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11T1,2&3 - Inheritance - Coggle Diagram
11T1,2&3 - Inheritance
Key definitions
Gene
Some characteristics are controlled by a single gene, such as fur colour in mice and red-green colour blindness in humans However, most characteristics are the result of many different genes interacting
A short section of DNA that codes for a specific protein and therefore contributes to its characteristics
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Allele
The different forms of the gene - humans have 2 alleles for each gene as they inherit one from each parent
Dominant allele - only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be expressed
Recessive allele - two copies are needed for it to be expressed and for the corresponding phenotype to be observed
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Homozygous - when both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles)
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Phenotype - The physical characteristics that are observes in the individual. Phenotypic features are the result of polygenic inheritance rather then single genes
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Sex determination
The human body has 23 pairs of chromosomes- 22 control characteristics and the chromosomes in each pair look very similar - the 23rd pair carries sex determining genes and the two chromosomes can look different to each other (Y chromosomes are smaller than X chromosomes)
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Males have one X chromosome and one Y chromosome so therefore can pass on X of Y chromosomes in their sperm
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Mitosis
Stage 1 (interphase) - The cell grows as organelles grow and increase in number, protein syntheses occurs where all 46 chromosomes are replicated and energy stores are increased
Stage 2 - The chromosomes line up at the equator of the cell and spindle fibres pull each chromosome of the 'X' to either side of the cell
Stage 3 - two identical daughter calls form when the cytoplasm and the cell membranes divide, each containing the same 46 chromosomes as the original cell
Occurs during growth and development, replacing damaged cells and cloning - vital part of asexual reproduction
Meiosis
1) The cell makes copies of its chromosomes, so it has double the amount of genetic information
2) The cell divides into two cells, each with half the amount of chromosomes , giving the normal amount of 46 chromosomes (diploid)
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Variation
Random fertilisation increases genetic variation between offspring as each gametes has variation due to meiosis and the fusing egg and sperm is random
Genetic variation - eye colour, blood type etc as these phenotypes are dependent on inheriting alleles from each parent
Environmental variation - caused by differences in lifestyle, diet, climate etc which could lead to organisms to adapt.
Both - e.g. height. A child might have the potential to grow tall due to their genetics but if they are malnourishes and do not eat well or enough then they will not grow as much and this is due too their environment
Mutations are rare, random change in genetic material that can be inherited
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