Genes and the environment Flashcards
What does phenotype refer to?
- the observable characteristics of an organism are its phenotype
what is phenotypic variation?
- phenotypic variation is the difference in phenotypes between organisms of the same species
What are some factors that can explain phenotypic variation?
- genetic factors
- environmental factors
- combination of genetic and environmental factors
Give an example on how a combination on both environmental and genetic factors can affect phenotypes
- the recessive allele that causes sickle cell anaemia has a high frequency in populations where malaria is prevalent due to heterozygous individuals being resistant to malaria
What is the equation that links environment, phenotype and genotype?
phenotype = genotype + environment
What does genetic variation refer to?
- genetic variation refers to the small differences in DNA base sequences between individual organisms within a species population
What does monogenic mean? What type of data does this show?
- characteristics (i.e. phenotype) that are controlled by a single gene are known as monogenic
- these characteristics usually show discontinuous data (e.g. blood group)
What does polygenic mean? What type of data does this show?
- characteristics (i.e. phenotype) that are controlled by several genes
- these characteristics tend to show continuous data (e.g. height, mass, skin colour)
What determines the phenotype of an organism? What do diploid organisms inherit?
- the different alleles an organism has at a single gene locus cant determine the phenotype
- diploid organisms will inherit two alleles of each gene
What type of variation occurs when there are quantitative differences? What type of variation occurs when there are qualitative differences?
- continuous variation occurs when there are quantitative differences
- discontinuous variation occurs when there are qualitative differences
What does qualitative differences in the phenotypes of individuals give rise to?
- qualitative difference in the phenotypes of individuals within a population give rise to discontinuous variation
- qualitative differences fall into discrete and distinguishable categories, unusually with no intermediates (features cant fall in between categories)
What are the features of discontinuous variation?
- distinct classes or categories exist (can be easily shown and identified on a table or graph)
- these characteristics cannot be measured over a range
- individuals cannot have features that fall between categories
What variation occurs when there are quantitative differences? What do quantitative differences fall in to?
- continuous variation occurs when there are quantitative differences in the phenotypes of individuals within a population for particular characteristics
- quantitative variation falls in to a range of values that exist between two extremes within which the phenotype will fall
What are some features of continuous variation?
- no distinct classes or categories exist
- characteristics can be measured and fall within a range between two extremes
What are polygenes?
- polygenes are when a large number of genes have a combined effect on the phenotype
What is polygenic inheritance?
- polygenic inheritance is when phenotypes are affected by multiple different genes or by multiple alleles for the same gene at many different loci as well as the environment
What is an oncogene?
- an oncogene is a mutated gene that has the potential to cause cancer
What is a proto-oncogene? What happens if it has a mutation?
- proto-oncogene are the genes that code for the positive cell cycle regulators
- if the proto-oncogene has a mutation and becomes an oncogene, it will divide (very) fast
What does metastasis refer to?
- the spreading of cancers where malignant tumour cells can break off the tumour and travel through the blood to form secondary growths
What are tumour suppressor genes?
- tumour suppressor genes are normal genes that code for proteins that regulate the cell cycle
What do DNA repair protein genes do?
- DNA repair genes code for proteins whose normal function is to correct errors that arise when cells duplicate their DNA prior to cell division
What are primary tumours
- primary tumours are tumours that grow where the tumour progression began
What are secondary tumours?
- secondary tumours are when cells reach another part of the body, grow and form another tumour
What are the 3 key genes that control cancer? What happens if all three have mutations?
- the three key genes are:
1. proto-oncogene = accelerator
2. tumour suppressor genes = brake
3. DNA repair genes = check checkpoints G1 & G2 - if a mutation occurs in all three of these genes cancer can occur
How many times do cells typically divide? What about cancerous cells?
- cells typically divide 50 times then die, cancerous cells keep dividing
