AQA AS Biology B9 Genetic Diversity Kerboodle Answers

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9.1 Genetic diversity and adaptation AQA AS Biology B9 Genetic Diversity Kerboodle Answers

Ans 1 Type of mutation is Deletion mutation because the fifth nucleotide has been lost. Ans 2 In a deletion, all codons after the deletion are affected (frame shift). Therefore most amino acids coded for by these codons will be different and the polypeptide will be significantly affected. In a substitution, only a single codon, and therefore a single amino acid, will be affected. The effect on the polypeptide is likely to be less severe. Ans 3 The mutation may result from the substitution of on  base in the mRNA with another. Although the codon affected will be different, as the genetic code is degenerate, the changed codon may still code for the same amino acid. The polypeptide will be unchanged and there will be no effect. Ans 4. The errors occurring at the time of DNA replication, may be inherited and may therefore have a permanent affect on the whole organism. Errors in transcription usually only affect specific cell, are temporary and are not inherited. They therefore are less damaging than the errors occurred at the time of DNA replication. Hybridization and polyploidy . 1Ans. Plant hybrids are the result of sexual reproduction between plants from two different taxa or species. Not all plant hybrids are sterile, but many are. Sterility in plant hybrids is most often the result of polyploidy, which occurs because of abnormal cell division and results in more than two sets of chromosomes in the cells of the hybrid offspring. Hybrids commonly form in nature between closely related species, but humans also produce sterile hybrid plants intentionally for commercial purposes. 2Ans. Short stems have two advantages: (1) the stems are stronger and therefore less likely to fall over, and (2) because less energy goes into making a shorter stem, more is left over to make grain. 3Ans They cannot breed to produce fertile offspring.

9.2 Meiosis andgenetic  variation AQA AS Biology B9 Genetic Diversity Kerboodle Answers

Ans. The cell is haploid. Because the chromosome number of the cell is an odd number. Diploid cells have even number of chromosomes because they have two sets of chromosomes. So the total of chromosomes will be even number. 2Ans Besides halving the number of chromosome, meiosis also produces variation in offspring. Variation may lead to adaptations thus better survival of offspring. Genetic variation is introduced by meiosis in the following ways:

• Homologous chromosomes are segregated independently.
• New combination of paternal and maternal alleles is generated by crossing over

3Ans. Figure 3. The combination of allele can be AA or AO. 4Ans The numbers of chromosomes in the hybrids do not allow them to form homologous pairs during prophase I of meiosis I. They cannot produce gametes. This would arise if the hybrid has an odd number of chromosomes. 5Ans The haploid number is 5 i.e. the same as homologous chromosome number. Thus by using formula (2ⁿ)² where n= the number of pairs of homologous chromosomes Possible combinations can be calculated. Thus (2⁵)²= 1024. So, 1024 is the possible combination produced from fertilisation of two gametes.

9.3 Genetic diversity and adaptation AQA AS Biology B9 Genetic Diversity Kerboodle Answers

1Ans a. By increasing the variety of alleles with a population genetic diversity will increase.

1. Breeding together closely related cats to develop varieties with longer fur will decrease the genetic variety because breeding closely related ones will result in less variable population.
2. mutation (permanent change of the DNA) of an allele can increase the genetic diversity if only the new allele formed after mutation is advantageous to that individual and the possessor can reproduce successfully and pass it to next generation.

2Ans: DNA determines the considerable variety of proteins that make up each organism. Thus genetic similarities and differences can be defined in terms of variation in DNA. Variation in DNA leads to vast genetic variety on Earth which we find. Natural Selection: 3Ans In the peppered moth population of Great Britain there is variation in the colour of the moth’s bodies. Some moths have a light body; some have a dark, or melanic body. Body colour is an inherited characteristic. Three moths camouflaged against different background colours and textures Before the industrial revolution, light moths had a selective advantage. Because they were well camouflaged against the lichen-covered trees, they were better able to avoid predation. During the nineteenth century pollution killed off some of the lichens and soot deposits caused the tree bark to appear darker. Light coloured moths were no longer camouflaged and were more likely to be eaten by birds. The dark moths were now better camouflaged. As a result, dark moths had a greater chance of reproducing and passing on the alleles that made them dark. This led to a gradual increase in the proportion of dark moths until light moths became very rare in industrial areas. The moth populations in these areas had evolved. This change from predominantly light to dark forms in industrial areas is called industrial melanism. Note that this change was not due to pollution making the moths darker. The dark variety had always existed in small numbers, but only had a selective advantage when the selection pressure changed.

9.4 Types of selection

AQA AS Biology B9 Genetic Diversity Kerboodle Answers

1.Ans Selection is the process by which organisms that are better adapted to their environment tend to survive and reproduce successfully, while those that are less adapted tend not to survive and reproduce. 2Ans stabilizing selection When selective pressures select against the two extremes of a trait, the population experiences stabilizing selection. For example, plant height might be acted on by stabilizing selection. A plant that is too short may not be able to compete with other plants for sunlight. However, extremely tall plants may be more susceptible to wind damage. Combined, these two selection pressures select to maintain plants of medium height. The number of plants of medium height will increase while the numbers of short and tall plants will decrease. Figure: The effect of stabilizing selection on trait distribution. Source: http://www.sparknotes.com/ biology/evolution/naturalselection/section1/   Directional selection In directional selection, one extreme of the trait distribution experiences selection against it. The result is that the population’s trait distribution shifts toward the other extreme. In the case of such selection, the mean of the population graph shifts. Using the familiar example of giraffe necks, there was a selection pressure against short necks, since individuals with short necks could not reach as many leaves on which to feed. As a result, the distribution of neck length shifted to favor individuals with long necks. Figure: The effect of directional selection on trait distribution. Source: http://www.sparknotes.com/ biology/evolution/naturalselection/section1/ 3Ans The selection taking place is directional selection because heavier birds (to one side of the mean) were being selected for, while lighter birds (to the other side of the mean) were being selected against. The population’s characteristics are being changed, not preserved. They must be cuckoo! 1Ans Cuckoos lay their eggs in the nests of other birds. The host birds will often raise these parasite chicks alongside their own. Removing cuckoo eggs means there will be more food for the magpies own chicks. These chicks have a greater probability of being successfully raised to adulthood. 2Ans Removing cuckoo eggs increases the probability of the alleles for this type of behaviour being passed on to subsequent generations. This can be explaining in the following manner:

1. Alleles for this type of behaviour are present in the adult birds.
2. There is a high probability that some of the chicks will inherit these alleles.
3. Removing cuckoo eggs increases the probability of more of these chicks surviving to breed and so passing on the alleles for this behaviour to subsequent generations.

3Ans This form of behaviour is not shown by magpies in those valleys where cuckoos have only recently arrived because of the fact that displaying this behaviour has previously been of no advantage to magpies so selection of this trait has not taken place earlier. But as cuckoo started to colonised now in the valley, it will take many generation for selection of trait and for allele frequencies to change. 4Ans.  Stabilising selection is taking place here in this case because the megpeis with the trait of removing cuckoo eggs are selected over the megpeis which will not remove the eggs of cuckoos. If the eggs are not removed from the next then the food resourced are divided among the cuckoo chicks and megpies chicks. Thus there will be limited resource and the megpies chicks have to compete further. They will be weak thus cannot survive. Hence the megpies trait of removing cuckoos eggs if selected and retained. 5Ans. Different behaviour of the two groups of magpies might lead to selection the produces a change within the megpies population. The reason is explained below:

1. Magpies that do not remove cuckoo eggs will raise both cuckoo and magpie chicks.
2. There will be less food/space for the magpie chicks compared to those raised in magpie nests and so less chance of them surviving to adulthood and breeding.
3. The chicks of magpies that remove cuckoo eggs will be selected for in preference to the chicks of parents that do not.
4. Over many generations the population will change to have a greater proportion of magpies that remove cuckoo eggs at the expense of those that do not.

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 Practice questions:

1a)iAns this base sequence could code for four amino acids. iiAns Mutation will lead change in sequence of amino acids which will result in change in hydrogen, ionic, disulphide bonds of the enzyme. Enzyme structure is dependent on these bonds thus this will alters tertiary structure of active site of enzyme. This will further result in loss of complementary substrate and so substrate cannot bind to enzyme. Enzyme substrate complexes will not form. Thus it is clear that mutation will lead to non-functioning PAH enzyme. bAns. Two symptoms of phenylketonuria disease:

1. Fair skin and blue eyes, because phenylalanine can’t transform into melanin — the pigment responsible for hair and skin tone
2. Neurological disorders and delayed development.

cAns This is an example of founder effect. A founder effect occurs when a new colony is started by a few members of the original population. This small population size means that the colony may have:

• Reduced genetic variation from the original population.
• A non-random sample of the genes in the original population.

2.a)Ans Allele is one of the different forms of a particular gene. bAns Chromosomes are made of two chromatides and these are attached with a centromere. Two chromatids are known as sister chromatids. c.i)Ans Gametes with new combination are produced as a result of crossing over. iiAns Only a few gametes are produced with the new combination because the crossing over is a rare phenomenon.

	Parent Cell				Gamete

d.ii)Ans There are a large number of possible combinations of chromosomes in a daughter. The possible combinations can be calculated using a mathematical formula which is based on the number of chromosomes in an organism. The formula is: 2ⁿ where n= the number of pairs of homologous chromosomes. Here is 3 pair of homologous chromosomes thus the possible combination will be 2³=8. E.i)Ans For diploid number 24, pair of homologous chromosomes will be 12. Thus the possible combination will be 2¹²= 4096. iiAns (4096)² 3.a)Ans Genetic diversity is considered to be the baseline of biodiversity. It is the cumulative sum of all the genetic traits or characters present in the genome of any given population or species. It can be described as the total number of different alleles in a population. b)Ans Environmental factors also cause variation within in a species. c)Ans 1. Reduced (genetic diversity) 2. As fewer different/varied alleles/genes /reduced gene pool 3. (Genetic) bottleneck a.i)Ans The number of chromosomes in male gamete of variety C is 22. iiAns In case of Variety B there is odd number of chromosomes. Thus the resulted offspring will be sterile. b.i)Ans Variety B is selected over variety A because of the fact that given in the table that growth rate of variety B is higher than the variety A. iiAns Breaking strength of leaf/arbitrary units is high in case of variety b than that of variety C. cAns Growing variety B on a large scale will affect the genetic diversity of bananas because of the following reasons: – Low genetic diversity because they are produced by mitosis – Will all be genetically identical/have same alleles Banner 3

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