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Chapter 6
Genetics- Exam 2- Fall 2026
| Question | Answer |
|---|---|
| What does it mean for genes to be linked? | They are located on the same chromosome. |
| What is a linkage group? | A group of genes located on the same chromosome. |
| How does the number of linkage groups relate to chromosome number? | The number of linkage groups corresponds to the haploid number of chromosomes. |
| What is independent assortment in the linkage overview? | The two genes are on different chromosomes and their gamete types occur in equal proportions. |
| What is complete linkage? | Genes on the same chromosome are so close together that recombination between them is absent or negligible; parental gametes are produced. |
| What is incomplete linkage? | Genes on the same chromosome are separated enough for crossing over to occur, producing unequal proportions of parental and recombinant gametes. |
| What happens when linked genes are very far apart? | Their gamete proportions can be equal, because recombination can make them behave like independently assorting genes. |
| What types of gametes can genotype aaBB produce? | Only aB gametes, because the individual is homozygous at both loci. |
| What is an allele? | An alternative form of the same gene. |
| What is a wild-type allele? | An allele commonly found in the natural population, arbitrarily treated as normal and associated with the wild-type phenotype. |
| What can a mutation do to a gene product? | It can change the activity of the cellular product and thereby change phenotype. |
| How are dominant and recessive alleles commonly symbolized for simple Mendelian traits? | Uppercase letters indicate dominant alleles and lowercase letters indicate recessive alleles. |
| How are Drosophila gene symbols chosen in the system described? | The gene symbol comes from the first mutant strain found. |
| How is a Drosophila wild-type allele represented? | By the same letter(s) with a superscript plus, or simply a plus symbol. |
| How is a recessive mutant allele represented in the Drosophila system? | With a lowercase symbol. |
| How is a dominant mutant allele represented in the Drosophila system? | With an uppercase symbol. |
| What do e and e+ represent in the slide example? | e is ebony body color; e+ is gray body color. |
| What phenotype does e+e+ produce in the ebony example? | Gray body color (homozygous wild type). |
| What phenotype does e+e produce in the ebony example? | Gray body color (heterozygous carrier). |
| What phenotype does ee produce in the ebony example? | Ebony body color. |
| What do Wr and Wr+ represent? | Wr is the dominant wrinkled-wing mutation; Wr+ represents normal wing shape. |
| What is the phenotype of Wr+Wr+? | Normal wing shape. |
| What is the phenotype of Wr+Wr? | Wrinkled wing shape. |
| What is the phenotype of WrWr? | Wrinkled wing shape. |
| Who independently rediscovered Mendel's work in 1900, as listed in the slides? | Hugo de Vries, Carl Correns, and Erich von Tschermak. |
| What did William Bateson show in 1902? | That Mendelian principles apply to animals. |
| Who proposed the chromosome theory of inheritance in 1902–1903? | Walter Sutton and Theodor Boveri independently recognized parallels between Mendelian factors and chromosomes during meiosis. |
| What did Sutton point out in 1903? | There are far fewer chromosomes than Mendelian factors, so each chromosome must carry many factors that can be inherited together. |
| What did Bateson and Reginald Punnett discover in sweet peas in 1905? | Flower color and pollen shape did not assort independently. |
| What did Frans A. Janssens observe in 1909? | Chiasmata in synapsed meiotic homologous chromosomes. |
| What did Thomas Hunt Morgan discover in 1910? | The first X-linked gene in Drosophila melanogaster. |
| What were the traits in Morgan's first two-factor cross? | Yellow versus gray body and white versus red eyes. |
| What were the traits in Morgan's second two-factor cross? | Miniature versus wild-type wings and white versus red eyes. |
| What did Morgan call the exchange of genetic material between linked genes? | Crossing over. |
| How does gene distance affect the likelihood of a chiasma between genes? | The closer two genes are, the less likely a chiasma will form between them. |
| What did Morgan hypothesize about gene arrangement on chromosomes? | Genes occur in a linear array, and linkage can be modified by crossing over. |
| Who created the first genetic map from recombination data? | Alfred H. Sturtevant. |
| What key insight did Sturtevant have? | If recombination frequency depends on distance between genes, it can reveal their relative locations on chromosomes. |
| What relationship did Sturtevant infer for y, w, and m? | The y gene is closer to w than it is to m. |
| What is recombination frequency (RF)? | The number of recombinant offspring divided by the total number of offspring, multiplied by 100. |
| What is the formula for recombination frequency? | RF (%) = (number of recombinant offspring ÷ total offspring) × 100. |
| What does notation such as yw/yw indicate in the slides? | The loci are on the same chromosome. |
| What does notation such as y/y and w/w indicate? | The loci are on different chromosomes. |
| What does yy ww indicate in the slide's notation examples? | The linkage arrangement of the loci is unknown. |
| What are the two configurations for a heterozygote with two linked genes? | Cis (coupling) and trans (repulsion). |
| What is crossing over? | The physical exchange of corresponding genetic segments between non-sister chromatids of homologous chromosomes. |
| During which meiotic stage does crossing over occur? | Prophase I, when the four chromatids are closely synapsed. |
| How does crossing over occur along a chromosome pair? | More or less randomly along its length and through reciprocal exchange of equal, corresponding segments. |
| When is crossing over not detectable between two marker genes? | If it occurs outside the region between the markers. |
| Why can an even number of crossovers be undetectable between two markers? | An even number of exchanges can restore the parental marker arrangement. |
| Can multiple crossovers occur in one tetrad? | Yes, multiple crossovers are possible in a single tetrad. |
| What is genetic mapping? | Determining the linear order of linked genes along the same chromosome; also called gene or chromosome mapping. |
| How do genetic maps estimate relative distances between genes? | By using the likelihood of crossover between them, estimated from the percentage of recombinant offspring. |
| How does gene distance relate to recombinant offspring frequency? | Genes farther apart generally yield more recombinant offspring; genes closer together yield fewer. |
| What are map units (mu) also called? | Centimorgans (cM). |
| v | A 1% recombination frequency. |
| What are four ways genetic distance may be represented? | Recombination frequency, percent recombination, map units, or centimorgans. |
| What is a testcross? | A cross between an individual heterozygous for two or more genes and an individual homozygous recessive for those same genes. |
| Why are testcrosses useful for genetic mapping? | Offspring phenotypes can reveal the gametes produced by the heterozygous parent, allowing recombinant types to be counted. |
| Which traits are used in the slide's example testcross? | Bristle length and body color in fruit flies. |
| What do s and s+ represent in the example? | s = short bristles; s+ = normal bristles. |
| What do e and e+ represent in the example? | e = ebony body color; e+ = gray body color. |
| What genotype does the double-recessive parent have in the example? | ss ee. |
| How are the alleles arranged in the heterozygous parent in the example? | s and e are linked on one chromosome; s+ and e+ are linked on the homologous chromosome. |
| What is the estimated distance between the s and e genes in the example? | (76 + 75) ÷ (542 + 537 + 76 + 75) × 100 = 12.3 map units. |
| What is the estimated distance between the s and e genes in the example? | 12.3 map units (12.3 cM). |
Created by:
KristenR2025