16.1. Passage of information from parents to offspring
A subsection of Biology, 9700, through 16. Inheritance
Listing 10 of 75 questions
Spermatogenesis, the production of male gametes, occurs in the testes of a human male from the age of puberty. outlines the sequence of events that occur during oogenesis. germinal epithelium process A one spermatogonium process B many spermatogonia process C primary spermatocyte process D secondary spermatocyte process E spermatid process F spermatozoan With reference to , state what is happening to cells during: process B process D process F. Female gametes develop inside follicles. shows a section through a mature (Graafian) follicle in a human ovary. H G J K Table 3.1 below lists a number of statements about the mature follicle. Each statement refers to one of the letters G, H, J and K shown in . Complete the table using the letters G, H, J and K. Table 3.1 statement letter contains protective fluid produces oestrogen has glycoprotein receptors contains 23 chromosomes A man and a woman may be described as infertile if they have failed to conceive a child after 12 months of trying. They may opt for in-vitro fertilisation (IVF) if the woman is producing some normal eggs. Outline the technique of IVF. Not all pregnancies due to IVF treatment result in live births. In the USA in 2008 the figures were: • 85% of these pregnancies result in live births for women under 35 years old • 66% of these pregnancies result in live births for women between 38–40 years old. Suggest reasons for the difference in percentage for the two groups of women.
9700_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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shows two chromosomes in one stage of meiosis. The letters G to M represent the dominant alleles of seven genes and the letters g to m represent the recessive alleles of the same seven genes. G H I J K L M G H I R J K L M g h i j k l m g h i j k l m S S Name the structures labelled R and S on . R S State three features visible on that identify the chromosomes as a homologous pair. shows the same two chromosomes a little later in the same stage of meiosis. Crossing over is beginning to occur at point T. G H I J K L M G H I T J K L M g h i j k l m g h i j k l m shows an outline of the same two chromosomes after crossing over has occurred. Complete by writing in the letters of the alleles along both chromosomes. Take care to clearly show the difference between letters representing dominant alleles and letters representing recessive alleles. State the stage in meiosis in which crossing over occurs. Crossing over results in genetic variation. Explain how random assortment of homologous chromosomes also results in genetic variation.
9700_m21_qp_42
THEORY
2021
Paper 4, Variant 2
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Meiosis is an important process that contributes to genetic variation in a population. shows a pair of homologous chromosomes during prophase I of meiosis. On , use the letter C with a label line to identify where crossing over occurs. Describe how crossing over produces genetic variation in a population. Wing pattern in the butterfly species Heliconius melpomene is controlled by genes on autosomal chromosomes. The gene for banding pattern on the upper wing has two alleles: • a dominant allele coding for a full band • a recessive allele coding for a broken band. The gene for ray pattern on the lower wing has two alleles: • a dominant allele coding for rays • a recessive allele coding for no rays. Scientists crossed a butterfly that was homozygous dominant for both genes with a butterfly that was homozygous recessive for both genes. The scientists wanted to check whether the phenotypic ratio for offspring in the F2 generation agreed with the expected phenotypic ratio of 9 : 3 : 3 : 1. The results of this genetic cross are shown in . × rays parental generation F1 generation F2 generation number of offspring of each phenotype full band no rays broken band Explain the term F1 generation. The scientists used the chi-squared ( χ 2) test to compare their data to the expected phenotypic ratio of 9 : 3 : 3 : 1. The formula for the chi-squared test is shown in . χ 2 = ! (O – E)2 E key to symbols O = observed value E = expected value Complete Table 4.1 and use the chi-squared formula in to calculate the χ 2 value for these data. Table 4.1 phenotype expected ratio O E O – E (O – E)2 (O – E)2 E full band and rays 76.5 22.5 506.25 6.62 full band and no rays 25.5 – 4.5 20.25 0.79 broken band and rays broken band and no rays 8.5 – 0.5 0.25 0.03 χ 2 = The critical value at the 0.05 probability level and three degrees of freedom is 7.81. Using the result of your calculation in , explain whether the results of the study agree with the expected ratio of phenotypes for the F2 generation. Suggest two reasons why phenotypic ratios in the F2 generation do not always match the expected ratios.
9700_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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Outline the technique of in-vitro fertilisation (IVF). For IVF to be successful, a sperm must have an undamaged plasma (cell surface) membrane, an intact acrosome (a sperm’s large lysosome) and be capable of producing ATP for movement. One method of assessing the quality of a sample of sperm is to mix it with three chemical probes that bind to specific components of the sperm. The probes fluoresce when the sperm are examined with a microscope using ultra-violet (Ulight, allowing their uptake to be determined. The three probes fluoresce with different colours. • Probe 1 combines with DNA and fluoresces red, but can enter a sperm only when its plasma membrane is damaged. • Probe 2 combines with sugars in the acrosome and fluoresces yellow, but can enter the acrosome only when the acrosome membrane is damaged. • Probe 3 combines with mitochondria and fluoresces bright green in sperm with active mitochondria and less brightly when the mitochondria are less active. A sample of sperm was mixed with all three probes and examined using UV light. Complete Table 3.1 by placing ticks (3) in the appropriate boxes to describe the appearance of sperm that would be suitable for use in IVF. Table 3.1 appearance of sperm suitable for use in IVF target of probe red yellow green colourless DNA acrosome mitochondria The technique of intracytoplasmic sperm injection (ICSinvolves injecting a single, chosen sperm into an oocyte. This technique is often used when standard IVF has failed. Researchers in Hawaii think that the acrosome of the sperm should be removed before the sperm is injected into the oocyte. Suggest one reason why it might improve the success rate of ICSI to remove the acrosome before injecting a sperm into an oocyte.
9700_s11_qp_41
THEORY
2011
Paper 4, Variant 1
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The cells in are from the same organism and look the same. The cells in have been produced by mitosis and the cells in have been produced by meiosis. Complete the table to show two differences between cells that have been produced by mitosis compared to cells that have been produced by meiosis. mitosis meiosis Explain why the organism produces cells by meiosis. is a transmission electron micrograph of a dividing cancer cell. X Y magnification x 3000 Calculate the actual width of the cell shown in at X-Y. Show your working and give your answer to the nearest micrometre (μm). answer μm The cancer cell shown in has more mitochondria and rough endoplasmic reticula (RER) compared to the non-cancerous cell from which it originated. Suggest why this is so.
9700_s13_qp_22
THEORY
2013
Paper 2, Variant 2
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Questions Discovered
75