Exam II Review Chs 5, 6 and 8 FA 24

Genetics Exam II Review

Chapter 5 – Non-Mendelian Inheritance

• Important Notes:

  • Conceptual Questions are found at the end of the chapter.

  • Even-numbered answers are located in Appendix B.

  • All answers are accessible in Connect.

Epigenetics and Maternal Effect

• Define Epigenetics: Study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.

• Maternal Effect:

  • C2: Inheritance pattern where the phenotype of the offspring is determined by the genotype of the mother.

  • Occurs at the cellular level where maternal RNAs and proteins deposited in the egg influence early development.

  • Proteins encoded by maternal effect genes play functional roles in early development, such as directing the formation of body axes.

• Developmental Implications:

  • C8: Maternal effect genes exert their effects during the early stages of development because they provide products necessary for zygote functioning before the zygotic genome is activated.

Dosage Compensation

• Definition: Mechanism to equalize gene expression between individuals with different numbers of sex chromosomes.

• Key Concepts:

  • C10: Dosage compensation is necessary because females (XX) have double the gene dosage of X-linked genes compared to males (XY).

  • C11: Barr Body: Inactivated X chromosome in females; reduces X-linked gene expression.

  • C12: Mechanisms:

    • X-inactivation (mammals)

    • Hyperactivation (Drosophila)

    • Dosage compensation complex (C. elegans)

  • C13: X-chromosome inactivation occurs early in embryogenesis; leads to phenotypic outcomes such as variegated coat patterns in mammals due to random inactivation of one X chromosome.

Genomic Imprinting

• Definition: Differential expression of a gene depending on whether it is inherited from the mother or father.

  • C20: Erasure and reestablishment occurs in germ cells, allowing proper expression of imprints according to parental origin.

Extranuclear Inheritance

• Definition: Genetic transmission that occurs outside the nucleus, often through mitochondria or chloroplasts.

  • C25: Examples include mitochondrial inheritance (from the mother) and chloroplast inheritance.

  • C30: Mitochondrial and chloroplast genomes likely originated from free-living prokaryotes; have reduced in size over evolutionary time due to gene transfer and redundancy.

Chapter 6—Genetic Linkage and Mapping in Eukaryotes

• Important Notes:

  • Conceptual and Experimental Questions are at the chapter's end.

  • Even-numbered answers are in Appendix B.

  • All answers are in Connect.

Gamete Types and Linkage

• Definitions:

  • Independent Assortment: Genes located on different chromosomes segregate independently during gamete formation.

  • Complete Linkage: Genes located on the same chromosome that tend to be inherited together.

  • Linkage: The tendency of alleles that are located close together on a chromosome to be inherited together.

• Gamete Classifications:

  • Parental/Non-Recombinant/non-Crossover: Original combinations of alleles.

  • Non-parental/Recombinant/Crossover: New allele combinations created through recombination.

Genetic Mapping Calculations

• C9: Sweet pea has seven linkage groups, indicating 7 linkage groups correspond to 7 chromosomes.

• E8: Calculation of offspring genotypes from testcross:

  • Given 12 mu distance, expected ratios need to be calculated based on recombination frequency.

Chapter 8—Variation in Chromosome Structure and Number

• Important Notes:

  • Conceptual and Experimental Questions are at the chapter's end.

  • Even-numbered answers are in Appendix B.

  • All answers are in Connect.

Changes in Chromosome Structure

• Consequences:

  • C1: Structural changes can alter the total amount of genetic material; deletions and duplications can affect phenotypes based on gene dosage.

  • Small changes often have minimal effects unless they impact critical genes.

  • C4: Gene Family: Groups of related genes that arise through duplication; have biological significance in redundancy and functional diversification.

• C6: Determine if inversions are pericentric or paracentric through sketching chromosome alignment during meiosis.

Changes in Chromosome Number

• C17: Chromosome count varies with ploidy alterations, providing different scenarios for diploid fruit flies.

• C18: Chromosomal composition: X, no Y, trisomy 21 indicates aneuploidy status.

• C26: Endopolyploidy: An organism exhibits fewer than the expected number of haploid sets, often in specific tissues.

• C30: Karyotype analysis in turtles shows replications leading to varying chromosome numbers, explanations provided based on evolutionary mechanisms.

• C41: Turner syndrome results from nondisjunction, can occur in both oogenesis and spermatogenesis but often indicates maternal age risks in chromosomal abnormities.