Ch 8

Equations to Memorize for Exam 2

• Frequency

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• Coefficient of Coincidence (COC)

  • 
    

• Interference (I)

  • $I = 1 - ext{COC}$

• Fitness (W)

  • W = rac{ ext{mean # offspring}}{ ext{mean # offspring in highest group}}

• Selection (S)

  • $s = 1 - w$

• Allelic Frequencies

  • $p = ext{frequency of allele A}$

  • $q = ext{frequency of allele a}$

  • Pertaining to Hardy-Weinberg Equilibrium:

    • $p^2 + 2pq + q^2 = 1$

    • $p + q = 1$

      
      

• Inbreeding Equations

  • $f(AA) = p^2 + Fpq$

  • $f(Aa) = 2pq - 2Fpq$

  • $f(aa) = q^2 + Fpq$

Exam Preparation

• Exam 2 Badges:

  • Complete by Tuesday 10/21

• Extra Problems:

  • Chapter 7 extra problems

  • Chapter 25 extra problems

  • Chapter 8 extra problems

• Unit 2 Resources:

  • Unit 2 Office Hours

  • Unit 2 Infographic

  • Chapter 7 Challenge Problems

  • Chapter 8 Challenge Problems

• LA Review Session:

  • Scheduled for Wednesday 10/22

Chapter 8 Outline

8.1 Chromosome Mutations

• Definitions include rearrangements, aneuploids, and polyploids.

8.2 Chromosome Rearrangements

• Alteration of Chromosome Structure

8.3 Aneuploidy

• Definition: an increase or decrease in the number of individual chromosomes.

8.4 Polyploidy

• Definition: the presence of more than two sets of chromosomes.

Types of Chromosomal Mutations

• Three Categories of Chromosome Mutations

  • Chromosomal rearrangement (duplication)

  • $2n = 6$

  • Aneuploidy (trisomy)

  • $2n + 1 = 7$

  • Polyploidy (autotriploidy)

  • $3n = 9$

Chromosome Rearrangements

• Types of Rearrangements:

  1. Duplications

  2. Deletions

  3. Inversions

  4. Translocations

Duplications

• Chromosome duplication occurs when a segment of the chromosome is duplicated.

  • Examples of Duplications:

  • Tandem Duplication: adjacent duplicated segment (e.g., AB·CDEFEFG).

  • Displaced Duplication: separate distance from original segment (e.g., AB·CDEFGEF).

  • Reverse Duplication: inverted duplication (e.g., AB·CDEFFEG).

Evidence of Chromosome Duplications

• Prophase I Alignment in Meiosis

  • Chromosome loops to align homologous sequences in case of duplications.

• Bar Phenotype Example

  • X-linked duplication leading to various phenotypes, resulting from unequal crossing over during meiosis.

Effects of Duplications

1. Developmental processes often rely on interactions of multiple genes.

2. Changes in gene dosage can create developmental issues if relative gene product amounts are altered.

3. Duplications may result in abnormal phenotypes due to disrupted interactions among proteins.

Deletions

• A chromosome deletion occurs when a segment of the chromosome is removed.

• Effects of Deletions:

  • Can be lethal if essential genes are deleted.

  • Pseudodominance: expression of normally recessive alleles when dominant alleles are deleted.

• Haploinsufficient Gene Example:

  • Notch mutations lead to developmental issues if one gene copy is missing.

Copy-Number Variation

• Common in the human genome affecting various phenotypes and potentially leading to diseases and evolutive functions.

Inversions

• Inversion occurs with segments of chromosomes being turned 180°.

• Types include:

  • Paracentric inversion (involving no centromere).

  • Pericentric inversion (involving the centromere).

• Effects of Inversions:

  • Dicentric and acentric chromatids produced during crossing over.

  • Altered gene expression due to position effects.

Translocations

• In translocation, a segment moves to a nonhomologous chromosome or a new location on the same chromosome.

  • Nonreciprocal vs. reciprocal translocation distinctions made, including the Robertsonian translocation type.

• Effects Include:

  • Gene disruption and position effects connecting genes that were once on separate chromosomes.

Aneuploidy

• Definition: Increase or decrease in chromosome number, with examples shown in various conditions such as Down syndrome and Turner syndrome.

• Acheived primarily through nondisjunction events during meiosis I or II, leading to trisomic or monosomic offspring.

Human Trisomy Disorders

• Trisomy 21 (Down Syndrome): Most common, with prevalence tied to maternal age.

• Other Trisomies:

  • Edwards Syndrome (Trisomy 18)

  • Patau Syndrome (Trisomy 13)

Polyploidy

• Definition: Presence of more than two sets of chromosomes.

  • Autopolyploidy: All chromosome sets from a single species.

  • Allopolyploidy: Chromosomes from two or more species.

• Evolutionary Significance: Increases genetic diversity and aids in species formation.