The introduction to this chapter described the search for genes that determine pattern baldness in humans. In 1916, Dorothy Osborn suggested that pattern baldness is a sex-influenced trait that is dominant in males and recessive in females. More research suggested that pattern baldness is an X-linked recessive trait. Would you expect to see independent assortment between genetic markers on the X chromosome and pattern baldness if (a) pattern baldness is sexinfluenced and (b) if pattern baldness is X-linked recessive? Explain your answer.

The introduction to this chapter described the search for genes that determine pattern baldness in humans. In 1916, Dorothy Osborn suggested that pattern baldness is a sex-influenced trait that is dominant in males and recessive in females. More research suggested that pattern baldness is an X-linked recessive trait. Would you expect to see independent assortment between genetic markers on the X chromosome and pattern baldness if (a) pattern baldness is sexinfluenced and (b) if pattern baldness is X-linked recessive? Explain your answer.

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Human Biology (MindTap Course List)

11th Edition

ISBN:9781305112100

Author:Cecie Starr, Beverly McMillan

Publisher:Cecie Starr, Beverly McMillan

Chapter20: Chromosomes And Human Genetics

Section: Chapter Questions

Problem 2CT: Human sex chromosomes are XX for females and XY for males. a. With respect to an X-linked gene, how...

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Males 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…
In 1916, Dorothy Osborn suggested that pattern baldness is a sex-influenced trait that is dominant in males and recessive in females. More research suggested that pattern baldness is an X-linked recessive trait. Would you expect to see independent assortment between genetic markers on the X chromosome and pattern baldness if (a) pattern baldness is sexinfluenced and (b) if pattern baldness is X-linked recessive? Explain your answer.
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.
Table 8.1 shows that Turner syndrome occurs when an individual inherits one X chromosome but lacks a second sex chromosome. Can Turner syndrome be due to nondisjunction during oogenesis, spermatogenesis, or both? If a phenotypically normal couple has a color-blind child (due to a recessive X-linked allele) with Turner syndrome, did nondisjunction occur duringoogenesis or spermatogenesis in this child’s parents? Explain your answer.
Normal vision (XA) in humans is dominant to color blindness (Xa) and is X-linked. A man with normal vision, whose father was colorblind, marries a colorblind woman. What are the chances that a son will be colorblind? What are the chances that a daughter will be colorblind? The determiner for brown eyes (B) is dominant to blue eyes (b) and is not X-linked. A colorblind man with brown eyes, whose mother was blue-eyed, marries a blue-eyed woman having normal vision, whose father was colorblind. Show the expected phenotypes ratio of their children involving eye color, color blindness, and sex.
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 ?
In humans, color vision depends on genes encoding three pigments. The R (red pigment) and G (green pigment) genes are close together on the X chromosome, whereas the B (blue pigment) gene is autosomal. A recessive mutation in any one of these genes can cause color blindness. Suppose that a color-blind man married a woman with normal color vision. The four sons from this marriage were color-blind, and the five daughters were normal. Specify the most likely genotypes of both parents and their children, explaining your reasoning. (A pedigree drawing will probably be helpful.) (Problem 50 is by Rosemary Redfield.)
: In Drosophila, yellow body is due to an X-linked gene that is recessive to the gene forgray body.(a) A homozygous gray female is crossed with a yellow male. The F1 are intercrossed toproduce F2. Give the genotypes and phenotypes, along with the expected proportions, of theF1 and F2 progeny.(b) A yellow female is crossed with a gray male. The F1 are intercrossed to produce the F2.Give the genotypes and phenotypes, along with the expected proportions, of the F1 and F2progeny.(c) A yellow female is crossed with a gray male. The F1 females are backcrossed with graymales. Give the genotypes and phenotypes, along with the expected proportions, of the F2progeny.(d) If the F2 flies in part b mate randomly, what are the expected phenotypic proportions offlies in the F3??
Anhidrotic ectodermal dysplasia is an X-linked recessive disorder in humans characterized by small teeth, no sweat glands, and sparse body hair. This trait is usually seen in men, but women who are heterozygous carriers of the trait often have irregular patches of skin with few or no sweat glands (see the illustration below). Q. Why does the distribution of the patches of skin lacking sweat glands differ among the females depicted in the illustration, even between the identical twins?
In Drosophila, the X-linked recessive mutation vermilion (v) causes bright red eyes, in contrast to the brick-red eyes of wild type. A separate autosomal recessive mutation, suppressor of vermilion (su-v), causes flies homozygous or hemizygous for v to have wildtype eyes. In the absence of vermilion alleles, su-v has no effect on eye color. Determine the F1 and F2 phenotypic ratios from a cross between a female with wild-type alleles at the vermilion locus, but who is homozygous for su-v, with a vermilion male who has wildtype alleles at the su-v locus
Butterflies have an X-Y sex-determination system that is different from that of flies or humans. Female butterflies may be either XY or X0, while butterflies with two or more X chromosomes are males. This photograph shows a tiger swallowtail gynandromorph, which is half male (left side) and half female (right side). Given that the first division of the zygote divides the embryo into the future right and left halves of the butterfly, propose a hypothesis that explains how nondisjunction during the first mitosis might have produced this unusual-looking butterfly. Question is also in the picture.
Duchenne muscular dystrophy is a recessive disorder caused by a rare,loss-of-function allele that is located on the X chromosome in humans. Anunaffected woman (i.e., without disease symptoms) who is heterozygousfor the X-linked allele causing Duchenne muscular dystrophy has childrenwith a man with a functional (non-disease-causing) allele. What is theprobability that this couple will have an unaffected son?