Essential Idea: the Inheritance of Genes Follows Patterns

Topic 3: Genetics + Topic 10: Genetics

3.4 Inheritance

Essential Idea: The inheritance of genes follows patterns.

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

U2 Gametes are haploid so contain only one allele of each gene.

U3 The alleles of each gene separate into different haploid daughter nuclei during meiosis.

U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.

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

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

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

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

U9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.

A1 Inheritance of ABO blood groups.

A2 Re-green color blindness and hemophilia as examples of sex-linked inheritance.

A3 Inheritance of cystic fibrosis and Huntington’s disease.

A4 Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.

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.

S3 Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.

NOS 1 Making quantitative measurements with replicates to ensure reliability, Mendel’s genetic crosses with peas plants generated numerical data.

10.2 Inheritance

Essential Idea: Genes may be linked or unlinked and are inherited accordingly.

U1 Gene loci are said to be linked if on the same chromosome.

U2 Unlinked genes segregate independently as a result of meiosis.

U3 Variations can be discrete or continuous.

U4 The phenotypes of polygenic characteristics tend to show continuous variation.

U5 Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant.

A1 Morgans’s discovery of non-Mendellian ratios in Drosophilia.

A2 Completion and analysis of Punnett squares for dihybrid traits.

A3 Polygenic traits such as human height may be influenced by environmental factors.

S1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.

S2 Identification of recombinants in crosses involving two linked genes.

S3 Use of chi-squared test on data from dihybrid crosses.

NOS1 Looking for patterns, trends and discrepancies- Mendel used observations of the natural world to find and explain patterns and tends, 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-Mendellian ratios in his experiments with Drosophilia.

3.5 Genetic Modification and Biotechnology

Essential Idea: Biologists have developed techniques for artificial manipulation of DNA, cells and organisms.

U1 Gel electrophoresis is used to separate proteins or fragments of DNA according to size.

U2 PCR can be used to amplify small amounts of DNA.

U3 DNA profiling involves comparison of DNA.

U4 Genetic modification is carried out by gene transfer between species.

U5 Clones are groups of genetically identical organisms, derived from a single original parent cell.

U6 Many plants species and some animal species have natural methods of cloning.

U7 Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells.

U8 Methods have been developed for cloning adult animals using differentiated cells.

A1 Use of DNA profiling in paternity and forensic investigations.

A2 Gene transfer in bacteria using plasmids makes use of restriction endonucleases and DNA ligases.

A3 Assessment of potential risks and benefits associated with genetic modification of crops.

A4 Production of clones embryos produced by somatic-cell nuclear transfer.

S1 Design of an experiment to assess one factor affecting the rooting of stem-cuttings.

S2 Analysis of examples of DNA profiles.

S3 Analysis of data on risks to monarch butterflies of Bt crops.

NOS1 Assessing risks associated with scientific

3.4+ 10.2 Inheritance

Please review p. 168-186/445-454 in the Oxford IB Text, p. 154-77 in the Campbell text and p. 115-128/358-368 in your Biozone.

1. Review key vocabulary:
2. Genotype:

1. Phenotype:

1. Dominant allele:

1. Recessive allele:

1. Co-dominant alleles:

1. Homozygous:

1. Heterozygous:

1. Carrier:

1. Pure-breeding:

1. Sex-chromosomes:

1. Sex-linkage:

1. Mutation Rate: What causes them and how often do they happen?

1. Gene-linkage: Include how linked genes segregate at meiosis

1. Recombinants: Include how recombinants can be identified.

1. Polygenic characteristics:

1. Review the Chi-squared test: How is it used in genetic problems?

1. State the null hypothesis

1. Genetic Crosses: Use Punnett squares to solve the following monohybrid or dihybrid crosses.
2. In angelfish, red is dominant and green recessive. A homozygous dominant male is crossed with a heterozygous female. What is the ratio of the genotypes in the offspring?

1. In squirrels, grey is dominant and brown recessive. A homozygous recessive female is crossed with a heterozygous male. Deduce how many of their offspring will be brown?

1. A pair of angelfish produces 400 offspring in one mating. 300 of them are red and 100 are green.
2. What is the genotype and phenotype of the parents?

1. Another pair of angel fish produces 400 offspring. 198 of them are green and 202 of them are red.
2. What is the ratio of phenotypes?

1. What is the genotype and phenotype of the parents?

1. Assume that a certain type of squirrel could have up to 80 offspring in one batch. If 21 of 80 babies are brown, that what is the ratio of phenotype of offspring.
2. Predict the genotype and phenotype of the parents.

1. You buy a red-bellied newt from a local pet store. You know that red-bellied (R) is dominant to yellow-bellied (r). If you don’t know what the parents of your red-bellied newt look like, what can you do to determine the genotype of your pet?
2. Name the procedure – it is used when trying to determine the genotype of an individual with a dominant phenotype but unknown genotype.

1. Show the 2 possible crosses, and provide the phenotypic ratios that will result from these crosses.

Di-hybrid question

In squirrels, a bushy tail is dominant and a skinny tail is recessive. A pure gray, pure bushy tailed squirrel is crossed with a pure brown, pure skinny tailed squirrel. Predict the ratio of phenotypes in the offspring. Make a Punnett Square to prove it.

Genotype / Phenotype or blood group
IAIA / A
IAi / A
IBIB / B
IBi / B
IAIB / AB
ii / O

1. One example of co-dominance is the ABO system of classifying human blood groups. There are IA, IB and i and each person has only two of the three alleles. Mary is blood group A and her husband is blood group B. Their daughter Sally is blood group O. Determine the genotypes of Mary and Ivan.

1. Analysis of pedigree chart: Study the following pedigree chart. How is this disorder inherited? Write in the genotypes for each individual.

3.5 Genetic Modification and Biotechnology

Please review p. 105-110/344-347 in the Oxford IB Text, p. 209/218-219/232-241 in the Campbell text and p. 129-155 in your Biozone.

1. What is DNA profiling? Describe the stages used to make a DNA profile.
2. Sample collection:

1. DNA extraction and amplification: Include which sections of DNA are used.

1. DNA cutting:

1. Electrophoresis:

1. Band staining:

1. How do the bands appear during electrophoresis

1. What is genetic modification?

1. Describe gene transfer using plasmids (include info on the use of restriction endonucleases and DNA ligases)- Such as when human insulin is produced.

1. What is a clone? How are plants and animals cloned?