GCSE Biology B1 (OCR)

Frage	Antworten
What is a fertilised cell called?	A zygote.
Where are the instructions to control how an organism _______ and ______ found? What are these called?	Function + Develop Nucleus Genes
What are genes?	Instructions for a cell that describe how to make proteins. They control which protein a cell makes. A gene is a section of DNA molecule.
Proteins may be ________ or _______. What is the difference between these?	Functional (eg. collagen) or Structural (eg. enzymes such as amylase). Structural proteins are needed to build the body - collagen is the protein found in tendons. Functional proteins are needed to take part in the chemical reactions of the body.
What are chromosomes made up of?	Very long DNA molecules.
What are some characteristics determined by.... Genes? The Environment? Both?	Eye colour, nose shape, blood group, gender, freckles. Scars, hair length, tattoos, language. Hair colour, skin colour, height, eye sight, foot size, personality.
Body cells contain pairs of chromosomes. How many of each pair do sex cells contain?	One
Why might the genes in a pair not be exactly the same?	Because they contain different versions of the same gene called alleles.
The alleles you inherit is called your _______.	Genotype
Your _______ is what you look like.	Phenotype
How many copies of a dominant allele to have its feature? And a recessive allele?	One dominant allele. Two recessive alleles.
How many alleles does a person usually have for each gene?	Two
Define Homozygous. Define Heterozygous.	Homozygous = The two alleles of each gene are the same (eg. J, J) Heterozygous = The two alleles of each gene are different (eg. J, j)
Why do offspring have similarities to their parents?	Because there is a combination of maternal and paternal alleles in the fertilised egg.
Why do different offspring from the same parents differ from each other?	Because they inherit a different combination of the maternal and paternal alleles.
How many dominant alleles do you need to show the associated characteristic? Recessive alleles?	Dominant = One Recessive = Two
Which sex chromosomes do males have? Females?	Male = XY Female = XX
How does the Y chromosome make a baby male?	The SRY gene on the Y chromosome triggers the development of testes. Testes produce androgens (male sex hormones) which make the embryo develop into a male.
What are Huntington's disease and cystic fibrosis caused by? Dominant or recessive alleles?	Faulty alleles of a single gene. Huntington's = Dominant CF = Recessive
What are the symptoms of Huntington's disease?	Late onset, tremor, clumsiness, memory loss, inability to concentrate, mood changes.
What are the symptoms of Cystic Fibrosis?	Thick mucus, difficulty breathing, chest infections, difficulty digesting food.
What are some treatments for cystic fibrosis?	- Pre-digested food or tablets (eg. milkshakes) - Being put on oxygen - Sport and fitness
What is the danger of carrying a recessive allele?	The person won't show the symptoms of the disorder, but they are a carrier and could pass it onto their offspring.
What are the uses of genetic testing for screening adults, children, and embryos?	- Testing embryos for embryo selection (PGD) - Predictive testing for genetic diseases - Testing before prescribing drugs
Amniocentesis: How? When? Risks?	How: Syringe extracts amniotic fluid, which contains fetal cells. These cells can then be tested. When: 15-18 weeks. Risks: 1% miscarriage risk. Small risk of infection. Results not 100% reliable.
Chronic Villus Sampling (CVS) How? When? Risks?	How: Sample of placenta is extracted through the abdomen or the cervix, and it is then tested. When: 10-12 weeks. Risks: 2% miscarriage risk. Results not 100% reliable.
What is genetic screening?	Genetic testing the whole population, or large groups.
What is pre-implantation genetic diagnosis (PGD)?	Several eggs are released and collected by a doctor. Sperm fertilises the eggs in a petri dish (IVF). Embryos reach the eight-cell stage, and one cell is taken from each. The cells are tested for the specific allele. Only embryos without the allele are implanted in the uterus.
What are the implications that need to be considered when testing adults a fetuses for alleles that cause genetic disorders?	- Risk of miscarriage as a result of cell sampling - Results may not be accurate (FP, FN) - Whether or not to have children - Whether a pregnancy should be terminated - Whether other members of the family should be informed
What are the implications of genetic testing by insurance companies?	- They might not insure someone, or they might charge a high premium. - People won't have genetic tests because they fear the insurance company will find out.
What are the implications of genetic testing by employers?	- Someone might not be hired because they have a certain genetic disease, which would cost the company money.
What are the implications of genetic testing by the police?	- There could be a national DNA database, which allows the police to catch criminals much more easily.
What is a clone?	An individual with identical genes to another.
Bacteria, plants, and some animals can reproduce _______ to form clones. How does this happen?	Asexually The single cell divides to from two new cells. The two cells' genes are identical.
Any differences between clones are due to.......	..... environmental factors.
What are some examples of plants producing clones naturally?	Bulbs and runners.
How do clones of animals occur?	- Naturally, when cells of an embryo separate, forming identical twins. - Artificially, when the nucleus from an adult body cell is transferred to an empty unfertilised egg cell.
What is the difference between a____ and e______ stem cells?	Adult stem cells are unspecialised cells that can develop into many, but not all, types of cell. (eg. brain, heart, bone marrow). Embryonic stem cells are unspecialised cells that can develop into any type of cell.
Give an example of when adult stem cells are used.	Adult stem cells from the bone marrow can be used to treat patients with leukemia, which is cancer of the blood.
What happens when someone else's cells are used in a transplant?	They are rejected.

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