Inheritance and variation

31 Which row shows possible effects of natural selection? natural selection can cause mutations to occur natural selection can lead to the extinction of a species A no no B no yes C yes no D yes yes

© UCLES 2025 5090/11/O/N/25 [Turn over 32 All organisms in the same species show variation. Some features of different types of variation are listed. 1 an example is body mass 2 has a limited number of possible forms with no intermediates 3 has any value from a minimum to a maximum 4 is unaffected by the environment 5 is usually caused by genes only Which statements refer to discontinuous variation? A 1, 3 and 5 B 1 and 3 only C 2, 4 and 5 D 2 and 4 only 16

34 What could be an advantage of genetically modifying crop plants? A increased biodiversity in an area B increased chance that the inserted genes will transfer to wild species C increased nutritional content of crop plants D increased use of pesticides

30 Which examples show continuous variation? 1 length of seedlings 2 mass of bananas 3 human skin colour A 1, 2 and 3 B 1 and 3 only C 1 only D 2 and 3 only

© UCLES 2025 5090/12/O/N/25 [Turn over 31 A man has six fingers on each hand and six toes on each foot. This genetically inherited condition is caused by a dominant allele. The man’s genotype is heterozygous. His wife does not have the condition. What is the probability that a child of this couple will be born with the condition? A 0.00 B 0.25 C 0.50 D 1.00 12

32 The diagram shows a family tree for the inheritance of eye colour. The allele for brown eyes is dominant and the allele for blue eyes is recessive. 1 2 3 5 4 7 6 key male with brown eyes male with blue eyes female with brown eyes female with blue eyes Which people must be heterozygous for eye colour? A 1, 3 and 7 B 2 and 6 C 3, 4 and 5 D 4 and 5 only

© UCLES 2025 5090/12/O/N/25 33 A karyotype is a photograph showing the chromosomes of an individual. 1 6 7 8 9 10 11 12 13 14 15 19 20 21 22 X Y 16 17 18 2 3 4 5 Which description matches an individual who has this karyotype? A female without Down’s syndrome B male without Down’s syndrome C female with Down’s syndrome D male with Down’s syndrome 13