H Week 15: Non-Mendelian Genetics

Non-Mendelian Genetics

Lecture Goals:

• Examine when Mendelian Genetics doesn't work (non-Mendelian Genetics) and why

• Predict genetic crosses using standard statistical methods

Course Competencies: 19. Compare and contrast the inheritance patterns of Mendelian and non-Mendelian traits and use standard statistical methods to predict the outcome of monohybrid and dihybrid crosses. (X)

Click the sound button for audio!

"Sweet pea flowers (1833)" by Swallowtail Garden Seeds is marked with Public Domain Mark 1.0.

Presentation Links

Non-Mendelian Genetics

Pedigrees

Genetics Review

Recall: Parts of a Genome

Terms to Remember

• Genes - regions of a chromosome that provide the "code" for a particular trait/physiological expression

• Allele - Different versions of the same gene that have different expression
• Dominant allele - version of the gene that will be expressed if present
• Recessive allele - version of the gene that will not be expressed if present with a dominant allele
• Codominant allele - version of the gene that will be expressed together if present with another codominant allele (will see both traits)

X Chromosome

More info

https://www.ncbi.nlm.nih.gov/books/NBK22266/

This image highlights genes found on the X chromosome that are associated with various diseases, such as Duchenne muscular distrophy.

Recall: Relationship Between Alleles

Symbols Used

• When written, an individual's genotype will have two letters (one allele from each homologous chromosome)
• Types of genotypes:
• Homozygous dominant - both alleles are the dominant allele

• Homozygous recessive - both alleles are the recessive allele

• Heterozygous - one allele is dominant while the other is recessive

• Codominant - both alleles are codominant, so they are expressed together, (even if different)

AA

aa

Aa

ABAC

Non-Mendelian Genetics

• Sometimes genes do not follow Mendel's scientific laws.

When Mendelian Genetics Doesn't Work

• Epistasis
• Sex-linked genes
• Extranuclear inheritance
• Infectious heredity
• Epigenetics (genomic imprinting)

• Codominance
• Incomplete dominance
• Linked genes
• Multiple alleles for one gene
• Polygenic trait
• Pleiotropy

Gregor Mendel: The Friar Who Grew Peas Paperback – Picture Book, 18 August 2015

• Codominance
• Both alleles are equally expressed when present together
• Example: roan cows and blood type
• Incomplete dominance
• Dominant allele doesn't fully prevent the expression of the recessive allele
• Results in blend of traits
• Example: a red and white flower produce a pink flower

Non-Mendelian Genetics

When Mendelian Genetics Doesn't Work

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Note about Audio!

https://igbiologyy.blogspot.com/2014/03/codominance.html https://byjus.com/biology/co-dominance-and-multiple-alleles/ https://www.a1adsupport.com/glossary/autosomal-codominant-pattern/

I named the alleles differently in the audio! Rr - red allele (I named this allele R in the audio) Rw - white allele (I named this allele R1 in the audio)

• Linked genes
• When genes are located close together on a chromosome so they don't independently assort
• Alleles for linked genes are inherited together
• Multiple alleles for one gene
• Example: blood type (A, B, or O allele)
• Polygenic trait
• More than one gene controls a trait
• Example: height

Non-Mendelian Genetics

When Mendelian Genetics Doesn't Work

2 genes found at loci close together on the chromosome

https://learn.genetics.utah.edu/content/pigeons/geneticlinkage/ https://biologynotesonline.com/pleiotropism-definition-types-examples/

Non-Mendelian Genetics

Multiple Alleles for One Gene

• Pleiotropy
• A single gene affects multiple traits
• Example: sickle-cell anemia
• Epistasis
• Interaction between genes where one gene influences the expression of a different gene
• Example: Hair color and baldness

Non-Mendelian Genetics

When Mendelian Genetics Doesn't Work

https://byjus.com/biology/pleiotropy/ https://biologynotesonline.com/pleiotropism-definition-types-examples/ https://digfir-published.macmillanusa.com/life11e/life11e_ch12_18.html

Non-Mendelian Genetics

Incomplete Dominance, Codominance, Polygenic Traits, & Epistasis Video

• Sex-linked genes
• Gene expression varies in different frequencies based on biological sex, since the gene is on a sex chromosome
• Example: colorblindness and hemophilia (both x-linked disorders)

Non-Mendelian Genetics

When Mendelian Genetics Doesn't Work

https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_%28Boundless%29/12%3A_Mendel%27s_Experiments_and_Heredity/12.02%3A__Patterns_of_Inheritance/12.2E%3A_Sex-Linked_Traits Credit: Jeremy Seto (CC-BY-SA) https://bio.libretexts.org/Bookshelves/Biotechnology/Bio-OER_(CUNY)/09%3A_Genetics/9.03%3A_Sex-linked_Genes

Non-Mendelian Genetics

Sex-Linked Genes

Non-Mendelian Genetics

Color Blindness: Ishihara Test

"File:Eight Ishihara charts for testing colour blindness, Europe Wellcome L0059163.jpg" is licensed under CC BY 4.0.

• Extranuclear inheritance
• Traits that come from DNA not found in the nucleus
• Example: mitochondrial DNA

Non-Mendelian Genetics

When Mendelian Genetics Doesn't Work

https://old-ib.bioninja.com.au/standard-level/topic-5-evolution-and-biodi/54-cladistics/mitochondrial-dna.html

Pedigrees

Visualizing Inheritance Patterns

• Pedigrees are used to see how a trait or disease is inherited over generations.

• How to read a pedigree...
• First generation at the top
• Male vs female individuals have different shapes
• Affected vs unaffected individuals have different colors

Pedigree for Recessive Disease

https://www.ck12.org/biology/pedigree/lesson/Pedigree-Analysis-MS-LS/

Recommended Textbook Reading

OpenStax Biology 2e: Chapter 13

Not required, but highly recommended (it can be very helpful to see the material again but phrased a little differently!)