Week 12 Tuesday - Mendelian Inheritance (1)

Important Exam Information

• Mendelian Inheritance Exam: One week from Thursday!

• Action Center:

  • When: Tuesdays and Thursdays, 4:30 - 6:30 PM

  • Where: Wagner Hall, Rooms 135, 140, 145

  • Format: Come and go as you please

• Action Tutoring:

  • Days/Times: Mon, Wed & Thurs | 8:00 - 10:00 PM; Tues | 8:00 - 10:00 PM

  • Where: Dunham A128 (Mon, Wed, Thurs) and Dunham A126 (Tues)

• Office Hours:

  • Dr. H: Tuesdays and Thursdays, 12:30 - 2:00 PM; Fridays, 9:30 - 1:00; GLCH 328

  • Laurens: Wednesdays, 2:00 - 3:00 PM; Thursdays, 1:30 - 2:30 PM; GLCH 308

Mendelian Genetics

Key Concepts

• Chromosomes, Alleles, & Genes:

  • Chromosomes: Structures containing genetic material located in the nucleus.

  • Alleles: Different forms of a gene, determining genetic traits.

  • Genotype vs Phenotype: Genotype is the genetic makeup, phenotype is the observable trait.

• Dominant vs Recessive Alleles: Dominant alleles mask the effect of recessive alleles in heterozygotes.

• True Breeding vs Heterozygotes:

  • True breeding organisms have identical alleles (homozygous).

  • Heterozygotes have different alleles for a trait (e.g., Rr).

Punnett Squares

• Purpose: To predict the genetic outcome of a specific cross.

• Genotypic Ratio: Proportions of the different genotypes resulting from the cross.

• Phenotypic Ratio: Proportions of observable traits resulting from the cross.

Chromosomes and Genes

• Number of Chromosomes: Each parent contributes 23 chromosomes, totaling 46.

• Karyotype: A display of all homologous pairs of chromosomes, including 22 pairs of autosomes and one pair of sex chromosomes (XX or XY).

• Homologous Pairs: Each pair of chromosomes has genes for the same traits but may have different alleles.

Case Study: FBN1 Gene and Marfan Syndrome

• Chromosome 15: Contains the FBN1 gene, essential for producing fibrillin protein.

• Marfan Syndrome: Result of a mutated version of the fibrillin protein.

• Gene Copies: Each person has two copies of the FBN1 gene (one from each parent).

• Expression: Only one copy of the mutated FBN1 can be enough to affect phenotype (dominant trait).

Genetic Concepts Explored

Alleles and Dominance

• The expressed allele determines phenotype; non-expressed alleles do not influence the trait.

• Myths about Dominance:

  • No strict rules; the dominance of an allele does not correlate with its frequency in the population.

  • Both dominant and recessive alleles can be rare or common.

Genotypes and Phenotypes

• Mendelian Phenotypes: Simple traits controlled by one gene.

• Non-Mendelian Traits: Often influenced by multiple genes or environmental factors.

Genetics in Humans: Misconceptions

• Many traits perceived as Mendelian are actually more complex:

  • Earlobe Attachment: Variation suggests it is likely polygenic.

  • Complex Genetics: Most traits are influenced by a combination of genetics and environment.

• Examples:

  • Tongue Rolling: Not strictly Mendelian due to learned behaviors and variations.

  • Eye and Hair Color: Polygenic traits with multiple contributing genes.

  • Dimples: Variability across individuals suggests environmental influence.

• Rare Traits: Some, like earwax type, follow Mendelian inheritance.

Conclusion on Genetics

• Human genetics is complexity; oversimplifying can lead to misunderstandings in biology.

• Teachers may present Mendelian principles for simplicity, but real-world cases demonstrate a range of inheritance patterns and gene interactions.