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Reproduction - Coggle Diagram
Reproduction
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DNA and the Genome
Chromosomes are found in the nucleus of cells. They contain the molecule DNA, our DNA determines all of our inherited features.
- DNA consists of two strands, each strand is a polymer.
- Each strand is made by joining up lots of smaller molecules.
- In DNA, the two strands wrap up around eachother to form a double helix.
- A gene is a small section of DNA.
- Proteins are made by joining amino acids, each gene encodes for a specific sequence of amino acids to make a specific protein.
The Genome is the entire genetic material of an organism, the human genome is the entire genetic material that makes a human.
Its benefits are:
- Search for genes linked to a disease
- Help and treat inherited disorders
- Trace human migration patterns from the past
Mutations
The base sequence of a gene determines the amino acid sequence of a protein. Once a protein is formed, it will fold up into a unique shape, this unique shape will determine its function.
- A change to a base is called a mutation.
- Mutations are common and often still lead to the same protein being made.
- Chromosomes contain non-coding parts of DNA, these regions switch on/off.
- Mutations in these non-coding regions can affect how genes are switched on/off.
- A gene may be turned on when it should not be, this could lead to the cell producing a protein when it should not have at the time.
- This could have a significant impact on the cell, e.g. uncontrollable mitosis leading to cancer.
Alleles
Alleles are versions of a gene.
- The genotype tells us the alleles present
- The phenotype is the characteristics caused by a persons alleles.
- Homozygous- Two copies of the same allele.
- Heterozygous- Two different alleles
Alleles can be dominant or recessive, the dominant allele will always be expressed in the phenotype even if there is only one copy present, a recessive allele will only be expressed when two copies are present.
Inheritance of Sex
Humans contain 23 pairs of chromosomes in normal body cells. 22 of those chromosome pairs contain the genes which determine inherited characteristics ONLY.
- The 23rd pair are called the sex chromosomes, these determine the sex of an offspring.
- Males have the sex chromosome 'XY'
- Females have the sex chromosome 'XX'
By completing a Punnett square we can see that the probability of male and female offspring are both 50% or a 1:1 ratio. This is just a probability and in actual fact, all offspring of parents could be male or all could be female.
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