Unit 19 Genetic Inheritance
EI: The inheritance of genes follows patterns.
Genes may be linked or unlinked and are inherited accordingly.
IB Syllabus Statements
Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.
NOS: Making quantitative measurements with replicates to ensure reliability, Mendel’s genetic crosses with peas plants generated numerical data.
Gametes are haploid so contain only one allele of each gene.
Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles
Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
Dominant alleles mask the effect of recessive alleles but codominant alleles have joint effects.
Many genetic diseases have been identified in humans but most are very rare.
Many genetic diseases in human are due to recessive alleles of autosomal genes.
Cause and treatment of phenylketonuria.
Some genetic diseases are sex-linked and some are due to dominant or codominant alleles.
Inheritance of cystic fibrosis and Huntington’s disease.
Inheritance of ABO blood groups.
The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes.
Re-green color blindness and hemophilia as examples of sex-linked inheritance.
Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases
Completion and analysis of Punnett squares for dihybrid traits.
Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.
Use of chi-squared test on data from dihybrid crosses.
The phenotypes of polygenic characteristics tend to show continuous variation.
Polygenic traits such as human height may be influenced by environmental factors.
Making careful observations- careful observations and record keeping turned up anomalous data that Mendel’s law of independent assortment could not account for. Thomas Hunt Morgan developed the notion of linked genes to account for the anomalies.
Looking for patterns, trends and discrepancies- Mendel used observations of the natural world to find and explain patterns and trends, Since then, scientists have looked for discrepancies and asked questions based on further observations to show exceptions to the rules. For example, Morgan discovered non-Mendelian ratios in his experiments with Drosophila.
Morgan’s discovery of non-Mendelian ratios in Drosophila.
Gene loci are said to be linked if on the same chromosome.
Identification of recombinants in crosses involving two linked genes.
"Pea Soup" Mendel Interactive
Mendel and Inheritance Reading
Gregor Mendel: Private Scientist Reading
Cause of Dominant / Recessive Reading
Single Gene Disorders Reading
Genetic Dominance Reading
Test Cross Reading
Huntington's Disease Reading
Fathered by the Mailman Reading
Thomas Hunt Morgan and Sex-Linkage Reading
Chi Square Reading