Genes and the environment

Question 1

What does phenotype refer to?

Answer 1

• the observable characteristics of an organism are its phenotype

Question 2

what is phenotypic variation?

Answer 2

• phenotypic variation is the difference in phenotypes between organisms of the same species

Question 3

What are some factors that can explain phenotypic variation?

Answer 3

• genetic factors
• environmental factors
• combination of genetic and environmental factors

Question 4

Give an example on how a combination on both environmental and genetic factors can affect phenotypes

Answer 4

• 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

Question 5

What is the equation that links environment, phenotype and genotype?

Answer 5

phenotype = genotype + environment

Question 6

What does genetic variation refer to?

Answer 6

• genetic variation refers to the small differences in DNA base sequences between individual organisms within a species population

Question 7

What does monogenic mean? What type of data does this show?

Answer 7

• 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)

Question 8

What does polygenic mean? What type of data does this show?

Answer 8

• characteristics (i.e. phenotype) that are controlled by several genes
• these characteristics tend to show continuous data (e.g. height, mass, skin colour)

Question 9

What determines the phenotype of an organism? What do diploid organisms inherit?

Answer 9

• the different alleles an organism has at a single gene locus cant determine the phenotype
• diploid organisms will inherit two alleles of each gene

Question 10

What type of variation occurs when there are quantitative differences? What type of variation occurs when there are qualitative differences?

Answer 10

• continuous variation occurs when there are quantitative differences
• discontinuous variation occurs when there are qualitative differences

Question 11

What does qualitative differences in the phenotypes of individuals give rise to?

Answer 11

• 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)

Question 12

What are the features of discontinuous variation?

Answer 12

• 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

Question 13

What variation occurs when there are quantitative differences? What do quantitative differences fall in to?

Answer 13

• 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

Question 14

What are some features of continuous variation?

Answer 14

• no distinct classes or categories exist
• characteristics can be measured and fall within a range between two extremes

Question 15

What are polygenes?

Answer 15

• polygenes are when a large number of genes have a combined effect on the phenotype

Question 16

What is polygenic inheritance?

Answer 16

• 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

Question 17

What is an oncogene?

Answer 17

• an oncogene is a mutated gene that has the potential to cause cancer

Question 18

What is a proto-oncogene? What happens if it has a mutation?

Answer 18

• 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

Question 19

What does metastasis refer to?

Answer 19

• the spreading of cancers where malignant tumour cells can break off the tumour and travel through the blood to form secondary growths

Question 20

What are tumour suppressor genes?

Answer 20

• tumour suppressor genes are normal genes that code for proteins that regulate the cell cycle

Question 21

What do DNA repair protein genes do?

Answer 21

• DNA repair genes code for proteins whose normal function is to correct errors that arise when cells duplicate their DNA prior to cell division

Question 22

What are primary tumours

Answer 22

• primary tumours are tumours that grow where the tumour progression began

Question 23

What are secondary tumours?

Answer 23

• secondary tumours are when cells reach another part of the body, grow and form another tumour

Question 24

What are the 3 key genes that control cancer? What happens if all three have mutations?

Answer 24

• 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

Question 25

How many times do cells typically divide? What about cancerous cells?

Answer 25

• cells typically divide 50 times then die, cancerous cells keep dividing