3.4: Inheritance

Essential idea: The inheritance of genes follows patterns.

NoS: Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data. (3.2)

U1: Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.

Exercise 1: Watch these two videos and connect-extend-challenge.

In addition, work through examples of inheritance given in the video using a punnett grid.

U5: Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

A1: Inheritance of ABO blood groups. 

Guidance: The expected notation for ABO blood group alleles is:

  Phenotype 

    O 

    A 

    B 

    AB

  Genotype 

    ii 

    |A| A or | Ai 

    |B| B or | Bi 

    |A| B

U7: Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes.

A2: Red-green colour blindness and hemophilia as examples of sex-linked inheritance. Guidance: Alleles carried on X chromosomes should be shown as superscript letters on an upper case X, such as Xh.

U6: Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles.

U8: Many genetic diseases have been identified in humans but most are very rare.

A3: Inheritance of cystic fibrosis and Huntington’s disease.

S1: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.

S2: Comparison of predicted and actual outcomes of genetic crosses using real data.

Exercise 7: Work through these problems.