4.3 Theoretical Genetics February 2015 Adapted from: Taylor, S. (2010). Theoretical Genetics (Presentation). Science Video Resources. [Online] Wordpress. Retrieved from biology.net/ibdpbio/04-genetics-and-genetic-engineering/theoretical-genetics/

How are chacteristics passed on from generation to generation? Mendel has the answer

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Gregor Mendel Born 1822 Began his work at age 21 A monk and school teacher interested in plant breeding Studied pea plants Discovered the basic principles of heredity

Study the video: How Mendel's pea plants helped us understand genetics

Genotype: the alleles of an organism. Phenotype: the characteristics of an organism. Allele for yellow color in seed Allele for green color in seed

Phenotype vs. Genotype

F2 (2nd generation) Proportions Genotypes: 25% YY 50% Yy 25% yy Phenotypes: 75% Yellow 25% Green Skill: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.

Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects. Dominant/ recessive: A (dominant) and a (recessive) – Sex-linked alleles: X H and X h Co-dominant alleles: C w and C r

Application: Inheritance of ABO blood groups

Sex Linkage Sex-linked traits are those which are carried on the X-chromosome in the non- homologous region. Sex-linked genetic disorders: -Haemophilia -Colour blindness Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes chromosome-ii-what-is-even-on-it/

Inheritance of colour blindness The gene loci is on the non- homologous region of the X. Colour blindness is more common in males. Males always inherit the colourblind allele from their mothers. Males cannot pass on colourblindness to their sons. Application: Red-green colour blindness and hemophilia as examples of sexlinked inheritance.

Inheritance of Haemophilia Persons suffering from haemophilia are unable to produce clotting factor. The gene is on the non- homologous region of the x- chromosome. Haemophilia is more common in men. Males inherit the allele from their mother. Application: Red-green colour blindness and hemophilia as examples of sexlinked inheritance.

Carrier are individuals that are heterozygous for the allele: they have dominant and recessive (disease) allele.

The chart show the typical symbol found in a pedigree chart. – Circles are female. – Squares are male. – Black means that the individual is affected by the condition. – White indicates that the individual is unaffected by the condition. Mating: Female 1 and male 2 (Horizontal line) Children: Female (3) and male (4) are the children of (1) and (2). Individuals (6) and (7) are the paternal grandchildren of (1) and (2). Skill: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.