Biology - B1

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An organism's GENOTYPE is all of the genes it has.
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The CHARACTERISTICS that an organism displays are called its PHENOTYPE.
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Some characteristics, e.g. DIMPLES, are contolloed ONLY by GENES. This can be one gene, or quite often the characteristic is controlled by SEVERAL GENES working together, e.g. eye colour.
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Environmental factors
Other characteristics, e.g. scars, are contolled ONLY by ENVIRONMENTAL FACTORS. They don't have anything to do with genes and are caused by things like HOW and WHERE YOU LIVE.
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Both Genes
There are also characteristics that are contolled by BOTH genes and environmental factors. For example, weight - if both your parents are skinny, you'll probably be skinny too.
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Sex Cell
The SEX CELLS (the sperm and the egg) are diffrent from ordinary body cells because they contain just 23 SINGLE CHROMOSOMES - that'sone chromosome from each pair.
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Children's Alleles
Children get SOME of their alleles from each of their parents.
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Chromosomes in a Pair
Each of the 23 chromosome pairs semerates INDEPENDENTLEY.
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Sex Chromosomes
They decide whether you turn out male or female.
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Genetic Disorders
Some DISORDERS are INHERITED - one or both parents carry a faulty allele and pass it on to their children.
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Recessive Alleles
Most of the DEFECTIVE ALLELES that are responsible for genetic disorders are RECESSIVE.
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Cystic Fibrosis
CYSTIC FIBROSIS is a GENETIC DISORDER of the CELL MEMBRANES caused by a faulty recessive allele.
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Cystic Fibrosis - Symptoms
Thick sticky mucus, breathing difficulty, chest infections, difficulty digesting food.
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Dominant Alleles
The dominant allele means there's a 50% chance of each child inheriting the disorder if just one parent is a carrier.
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Huntingtons Disease
The disorder causes shaking, clumsiness, memory loss, mood changes and poor concerntraion. There is no cure.
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Genetic Testing
When EMBRYOS are produced using IVF (in virto fertilisation), docotors can test the embryos to check if they've go certain genetic disorders.
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Geneticly testing Fetus'
Doctors can also test fetuses in the womb for genetic disorders by testing the fluid surrounding the fetus.
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Errors in Genetic testing
The results of genetic tests may not be 100% accurate. There are often errors due ti things like samples getting contaminated or misinterpretation of results.
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Tests during Pregnancy
Like most medical procedures, tests carried out during pregnancy aren't 100% safe, e.g. doing a genetic test on the fluif around the fetus causes miscarage in 0.5% to 1% of cases.
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What is a clone?
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Clones are genetically identical organisms - they have the same genes, and the same alleles of those genes.
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Diffrences in Clones
Clones have the same alleles, any diffrence between them must ve due to diffrence in environment, - e.g. being better nourished than your clone as a child, you woud probably be taller than your clone, even though your alleles are still the same.
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Asexual Reproduction
ASEXUAL reproduction means that there is only ONE PARENT, and the offspring are GENETICALLY IDENTICAL to each other and the PARENT.
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Animal Clones
The NUCLEUS of an EGG CELL is REMOVED - this leaves the egg cell WITHOUT any genetic imformation.
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Animal Clones (part 2)
A NUCLEUS from an adult donor cell is INSERTED in its place. The cell is then STIMULATED so that it starts dividing as if it was a normall embryo (fertilised egg).
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Animal Clones (part 3)
The embryo produced is GENETICLLY IDENTICAL to the DONOR CELL.
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The CHARACTERISTICS that an organism displays are called its PHENOTYPE.

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Environmental factors


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Both Genes


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