Apair of homologous chromosomes at the metaphase stage of meiosis I is shown bel

Question

Apair of homologous chromosomes at the metaphase stage of meiosis I is shown below, with different shading to represent the different chromosomes of the homologous pair, and shaded circles to represent centromeres. These chromosomes carry the gene "A, and the diagram represents chromosomes from an individual that is heterozygous for this gene. Circle the correct answer for each of the questions below to explain the origins of these chromosomes. (5 marks) i) The two different homologous chromosomes (ie. with A or a) originate from two different parents / two different cells in one person / two different species (i) The total number of sister chromatids shown in the diagram above is one/ two I four (ii) The letters A and a indicate two different genes / two different alleles/ a typing error as both should be A (iv) Assuming no crossing over occurred, the two strands that are attached together b a centromere should have DNA sequences that are identical / different/a mixture of different and identical (v) The process involved in making the two attached strands discussed in (iv) is transcription / replication/ mitosis meiosis

Explanation / Answer

Answer i) two different homologous chromosomes originates from two different parents. When meiosis occurs homologous chromosomes pairs from different parents i.e mother and father.

ii)four because one chromosomes have two chromatids.

iii) A and a represents the two different allele as A represent the dominant allele( dominant allele always written in capital letters) while a represents recessive allele ( recessive are denoted by small letter)

iv) identical.. if there no crossing over occurred then there will be no mixing of chromosome then DNA sequence will be identical.

v) meiosis because meiosis is the process in which crossing over occurs in prophase 1 ( meiosis 1)

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