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Genes Inheritance

Revision for the Second Year 8 Test

What are alleles? These are different versions of the same gene. For example there are different alleles for eye colour.
What is a chromosome? This is a thread like structure containing highly coiled DNA.
What does DNA stand for? Deoxyribonucleic acid.
What is a dominant allele? The strongest allele in a pair.
What is the function of DNA? It contains the code that determines all the inherited characteristics of a living organism.
What are gametes? In humans, these are eggs and sperm, They each contain half the number of chromosomes of each parent and combine during fertilisation.
What is genetic modification? This is manipulating an organism's DNA in a laboratory.
What does 'genotype' mean? This describes the pair of alleles that an organism has for a certain characteristic.
What is the meaning of 'heterozygous'? An organism that has two different alleles for the same characteristic.
What does 'homozygous' mean? This is an organism that has two identical alleles for the same characteristic.
What is the human genome? The complete sequence of human genes.
What are inherited characteristics? Features that are passed from parents to offspring.
What is mutation? A change in DNA.
What is the function of a nucleus? This controls the cell's activities, growth and reproduction.
What is a person's phenotype? This is their outward appearance.
What does 'recessive' mean? This is the weaker allele of a pair. An organism needs to have two of these for a characteristic to show e.g. blue eyes.
What shape is DNA? A double helix.
Which bases pair up? A pairs with T, C pairs with G. (Apples grow on trees, cars go in a garage).
Can you remember what ATCG stand for? Adenosine, Thymine, Cytosine, Guanine
What do the blocks of three bases code for? Amino acids
What do amino acids join to form? Protein molecules.
If you stretched out all the DNA in your body how far would it go? 9 million kilometres.
How long is the DNA in one human cell nucleus? 2 metres
How many chromosomes do humans have? 46 chromosomes (23 pairs)
What is a gene? This is a section of DNA that contains the instructions for an inherited characteristic. E.G. eye colour.
Where did each pair of your chromosomes come from? One of the pair came from your father and the other one came from your mother.
How many chromosomes do human eggs and sperm have? 23
How many genes does the human genome contain? 24,000
If a person has brown eyes and are heterozygous for eye colour, what would their genotype be? Bb
What is the genotype of someone with blue eyes? bb
What is the genotype for someone who is homozygous for brown eyes? BB
If a brown eyed person (BB) and a blue eyed person (bb) have children, what colour eyes could the children have? Brown eyes. Bb
If a brown eyed person (Bb) and a blue eyed person (bb) have children, what colour eyes could the children have? They could have brown eyes (Bb) or blue eyes (bb).
If two heterozygous brown eyed parents (Bb) have children. What could the children's genotypes be? BB, Bb or bb.
What is special about identical twins? They have identical DNA.
What are some symptoms of Cystic Fibrosis? Problems with the lungs due to excessive mucous. Problems in the digestive system for the same reason.
Cystic Fibrosis is caused by a recessive allele (f). What genotype does a person have to have in order to have the disease? ff
What do we call a person who has the recessive allele for Cystic Fibrosis plus the dominant normal allele Ff? A carrier - because they don't actually have the disease but they carry the allele for it.
What does 'polydactyly' mean? Many digits.
Polydactyly is a dominant allele. Why would it be impossible for someone with polydactyly to have two normal parents.
Why aren't all twins identical? Identical twins came from one egg and have identical DNA. Fraternal twins came from two eggs (one egg each) and are no more similar than brothers and sisters.
Why can't you tell whether twins are identical or fraternal from their weight (mass)? Weight is not controlled by genes. It is an environmental factor. Weight is determined by how much you eat, what you eat and how much you exercise.
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