D3.2  Inheritance

Theme:  Continuity and Change

There are predictable patterns of inheritance of traits through lineages.

• During meiosis, the two allele of a gene separate so that each gamete carries only one. This allows for the diploid state to be restored at fertilization, preserving the species' chromosome number over generations.
• In a monohybrid cross, the 3:1 ratio in the F2 generation demonstrates that recessive alleles continue through the generations unchanged in their sequence.
• There are two copies of every autosome, ensuring a backup system. Even if one parent provides a non-functional allele, the continuity of the trait's function is often maintained by the dominant allele from the other parent.
• In plants, self-pollination of homozygous individuals results in offspring that express the same phenotype as the parent, preserving a specific set of traits without any change over time.
• If a parent has alleles for two different traits on the same chromosome, those traits are likely to stay together in the offspring. This maintains the "package" of traits that worked for the parent, preserving successful combinations across generations. 

While the process of inheritance is continuous, the outcome is often change with different combinations of alleles and new genetic variations resulting in diversity within a population.

• The random combination of paternal and maternal alleles during fertilization ensures that offspring possess a unique genotype, which can result in a change in expressed phenotypes.
• There is more variation possibilities when a gene has more than two alleles. The interaction between three ABO blood type alleles results in four possible blood types.
• Because some genes are located on the X-chromosome but missing from the Y-chromosome, the pattern of inheritance changes based on biological sex, leading to different phenotypic frequencies in males and females.
• Linked genes can be separated from each other due to crossing over during meiosis.  This results in recombinant chromosomes, representing a distinct genetic change from the previous generation.
  

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• What patterns of inheritance exist in plants and animals?
• What is the molecular basis of inheritance patterns?​

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What are the principles of effective sampling in biological research?
• What biological processes involve doubling and halving? 

Key Terms to Know: * higher level only

1:1:1:1 Ratio (of Dihybrid Cross)*
9:3:3:1 Ratio (of Dihybrid Cross)*
ABO Blood Groups
Allele
Alternative Hypothesis*
Autosome
Biological Law*
Box-and-Whisker Plot
Central Tendency
Chi-Square Test*
Codominance
Continuous Variation
Crop Plant
Deductive Reasoning
Dihybrid Cross*
Diploid
Discrete Variation
Dominant Allele
Eukaryote
Expected Results*
F1 Generation
F2 Generation
Female Gamete
First Quartile
Four O'Clock Flower
Gamete
Gene
Gene Expression
Gene Linkage*
Gene Pool
Genetic Cross

Genotype
Haemophilia
Haploid
Heterozygous
Homologous Chromosome*
Homozygous
Incomplete Dominance
Independent Assortment*
Inductive Reasoning
Inheritance
Loci*
Male Gamete
Marvel of Peru Flower
Maximum (of Data Set)
Mean
Median
Meiosis*
Mendel'S Second Law*
Minimum (of Data Set)
Mode
Multiple Alleles
Mutation
Null Hypothesis*
Observed Results*
Ornamental Plant
Outlier
Ovary (Plant)
P Generation
P=0.05*
Pedigree Chart
Phenotype

Phenotype Plasticity
Phenylalanine
Phenylketonuria (PKU)
Pollen
Pollination
Polygenic Inheritance
Population*
Punnett Grid
Recessive Allele
Recessive Disease
Recombinant Gamete*
Recombinant Genotype*
Recombinant Phenotype*
Repeated Measures*
Sample*
Segregation of Alleles*
Self-Fertilization
Self-Pollination
Sex Chromosome
Sex Determination
Sex-Linked
Sexual Lifecycle
Single-Nucleotide Polymorphism
Sperm
Statistical Significance*
Third Quartile
Tyrosine
Unlinked Genes*
X Chromosome
Y Chromosome
Zygote

D3.2.1-- Production of haploid gametes in parents and their fusion to form a diploid zygote as the means of inheritance.

• Define gamete and zygote.
• Define diploid and haploid.
• Explain why diploid cells have two copies of each autosomal gene.​

D3.2.2— Methods for conducting genetic crosses in flowering plants.

• Define P, F1 and F2.
• Outline the process of experimentally performing a genetic cross in flowering plants using cross pollination and self-fertilization. 
• State an application of performing genetic crosses in plants. 
• Determine possible alleles present in gametes given parent genotypes.
• Construct Punnett grids for single gene crosses to predict the offspring genotype and phenotype ratios.

D3.2.3-- Genotype as the combination of alleles inherited by an organism.

• Distinguish between gene and allele. 
• Compare and contrast different alleles of the same gene.
• Define homozygous and heterozygous.

D3.2.4-- Phenotype as the observable traits of an organism resulting from genotype and environmental factors.

• Distinguish between genotype and phenotype.
• State a phenotype in humans that is due to genotype only.
• State a phenotype in humans that is due to the environment only.
• State a phenotype in humans that is due to the interaction of genotype and the environment. ​

D3.2.5— Effects of dominant and recessive alleles on phenotype.

• Define dominant allele and recessive allele.
• Explain the usual cause of one allele being dominant over another. ​

D3.2.6- Phenotypic plasticity as the capacity to develop traits suited to the environment experienced by an organism, by varying patterns of gene expression.

• ​Define phenotypic plasticity.
• Outline an example of phenotypic plasticity.

 ​​​​D3.2.7- Phenylketonuria as an example of a human disease due to a recessive allele.

• Define “carrier” as related to genetic diseases.
• Explain why genetic diseases usually appear unexpectedly in a population.
• Outline the genetic cause of phenylketonuria.
• List consequences of phenylketonuria if untreated.
• State how phenylketonuria is treated.

D3.2.8- Single-nucleotide polymorphisms and multiple alleles in gene pools.

• State that new alleles of a gene are the result of mutation.
• Define single-nucleotide polymorphism.
• Define gene pool.
  
• Explain why any number of alleles of a gene can exist in the gene pool but an individual only inherits two alleles.
• Outline how the multiple alleles of the S-gene in the apple gene pool are a mechanism for preventing self-pollination.

D3.2.9- ABO blood groups as an example of multiple alleles.

• Describe ABO blood groups as an example of complete dominance and codominance.
• Outline the differences in glycoproteins present in people with different blood types.

D3.2.10- Incomplete dominance and codominance.

• Define codominant and incomplete dominant alleles.
• Using the correct notation, outline AB blood type as an example of codominant alleles.
• Using the correct notation, outline an example of incompletely dominant alleles in a flowering plant.​

D3.2.11- Sex determination in humans and inheritance of genes on sex chromosomes.

• Outline the structure and function of the two human sex chromosomes.
• Outline sex determination by sex chromosomes.
• Describe the mechanism by which the SRY gene  regulates embryonic gonad development.​

D3.2.12- Hemophilia as an example of a sex-linked genetic disorder.

• Define sex linkage.
• Using the correct notation, outline an example of the inheritance of hemophilia. 
• Describe the pattern of inheritance for sex linked genes.
• Describe the cause and effect of hemophilia.​

​​​​​​D3.2.13- Pedigree charts to deduce patterns of inheritance of genetic disorders.

• Outline the conventions for constructing pedigree charts.
• Deduce inheritance patterns given a pedigree chart.​

D3.2.14- Continuous variation due to polygenic inheritance and/or environmental factors.

• Compare continuous to discrete variation.
• State that a normal distribution of variation is often the result of polygenic inheritance.
• Explain polygenic inheritance using an example of a two gene cross with codominant alleles.
• State example human characteristics that are associated with polygenic inheritance.
• Outline two example environmental factors that can influence phenotypes.​

D3.2.15- Box-and-whisker plots to represent data for a continuous variable such as student height.

• Compare quantitative and qualitative data.
• Compare discrete and continuous data. 
• Determine if a data set contains an outlier. 
• Quantify variation using descriptive statistics.
• Create visualizations of biological variation using graphs. ​​​

AHL ​​​​​​D3.2.16- Segregation and independent assortment of unlinked genes in meiosis.

• State the outcome of allele segregation during meiosis.
• Describe random orientation of chromosomes and the resulting independent assortment of unlinked genes during meiosis I.
• Distinguish between independent assortment of genes and segregation of alleles.​
• Determine possible allele combinations in gametes that result from independent assortment of two unlinked genes.
  

AHL ​​​​​​D3.2.17-  Punnett grids for predicting genotypic and phenotypic ratios in dihybrid crosses involving pairs of unlinked autosomal genes.

• Use correct notation to depict a dihybrid cross between two unlinked genes.
• Construct a Punnett square to determine the predicted genotype and phenotype ratios of F1 and F2 offspring of dihybrid crosses. ​

AHL ​​​​​​D3.2.18- Loci of human genes and their polypeptide products.

• Define gene locus.​
  

AHL ​​​​​​D3.2.19- Autosomal gene linkage.

• Describe what makes genes “linked.”
• Outline why linked genes fail to assort independently during meiosis. 
• Using correct notation, construct a Punnett square to show the possible genotype and phenotype outcomes in a dihybrid cross involving linked genes. ​

AHL ​​​​​​D3.2.20- Recombinants in crosses involving two linked or unlinked genes.

• Define recombinant.
• Explain how independent assortment of unlinked genes can lead to genetic recombinants.
• Explain how crossing over between linked genes can lead to genetic recombinants.
• Construct a Punnett grid to identify the recombinants of a dihybrid cross involving unlinked genes. 
• Construct a Punnett grid to identify the recombinants of a dihybrid cross involving linked genes. ​

AHL ​​​​​​D3.2.21- Use of a chi-squared test on data from dihybrid crosses.

• Calculate a chi-square value to compare observed and expected results of a dihybrid genetic cross.
• With reference to a p value and the null/alternative hypothesis, determine if there is a significant difference between observed and expected results of a dihybrid cross. ​