16. Inheritance
A section of Biology, 9700
Listing 10 of 199 questions
Flowers are the organs of sexual reproduction in plants. Before fertilisation and seed development can take place, pollination must occur. This can be either self-pollination or cross-pollination, and can be carried out by insects or by wind. Explain the meaning of the term self-pollination. Explain why cross-pollination may be more beneficial to a species than self-pollination. In maize, wind pollination occurs. An investigation was carried out to find out how the length of time that maize pollen is in the air affects its ability to bring about fertilisation in a female flower. • Pollen grains were removed from maize flowers and left exposed to the air for varying times. • The pollen grains were then placed onto groups of female flowers. • The groups of fertilised flowers developed into ‘ears’, each containing many seeds. The number of seeds per ear was counted. The results are shown in . time of exposure of pollen to air / minutes number of seeds produced per ear Describe the effect of exposure to the air on maize pollen. A wild relative of maize, called teosinte, grows in Mexico. There are concerns that pollen from genetically-modified maize could pollinate wild teosinte and transfer new genes to it. Suggest how the results shown in could be used to devise strategies that would reduce the possibility of this happening.
9700_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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Flowers are the organs of sexual reproduction in plants. Before fertilisation and seed development can take place, pollination must occur. This can be either self-pollination or cross-pollination, and can be carried out by insects or by wind. Explain the meaning of the term self-pollination. Explain why cross-pollination may be more beneficial to a species than self-pollination. In maize, wind pollination occurs. An investigation was carried out to find out how the length of time that maize pollen is in the air affects its ability to bring about fertilisation in a female flower. • Pollen grains were removed from maize flowers and left exposed to the air for varying times. • The pollen grains were then placed onto groups of female flowers. • The groups of fertilised flowers developed into ‘ears’, each containing many seeds. The number of seeds per ear was counted. The results are shown in . time of exposure of pollen to air / minutes number of seeds produced per ear Describe the effect of exposure to the air on maize pollen. A wild relative of maize, called teosinte, grows in Mexico. There are concerns that pollen from genetically-modified maize could pollinate wild teosinte and transfer new genes to it. Suggest how the results shown in could be used to devise strategies that would reduce the possibility of this happening.
9700_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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The photomicrographs in show stages of the mitotic cell cycle occurring in the root tip of the onion, Allium sp. They are all of the same magnification. Stages A to C are in the correct sequence and stages K to N are not in the correct sequence. stages in correct sequence stages not in correct sequence A B C K L N M Name stages A and C. A C Put stages K to N in the correct sequence, starting with the stage that immediately follows stage C. C Explain how the behaviour of the chromosomes and spindle during stage L in ensures that the two daughter cells will be genetically identical.
9700_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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The sweet pea, Lathyrus odoratus, is a flowering plant that grows in many parts of Europe. The inheritance of flower colour and shape of pollen grains is controlled by genes that display autosomal linkage. Explain what is meant by autosomal linkage. In sweet peas, the allele for purple flowers is dominant to the allele for red flowers and the allele for long pollen grains is dominant to the allele for round pollen grains. A sweet pea plant that is heterozygous for both purple flowers and long pollen grains is crossed with a sweet pea plant with red flowers and round pollen grains. The results of this cross are shown in Table 8.1. Table 8.1 offspring phenotype percentage of offspring purple flowers, long pollen grains red flowers, round pollen grains purple flowers, round pollen grains red flowers, long pollen grains Describe and explain the results shown in Table 8.1. Different alleles affecting flower colour in the sweet pea plant are the result of gene mutations. State how a gene mutation may occur.
9700_w17_qp_42
THEORY
2017
Paper 4, Variant 2
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Mammals such as sheep, Ovis aries, and goats, Capra hircus, are important agricultural animals that are sometimes kept together in mixed flocks. Very occasionally, live offspring are born from a mating between a male sheep and a female goat. In sheep 2n = 54 and in goats 2n = 60. Calculate the diploid chromosome number of the hybrid offspring of a sheep and a goat. Outline why the classification of sheep and goats suggests that hybridisation between them should not be likely to occur. Normal (wild-type) goats have a gold and black coat colour pattern, known as bezoar, and are also horned (have horns). Domestic goats may have a white coat and may be hornless (do not have horns). These variations are coded for by two unlinked genes: • white coat colour, coded for by the dominant allele of the gene A/a • hornless, coded by the dominant allele of the gene H/h. A cross between a white hornless goat and a bezoar horned goat produced offspring of four different phenotypes. Draw a genetic diagram to show the genotypes of the two parents, their gametes and the offspring, and the phenotypes of the offspring. Horns on agricultural animals such as goats and cattle can be dangerous to the farmer and to other animals. Horns are often prevented from growing in 5-day-old animals by a stressful procedure called disbudding. Genetic modification can cause a deletion in the allele h coding for horns in cattle embryos, so that the allele no longer codes for a functional protein and the embryos grow into cattle that are hornless. State an ethical advantage of this example of genetic modification. Suggest why genetic modification that causes a deletion in the horned allele, in established breeds of dairy cattle, is preferable to selective breeding for hornless animals.
9700_w18_qp_42
THEORY
2018
Paper 4, Variant 2
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The early development of an animal involves divisions of the zygote and daughter cells by mitosis to form an embryo consisting of genetically identical cells. shows several cells at various stages of the cell cycle in an embryo of whitefish, Coregonus artedi. magnification ×1200 microtubules A C B Name the stage of mitosis in cell A and in cell B, shown in . A B shows microtubules in the cells that are dividing. Describe the role of microtubules in mitosis. State what happens in cell C, shown in , until two new cells are formed. The cells produced in the developing whitefish are genetically identical. Identify and explain two events that occur during the cell cycle that lead to daughter cells being genetically identical.
9700_w22_qp_23
THEORY
2022
Paper 2, Variant 3
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In a species of snail, shell colour is controlled by a gene with three alleles: • allele CB codes for a brown shell • allele CP codes for a pink shell • allele CY codes for a yellow shell. Allele CB is dominant to both CP and CY. Allele CP is dominant to CY. The shells of this snail may be banded (have dark stripes) or non-banded. The allele for non-banded, N, is dominant to the allele for banded, n. State what is meant by the terms dominant and allele. dominant allele A cross between a brown, non-banded snail and a pink, non-banded snail produces some offspring that are both yellow and banded. State the genotypes of both parents. brown, non-banded pink, non-banded List the parental gametes. brown, non-banded pink, non-banded State the genotype of the offspring that are both yellow and banded. Suggest the proportion of offspring expected to be both yellow and banded.
9700_m16_qp_42
THEORY
2016
Paper 4, Variant 2
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In humans a rare, sex-linked, recessive allele results in a change in the shape of the iris in the eye. This condition is know as cleft iris (C. Explain what is meant by the term sex linkage. Using suitable symbols complete the genetic diagram below. Key to symbols recessive allele dominant allele parental phenotypes male with CI X normal female parental phenotypes gametes offspring genotypes offspring phenotypes A woman who is heterozygous for CI becomes pregnant by a man with a normal iris. State the probability that their child will have CI.
9700_s10_qp_42
THEORY
2010
Paper 4, Variant 2
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In humans a rare, sex-linked, recessive allele results in a change in the shape of the iris in the eye. This condition is know as cleft iris (C. Explain what is meant by the term sex linkage. Using suitable symbols complete the genetic diagram below. Key to symbols recessive allele dominant allele parental phenotypes male with CI X normal female parental phenotypes gametes offspring genotypes offspring phenotypes A woman who is heterozygous for CI becomes pregnant by a man with a normal iris. State the probability that their child will have CI.
9700_s10_qp_43
THEORY
2010
Paper 4, Variant 3
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Questions Discovered
199