exam qs (gene expression)

• give the meaning of the term polygenic

  characteristic showing continuous variation

  caused by multiple genes at different loci
• There are 575 identified mutations to the F9 gene that cause severe symptoms of haemophilia.

  The same percentage of these types of mutation is found in the F8 gene.

  Calculate the number of mutations to the F8 gene that produce severe symptoms. 2931 mutations for F8 gene, 1133 mutations to F9 gene

  575/1133 x100 = 50.75%

  2931 x 0.51 = 1495
• Explain how epigenetic changes affect the development of tissues in the embryo.

  DNA is wrapped around histones

  acetylation of the histone affects binding of RNA polymerase

  methylation of DNA affects transcription of genes

  therefore gene expression is altered
• Describe how cells become specialised.

  chemical signals cause some gene to be switched on

  only activated genes are transcribed

  mRNA leads to synthesis of specific proteins which cause cell modification
• Stem cells can be used to repair damaged organs.

  Part of the eye contains stem cells. These cells can be used to repair damaged corneas in

  the eye.

  (i) Explain why stem cells from the heart cannot be used to grow cells to repair the cornea.

  these cells are not totipotent

  therefore some genes have already been activated and deactivated

  therefore will not be able to specialise into cornea cells
• (ii) Explain why chemicals from the eye are needed to produce corneal cells from a suitable source of stem cells.

  chemicals cause some genes to be switched on

  these genes are transcribed producing specific mRNA

  specific mRNA is translated into specific proteins

  these proteins cause the cell to develop into a corneal cell
• (i) Explain what is meant by the term sex-linked disorder.

  a disorder caused by a mutated gene

  located on the X chromosome

  therefore the disorder is more likely in one gender than another
• duchenne muscular dystrophy (DMD) is a sex-linked disorder

  (ii) explain why the genotype frequency for males with DMD cannot be calculated using this hardy-weinberg equation

  males only have one allele for this gene

  males cannot be heterozygous

  the hardy-weinberg equation assumes all individuals have two alleles for the gene
• epigenetic changes can cause monozygotic twins to have different body masses

  explain how epigenetic changes can cause differences in a characteristic

  DNA methylation

  affects activation of genes

  affecting metabolism
• as pluripotent stem cells divide, epigenetic changes are passed on

  explain how epigenetic changes affect the activation of genes in daughter cells

  genes activated in stem cells

  because of methylation of DNA

  therefore the same genes will be activated in the daughter cells
• explain why an individual may have a greater adult height than their biological parents

  height affected by the environment as well as genotype

  height is an example of polygenic inheritance

  therefore offspring can inherit a mixture of alleles from both parents (that increase height)

  higher protein diet/more calcium in diet/better healthcare can affect height