Examining Frequency Data 5.4

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Content Descriptor: Model the formation of new combination of genotypes produced during meiosis, including but not limited to:

Interpreting examples of autosomal, sex-linkage, co-dominance, incomplete dominance and multiple alleles: (5.4.1)

Discrete genes: Distinct differences between gene expression such as blood type Continuous genes: Spectrum of gene expression such as skin colour

Autosomal recessive:

  • Malesand females affected equally
  • Canappear to skip generations

Examples include cystic fibrosis, sickle cell anaemia 

- Autosomal dominant:

  • Malesand females affected equally
  • Allaffected individuals have affected parents
  • Example includes Huntington’s diseaseSex (X) linked recessive:
  • Malesaffected more frequently
  • Appearsto be passed from grandfather to grandchild
  • Affectedfemale’s sons will all be affected
  • HaemophiliaSex (X) linked dominant:
  • Malesand females affected equally
  • Allaffected individuals have affected parents
  • Affectedfather’s daughters will all be affected
  • Rett syndromeIncomplete dominance:
  • Multiple alleles which appears as a blend of two other alleles. Neither allele is expressed overthe other, rather they are blended together, e.g curly, straight and wavy 

- Co-dominance:

  • Newphenotype produced as both of the genes are expressed, e.g blood type in 



Constructing and interpreting information and data from pedigrees and Punnett squares: (5.4.2)







A pedigree should:

  • Labelthe generation from the top down using roman numerals
  • Label the individuals left to right using Arabic numerals. As much as possible, the leftmostindividual is the oldest, while the rightmost is the youngest. This may not always be possible due to large scale pedigrees, however where siblings and partners are concerned from a single descendent, this should be followed
  • Usea key as shown above

Content Descriptor: Collect, record and present data to represent frequencies of some characteristics in order to identify trends, patterns, relationships and limitation in data, for example:

Examining frequency data: (5.4.3)

Sickle cell anaemia:


Group of diseases which affect haemoglobin, the molecule which carries and delivers oxygen to cells. The disorder causes abnormal structure of haemoglobin, distorting red blood cells into a sickle shape. Those with a single copy of the gene typically live normal lives without health problems resulting from the condition.

It currently affects approximately 100,000 Americans. It is most common among those of African ancestry, occurring in 1/500 African Americans and 1/1000 Hispanic Americans. The sickle cell gene is carried by 1/12 African Americans and occurs in about 1/365 births

The pattern of data shows incidence higher for those of African descent. This is suspected to be because a single sickle cell gene offers slight resistant to malaria, conferring an evolutionary advantage where malaria is particularly common.

Analysing single nucleotide polymorphism (SNP): (5.4.4)

A SNP is a variation in a single base pair occurring at a specific locus on the genome. They are the most common type of genetic variation; must occur in at least 1% of the population. They usually occur during DNA replication. Since SNPs may be inherited from parents, they can be used to track family disease and family history.

  • SNPSoccur in 1/300 bases
  • Approximately 10 million SNPS in the genomeEffects:
  • Ifoccurring at introns they do not lead to phenotypically expressed changes.
  • However,if occurring in exons, they can cause issues in health.
  • SomeSNPs have been shown to lower risk from Alzheimer’s or prostate cancer

Inquiry Question Review: How can the genetic similarities and differences within and between species be compared? (5.4.5)

You should be able to:

  • Describea method to model meiosis
  • Understandthe implications of different types of inheritance and gene expression
  • Beable to interpret pedigrees and Punnet squares
  • UnderstandSNPs