16.1. Passage of information from parents to offspring
A subsection of Biology, 9700, through 16. Inheritance
Listing 10 of 75 questions
The slime mould, Dictyostelium discoideum, is a eukaryote and a decomposer of protein-rich material. shows the life cycle of D. discoideum. X Y spores spores amoeboid cells fusion of amoeboid cells aggregation of amoeboid cells State the type of nuclear division that occurs at X and at Y. X Y State what is meant by the term reduction division and explain why this division is necessary in a life cycle, such as that shown in . The amoeboid cells of D. discoideum feed on protein-rich material and break it down to form ammonium ions (NH4 +). The cell membranes of D. discoideum have transporter proteins that are responsible for the excretion of ammonium ions. Describe what happens to the ammonium ions excreted by D. discoideum into the soil. Suggest why a transporter protein is required for the removal of ammonium ions from D. discoideum.
9700_s12_qp_21
THEORY
2012
Paper 2, Variant 1
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Occasionally during meiosis, homologous chromosomes fail to separate at anaphase. This is known as non-disjunction. Turner’s syndrome is the most common chromosome mutation in human females. It can occur due to non-disjunction in meiosis during gametogenesis. Some resulting gametes will be missing an X chromosome. Some forms of Turner’s syndrome occur when one of the pair of X chromosomes is not missing but has become damaged. The damaged X chromosome may have been broken and re-formed so that part of its structure is lost. is a diagram of a normal X chromosome and two forms of ‘damaged’ X chromosomes, X1 and X2. • In X1, a section of the ‘p’ arm of the chromosome is missing. This deletion leads to reduced height of the female and abnormalities such as narrowing of the aorta. • In X2, a section of the ‘q’ arm of the chromosome is missing. This deletion leads to little or no development of the ovaries. K p q normal X X1 X2 p q p q Name structure K. Explain why X1 and X2 result in different phenotypes. Mothers with the X1 form of Turner’s syndrome can pass on the chromosome mutation to their daughters but not to their sons. Complete the genetic diagram below to show how the chromosome mutation X1 may be passed on to daughters from a mother with Turner’s syndrome. parental female with normal male phenotypes Turner’s syndrome parental genotypes XX1 gametes genotypes of daughters phenotypes of daughters
9700_s14_qp_41
THEORY
2014
Paper 4, Variant 1
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Occasionally during meiosis, homologous chromosomes fail to separate at anaphase. This is known as non-disjunction. Turner’s syndrome is the most common chromosome mutation in human females. It can occur due to non-disjunction in meiosis during gametogenesis. Some resulting gametes will be missing an X chromosome. Some forms of Turner’s syndrome occur when one of the pair of X chromosomes is not missing but has become damaged. The damaged X chromosome may have been broken and re-formed so that part of its structure is lost. is a diagram of a normal X chromosome and two forms of ‘damaged’ X chromosomes, X1 and X2. • In X1, a section of the ‘p’ arm of the chromosome is missing. This deletion leads to reduced height of the female and abnormalities such as narrowing of the aorta. • In X2, a section of the ‘q’ arm of the chromosome is missing. This deletion leads to little or no development of the ovaries. K p q normal X X1 X2 p q p q Name structure K. Explain why X1 and X2 result in different phenotypes. Mothers with the X1 form of Turner’s syndrome can pass on the chromosome mutation to their daughters but not to their sons. Complete the genetic diagram below to show how the chromosome mutation X1 may be passed on to daughters from a mother with Turner’s syndrome. parental female with normal male phenotypes Turner’s syndrome parental genotypes XX1 gametes genotypes of daughters phenotypes of daughters
9700_s14_qp_43
THEORY
2014
Paper 4, Variant 3
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Intracytoplasmic sperm injection (ICSis a modification of the procedure for in-vitro fertilisation (IVF). A single sperm is injected into an oocyte rather than allowing one of many sperm to fertilise the oocyte. Suggest one problem that may arise from the use of ICSI. In preparation for ICSI, infertile women are injected at daily intervals with human follicle stimulating hormone (hFSH) to stimulate the growth and maturation of a number of ovarian follicles. Women may be treated with hFSH extracted from urine (u-hFSH) or with recombinant hFSH (r-hFSH) produced by genetically modified mammalian cells. Each molecule of hFSH consists of two different polypeptide chains, α and β. The genes for the α and β chains of hFSH, together with their promoters, have been inserted into mammalian ovary cells. Explain why promoters need to be transferred with desired genes when producing a genetically modified cell. After treatment with hFSH, oocytes are collected from mature ovarian follicles and examined to check that they have reached metaphase II of meiosis. Describe how an oocyte in metaphase I of meiosis can be distinguished from one in metaphase II of meiosis. You may use labelled diagrams to illustrate your answer. Two groups of women who were being prepared for ICSI were injected at daily intervals with either r-hFSH or with u-hFSH. The results of their treatment are shown in Table 2.1. Table 2.1 group of women receiving r-hFSH group of women receiving u-hFSH number of women total number of oocytes collected number of oocytes in metaphase II of meiosis With reference to Table 2.1, compare the effects of treatment with r-hFSH and u-hFSH and suggest an explanation for any differences. Whilst the two groups of women described in were being injected at daily intervals with FSH, the concentrations of oestrogen in their blood were measured. The results are shown in . days of FSH injection mean concentration of oestrogen / n mol dm–3 women injected with r-hFSH women injected with u-hFSH With reference to , compare the results for the two groups of women. Describe the role of oestrogen in the preparation of these women to receive an embryo.
9700_s15_qp_42
THEORY
2015
Paper 4, Variant 2
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Malaria is a serious and often fatal disease that is transmitted by the mosquito Anopheles gambiae. One method of reducing the incidence of malaria is to control the numbers of these mosquitoes. In mosquitoes, as in humans, males have an X chromosome and a Y chromosome, while females have two X chromosomes. Researchers investigated the possibility of producing genetically modified (GM), fertile male mosquitoes in which most of the sperm contained a Y chromosome and not an X chromosome. They predicted that introducing these males into a population of A. gambiae could greatly reduce the number of females in each generation and therefore reduce the numbers of eggs laid. In order to produce the GM males, the researchers inserted the gene coding for a restriction endonuclease called I-PpoI. This restriction endonuclease was known to destroy the X chromosome of A. gambiae. Explain the meaning of the term restriction endonuclease and suggest why I-PpoI destroys the X chromosome, but not the Y chromosome. The researchers introduced the gene for I-PpoI and also a gene for green fluorescent protein (GFP) into one of the autosomes (a chromosome other than X or Y) of male mosquitoes. Explain why the researchers introduced the gene for GFP, as well as the gene for I-Ppol. The researchers found that I-Ppol destroyed the X chromosome during meiosis in the GM male mosquitoes. This prevented these males from producing sperm containing an X chromosome. However, I-PpoI was still active in zygotes produced by the fusion of female gametes with sperm containing a Y chromosome. Explain why this meant that the GM males produced no offspring at all. The researchers modified the gene for I-Ppol, so that it produced a version of I-PpoI that was active only during meiosis in the males, and was not active in the zygote. They then tested the effect of introducing these GM males into a mosquito population. • Several cages were set up. 50 adult male mosquitoes and 50 adult female mosquitoes without the I-Ppol gene were placed in each cage. • 150 adult GM males were introduced into each cage. In half of the cages (A), these GM males had the normal gene for I-Ppol. In the rest of the cages (B), the GM males had the modified gene for I-Ppol. • The mean number of adult female offspring per cage was determined over the next six generations. shows the results. mean number of adult females generation GM males introduced % $ Describe and suggest explanations for the differences between the mean numbers of adult females in the two sets of cages during the experiment. Suggest possible difficulties that might arise if the technique of releasing GM male mosquitoes with the modified I-Ppol gene were used to try to control populations of A. gambiae that occur naturally in the wild.
9700_s16_qp_42
THEORY
2016
Paper 4, Variant 2
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Questions Discovered
75