Genetics, Evolution & Ecology P2 Flashcards Preview

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Flashcards in Genetics, Evolution & Ecology P2 Deck (26):

State two differences between structure of DNA and RNA

Deoxyribose vs. ribose; thymine vs. uracil; 2 strands vs. 1 strand;


State the names of the structures above.

State the name of a structure on the diagram that has an anticodon.

I: Small sub-unit of ribosome;
II: Large subunit of ribosome;



Explain why the process used during protein synthesis is called translation.

Each codon in an mRNA molecule (nucleic acid) codes for one amino acid (protein structural unit); hence, genetic code has to be translated;


Explain briefly how termination of translation occurs.

Stop codon reached; polypeptide released; mRNA detaches from ribosome; ribosome subunit separates;


A gene in humans called APC is located on chromosome 5. This gene controls cell division and is known as a tumour suppressor gene. Mutations of APC cause a genetic disease called FAP (Familial Adenomatous Polyposis).

State, with a reason, whether FAP is a sex-linked genetic disease or not.

50% of the gametes produced by a person with FAP have an APC gene with the mutation. Identify, with a reason, whether FAP follows a dominant or recessive pattern of inheritance.

In a person with FAP, each cell contains a copy of the APC gene with the mutation. If a mutation occurs on the cell’s other copy of the APC gene, the cell becomes a tumour cell. Almost everyone with FAP develops cancer before the age of 50. Explain why almost everyone with FAP eventually develops cancer.

Not sex-linked because gene is on an autosome.

Dominant; because person with FAP is heterozygous;

Mutation only has to occur once; tumour develops from one cell; all cells in body could become tumour cells; tumour formation not suppressed if both copies of APC gene in cell are mutant.


In 2004, doctors in Britain were given permission to test embryos to see whether an APC gene with the mutation is present. This test can be used where one of the parents is known to have FAP. The procedure involves the parents using in-vitro fertilisation (IVF) to produce embryos, testing the embryos for the gene and implanting only embryos that do not have the mutation.

State the name of this test.

State one advantage and one disadvantage of testing embryos in this way.

Genetic Screening

Advantage: Prevent birth of children with FAP / Eliminate mutation from population / Reduce stress for parents

Disadvantage: Allows selection of embryos for implantation (unethical) / leads to euthanising of embryos with mutation (unethical) / expensive procedure.


Outline the role of variation in evolution.

Members of population show variation;
Variation occurs as a result of meiosis or mutation; Some variations allow an individual to be better adapted; and survive to reproductive age; which leads to evolution, the cumulative increase in frequency of advantageous alleles over time;


Explain how polygenic inheritance leads to continuous variation.

Polygenic inheritance is when a characteristic/ phenotype is determined by >1 gene;
As the number of genes involved increases, the number of intermediate phenotypes increases;
causing phenotypes to become continuous;


Define the term community as it relates to ecosystems.

Community: Group of populations living (and interacting with each other) in an area.


Define allele.

Alternative forms of a gene on the same locus.


Outline the consequences of a base substitution mutation.

Base substitution mutations change codon; and thus may cause coding for different amino acid; and therefore a different primary structure, which may cause sequence to code for a different protein;

An example of this is sickle cell anaemia, which causes faulty red blood cells to be produced;


Mendel crossed tall, round-seeded plants with short, wrinkled-seeded plants. All F1 produced were tall, round-seeded plants. When F1 plants were crossed with other F1 plants, the F2 generation produced many more than 1/16 short, wrinkled-seeded plants.

Deduce, with reasons, the inheritance of these genes.

The same cross was later repeated but gave fewer F2 short, wrinkled-seeded plants although still more than 1/16. Outline a named statistical test that could indicate if your deduction about the inheritance of these two genes is likely to be correct.

Dihybrid cross would give 9:3:3:1 ratio in this F2 if genes not linked; therefore the genes are linked; more homozygous recessive offspring / 3:1 ratio expected if linked; (only 2 marks)

chi-squared (test); compares observed and expected values/results; producing a (chi-squared) value; a statistical table is used to determine probability of genes being linked or not;


Suggest one role of bacteria in a soil ecosystem.

Decomposers / recycle nutrients / cause decay / nitrification / nitrogen fixation / denitrification.


List two examples of how human life depends on mitosis.

Growth and production of body cells rely on mitosis;
1st stage of gametogenesis requires oogonia/ spermatogonia to undergo mitosis;
Embryo development; 
Wound Healing/Tissue repair;

Clonal selection;


Outline the bonding between DNA nucleotides.

H-bonds between complementary bases; covalent/phosphodiester bonds between deoxyribose and phosphate of neighbouring nucleotides;


Explain why carriers of sex-linked (X-linked) genes must be heterozygous.

Carrier has 1 copy of recessive allele; so they must have dominant allele to not have condition;


Label the diagram below which shows a basic gene transfer.

I. bacterium;

II. plasmid;

III. desired DNA;

IV. genetically modified cell


State two general types of enzymes used in gene transfer.

Restriction endonucleases; ligases;
reverse transcriptase;


Outline the method that can be used to amplify small quantities of DNA to obtain
large enough quantities for DNA profiling.

PCR; DNA obtained from blood/semen/hairs; combined with Taq polymerase and high temps; in thermal cycler; and DNA replicated many times;


Outline the evidence for evolution provided by fossils.

Fossils show changes over time in organisms; as fossilised organisms are different from existing ones;
 yet share homologous structures features with existing organisms; which suggest common ancestry;
they also show intermediate stages in evolution of groups;


Suggest how species with large eyes could evolve from species with smaller eyes.

Natural selection; over time; could cause evolution of tribolites. 
Variation in trilobite eye sizes within population already existed; but individuals with larger eyes were more likely to survive; as they could more easily find food/see predators; hence the environment selects for this trait (having large eyes).
This meant that surviving individuals reproduced & passed on their genes to offspring; so that they too have large eyes.
This process leads to evolution of species.


Explain how the flow of energy in a food web differs from the movement of nutrients.

Nutrients are recycled in food web, whilst energy enters & leaves (isn’t recycled);

Nutrients are recycled by saprotrophs and reused; whereas energy is dispersed as heat;


Discuss reasons why the levels of a pyramid of energy differ in size.

The shape of the pyramid shows that energy is lost from base to top of pyramid (only 10% passed on to successive trophic levels; This is because lots of energy is released through cell respiration as heat at each trophic level; Additionally not all tissues are eaten i.e. bone/ cellulose & some organisms die before eating;


Label the sense and antisense strands.

Draw an arrow on diagram to show where the next nucleotide will be added to the growing mRNA strand.



State an external feature that is different in Cnidaria and Mollusca

State an external feature that is different in Mollusca and Annelida

Cnidaria have radial symmetry while Mollusca have bilateral symmetry; 
Cnidaria have tentacles while Mollusca do not; 
Mollusca (may) have a (hard) shell while Cnidaria do not;

Mollusca have mouth and anus while Cnidaria have only one opening; 
Mollusca have a muscular/large foot while Cnidaria do not;

Annelida are segmented while Mollusca aren't (visibly segmented); 
Annelida may have bristles while Mollusca do not; 
Mollusca (may) have a (hard) shell while Annelida don't;

Mollusca have a muscular/ large foot while Annelida don't;


Explain how meiosis promotes variation.

In prophase I, crossing over between non-sister chromatids occurs;

In metaphase I, bivalents are randomly aligned;

In metaphase II, sister chromatids are also randomly aligned;

--> combinations of alleles in gametes is essentially unlimited;