Heredity and Development Second Edition (1972) / Chapter Skim
Currently Skimming:
9 The Genetics of Man
9 The Genetics of Man
Pages 209-226
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 209... ...
Nevertheless, many of the statements that will be made in this chapter are more in the nature of probable hypothesis than of fact. Many patterns of inheritance, originally thought to be clear examples of autosomal recessives, autosomal dominants, sex-linked genes, and so on, have been shown by later data to be more complex.
|
From page 210... ...
Figure 9–1 shows a hypothetical example of the inheritance of red hair (r) , which seems to be an autosomal recessive to non-red hair (R)
|
From page 211... ...
analbuminemia lack of serum albumen anophthalmos lack of eyes bird-headed dwarf abnormally shaped head congenital cataract opacity of lens color blindness lack of cones in eye congenital deafmutism deaf at birth; rarely learns to speak cretinism abnormal development due to defective thyroid Friedreich's ataxia degeneration of parts of nervous system hermaphroditism ovary and testis in same individual hypotrichosis little or no hair lactase deficiency lactase enzyme absent in adults microcephaly brain greatly reduced in size muscular atrophy degeneration of muscles. Death in infancy muscular dystrophy degeneration of muscles in later life pernicious anemia abnormal blood cells; caused by lack of absorption of vitamin B12 in intestine phenylketonuria mental retardation due to lack of an enzyme pituitary dwarfism small size due to deficiency in growth hormone of the pituitary Even this short list reveals the broad spectrum of phenotypes caused by homozygosity for autosomal genes.
|
From page 212... ...
Here are some of them. achondroplasia skull and other skeletal abnormalities aniridia absence of iris baldness possibly a recessive in females brachydactyly short fingers canine teeth upper canines absent hereditary cataract opacity of lens cleft palate separation of palate and often of upper lip corneal dystrophy clouding of the cornea congenital deafness can be caused by many different genes
|
From page 213... ...
. The males inherit their X chromosomes solely from their mothers and transmit them solely to their daughters.
|
From page 214... ...
ocular albinism iris nearly colorless albinism with deafness little or no pigment; little or no hearing congenital cataract opacity of the lens color blindness nearly complete absence of cones in eye congenital deafness one of the many genes causing deafness diabetes insipidus excess urine related to neurohypophyseal abnormality ectodermal dysplasia absence of teeth, hair, and sweat glands G6PD absence or deficiency of the enzyme glu cose-6-phosphate dehydrogenase classical hemophilia defective coagulation of blood hypophosphatemia low blood phosphorus resulting in rickets not cured by vitamin D ichthyosis scaly skin megalocornea enlarged cornea mental deficiency many genes, including those on the X, can be a cause microphthalmia eyes reduced or absent muscular dystrophy degeneration of muscles night blindness poor vision at night retinoschisis degeneration of the retina Most of the X chromosome mutants behave as recessives. They will, naturally, be expressed in males whether they are dominant or recessive.
|
From page 215... ...
But this is only the beginning of the complexity. Earlier we saw that a change in the β cistron resulted in the substitution of one amino acid for another and the consequence was sickle cell hemoglobin (page 182)
|
From page 216... ...
The agglutinated erythrocytes are destroyed, a severe anemia results, and the baby's blood-forming system is stimulated into abnormal activity. The frequency of these events -- an Rh-negative mother first conceiving an Rh-positive child, then producing antibodies against the Rhesus anti
|
From page 217... ...
A discovery that was made in the cat was later extended to man. If the epidermal cells scraped from the inside of the cheek are stained, and studied, it is found that the resting nucleus has a small, deeply staining area, which was given the name Barr body after its discoverer Murray Barr.
|
From page 218... ...
A male would have only a single X, that is there would be one less chromosome in Group C His Y would resemble one of the G Group chromosomes.
|
From page 219... ...
There is no Barr body in the nucleus of normal males, which means that the single X is not condensed. When the various techniques for the study of human chromosomes were perfected, they were used for some difficult medical problems, ones that had baffled diagnosticians.
|
From page 220... ...
Trisomy is known for other autosomes as well: chromosome 16, chromosome 18, and one of the chromosomes of the D group. These variations in chromosome number, of both sex chromosomes and autosomes, are assumed to be due to errors in meiosis.
|
From page 221... ...
It is also probable that many spontaneous abortions are of embryos that have specific gene defects (as distinct from the gross chromosomal defects)
|
From page 222... ...
Success on an intelligence test is greatly influenced by innate ability but to this we must add the influences of the home environment, schools, mass media, books, friends, opportunities, community, and the historic period in which a person lives. Some geneticists have made a guess that heredity contributes about 80 per cent and the environment 20 per cent to one's performance on an intelligence test.
|
From page 223... ...
In spite of the enormous amount of time and effort that has gone into attempts to measure intelligence, it is the overwhelming opinion of geneticists, psychologists, and sociologists that no innate differences in ability have been demonstrated for various races and ethnic groups. As of today, one cannot say that the intelligence of men or women or of blacks and whites is different; neither can one say they are the same.
|
From page 224... ...
But if man is unwilling to select for what is ‘good,' might he be willing to prevent what is ‘bad'? There are some inherited characteristics of man that most individuals would agree are undesirable: congenital deafness, blindness, gross deformities of the body, idiocy, and so on.
|
From page 225... ...
How would you suggest that this information be used? Suggested Readings Chapter 8 of the Readings reproduces an article by Joshua Lederberg in which he explores some of the possibilities of using genetics for human welfare.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.