16. Inheritance
A section of Biology, 9700
Listing 10 of 199 questions
As part of the technique of In-vitro fertilisation (IVF), several oocytes are collected from a woman who is undergoing treatment. Each oocyte is checked under a microscope. Explain why oocytes that have a first polar body are used in the fertilisation process. It is possible to freeze embryos that are produced by IVF, using a solution containing sucrose and various salts. The embryos can later be thawed and implanted. A trial was carried out to compare the success rates of freezing oocytes in • solution A, the same solution as is used for freezing embryos • solution B, a different solution containing different concentrations of sucrose and salts. Oocytes were placed into either solution A or solution B. They were then frozen and stored at a temperature of −33 °C. Later, the oocytes were thawed and then fertilised, using intracytoplasmic sperm injection (ICS. When the oocytes were placed into solution A or solution B, they quickly reduced in size. Explain why this happened. Table 5.1 shows the results of the trial. Table 5.1 number of oocytes frozen number of oocytes thawed number of oocytes that survived after thawing number of oocytes that underwent ICSI number of oocytes that were successfully fertilised solution A solution B With reference to Table 5.1, explain which solution is the better solution to use. Suggest one advantage of being able to freeze and thaw oocytes as part of the IVF procedure.
9700_s13_qp_41
THEORY
2013
Paper 4, Variant 1
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As part of the technique of In-vitro fertilisation (IVF), several oocytes are collected from a woman who is undergoing treatment. Each oocyte is checked under a microscope. Explain why oocytes that have a first polar body are used in the fertilisation process. It is possible to freeze embryos that are produced by IVF, using a solution containing sucrose and various salts. The embryos can later be thawed and implanted. A trial was carried out to compare the success rates of freezing oocytes in • solution A, the same solution as is used for freezing embryos • solution B, a different solution containing different concentrations of sucrose and salts. Oocytes were placed into either solution A or solution B. They were then frozen and stored at a temperature of −33 °C. Later, the oocytes were thawed and then fertilised, using intracytoplasmic sperm injection (ICS. When the oocytes were placed into solution A or solution B, they quickly reduced in size. Explain why this happened. Table 5.1 shows the results of the trial. Table 5.1 number of oocytes frozen number of oocytes thawed number of oocytes that survived after thawing number of oocytes that underwent ICSI number of oocytes that were successfully fertilised solution A solution B With reference to Table 5.1, explain which solution is the better solution to use. Suggest one advantage of being able to freeze and thaw oocytes as part of the IVF procedure.
9700_s13_qp_43
THEORY
2013
Paper 4, Variant 3
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Spermatogenesis takes place in the seminiferous tubules, in the testis. is a diagram showing some of the cells in a small sector of a seminiferous tubule. spermatogonium primary spermatocyte secondary spermatocyte spermatid spermatozoan On , state whether each of the labelled cells is haploid or diploid. Write n if the cell is haploid and 2n if the cell is diploid. Spermatogenesis involves meiosis, mitosis, growth and maturation. State which of these processes is involved in each of the following steps in spermatogenesis. spermatogonium to primary spermatocyte spermatid to spermatozoan State one role of a Sertoli cell. In some men, spermatogenesis does not take place successfully and the sperm that are produced are unable to fertilise an egg. A form of IVF called intra-cytoplasmic sperm injection (ICSmay enable them to father a child with their partner. In ICSI, a sperm cell is inserted into a secondary oocyte using a very tiny needle. Outline the treatment required in order to obtain mature oocytes as part of an IVF procedure. One approach to helping an infertile man to father children is to extract immature spermatids from his testes and culture them in the laboratory, in conditions that may increase the number of them that develop into functioning sperm. These can then be used for IVF. An investigation was carried out to see if adding reproductive hormones to a culture of immature spermatids affects their development. Samples of spermatids were collected from men in whom the spermatids did not normally develop into functioning sperm. The spermatids were cultured in a suitable liquid medium, kept at 30 °C. The samples were divided into four groups. No hormones were added to one group. FSH, testosterone or both were added to the other groups. The percentage of spermatids that developed into elongated cells in each group after 24 hours and 48 hours was calculated. The results are shown in Table 4.1. Table 4.1 hormones added percentage of spermatids that developed into elongated cells after 24 hours after 48 hours none FSH testosterone FSH and testosterone With reference to Table 4.1, describe the effects of adding reproductive hormones on the development of the spermatids after 48 hours. Suggest a reason for the apparent reduction in the percentage of elongated cells between 24 hours and 48 hours in some of the samples. Suggest why the culture medium was maintained at a temperature of 30 °C, and not at core body temperature (37 °C).
9700_s14_qp_41
THEORY
2014
Paper 4, Variant 1
View
Spermatogenesis takes place in the seminiferous tubules, in the testis. is a diagram showing some of the cells in a small sector of a seminiferous tubule. spermatogonium primary spermatocyte secondary spermatocyte spermatid spermatozoan On , state whether each of the labelled cells is haploid or diploid. Write n if the cell is haploid and 2n if the cell is diploid. Spermatogenesis involves meiosis, mitosis, growth and maturation. State which of these processes is involved in each of the following steps in spermatogenesis. spermatogonium to primary spermatocyte spermatid to spermatozoan State one role of a Sertoli cell. In some men, spermatogenesis does not take place successfully and the sperm that are produced are unable to fertilise an egg. A form of IVF called intra-cytoplasmic sperm injection (ICSmay enable them to father a child with their partner. In ICSI, a sperm cell is inserted into a secondary oocyte using a very tiny needle. Outline the treatment required in order to obtain mature oocytes as part of an IVF procedure. One approach to helping an infertile man to father children is to extract immature spermatids from his testes and culture them in the laboratory, in conditions that may increase the number of them that develop into functioning sperm. These can then be used for IVF. An investigation was carried out to see if adding reproductive hormones to a culture of immature spermatids affects their development. Samples of spermatids were collected from men in whom the spermatids did not normally develop into functioning sperm. The spermatids were cultured in a suitable liquid medium, kept at 30 °C. The samples were divided into four groups. No hormones were added to one group. FSH, testosterone or both were added to the other groups. The percentage of spermatids that developed into elongated cells in each group after 24 hours and 48 hours was calculated. The results are shown in Table 4.1. Table 4.1 hormones added percentage of spermatids that developed into elongated cells after 24 hours after 48 hours none FSH testosterone FSH and testosterone With reference to Table 4.1, describe the effects of adding reproductive hormones on the development of the spermatids after 48 hours. Suggest a reason for the apparent reduction in the percentage of elongated cells between 24 hours and 48 hours in some of the samples. Suggest why the culture medium was maintained at a temperature of 30 °C, and not at core body temperature (37 °C).
9700_s14_qp_43
THEORY
2014
Paper 4, Variant 3
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People vary in which molecules are present on the surface of their red blood cells. For example, in the ABO blood group system, people may be categorised into one of four blood groups: A, B, AB and O. A single gene, I, with three alleles, determines these blood groups. Gene I is an example of a gene with multiple alleles. • Alleles IA and IB are codominant. • Allele Io is recessive to alleles IA and IB. Explain what is meant by codominant and recessive. codominant recessive Table 7.1 shows a cross between a person with blood group A and a person with blood group B. Complete Table 7.1. Table 7.1 parental phenotype (blood group) A B parental genotype IA Io IB Io gametes offspring genotype offspring phenotype (blood group) Haemophilia is a blood condition where bleeding continues for a long period of time after a blood vessel has been damaged. A person with haemophilia has a mutation in a gene on the X chromosome, which results in the lack of a blood clotting factor. Explain why a man who has haemophilia cannot pass the condition to his male offspring.
9700_s21_qp_41
THEORY
2021
Paper 4, Variant 1
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Questions Discovered
199