Based on the human karyotype in Diagram
(a) (i) State the total chromosome number in a somatic cell for individual M and individual N. [1 m]
(ii) State one difference between individual M and N .[1m]
(b) (i) S and T represent the gametes produced through process P.
Complete Diagram to show the number and type of chromosomes inherited by gamete S and T.[2 marks]
(ii) Based on your answer in (b) (i), explain the process P.[2 marks]
(c) Based on your biological knowledge, describe how the karyotype for individual M is formed. [4m]
(d) Explain the type of variation shown by individual M and N. [2m]
Suggested Answer:
(a)(i)Individual M - 47 , Individual N - 46
(ii) D1: M – Syndrome Down whereas N is normal
D2: M – male / XY sex chromosomes whereas N is a female / XX sex chromosomes
D3: M – There are three chromosomes number 21 whereas in N - there are two chromosomes number 21
(b)(i)
Gamete S : 22 + X
Gamete T : 22 + X
(ii)
F: Process P is meiosis
P: Each pair of homologous chromosomes are separated into different daughter cells
(c)P1: At metaphase 1 of meiosis, the homologous pairs of chromosomes are arranged on the metaphase plate ( at random )
P2: Each homologous pair separated and move to the opposite pole except chromosome number 21.
P3: Both chromosomes number 21 move to one pole
P4: One of the gamete contain 24 chromosomes and the other one gamete contain 22 chromosomes.
P5: The gamete which contain 24 chromosomes been fertilized by normal gamete / gamete which contain 23 chromosomes.
(d) F : Discontinuous variation
P : Effects of genetic factors // There is no gradual change between the two extreme / no intermediates. // not influenced by environmental conditions
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