Cellular Control Questions F215

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1.

(a) (i) A gene controlling coat colour in cats is sex linked. The two alleles of this gene are black and orange. When both are present the coat colour is called tortoiseshell. Define the following terms: gene........................................................................................................ ................................................................................................................ allele ....................................................................................................... ................................................................................................................[2]

(ii)

Explain why there are no male tortoiseshell cats. ................................................................................................................ ................................................................................................................ ................................................................................................................ ................................................................................................................[2]

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Two pure breeding strains of snapdragon, a garden plant, were obtained. One strain had red flowers and the other had white flowers. The two strains were crossed yielding F1 plants all with pink flowers. The F1 were then interbred to produce F2 plants with the following colours: red pink white 62 131 67

The following hypothesis was proposed: Flower colour is controlled by a single gene with two codominant alleles. (b) Complete the genetic diagram to explain this cross. Use the following symbols to represent the alleles: C = red, C = white Parental phenotypes: flowers red flowers x whiter w

Parental genotypes: .................................... ........................................ Gametes: .................................... ........................................

F1 genotypes: .................................................................................................. F1 phenotypes: ................................................................................................ Gametes: ........................................................................................................

F2 genotypes: .................................................................................................. F2 phenotypes: ................................................................................................ Expected F2 phenotypic ratio:.........................................................................[6] The Henrietta Barnett School 2

(c)

A chi-squared ( ) test is carried out on the experimental data to determine whether the hypothesis is supported. (i) Complete the table below by calculating the expected numbers. F2 phenotype red pink white total observed numbers 62 131 67 260 260[3]

2

expected numbers

The statistic is calculated in the following way: 2 =

2

( observed expected) 2expected

= sum of ...

(ii)

Calculate the value of for the above data. Show your working.

2

value = ................................................................................................[2]

2

(iii)

The critical value of for this type of investigation with two degrees of freedom is 5.991. Explain whether your answer to (b) (ii) supports the hypothesis. ................................................................................................................ ................................................................................................................[1] [Total 16 marks]

2

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2.

In guinea pigs, the genes for coat texture and coat colour are found on separate chromosomes. The allele for rough coat is dominant to the allele for smooth coat. The allele for black coat is dominant to the allele for white coat. A black guinea pig with a rough coat was crossed with a white guinea pig with a rough coat. The cross was repeated on a number of occasions and the phenotypes of the offspring were as follows: 28 rough and black coats 31 rough and white coats 11 smooth and black coats 10 smooth and white coats

Complete the genetic diagram to explain this cross. Use the following symbols to represent the alleles: R = rough r = smooth B = black b = white Parental phenotypes: coat Parental genotypes: .................................. Gametes: .................................. rough and black coat ................................. ................................. rough and white

Offspring genotypes: ............................................................................................... Offspring phenotypes: ............................................................................................. Expected phenotypic ratio: ......................................................................................[Total 5 marks]

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3.

An enzyme, such as amylase, has a specific 3-dimensional shape. Explain how DNA structure determines the specific shape of enzymes. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ..................................................................................................................................[Total 4 marks]

4.

(a) Repeating nucleotide sequences are common in the genomes of eukaryotes, for example in the centromeres and in the regions, called introns, which appear to interrupt the genes. Repeating sequences have been referred to as junk DNA. Suggest why the term junk DNA is misleading. ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .........................................................................................................................[2]

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(b)

Some species of plant are able to grow on soils that contain very little phosphate, while other species, for example stinging nettles, can only grow well in soils that are rich in phosphate. Each nucleotide in a DNA molecule includes a phosphate group. If much of the non-coding DNA can be correctly regarded as functionless junk, there may be a correlation between the percentage of DNA that is non-coding and the minimum concentration of phosphate ions needed for healthy growth. Draw a straight line graph, using the axes in the figure below, to show the correlation that you would predict. p e r c e n t a g e o f D N A t h a t is n o n - c o d i n g

m in i m u m c o n c e p h o s p h a t e io n s f o r h e a lt h y g r o w

n t r a n e e in g

t io n d e d[1]

o

(c)

Name a substance other than DNA that is found in cells and has one or more phosphate groups as part of its chemical structure. .........................................................................................................................[1] [Total 4 marks]

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5.

Muscle fibres may become torn and damaged. Damaged muscle fibres have an increased messenger RNA (mRNA) concentration and a higher rate of oxygen consumption, at rest, than undamaged muscle fibres. Explain these observations: increased mRNA concentration; .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ..................................................................................................................................

higher rate of oxygen consumption. .................................................................................................................................. .................................................................................................................................. ..............................................