Topic 3: Genes and the Environment

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Phenotype
Characteristics of an organism e.g. size, shape, blood etc.
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Discontinuous variation
characteristics of a species that can only take one of a limited no. of types, eg. a person's blood type
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Continous Variation
characteristics of a species that can take any type in a range e.g. a person's height.
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Polygenic inheritance
characteristics that are controlled by the interaction of genes at many loci and the environment by indirectly or directly influencing the gene's expression.
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Multifactorial
several genetic factors and 1 or more environmental factors are involved.
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Monohybrid inheritance
each locus is responsible for a different heritable feature.
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How is eye colour an example of polygenic inheritance?
Alleles at several different loci control eye colour. Eye colour ranges from blue to brown depending on how much pigment is added. More pigment = darker brown, less pigment = lighter blue.
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Potential height Vs. Actual Height
Potential height is given by the person's genotype whereas their actual height is a result of their genotype plus the effects of their environment.
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Genes and the environment affecting height.
Person's heigh is determined by the interactions between their genes for height and their environmental influences. Person may've genes for being tall but can't reach full height potential due to malnutrition.
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Genes and the environment affecting melanin production.
Melanin is made in melanocyte cells, activated by MSH, and transported in melanosomes to collect around the nucleus, protecting the nucleus & therefore DNA from UV light. Increased UV light = increased amounts of MSH and MSH receptors = darker skin.
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How do Arctic foxes produce a white winter coat during the summer?
White coat grows under brown coat & revolved through moulting. In summer, reduced amount of MSH receptors so MSH has no effect= no melanin in hair follicles= white coat.
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How does mutation to the enzyme tyrosinase affect melanin production?
Tyrosinase catalyses 1st step in chemical pathway to change tyrosine-> melanin. Mutant alleles for the enzyme cause it to be unstable & inactive at normal body temp
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How can a human have dark leg hair but blonde hair under their arms?
They have a mutant allele causing heat sensitive tyrosinase. Hair under armpit is white due to increased heat inactivating the enzyme so no melanin production. Legs are a cooler environment allowing active enzyme to produce melanin= darker hairs.
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Give 3 causes of cancer.
Cell multiplication is faster than cell death causing a tutor. DNA is damaged through carcinogens. Mutation to DNA occurs during cell division.
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How is the cell cycle regulated?
Cells produce proteins that prevent progress from one stage to the next by inhibiting enzymes that initiate the reactions in the next stage of the cycle.
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Oncogenes
Code for proteins that stimulate transition from one stage of cell cycle to next. DNA mutations/epigenetic changes in these genes can lead to cell cycle being continually active = excessive cell division= tumour growth.
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Tumour suppressor genes
Produce suppressor proteins that stop the cycle. DNA mutations/epigenetic changes means there's no break in the cycle.
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What does the protein p53 do? How do mutations/epigenetic changes affect this gene?
Stops the cycle by inhibiting enzymes of G1/S transition, preventing cell from replicating DNA. In a cancer cell, lack of p53=means cell can't stop entry into s phase so the cell's lost control of the cell cycle.
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Why is cancer unlikely in any particular cell in regards to changes in the cell cycle?
Because the complexity of the network of signals and inhibitors controlling the cell cycle means damage needs to be done to more than 1 part of the cell control system for cancer to occur.
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How is inherited cancer formed?
When DNA is copied incorrectly in the formation of a gamete.
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How does having an allele with a mutation in gene BRCA1 not definitely mean cancer?
Because only 1 allele of the 2 inherited is mutated. It may cause cancer later on in life if the non-mutated allele in damaged in the breast tissue cells. Doesn't mean cancer but individuals are more susceptible to cancer through environmental change
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Give an example of chemical damage caused by the environment.
Chemical risk of smoking. Increases risk of cancer through actions of carcinogens in tar: tar lodges in the bronchi + causes damage to DNA in surrounding epithelial cells.
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Give an example of physical damage caused by the environment.
UV light physically damages DNA in skin cells. Sometimes a mole is affected by UV light & starts to grow bigger, developing into a tumour. If not removed, cancer cells can spread to rest of body carried in blood & lymphatic system.
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Why are root tips used to observe mitosis?
As this is the point of growth so cells will be rapidly be dividing.
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Why are the tips placed in a water bath with HCL?
The water bath and HCL help break down the links in the plant cell's cellulose walls allowing the cells to break apart for better viewing under the microscope.
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What is the stain used for this experiment called?
Aceto-Orcein
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Which parts of the cell takes up the stain?
The nucleus and its contents
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The chromosomes of the cell are not condensed, why?
Because the cell is in interphase so the chromosomes are visible as uncondensed, loosely distributed chromatin.
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Why is a napkin or filter paper placed over the coverslip when using the mounted needles?
To ensure the coverslip doesn't get dirty or damaged.
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Card 2

Front

Discontinuous variation

Back

characteristics of a species that can only take one of a limited no. of types, eg. a person's blood type

Card 3

Front

Continous Variation

Back

Preview of the front of card 3

Card 4

Front

Polygenic inheritance

Back

Preview of the front of card 4

Card 5

Front

Multifactorial

Back

Preview of the front of card 5
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