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Flashcards in Genetics Deck (90)
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1

DNA

- Deoxyribose nucleic acid - Found in the nucleus - All DNA has a similar structure

2

Major components of DNA

- Sugars - Phosphates - Bases - These make up the ‘back bone’ of the DNA structure

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4 types of bases (an their pairs)

- Adenine always pairs with thymine - Guanine always pairs with cytosine

4

What is a nucleotide?

- Sub-unit of the DNA molecule - Consists of one sugar, one phosphate and one base molecule

5

What is a chromosome?

DNA wrapped into a double helix structure around proteins called histones

6

What is a gene?

- Each section of DNA that controls a trait - Humans have around 25,000 genes in their chromosomes - Genes for a particular trait are controlled at a particular point in the chromosome

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Somatic cells

46 chromosomes (23 pairs)

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Gametes

23 single chromosomes

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Homologous pair

a pair of chromosomes containing the pair of genes for a particular trait

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What are alleles?

- The alternative forms of a gene that are available - The pairs of alleles that each person inherits from their parents control and determine the characteristics of the individual - Many genes have two alleles (dominant and recessive)

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What is a genotype?

- The genetic makeup of an individual - It is inherited - E.g. BB/bb/Bb

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What is a phenotype

- The observed expression of the alleles for the characteristics - Determined by the genotype and the environment

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What is monogenic inheritance?

- Exists when an individual receives just one pair of alleles for a trait - E.g. blood groupings - The traits are discrete (either there or not there) - Only two alleles for the trait - Only two phenotype

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What is polygenic inheritance

- Many pairs of genes control the trait - Continuous variation of the trait - Alleles will have an additive effect - E.g. skin colour height and weight - Continuous traits = many phenotypes

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Skin colour

- Is a polygenic trait - Many genes contribute - Continuous variation - Depends on the amount of melanin in the skin

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What do melanocytes produce?

Melanocytes produce structures called melanosomes that contain melanin and are found in the bottom of the epidermis of the skin

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How is melanin produced?

It is made from an amino acid called tyrosine

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Amounts of melanocytes and melanosomes in different people

Most people have similar amounts of melanocytes and varying amounts of melanosomes

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Darker skinned people

- Can convert more tyrosine into melanin because they have more tyrosinase - More melanosomes containing more melanin - There are also more evenly distributed throughout the skin - This prevents burning

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Pale skin

- Less tyrosinase and therefore can’t convert as much tyrosine into melanin - Melanin is not evenly distributed and form clumps - Burns when exposed to UV light

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Tyrosinase (enzyme)

- Brings about the production of melanin - Stimulated by UV rays - People with the enzyme will become darker skinned in the sun - Those with less tyrosinase will tan less well - Therefore, the environment affects the phenotype - Darker skin will prevent sun burn

22

What is a mutation?

- A permanent change to a gene or chromosome leading to a new characteristic in an organism - Due to changes in the base sequences in a section of DNA which alters the types of proteins that will be synthesised by the body - Can be advantageous or disadvantageous

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What is a mutant?

An organism with a characteristic resulting from a mutation

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What are mutagens?

- Agents that are known to increase the rate at which mutations occur - E.g. UV light, X-rays, radiation, chemicals such as sulphur dioxide or antibiotics

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Somatic mutations

- Occur in a body cell - The reproductive cells are not affected and once the organism dies, the mutation will be lost

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Germ-line mutations

- Mutation occurring in the gametes - The individual is not usually affected - The individual will produce gametes with changed DNA

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Main types of mutations

- Gene mutations - Chromosomal mutations

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Gene mutations

- Change in a single gene - They occur during the replication of the DNA molecule before cell division - If the DNA copies incorrectly, the changed DNA will continue to be copied in all future divisions - May code for a new amino acid and a completely different protein

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What is a point mutation?

a change in one base

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Albinism

- The result of a missing protein - The protein responsible for the pigment (melanin) of hair, skin and eyes is missing - Patients have whitish blond hair, extremely pale skin and pinkish eyes