Concept explainers
In the wasp Bracon hebetor, a form of parthenogenesis (the development of unfertilized eggs into progeny) resulting in haploid organisms is not uncommon. All haploids are males. When offspring arise from fertilization, females almost invariably result. P. W. Whiting has shown that an X-linked gene with nine multiple alleles (Xa, Xb, etc.) controls sex determination. Any homozygous or hemizygous condition results in males, and any heterozygous condition results in females. If an Xa/Xb female mates with an Xa male and lays 50 percent fertilized and 50 percent unfertilized eggs, what proportion of male and female offspring will result?
Want to see the full answer?
Check out a sample textbook solutionChapter 7 Solutions
Concepts of Genetics Plus Mastering Genetics with Pearson eText -- Access Card Package (12th Edition) (What's New in Genetics)
- Barr bodies are formed to adjust X chromosome dosage in species other than humans, such as Drosophila (fruit flies) and C. elegans (nematodes). True or False ?arrow_forwardMales of many diploid species (like us) have X and Y sex chromosomes. They are hemizygous for most X- linked genes. Thus, males express most X-linked alleles, whether they are dominant or recessive in females. In the fruit fly Drosophila, it is common to achieve the equivalent of a test cross of X-linked genes in females by assessing the readily observed phenotypes of their male progeny. Since males do not receive X-linked genes from their father, sires of these crosses can be normal or wild-type flies. In fly genetics, it is conventional to name a gene after the mutant phenotype that enabled its discovery. Your challenge is to establish gene order and map distances between three X-linked genes in Drosophila. Each gene is represented by recessive mutant alleles that express rather distinctive phenotypes relative to their dominant wild-type alternative alleles. Flies expressing fruitless (f) are bisexual, lush (1) have a heightened responses to ethanol, and ken&barbie (kb) lack external…arrow_forwardIn C. elegans, lon-2 and unc-2 are recessive mutations that are 8 map units apart on the X chromosome. An hermaphrodite who is Lon and Unc is mated to a wild-type male. An F1 hermaphrodite is mated to a wild-type male. What are the expected percentages of the different phenotypes among the male progeny?arrow_forward
- Termites have a haplo-diploid sex determination system where females develop from a fertilized egg (they are diploid, having one allele from the female cueen and one allele from the male), and males develop from unfertilized eggs (they are haploid, having only one allele from the queen). Assuming that the female parent (queen) is heterozygous for a particular gene, what is the probability that a female offspring will inherit the recessive allele from her mother? What is the probability that a male offspring will inherit a recessive allele from his mother? O A. The probability that a daughter will inherit a recessive allele from her mother is 50%; the probability that a son will inherit a recessive allele from his mather is 50%. OB. Ihe probobility that a daughter will inherit a recessive allele from her mother is 0%; the probability that a son will inherit a recessive allele from his mother is 100%. O C. The probability that a daughter will inherit a recessive allele from her mother is…arrow_forwardThe picture below represents a G1 cell from a newly discovered species that uses the X/Y sex determination system. Alleles for the different autosomal genes of interest are indicated on the chromosomes, and genes R and T are 16 cM apart. Red lines show maternal chromosomes, and blue lines show paternal chromosomes. Answer the following questions about this individual.d) Provide the genotype of the fertilizing male gamete that produced this individual. e) This individual can produce a pool of different gametes. List any TWO potential gametes that will occur at different frequencies. Give the alleles of each gamete contained within a set of brackets, and indicate the expected frequency (up to two decimals) at which that gamete would occur.arrow_forwardThe picture below represents a G1 cell from a newly discovered species that uses the X/Y sex determination system. Alleles for the different autosomal genes of interest are indicated on the chromosomes, and genes R and T are 36 cM apart. Red lines show maternal chromosomes, and blue lines show paternal chromosomes. Answer the following questions about this individual. a) This individual can produce a pool of different gametes. List any TWO potential gametes that will occur at different frequencies. Give the alleles of each gamete contained within a set of brackets, and indicate the expected frequency (up to two decimals) at which that gamete would occur. b) Name any two loci in this individual that can result in recombination in the gametes via the process of independent assortment. c) What is the sex of this individual? Justify your answer. d) Give the term that will describe the morphology of the chromosome that carries the R/T alleles. e) Provide the genotype of the fertilizing male…arrow_forward
- One reason that worker bees forgo their own reproduction to help their sister (the queen) reproduce is that female bees are more closely related to their sisters than they are to their own offspring. This quirk of genetics results from the fact that bees have haplodiploid sex determination, in which females are diploid, with a mother and a father, but males are haploid, developing from unfertilized eggs. Because males are haploid, they produce sperm by mitosis. Explainwhy haplodiploid sex determination causes females to be more closely related to their sisters than to their offspring.arrow_forwardThe picture below represents a G1 cell from a newly discovered species that uses the X/Y sex determination system. Alleles for the different autosomal genes of interest are indicated on the chromosomes, and genes R and T are 36 cM apart. Red lines show maternal chromosomes, and blue lines show paternal chromosomes. Answer the following questions about this individual. g|G a) This individual can produce a pool of different gametes. List any TWO potential gametes that will occur at different frequencies. Give the alleles of each gamete contained within a set of brackets, and indicate the expected frequency (up to two decimals) at which that gamete would occur. b) Name any two loci in this individual that can result in recombination in the gametes via the process of independent assortment. c) What is the sex of this individual? Justify your answer. d) Give the term that will describe the morphology of the chromosome that carries the R/T alleles. e) Provide the genotype of the fertilizing…arrow_forwardAn insect species is discovered in which the heterogametic sex isunknown. An X-linked recessive mutation for reduced wing (rw)is discovered. Contrast the F1 and F2 generations from a crossbetween a female with reduced wings and a male with normalsizedwings when(a) the female is the heterogametic sex.(b) the male is the heterogametic sex.arrow_forward
- Let’s suppose that two different X-linked genes exist in mice,designated with the letters N and L. Gene N exists in a dominant,normal allele and in a recessive allele, n, that is lethal. Similarly,gene L exists in a dominant, normal allele and in a recessive allele,l, that is lethal. Heterozygous females are normal, but males thatcarry either recessive allele are born dead. Explain whether or notit would be possible to map the distance between these two genesby making crosses and analyzing the number of living and deadoffspring. You may assume that you have strains of mice in whichfemales are heterozygous for one or both genes.arrow_forwardIn certain salamanders, the sex of a genetic female can be altered, changing her into a functional male; these salamanders are called sex reversed males. When a sex-reversed male is mated with a normal female, approximately 23 of the offspring are female and 13 are male. How is sex determined in these salamanders? Explain the results of this crossarrow_forwardIn elegans, lon-2 and unc-2 are recessive mutations that are 8 map units apart on the X chromosome. An hermaphrodite who is Lon and Unc is mated to a wild-type male. An F1 hermaphrodite is mated to a wild-type male. What are the expected percentages of the different recombinant phenotypes among the male progeny?arrow_forward
- Biology: The Unity and Diversity of Life (MindTap...BiologyISBN:9781305073951Author:Cecie Starr, Ralph Taggart, Christine Evers, Lisa StarrPublisher:Cengage LearningHuman Biology (MindTap Course List)BiologyISBN:9781305112100Author:Cecie Starr, Beverly McMillanPublisher:Cengage Learning