B1 - You and your genes Flashcards
What are genes?
Instructions that control how an organism develops and functions.
Where are genes found?
In the nucleus of its cells.
How do genes work?
They tell the cells to make proteins needed for your body to work.
What is DNA?
A very long molecule that determines the order of amino acids in a protein (according to the order of the 4 bases)
What does DNA consist of?
Chromosomes, bases, phosphates and sugar molecules.
What is a Chromosome?
Thread-like structures in the nucleus of the cell that carry genetic information.
What are the two types of proteins?
- FUNCTIONAL: Enable the body to function.
Examples: ENZYMES, ANTIBODIES and HORMONES. - STRUCTURAL: Give the body structure, rigidity and strength.
Examples: Collagen in ligaments, keratin in skin.
What is a genome?
A complete gene set of an organism.
What are our characteristics controlled by?
Genes (e.g. dimples), our Environment (e.g. scars), or a COMBINATION of these (e.g. weight)
What do differences in genes produce in terms of offspring?
A VARIATION in offspring.
What are some characteristics controlled by? What do these show?
Some are controlled by several genes working together. These show CONTINUOUS VARIATION across a population, e.g. the continuous range of eye colour.
What do our body cells contain? What do our sex cells contain?
Our body cells contain 23 PAIRS OF CHROMOSOMES
( = 46)
Sex cells contain only ONE CHROMOSOME from each pair ( = 23)
What are alleles? How many alleles does an individual usually have for each gene?
The different forms in which the genes controlling a characteristic can occur. An individual usually has two alleles for each gene.
What is an example of alleles?
Dimples: there is one allele for the presence of dimples and another allele for the lack of dimples.
What does HOMOZYGOUS mean?
When the two alleles of a gene are identical. (e.g. DD)
What does HETEROZYGOUS mean?
When the two alleles of a gene are different. (e.g. Dd)
What happens at fertilisation?
An egg and sperm join together to produce a zygote.
What is a zygote?
A full set of 46 chromosomes - 23 from father, 23 from mother.
Why do offspring have some similarities to their parents?
Because of the combination of maternal and paternal alleles in the fertilised egg.
Why is that different offspring from the same parents can differ from each other?
Because they inherit a different combination of maternal and paternal alleles.
Alleles for a trait can either be ______ or ______
DOMINANT or RECESSIVE.
How are dominant alleles written in genetic diagrams?
With UPPER-CASE letters, e.g. H for hairy toes.
How are recessive alleles written in genetic diagrams?
With LOWER-CASE letters, e.g. h for hairless toes.
An individual with ONE OR BOTH dominant alleles will….?
SHOW the associated DOMINANT characteristic
e.g. HH or Hh will show hairy toes
An individual with ONE recessive allele will….?
NOT SHOW the associated recessive characteristic
e.g. Hh will still show hairy toes NOT hairless toes
An individual with BOTH recessive alleles will…?
SHOW the associated RECESSIVE characteristic
e.g. hh will show hairless toes
What are the two ways in which we can visualise the genetic inheritance of a trait?
- Punnett Square
(can show genetic crosses and the probability of two parents producing different types of offspring) - Family Tree Diagram
(shows the inheritance of a trait/genetic disorder)
What does the 23rd pair of chromosomes determine?
Our SEX (Male/Female)
Males have __ sex chromosomes.
Females have __ sex chromosomes.
Males have XY sex chromosomes.
Females have XX sex chromosomes.
What does the sex-determining gene on the Y chromosome trigger?
What does the sex-determining gene on the X chromosome trigger?
Y - The development of testes.
X - The development of ovaries.
If a defective gene is found on a part of an X chromosome, what can this result in?
A sexlinked disorder.
What are 2 examples of sex-linked diseases?
Are this likely to be present in males or females?
- Haemophilia (blood clotting disorder)
- Red-green colorblindness
They are far more likely to be present in males.
What is a genotype?
A person’s genetic makeup. (e.g. DD for dimples.)
What is a phenotype?
A person’s observable physical features.
Why do identical twins have identical genotypes?
They develop after a fertilised egg splits into two.
What are a small number of disorders caused by?
Defective/Faulty alleles of a single gene.
What are the 2 main examples of genetic disorders caused by faulty alleles?
- Huntington’s disease
2. Cystic fibrosis
What is Huntington’s disease caused by?
- Caused by DOMINANT alleles. The presence of a SINGLE dominant allele will cause the disease, e.g. Hh or HH makes you a SUFFERER.
When does Huntington’s disease occur?
What are 5 symptoms of Huntington’s disease?
It occurs in middle age (late-onset)
Symptoms include: tremor, clumsiness, memory loss, inability to concentrate, mood changes.
What is cystic fibrosis caused by?
-Caused by RECESSIVE alleles. The presence of BOTH recessive alleles will cause the disease, e.g. hh will make you a SUFFERER.
What are 4 symptoms of cystic fibrosis?
- Thick mucus
- Difficulty breathing
- Chest infections
- Difficulty in digesting food.
You can become a CARRIER of a recessive disorder, such as cystic fibrosis, if…?
You have AT LEAST one single recessive allele in a pair. (e.g. Ff makes you a carrier, not a sufferer.)
What is genetic screening?
A screening used to check for a particular disorder, even when there is no history of it in the family.
What is genetic testing?
A test used to check if there is a genetic disease (e.g. cystic fibrosis) that runs in the family.
Why is genetic testing beneficial (1) ?
It allows people to get treatment for the disease or to plan for the future.
What are 5 things to consider, in terms of ethical concerns, about genetic testing?
- The results are not 100% accurate (false positive, false negative)
- There’s a chance of miscarriage during tests.. (0.5 - 1%)
- Is it right to terminate a pregnancy?
- Discrimination from employers
- Insurance companies may refuse to give life insurance
What are two types of CELL SAMPLING of genetic testing during pregnancy?
- Amniocentesis (collecting cells from the developing fetus which are present in amniotic fluid)
- Chorionic villus sampling (testing a sample of cells taken from placenta)
Why is embryo screening used?
To investigate families with a known history of a disorder, such as cystic fibrosis. It allows doctors to remove any embryos suffering from a disorder and implant only embryos.
What is the scientific name for screening embryos prior to implantation and only using healthy embryos?
Pre-implantation genetic diagnosis (PGD)
What do guidelines in clinics and research centres cover in terms of these screenings?
They cover ethical and moral considerations for embryo use.
What are the 2 decisions that parent are likely to make when passing on a genetic abnormality?
- May decide to not have a family
2. May need to decide on whether to continue with the pregnancy or terminate it.
What is false negative?
What is false positive?
False negative - when a patient is told that they are healthy but the actual results show that they are actually sufferers/carriers of a disease.
False positive - when a patient is told that they are sufferers/carriers of a disease but the actual results show that they are healthy.
What are clones?
Individuals with identical genes
What DNA is present in the offspring in asexual reproduction?
The offspring has IDENTICAL DNA to the parent.
What are 3 examples of organisms that reproduce asexually?
- Bacteria
- (Some) plants
- Simple animals, e.g. Hydra
What are the 2 ways in which plants can reproduce asexually?
- Using runners (e.g. strawberries) - shoots sent out that grow into identical plants.
- Producing bulbs (e.g. daffodils)
How are human clones (i.e. identical twins) produced?
When a fertilised egg splits, resulting in two genetically identical individuals.
As clones have identical DNA, any differences between individuals in a clone and their parent MUST be a result of…..?
The ENVIRONMENT and NOT genes.
What are 2 advantages of producing clones/asexual reproduction?
- Successful characteristics are seen in offspring
2. Asexual reproduction is useful where plants and animals live in isolation.
What is the main disadvantage of producing clones/asexual reproduction?
There is no genetic variation.
This means that if conditions change or there is disease, the population could be wiped out.
What are 2 examples of artificial animal cloning?
- Dolly the Sheep
2. Snuppy the Dog
How does artificial animal cloning work?
Describe the 3 stages.
- Nucleus from a body cell is extracted.
- Nucleus is inserted into an egg cell that has had its nucleus removed. This gives the egg cell a full set of genes without having fertilised.
- The embryo is implanted into a suitable surrogate mother.
Why do people not create clones of humans
(in many countries, including the UK) ?
It is ILLEGAL to create clones of humans in many countries.
What is differentiation?
When most of the cells (which soon develop into a baby) become specialised to do different jobs.
After five days of fertilisation, how does the embryo develop?
The embryos become a ball of cells containing EMBRYONIC STEM CELLS.
What type of stem cells remain in certain parts of our bodies?
ADULT stem cells.
What can adult stem cells perform?
They can repair/replace certain cell types.
For example, bone marrow cells are able to develop into different types of blood cells.
What is the benefit of using adult stem cells?
What is the main drawback of adult stem cells?
Benefit - They can be used to treat various diseases.
Drawback - They have limited uses.
What makes embryonic stem cells have such huge potential?
They can develop into ANY cell types.
What are 2 reasons as to why using embryonic stem cells are controversial?
- They are usually taken from unused embryos following fertility treatments.
- Their use involves the destruction of the embryo.
What is recent research focusing on, in terms of the use of embryonic stem cells?
They are focusing on reprogramming adult body cells into stem cells, and collecting cells from the umbilical cord blood when a baby is born.
What are 3 uses of stem cells?
- The testing of new drugs
- Understanding how cells become specialised in the early stages of human development by the switching on/off of particular genes.
- Renewing damaged/destroyed cells in spinal injuries, heart disease, Alzheimer’s disease and Parkinson’s disease.
