CIE iGCSE Co-Ordinated Science B16.1 Chromosomes and genes Exam Style Questions Paper 3
Question
(a) Scientists record the mass of each baby at birth in one country.
The results are shown in Fig. 10.1
(i) Complete the sentences about the mass of babies at birth as shown in Fig. 10.1.
The lowest mass at birth was ……………………………………….. g.
The most frequent mass at birth was ……………………………………….. g.
Fig. 10.1 shows that mass of babies at birth is an example of continuous variation.
This is because there is a ……………………………………….. of phenotypes between two extremes.
A phenotype is defined as the ……………………………………….. features of an organism.
(ii) State one other example of continuous variation in humans.
(b) The statements A–E describe stages of natural selection.
They are not in the correct order.
A There is competition for resources.
B Those with adaptations best suited to their environment survive and reproduce.
C This process is repeated over several generations.
D There is variation in a population.
E Alleles are passed on to the next generation.
Complete the answer spaces to show the correct order.
One has been done for you.
(c) Alleles are made of DNA.
(i) Define the term allele.
(ii) State where alleles are found in a cell.
▶️Answer/Explanation
Ans : 10(a)(i) 800 (g) ;
2400 (g) ;
range / AW ;
observable / AW ;
10(a)(ii) height / AVP ;
10(b) D in first box ;
B, E, C ;
10(c)(i) a version of a gene ;
10(c)(ii) nucleus ;
Question
(a) Tick (√) the correct definition of inheritance.
Inheritance is the transmission of genetic information from the environment. 
Inheritance is the transmission of physical information from the nervous system.
Inheritance is the transmission of genetic information from generation to generation.
Inheritance is the transmission of verbal information from the environment.
(b) The shape of peas is an inherited characteristic controlled by a single gene.
The allele for smooth peas is dominant R.
The allele for wrinkled peas is recessive r.
Fig. 7.1 is a photograph of two peas with different shapes.
(i) The boxes on the left show some examples used to show inheritance of shape in peas.
The boxes on the right show descriptive terms.
Draw lines to link each box on the left to its descriptive term on the right.
One has been done for you.
ii) Complete the genetic diagram in Fig. 7.2 to calculate the likelihood of the offspring having a wrinkled shape
percentage likelihood of offspring
having a wrinkled shape = ………………………………………………….. %
(c) The list shows some structures involved in inheritance.
cell chromosome gene nucleus
Put these in order from smallest to largest.
One has been done for you.
▶️Answer/Explanation
Ans : 7(a) inheritance is the transmission of genetic information from generation to generation ✓ ;
7(b)(i)
;;;
7(b)(ii)
;
(percentage likelihood of offspring having a wrinkled shape =) 25 (%) ;
7(c) (gene), chromosome, nucleus, cell ;
1 mark for any one in the correct order
2 marks for the rest in the correct order
Question
Pea colour and shape are inherited characteristics that are controlled by a single gene.
(a) Define the term gene.
(b) A farmer recorded the colour and shape of a sample of 14 peas.
Fig. 7.1 shows a graph of the results.
(i) Identify the most frequent pea colour and shape in Fig. 7.1.
(ii) State the frequency of wrinkled green peas in Fig. 7.1.
(iii) Describe evidence from Fig. 7.1 that shows that pea colour and shape are examples of
discontinuous variation.
(iv) State one example of continuous variation in humans.
(c) The farmer found that smooth green peas were the most popular with food buyers.
Describe how the farmer uses selective breeding to increase the number of smooth green
peas.
(d) Name the type of selection that results in species being adapted to the environment they live
in.
▶Answer/Explanation
Ans:
7(a) length of DNA ;
that codes for a protein ;
7(b)(i) wrinkled yellow ;
7(b)(ii) 3 ;
7(b)(iii) there are, a limited number of phenotypes / no intermediates / AW ;
7(b)(iv) height / AVP ;
7(c) any two from:
farmer selects smooth green peas plants ;
uses these plants to breed ;
observes / selects, offspring (for smooth green peas) ;
repeats the process (for many generations) ;
7(d) natural (selection) ;
Question
(a) Polydactyly is a condition that results in the growth of extra fingers or toes.
The allele for polydactyly is dominant D.
The allele for no polydactyly is recessive d.
Table 4.1 shows the genotypes of one family.
State the number of people in Table 4.1:
with polydactyly ……………………………………………………….
with a heterozygous genotype ……………………………………………………….
(b) The parents in Table 4.1 have another child.
Complete the genetic diagram in Fig. 4.1 to show the percentage likelihood of the offspring not having polydactyly.
percentage likelihood of the offspring not having polydactyly ……………………………………………………%
Fig. 4.1
(c) Genes and chromosomes are involved in inheritance.
(i) Define the term gene.
……………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………….
(ii) State the sex chromosomes present in the body cells of human males.
…………………………………………………………………………………………………………………….
(iii) State the name of the structure in cells that contains the genetic material.
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 4(a) 5 ;
4 ;
4(b)
;
25 (%) ;
4(c)(i) length / AW, of DNA ;
that codes for a protein ;
4(c)(ii) XY ;
4(c)(iii) nucleus ;
Question
(a) Albinism is a condition in humans where no pigment is made by the skin.
The allele for no albinism is dominant and represented by the letter A.
The allele for albinism is recessive and represented by the letter a.
(i) Table 4.1 shows some genotypes, phenotypes and descriptions of the genotypes for three people.
Complete Table 4.1.
(ii) Person 2 and person 3 have a child together.
Complete the Punnett square diagram in Fig. 4.1 to show the possible genotypes of the offspring.
(b) Chromosomes carry genetic information.
(i) Complete the definition of the term chromosome.
A chromosome is a thread-like structure of …………………………… ,
carrying genetic information in the form of …………………………… .
(ii) State where chromosomes are found in human cells.
(iii) State the sex chromosomes found in male gametes in humans.
……………………………… or ………………………………
(c) State the name of the male gametes in humans.
(d) State the name of the organ where male gametes are produced in humans.
▶️Answer/Explanation
Ans : 4(a)(i) 
4(a)(ii) 
4(b)(i) DNA ;
genes ;
4(b)(ii) nucleus ;
4(b)(iii) X and Y ;
4(c) sperm ;
4(d) testes ;
Question
4(a) The inheritance of smooth or wrinkled skin in pea plants is controlled by a single gene.
- The allele for smooth skin is R.
- The allele for wrinkled skin is r.
Fig. 4.1 is a photograph of two peas:
- Pea A has wrinkled skin.
- Pea B has smooth skin.
4(a)(i) Table 4.1 shows the genotypes and genotype descriptions of the peas shown in Fig. 4.1.
Complete Table 4.1.
| pea | genotype | description of genotype |
|---|---|---|
| A | homozygous recessive | |
| B | Rr |
▶️Answer/Explanation
Answer:
Pea A: genotype = rr, description = homozygous recessive
Pea B: genotype = Rr, description = heterozygous
4(a)(ii) A scientist crossed two pea plants and observed the results. Complete the genetic diagram in Fig. 4.2 to identify the parental gametes.
▶️Answer/Explanation
Answer:
Parental gametes: R and r
4(a)(iii) State the ratio of smooth peas to wrinkled peas from Fig. 4.2.
smooth …… : wrinkled ……
▶️Answer/Explanation
Answer:
smooth 3 : wrinkled 1
4(b) Fertilisation in plants occurs when the nuclei of the male and female gametes fuse. Name these two gametes.
▶️Answer/Explanation
Answer:
1. pollen
2. ovule
4(c) State the name of the female gamete in humans.
▶️Answer/Explanation
Answer:
egg / ovum
4(d) Table 4.2 contains one term and two definitions linked to inheritance. Complete Table 4.2.
| term | definition |
|---|---|
| A thread-like structure of DNA, carrying genetic information in the form of genes. | |
| gene | |
| A version of a gene. |
▶️Answer/Explanation
Answer:
term: chromosome, gene, allele
definition: A thread-like structure of DNA, carrying genetic information in the form of genes; A length of DNA that codes for a protein; A version of a gene.
Question
(a) A farmer keeps ponies. The ponies show variation in height. The farmer sells the smaller ponies for more money than the larger ponies.
(i) Name the type of variation shown by differences in height of the ponies.
▶️Answer/Explanation
Answer: Continuous variation.
Explanation: Continuous variation refers to differences in characteristics that can take any value within a range, such as height, weight, or skin color. In this case, the height of the ponies can vary across a spectrum, making it an example of continuous variation.
(ii) Complete the sentences to describe the method the farmer uses to increase the number of smaller ponies on the farm.
The farmer selects the ponies with the desirable feature.
These ponies are then ………….. .
The ………….. offspring are then selected and used for ………….. .
This process is then ………….. over many generations.
▶️Answer/Explanation
Answer:
These ponies are then bred.
The smallest offspring are then selected and used for breeding.
This process is then repeated over many generations.
Explanation: The farmer is using selective breeding to increase the number of smaller ponies. By selecting the smallest ponies and breeding them, the farmer ensures that the desirable trait (smaller size) is passed on to future generations. This process is repeated over many generations to achieve the desired outcome.
(iii) State the name of the process the farmer uses.
▶️Answer/Explanation
Answer: Selective breeding.
Explanation: Selective breeding is the process of choosing specific animals or plants with desirable traits to breed together, with the aim of producing offspring with those traits. In this case, the farmer is selectively breeding ponies to produce smaller offspring.
(b) The inheritance of sex in ponies is the same as in humans.
(i) Complete Table 10.1 to show the inheritance of sex.
▶️Answer/Explanation
Answer:
Explanation: In most mammals, including ponies and humans, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). This determines the sex of the offspring.
(ii) State the ratio of male to female offspring shown in Table 10.1.
▶️Answer/Explanation
Answer: 1:1
Explanation: The ratio of male to female offspring is 1:1 because there is an equal chance of inheriting either an X or a Y chromosome from the father, resulting in an equal number of males (XY) and females (XX).
(c) Chromosomes contain genes.
Define the term gene.
▶️Answer/Explanation
Answer: A gene is a length of DNA that codes for a protein.
Explanation: Genes are segments of DNA located on chromosomes that contain the instructions for the synthesis of proteins. These proteins are responsible for various traits and functions in an organism.
Question
Carbon occurs as a free element in the Earth’s crust. Carbon also occurs in millions of different compounds.
(a) Fig. 11.1 shows the structures of two forms of carbon, A and B.
(i) State the names of these forms of carbon.
▶️Answer/Explanation
A: Diamond
B: Graphite
Detailed Solution:
11(a)(i): The two forms of carbon shown in Fig. 11.1 are diamond and graphite. Diamond has a tetrahedral structure where each carbon atom is bonded to four other carbon atoms, forming a rigid three-dimensional network. Graphite, on the other hand, has a layered structure where each carbon atom is bonded to three others, forming hexagonal rings. The layers are held together by weak van der Waals forces, allowing them to slide over each other.
(ii) State the type of chemical bonding and structure present in both A and B.
▶️Answer/Explanation
Type of bonding: Covalent
Type of structure: Giant
Detailed Solution:
11(a)(ii): Both diamond and graphite are composed of carbon atoms bonded together by strong covalent bonds. However, the type of structure differs: diamond has a giant covalent structure, while graphite also has a giant covalent structure but with layers that can slide over each other due to weak interlayer forces.
(b) The pie charts in Fig. 11.2 show the compositions of two gas mixtures, L and M.
(i) Gas mixture L is the fossil fuel, natural gas. Identify gas Q.
▶️Answer/Explanation
Gas Q: Methane (CH4)
Detailed Solution:
11(b)(i): Natural gas primarily consists of methane (CH4), which is a simple hydrocarbon. Methane is a major component of natural gas and is used as a fuel.
(ii) A student wants to distinguish between mixture L and mixture M. Describe a test he can do. Include the results in each case.
▶️Answer/Explanation
Test: Use damp red litmus paper.
Result with L: No reaction (remains red).
Result with M: Turns blue (indicating the presence of ammonia).
Detailed Solution:
11(b)(ii): To distinguish between natural gas (L) and a mixture containing ammonia (M), a simple test using damp red litmus paper can be performed. Ammonia is a basic gas and will turn damp red litmus paper blue, whereas natural gas (methane) is neutral and will not affect the litmus paper.