exam questions

• Explain what is meant by the term sex linked disorder (2)

  -       Faulty/mutated gene is found on only one sex chromosome Y or X

  -       Therefore, more likely to be inherited by one gender
• Explain why some genes show linkage and others show sex linkage (3)

  -       There are more genes than there is chromosome 

  -       Linkage relates to genes located on the same (non-sex) chromosome 

  -       Sex linkage relates to genes on the sex chromosomes
• Explain how crossing over may differ in sex chromosomes (2)

  -       Crossovers cannot form between some sections of the X and Y chromosomes 

  -       As the Y chromosome is shorter so there are alleles on X which aren’t on Y
• Describe how each gamete receives only one allele of each gene (3)

  -       In meiosis homologous chromosomes are separated for one another 

  -       Sister chromatids, containing copies of the same alleles, are also separated from one another 

  -       Spindle fibres pull the chromosomes to opposite poles of the cell

   
• Explain why genes found on the sex chromosome pair have a pattern of inheritance that is different from genes found on other chromosome pairs (2)

  -       Because X chromosomes carry genes which are not present on the Y chromosome 

  -       Males have only one copy of some genes (as they have no Y chromosome)

  -       If only one allele is inherited it will be expressed.