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B1
Descripción
GCSE Biology Mapa Mental sobre B1, creado por benevans2000 el 03/02/2016.
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biology ocr
biology
gcse
Mapa Mental por
benevans2000
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benevans2000
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Resumen del Recurso
B1
Genes, Chromosomes and DNA
Most cells in body have a nucleus - contains genetic material
Genetic material arranged into chromosmes
Human body has 23 pairs of chromosomes
Chromosomes is a long molecule of DNA coiled up
A gene is a short length of chromosome
Genes control the development of different characteristics
Genes have different variations, which form different characteristics
Genes encode certain proteins
Structural proteins make up things like skin, hair, blood
Functional proteins make up enzymes etc.
Genotype describes all the genes it has
Phenotype is the characteristic of the gene
Genetic factors affect things like dimples, eye colour or natural hair colour
Environmental factors are physical changes like scars or the dyeing of hair
Genes and Variation
Chromosomes come in pairs (because we have 2 parents)
Each sex cell contains 23 individual chromosomes
Upon fertilisation, the 23 chromosomes from each sex cell combine to make 23 pairs.
The two chromosomes in the pair contain the exact same genes in the exact same places, they may contain varying alleles
Half a child's chromosomes come from each parent
Children get some alleles from each parent
Children look similar to both but identical to neither of their parents
Homozygous: two alleles the same for the particular gene
Heterozygous: two alleles different for the particular gene
Dominant allele: only the characteristic of the dominant allele is shown, as long as it is present no matter what the genotype is
Recessive allele: the characteristic is only shown if the genotype is homozygous recessive
Sex Chromosomes
23rd chromosome pair labelled XY
Men have XY
Y causes male characteristics
Women have XX
Lack of Y causes female characteristics
Genetic Disorders
Cystic Fibrosis
Symptoms
Thick sticky mucus in air passages
Breathing difficulty
Chest infections
Difficulty digesting food
Caused by recessive allele
Carried by 1 in 25 people
For a child to have CF, parents must be carriers or sufferers
1 in 4 chance if both parents are carriers
Huntington's
Symptoms
Tremors
Clumsiness
Memory Loss
Mood changes
Poor Concentration
Caused by a dominant allele
Late onset
50% chance of child inheriting if parent is a carrier
Genetic Testing
Embryos produced via IVF are tested using pre-implantation gnetic diagnosis. Only used if parent has history of genetic disorders.
Healthy embryos implanted
Faulty embryos discarded
Tests aren't 100% accurate
Misinterpreted
Contaminated
Not 100% safe. e.g. risk of miscarriage when testing fetuses
Insurance refused for wrong alleles
Clones
Clones are genetically identical organisms
Differences arise due to to environmental factors
Natural Clones
Asexual reproduction results in identical offspring to the parent and all siblings
Bacteria (dividing into two)
Some plants reproduce asexually also. Strawberry plants send out runners to plant new clones at their tips
Some animals reproduce asexually. Female greenfly don't need to mate, they can just lay eggs.
Identical twins are also clones
A single egg fertilised by sperm splits into two.
The two embryos are genetically identical, two genetically identical babies are born.
Scientific Clones
Nucleus of an egg is removed
Nucleus from a donor cell is removed (non -sex-cell)
Cell is stimulated so it starts dividing
Embryo produced is genetically identical to donor cell
Stem Cells
Can become other types of cell
Most normal cells are already specialised
Stem cells can specialise into other types of cells, depending on the instructions given
Embryonic Stem cells
Unspecialised cells found in early embryos
Removed, embryo is then destroyed
They can specialise into ANY type of cell
Adult Stem Cells
Unspecialised cells found in adult animals
Involved in maintaining and repairing old and damaged tissues
Safely removed e.g. from bone marrow - no embryos have to be destroyed
Can be used to replace blood cells to cure sickle cell anaemia
Embryonic stem cells could be used to replace faulty cells in sick people. e.g. new organs
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