleles, which can lead to different phenotypes
-Can because my new alleles arising through mutations - sexual reproduction also causes genetic variation since it results in a alleles being combined in lots of different ways in offspring
Why is there a lot of genetic variation within a population?
This is mostly due to neutral mutations
Environmental ways variation caused
- A plant that grows on a nice sunny windowsill would be luscious and green
- The same plants can be grown in darkness and would be tall and spindly, and it’s leaves would be yellow
Acquired characteristics
Environmental variation in phenotypes are also known as acquired characteristics, the characteristics that organisms acquire during their lifetimes
What are mutations?
Mutations are changes to the base sequence of DNA
What happens when mutations occur?
When they occur within a gene, they result in an allele or a different version of a gene
They don’t always have a big affect on a phenotype of an organism. Most mutations don’t have any effect in other words, they are neutral
What happens when some mutations have a small effect on the phenotype?
They alter an individuals characteristics, but only very slightly
What happens when a mutation had a big affect on the phenotype?
Very rarely a single mutation will have a big effect. It might result in the production of a protein that is so different that It can no longer carry out its function.
Testing and treatment for inherited disorders
- Inherited disorders like cystic fibrosis are caused by the presence of one or more faulty alleles in a person is genome.
- Because of the human genome project, scientists are now able to identify the genes and alleles that suspected of causing an inherited disorder much more quickly.
- Once an allele that causes an inherited disorder has been identified, people can be tested for it, and it may be possible to develop better treatments or even a cure for disease.
New and better medicine
- The genome project has highlighted some common genetic variation between people.
- some variations affect our individual bodies will react to certain diseases and to the possible treatment for them. - Scientists cannot use this knowledge to design new drugs that are specifically tailored to people with a particular genetic variation.
-They could also determine how well an existing drug for work for an individual.
-Tests can identify whether or not someone with breast cancer respond to a particular truck and what dosage is most appropriate for certain drugs in different patients. - Knowing our disease affects us on a molecular level, should make it possible to design more effective treatments with fewer side-effects.
What are the drawbacks of the human genome project
- Increased stress.
- Gene-ism
- Discrimination by employers and insurers.
Increase stress
If someone knew from an early age that they are susceptible to a disease they would panic every time they get a symptom
Gene-ism
People with genetic problems could come under pressure, not have children
Discrimination by employers and insurers
Life insurance could become impossible to get more expensive if you take any genetic likelihood of a serious disease.
Employers need discriminate against people who are genetically likely to get to get a disease
