16. Inheritance
A section of Biology, 9700
Listing 10 of 199 questions
Use shows a section through part of a human testis. A B Name structures A and B. A ……………………………………………………… B ……………………………………………………… Spermatogenesis, the production of sperm, begins in the testes of a boy around the age of 11 and can continue for the rest of his life. outlines the sequence of events that occur during spermatogenesis. germinal epithelium spermatogonium cell division 1 stage C cell division 2 cell division 3 maturation cell D cell E cell F spermatozoan Examiner’s Use With reference to , state which cell division is mitotic, state which cells are haploid, state what is happening to the cell during stage C. The middle piece of a spermatozoan contains many mitochondria. Suggest why a spermatozoan needs so many mitochondria. Some couples have difficulty in conceiving. This could be due to a problem with either the male or female reproductive systems. Suggest reasons why a man may be infertile. Examiner’s Use In vitro fertilisation (IVF) is a widely used treatment for infertility. Explain what is meant by the term in vitro fertilisation. At one IVF clinic, over 1000 treatment cycles were monitored. The number of live births was recorded as a percentage of the number of treatment cycles for each age group. The results are shown in Table 5.1. Table 5.1 age of women/years percentage of live births per treatment cycle under 34 27.6 34 to 36 22.3 37 to 39 18.3 40 to 42 10.0 above 42 less than 5.0 The data in Table 5.1 show that there is a decrease in the percentage of live births per treatment cycle with increasing age. Explain this trend.
9700_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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Describe the maturation of a spermatid into a spermatozoon . A method of sorting damaged from undamaged sperm has undergone trials at an in vitro fertilisation (IVF) clinic in Australia. It is hoped to use the procedure when attempting IVF with sperm from men with fertility problems. The sorting process is shown in . sperm sample placed in upper chamber plate with negative charge filter with 5 µm holes about 20 % of the sperm move into the lower chamber plate with positive charge Sperm left in the upper chamber have, on average, twice as much damage to their DNA as those that move into the lower chamber. In the body, sperm which mature normally move slowly through the epididymis, gradually accumulating molecules of a negatively charged protein in their cell surface membranes. Other sperm move more quickly through the epididymis.
9700_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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Outline the differences in the process of gametogenesis in a man compared with that in a woman. The hormone testosterone is secreted by Leydig cells in the testis. These cells form an endocrine gland. Explain what is meant by an endocrine gland. In 2009, a research laboratory for family planning in Beijing announced that it had injected 1000 healthy, fertile men with testosterone over a two-year period and found that only 10 of the men were then able to father a child. The men’s normal fertility was restored six months after their last injections. The injections, each of 500 mg of testosterone, resulted in a reduced production of follicle stimulating hormone (FSH) and of luteinising hormone (LH) in the injected men. Describe the similarities between the effect of these testosterone injections on a fertile man with the effect of the oestrogen/progesterone contraceptive pill on production of FSH and LH by a fertile woman.
9700_w11_qp_41
THEORY
2011
Paper 4, Variant 1
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Outline the differences in the process of gametogenesis in a man compared with that in a woman. The hormone testosterone is secreted by Leydig cells in the testis. These cells form an endocrine gland. Explain what is meant by an endocrine gland. In 2009, a research laboratory for family planning in Beijing announced that it had injected 1000 healthy, fertile men with testosterone over a two-year period and found that only 10 of the men were then able to father a child. The men’s normal fertility was restored six months after their last injections. The injections, each of 500 mg of testosterone, resulted in a reduced production of follicle stimulating hormone (FSH) and of luteinising hormone (LH) in the injected men. Describe the similarities between the effect of these testosterone injections on a fertile man with the effect of the oestrogen/progesterone contraceptive pill on production of FSH and LH by a fertile woman.
9700_w11_qp_42
THEORY
2011
Paper 4, Variant 2
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shows the stages in spermatogenesis in a mammal. A B W X Y E D spermatid C State the letterof the arrow or arrows that represent mitosis. Name the cells W, X and Y. W X Y is a light micrograph of a transverse section through a seminiferous tubule in a mammalian testis. use this sector On the sector indicated on , use label lines and letters to label: G a cell in the germinal epithelium M a maturing sperm cell Y an area where spermatids are found. In all animals so far studied, the production of fully functional sperm is sensitive to temperature. In the nematode worm, Caenorhabditis elegans, spermatogenesis takes place in a similar way to mammals. Two proteins known as argonaute proteins are important in the development of sperm. They are coded for by the genes alg-3 and alg-4. Table 4.1 shows the effect of mutations in one or both of these genes on the fertility of male worms, at temperatures of 20 °C and 25 °C. Fertility was measured as the mean number of offspring produced when the male worms mated with normal females. Table 4.1 male worms mean number of offspring produced at 20 °C at 25 °C normal at both gene loci mutation in alg-3 only mutation in alg-4 only mutations in both alg-3 and alg-4 Describe the effect of increased temperature on the fertility of normal male worms. Compare the effect of increased temperature on the fertility of alg-3 mutant male worms with the effect on fertility of alg-4 mutant male worms. An investigation showed that at 20 °C the number of spermatids produced in worms with both mutations, in alg-3 and alg-4, was the same as in normal worms. However, at 25 °C, these mutant worms produced 29% fewer spermatids than the normal worms. Microscopic examination of their testes showed that many of the secondary spermatocytes had failed to complete meiosis. Use this information to state the letter of one arrow on that represents a stage of spermatogenesis affected by mutations in both the alg-3 and alg-4 genes. Table 4.2 shows the effect of temperature on the percentage of spermatids that developed full motility at 20 °C and 25 °C in normal worms and in worms with mutations in both alg-3 and alg-4. Table 4.2 male worms percentage of sperms with full motility at 20 °C at 25 °C normal mutations in both alg-3 and alg-4 With reference to Table 4.2, and the information in , state the cause or causes of reduced fertility in these mutant worms at each temperature. at 20 °C at 25 °C
9700_w12_qp_41
THEORY
2012
Paper 4, Variant 1
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shows the stages in spermatogenesis in a mammal. A B W X Y E D spermatid C State the letterof the arrow or arrows that represent mitosis. Name the cells W, X and Y. W X Y is a light micrograph of a transverse section through a seminiferous tubule in a mammalian testis. use this sector On the sector indicated on , use label lines and letters to label: G a cell in the germinal epithelium M a maturing sperm cell Y an area where spermatids are found. In all animals so far studied, the production of fully functional sperm is sensitive to temperature. In the nematode worm, Caenorhabditis elegans, spermatogenesis takes place in a similar way to mammals. Two proteins known as argonaute proteins are important in the development of sperm. They are coded for by the genes alg-3 and alg-4. Table 4.1 shows the effect of mutations in one or both of these genes on the fertility of male worms, at temperatures of 20 °C and 25 °C. Fertility was measured as the mean number of offspring produced when the male worms mated with normal females. Table 4.1 male worms mean number of offspring produced at 20 °C at 25 °C normal at both gene loci mutation in alg-3 only mutation in alg-4 only mutations in both alg-3 and alg-4 Describe the effect of increased temperature on the fertility of normal male worms. Compare the effect of increased temperature on the fertility of alg-3 mutant male worms with the effect on fertility of alg-4 mutant male worms. An investigation showed that at 20 °C the number of spermatids produced in worms with both mutations, in alg-3 and alg-4, was the same as in normal worms. However, at 25 °C, these mutant worms produced 29% fewer spermatids than the normal worms. Microscopic examination of their testes showed that many of the secondary spermatocytes had failed to complete meiosis. Use this information to state the letter of one arrow on that represents a stage of spermatogenesis affected by mutations in both the alg-3 and alg-4 genes. Table 4.2 shows the effect of temperature on the percentage of spermatids that developed full motility at 20 °C and 25 °C in normal worms and in worms with mutations in both alg-3 and alg-4. Table 4.2 male worms percentage of sperms with full motility at 20 °C at 25 °C normal mutations in both alg-3 and alg-4 With reference to Table 4.2, and the information in , state the cause or causes of reduced fertility in these mutant worms at each temperature. at 20 °C at 25 °C
9700_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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Questions Discovered
199