2.1 The diagram below represents a portion of a DNA molecule - NSC Life Sciences - Question 2 - 2019 - Paper 2
Question 2
2.1 The diagram below represents a portion of a DNA molecule.
2.1.1 Identify B and C.
2.1.2 Name:
(a) Monomer A
(b) TWO scientists who received a Nobel prize for ... show full transcript
Worked Solution & Example Answer:2.1 The diagram below represents a portion of a DNA molecule - NSC Life Sciences - Question 2 - 2019 - Paper 2
Step 1
Identify B and C.
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Answer
B is identified as a nitrogen base, while C is identified as a phosphate.
Step 2
Name:
(a) Monomer A
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Monomer A is a nucleotide.
Step 3
(b) TWO scientists who received a Nobel prize for discovering the DNA molecule
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The two scientists are James Watson and Francis Crick.
Step 4
(c) ONE organelle in a cell where DNA is located
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One organelle where DNA is located is the nucleus.
Step 5
Describe how a mutation on DNA may change the structure of a protein.
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A mutation in DNA can alter the sequence of nucleotides, which may lead to changes in mRNA during transcription. This, in turn, can affect the sequence of amino acids in a protein during translation, resulting in a protein that has a different structure and possibly different function.
Step 6
Tabulate TWO structural differences between a monomer of RNA and a monomer of DNA.
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Answer
Characteristic
RNA Monomer
DNA Monomer
Sugar
Contains ribose
Contains deoxyribose
Nitrogenous Base
Contains uracil instead of thymine
Contains thymine
Step 7
How many offspring are affected by PKD?
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In a scenario where both parents are heterozygous for PKD, 25% of the offspring would be expected to be affected by Polycystic Kidney Disease (PKD).
Step 8
Explain how the genotype of offspring A shows that both parents are heterozygous.
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For offspring A to exhibit a phenotype without PKD, it must inherit one dominant allele from each parent (H). If both parents had PKD, they each must contribute a recessive allele to give offspring A a genotype of Hh. This indicates that both parents carry one dominant allele (H) and one recessive allele (h), demonstrating heterozygosity.
Step 9
Define a species.
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A species is defined as a group of organisms that can interbreed and produce fertile offspring.
Step 10
Name TWO structures in a flower where meiosis takes place.
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Meiosis occurs in the anthers and ovules of a flower.
Step 11
How many of each of the following structures is present in each cell of Brassica oleracea in the process of meiosis:
(a) Chromosomes at the end of telophase II
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(a) There are 9 chromosomes present at the end of telophase II.
Step 12
(b) Chromatids during metaphase I
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(b) There are 36 chromatids present during metaphase I.
Step 13
Describe the events of anaphase II.
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During anaphase II, the spindle fibers contract, pulling the sister chromatids apart towards opposite poles of the cell, ensuring that each new cell will have an equal number of chromosomes.
Step 14
Explain why the focus is now on increasing resistance to insects and diseases.
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The focus on increasing resistance to insects and diseases is essential because it helps improve crop yield, food security, and reduces the dependency on chemical pesticides, which can have harmful environmental effects.
Step 15
Name and describe the type of dominance shown here.
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The type of dominance shown is incomplete dominance, where heterozygous individuals (with one allele for elongated fins and one for short fins) exhibit a phenotype that is intermediate, resulting in medium fins.
Step 16
Use a genetic cross to show the phenotypes of two fish with medium fins having offspring with short fins.
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Answer
In a genetic cross between two medium fin fishes (ES x ES):
Possible gametes: E, S from each parent.
Offspring genotypes:
EE (elongated fins)
ES (medium fins)
ES (medium fins)
SS (short fins)
This results in a phenotypic ratio of 25% elongated, 50% medium, and 25% short fins.
