Inheritance, Genes & Cell Division (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

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Fig. 1 shows some cells from the shoot tip of an onion, Allium cepa.

Fig. 1

State the evidence visible in Fig. 1 that identifies the cells of A. cepa as plant cells.

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Cell A is dividing by mitosis.

State the role of mitosis in a shoot tip.

[1]

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In Fig. 1, the area labelled M is a mitochondrion.

Explain why mitochondria have an important role in dividing cells.

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Some cells in shoot tips become leaf cells and others become cells in the stem or in flowers.

Explain why it is important that only some of the genes in cell A are expressed in these cells.

Fig. 1 shows a dwarf sunflower and a tall sunflower, Helianthus annuus.

The height of the dwarf sunflower is 0.45 m and the height of the tall sunflower is 4.5 m.

Fig. 1

Dwarf plants like the one in Fig. 1 have mutant alleles.

Define the term allele.

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Fig. 2

Explain how a mutation in DNA results in an abnormal enzyme which does not catalyse the reaction shown in Fig. 2.

Explain how it is possible for two tall parent plants to have this percentage of dwarf offspring.

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Fig. 3

Explain the type of reproduction that produces plants by the method shown in Fig. 3.

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Explain the disadvantages of the type of reproduction shown in Fig. 3.

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Organisms pass on their genetic information in their gametes.

State the name of the type of cell division that produces gametes.

[1]

State the name of the cell formed when the nuclei of two gametes join together.

A rabbit that was homozygous for black fur was crossed with a rabbit that was homozygous for brown fur.

All of their offspring had black fur.

This is shown in Fig. 1.

Fig. 1

Define the term homozygous.

[1]

State the dominant allele for the rabbits' fur colour and give a reason for your answer.

The F₁ offspring all have the same phenotype as the male parent but their genotype is not the same as the male parent.

State how the phenotype of an organism is different to its genotype.

A rabbit with brown fur is mated with one of the F₁ rabbits with black fur.

Complete the genetic diagram to show the possible fur colours that could occur from this mating.

New breeds of rabbits can be produced by selective breeding.

Describe the stages in the process of selective breeding.

The Indian muntjac deer, Muntiacus muntjak, is recorded as the mammal with the lowest number of chromosomes.

Fig. 1 is an image of the chromosomes in the nucleus of a diploid cell of a female muntjac deer.

Fig 1

State the diploid number of chromosomes for the female muntjac deer.

Fig. 2 is an image of the chromosomes in the nucleus of a diploid cell of a male muntjac deer.

Fig 2

Describe how the sex chromosomes of the male muntjac deer shown in Fig. 2 differ from those of the female shown in Fig. 1.

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Explain how meiosis can result in variation in a species.

Use the words chromosome and gametes in your answer.

Another cause of variation is the formation of new alleles.

Describe how new alleles can be formed.

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Fig. 1 shows the sequence of events that occur in sexual reproduction.

Fig 1

State the name of cell T in Fig. 1.

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(ii)

State the name of the process that takes place at S to form cell T in Fig. 1.

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(iii)

State where in the human body process S takes place.

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Some humans have the ability to roll their tongues and some cannot roll their tongues.

This characteristic is controlled by genes.

Fig. 2 shows two boys: boy A cannot roll his tongue and boy B can roll his tongue.

Fig. 2

The allele for tongue rolling (T) is dominant to the allele for non-tongue rolling (t).

Fig. 3 shows a family tree for this characteristic. Individual 1 and his partner are both heterozygous for tongue rolling.

Fig. 3

Complete Table 1 by inserting the genotypes of the numbered individuals in Fig. 3.

Table 1

[3]

Individual 2 in Fig. 3 is heterozygous for tongue rolling. He marries a woman who cannot roll her tongue.

State all of the possible genotypes of their children and predict the ratio of phenotypes for their children.

Possible offspring genotypes: .............................................

Ratio of phenotypes: ..............................................................

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