Study Guide: Non-Mendelian and Human Genetics (Chapters 14 & 15)

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Q1. Explain the difference between incomplete dominance and codominance using the snapdragon flower color and the MN blood group as examples.

Background

Topic: Patterns of Inheritance – Non-Mendelian Genetics

This question tests your understanding of how some traits do not follow simple Mendelian dominant/recessive inheritance, but instead show incomplete dominance or codominance. You are asked to use specific examples: snapdragon flower color (incomplete dominance) and the MN blood group (codominance).

Key Terms:

Incomplete dominance: A situation where the heterozygote has a phenotype that is intermediate between the two homozygotes.
Codominance: A situation where both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows both traits simultaneously.
Allele: A variant form of a gene.

Step-by-Step Guidance

Define incomplete dominance and describe what happens in the heterozygote (use the snapdragon flower color as your example).
Define codominance and describe what happens in the heterozygote (use the MN blood group as your example).
Compare and contrast the two patterns, focusing on how the heterozygote phenotype differs in each case.
Think about how you would represent the genotypes and phenotypes for each example.

Try explaining these concepts in your own words before checking the answer!

Q2. Explain how the ABO blood group in humans exhibits multiple alleles.

Background

Topic: Multiple Alleles in Human Genetics

This question is about how the ABO blood group system is determined by more than two alleles, which is a departure from simple Mendelian inheritance.

Key Terms:

Multiple alleles: More than two alternative forms of a gene (alleles) exist in a population.
ABO blood group: Determined by three alleles: , , and .

Step-by-Step Guidance

List the three alleles involved in the ABO blood group system and their possible combinations.
Explain how these alleles interact to produce the four blood types (A, B, AB, O).
Describe how codominance and simple dominance are both involved in this system.
Consider how this is different from a gene with only two alleles.

Try to outline the allele combinations and resulting blood types before checking the answer!

Q3. Explain pleiotropy and give some examples.

Background

Topic: Pleiotropy in Genetics

This question asks you to understand how a single gene can affect multiple traits in an organism.

Key Terms:

Pleiotropy: When one gene influences two or more seemingly unrelated phenotypic traits.

Step-by-Step Guidance

Define pleiotropy and explain why it occurs.
Think of at least one example in humans (e.g., sickle cell disease) and one in another organism if possible.
Describe how the gene in your example leads to multiple effects.

Try to come up with your own examples before checking the answer!

Q4. Explain epistasis using the Labrador retriever coat color inheritance pattern example.

Background

Topic: Epistasis – Gene Interactions

This question is about how the expression of one gene can affect or mask the expression of another gene, using Labrador retriever coat color as an example.

Key Terms:

Epistasis: When the effect of one gene is dependent on the presence of one or more 'modifier genes'.
Labrador retriever coat color: Determined by at least two genes: one for pigment color (B/b) and one for pigment deposition (E/e).

Step-by-Step Guidance

Define epistasis and explain how it differs from simple dominance.
Describe the two genes involved in Labrador coat color and what each controls.
Explain how the genotype at one locus (E/e) can mask the expression of the other locus (B/b).
Think about the possible genotypes and resulting phenotypes.

Try to map out the gene interactions before checking the answer!

Q5. Explain polygenic inheritance using human skin color. Give some examples of other quantitative characters that exhibit polygenic inheritance.

Background

Topic: Polygenic Inheritance

This question is about traits that are controlled by two or more genes, resulting in continuous variation (quantitative traits).

Key Terms:

Polygenic inheritance: When a trait is controlled by two or more genes, each contributing to the phenotype.
Quantitative character: A trait that varies along a continuum, such as height or skin color.

Step-by-Step Guidance

Define polygenic inheritance and explain how it leads to continuous variation.
Describe how human skin color is determined by multiple genes.
List other examples of quantitative traits in humans or other organisms.

Try to think of at least two other quantitative traits before checking the answer!

Q6. Explain nature and nurture and give some examples. What does multifactorial mean?

Background

Topic: Environmental and Genetic Influences on Phenotype

This question is about how both genetic and environmental factors influence traits, and what is meant by 'multifactorial'.

Key Terms:

Nature: Genetic influences on phenotype.
Nurture: Environmental influences on phenotype.
Multifactorial: Traits that are influenced by multiple genetic and environmental factors.

Step-by-Step Guidance

Define 'nature' and 'nurture' in the context of genetics.
Give examples of traits influenced by both genetics and environment.
Explain what is meant by 'multifactorial' and how it applies to these traits.

Try to come up with your own examples before checking the answer!

Q7. How is the sickle-cell allele recessive, incompletely dominant, and codominant?

Background

Topic: Sickle-Cell Disease and Patterns of Inheritance

This question explores how the sickle-cell allele can show different inheritance patterns depending on the level of observation (organismal, cellular, molecular).

Key Terms:

Recessive: Trait only appears when two copies of the allele are present.
Incomplete dominance: Heterozygotes show an intermediate phenotype.
Codominance: Both alleles are expressed in the heterozygote.

Step-by-Step Guidance

Describe how the sickle-cell allele behaves at the organismal level (disease symptoms).
Explain what happens at the cellular level in heterozygotes.
Discuss how the molecular products (hemoglobin proteins) show codominance.

Try to explain each level before checking the answer!

Q8. Explain why the sickle-cell allele is favored under certain conditions and has not been selected against by evolutionary processes.

Background

Topic: Evolutionary Genetics – Heterozygote Advantage

This question is about why the sickle-cell allele persists in populations, especially in regions where malaria is common.

Key Terms:

Heterozygote advantage: When individuals with one copy of a mutant allele have a survival advantage.
Natural selection: The process by which certain traits become more common in a population due to survival/reproductive advantages.

Step-by-Step Guidance

Explain the relationship between sickle-cell allele and malaria resistance.
Describe how heterozygotes are protected from malaria.
Discuss why this leads to the persistence of the sickle-cell allele in certain populations.

Try to connect the concepts of selection and disease resistance before checking the answer!

Q9. Morgan studied Drosophila melanogaster. What are the advantages to using the fruit fly to study genetics? What sex chromosomes do male and female fruit flies possess?

Background

Topic: Model Organisms in Genetics

This question is about why Drosophila is a useful model organism and the basics of its sex chromosome system.

Key Terms:

Drosophila melanogaster: The fruit fly, a common model organism in genetics.
Sex chromosomes: Chromosomes that determine the sex of an organism (X and Y in Drosophila).

Step-by-Step Guidance

List at least three reasons why Drosophila is a good model for genetic studies.
Identify the sex chromosome combinations for male and female fruit flies.

Try to recall the advantages and chromosome systems before checking the answer!

Q10. Explain the following terms: wild-type phenotype, mutant phenotype.

Background

Topic: Genetic Terminology

This question is about understanding the standard terms used to describe phenotypes in genetic studies.

Key Terms:

Wild-type phenotype: The most common phenotype observed in natural populations.
Mutant phenotype: A phenotype that results from a mutation and differs from the wild-type.

Step-by-Step Guidance

Define 'wild-type' and explain its significance in genetics.
Define 'mutant' and describe how it arises.
Give an example of each from Drosophila or another organism.

Try to come up with your own examples before checking the answer!

Q11. Explain two important ideas that came from Morgan’s research.

Background

Topic: Discoveries in Chromosomal Genetics

This question is about the key findings from Thomas Hunt Morgan's work with fruit flies.

Key Terms:

Chromosomal theory of inheritance: The idea that genes are located on chromosomes.
Sex-linked inheritance: Traits associated with genes located on sex chromosomes.

Step-by-Step Guidance

Identify two major conclusions from Morgan's experiments.
Briefly explain the significance of each idea.

Try to summarize Morgan's contributions before checking the answer!

Q12. Review Fig 15.5 and 15.6 for examples of chromosomal systems of sex determination. Draw the symbol for female and the symbol for male. How is sex determined in mammals? How do the X and Y chromosomes compare? How do they act as a homologous pair in meiosis?

Background

Topic: Sex Determination Systems

This question covers the chromosomal basis of sex determination and the behavior of sex chromosomes during meiosis.

Key Terms:

Sex chromosomes: X and Y in mammals.
Homologous chromosomes: Chromosome pairs, one from each parent, that are similar in shape and size.

Step-by-Step Guidance

Draw or describe the standard symbols for male (♂) and female (♀).
Explain how sex is determined in mammals (XX vs. XY system).
Compare the X and Y chromosomes in terms of size and gene content.
Describe how X and Y chromosomes pair during meiosis despite differences.

Try to sketch the symbols and summarize the differences before checking the answer!

Q13. Explain the following terms: SRY gene, sex linked gene, X-linked gene, Y-linked gene, WNT4 gene.

Background

Topic: Genes Involved in Sex Determination

This question is about understanding specific genes and terms related to sex determination and sex-linked inheritance.

Key Terms:

SRY gene: Sex-determining Region Y gene, triggers male development.
Sex-linked gene: A gene located on a sex chromosome.
X-linked gene: A gene located on the X chromosome.
Y-linked gene: A gene located on the Y chromosome.
WNT4 gene: A gene important for female development.

Step-by-Step Guidance

Define each term and explain its role in sex determination or inheritance.
Give a brief example or function for each gene.

Try to define each term in your own words before checking the answer!

Q14. Are most Y-linked and X-linked genes related to sex determination?

Background

Topic: Sex-Linked Genes

This question asks you to consider the functions of genes located on the sex chromosomes.

Key Terms:

Sex-linked genes: Genes located on the X or Y chromosomes.

Step-by-Step Guidance

Consider the total number of genes on the X and Y chromosomes.
Think about whether most of these genes are involved in sex determination or other functions.

Try to reason through the functions of sex-linked genes before checking the answer!

Q15. Provide some examples of human X-linked genes. What is the notation for X-linked alleles?

Background

Topic: X-Linked Inheritance

This question is about identifying examples of X-linked genes and understanding how their alleles are notated.

Key Terms:

X-linked gene: A gene located on the X chromosome.
Allele notation: How alleles are written to indicate their location on the X chromosome (e.g., , ).

Step-by-Step Guidance

List at least two examples of human X-linked genes (e.g., colorblindness, hemophilia).
Describe the standard notation for X-linked alleles.

Try to write out the allele notation before checking the answer!

Q16. Explain the following terms: X inactivation, Barr body, mosaic.

Background

Topic: Dosage Compensation in Females

This question is about how females compensate for having two X chromosomes and the resulting effects.

Key Terms:

X inactivation: The process by which one X chromosome in female mammals is randomly inactivated.
Barr body: The condensed, inactivated X chromosome visible in the nucleus.
Mosaic: An individual with cells expressing different alleles due to X inactivation.

Step-by-Step Guidance

Define each term and explain how they are related.
Describe the consequences of X inactivation for female phenotypes.

Try to connect these terms before checking the answer!

Q17. Review Fig 15.13 and explain nondisjunction in meiosis using the following terms: aneuploidy, monosomic, trisomic.

Background

Topic: Chromosomal Abnormalities

This question is about errors in chromosome separation during meiosis and the resulting conditions.

Key Terms:

Nondisjunction: Failure of chromosomes to separate properly during meiosis.
Aneuploidy: Abnormal number of chromosomes.
Monosomic: Missing one chromosome (2n-1).
Trisomic: Having an extra chromosome (2n+1).

Step-by-Step Guidance

Define nondisjunction and describe when it can occur during meiosis.
Explain how nondisjunction leads to aneuploidy.
Define monosomic and trisomic and give an example of each.

Try to explain the process and terms before checking the answer!

Q18. Briefly explain nondisjunction in mitosis.

Background

Topic: Chromosomal Errors in Cell Division

This question is about how nondisjunction can also occur during mitosis, not just meiosis.

Key Terms:

Nondisjunction: Failure of sister chromatids to separate during cell division.

Step-by-Step Guidance

Define nondisjunction in the context of mitosis.
Describe the consequences for the resulting daughter cells.

Try to summarize the process before checking the answer!

Q19. Review the four chromosomal structure alterations in Figure 15.14. What can cause these changes in chromosomal structure?

Background

Topic: Chromosomal Mutations

This question is about the types of structural changes that can occur in chromosomes and their causes.

Key Terms:

Deletion: Loss of a chromosome segment.
Duplication: Repetition of a chromosome segment.
Inversion: Reversal of a chromosome segment.
Translocation: Movement of a segment from one chromosome to another.

Step-by-Step Guidance

List and define the four types of chromosomal structure alterations.
Describe possible causes for these changes (e.g., errors in crossing over, radiation).

Try to recall the definitions and causes before checking the answer!

Q20. Review these Human aneuploidies: trisomy 21, XXY, XYY, XXX, X0.

Background

Topic: Human Chromosomal Disorders

This question is about specific examples of human aneuploidies and their chromosomal makeup.

Key Terms:

Trisomy 21: Down syndrome (three copies of chromosome 21).
XXY: Klinefelter syndrome.
XYY: Jacobs syndrome.
XXX: Triple X syndrome.
X0: Turner syndrome.

Step-by-Step Guidance

List each condition and the chromosomal abnormality involved.
Briefly describe the main features or symptoms of each condition.

Try to match each syndrome to its chromosomal pattern before checking the answer!

Q21. How can genes in the mitochondrion and chloroplast affect organisms? Explain “3-parent babies”.

Background

Topic: Non-Nuclear Inheritance

This question is about how genes outside the nucleus (in mitochondria and chloroplasts) can influence traits, and the concept of mitochondrial replacement therapy.

Key Terms:

Mitochondrial DNA: DNA found in mitochondria, inherited maternally.
Chloroplast DNA: DNA found in chloroplasts (in plants).
3-parent babies: Offspring produced using nuclear DNA from two parents and mitochondrial DNA from a donor.

Step-by-Step Guidance

Explain how mitochondrial and chloroplast genes are inherited and their effects on the organism.
Describe the concept and purpose of “3-parent babies”.