5 Four things that cause mutations Four things that cause mutations. 1) Errors in replication 2) Errors in transcription 3) Errors in cell division 4) External agents
6 Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides within a gene in a sperm or an egg cell.
7 If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the offspring.
8 The mutation may produce a new trait or it may result in a protein that does not work correctly.
9 Sometimes, the mutation results in a protein that is nonfunctional, and the embryo may not survive. In some rare cases, a gene mutation may have positive effects.
10 If the DNA of a non-reproductive cell is changed, the mutation would not be passed on to offspring. However, the mutation may cause problems for the individual.
11 Mutations that produce changes in whole chromosomes are known as chromosomal mutations. A karyotype is an organized profile of a person's chromosomes. In a karyotype, chromosomes are arranged and numbered by size, from largest to smallest. This helps scientists quickly identify chromosomal changes that may result in a genetic disorder.
12 Few chromosomal mutations are passed on to the next generation because the zygote usually dies.
13 In cases where the zygote lives and develops, the mature organism is often sterile and thus incapable of producing offspring.
14 The 4 kinds of chromosomal mutations are: deletions, duplications, inversions, and translocations.
15 Cri-du-chatBabies with the cry of the cat syndrome have a cry which sounds like that of a cat in distress because the infant’s larynx is improperly developed. Cri-du0chat babies are severely mentally retarded and have a small cranium. The incidences of this syndrome is 1 in 100,000 live births.Caused by a partial deletion of chromosome 5
16 Polyploidy is a condition in which an organism has extra sets of chromosomes.
17 Trisomy occurs when someone is born with three copies of a chromosome Trisomy occurs when someone is born with three copies of a chromosome. Down Syndrome is the most common form of trisomy. In Down Syndrome, chromosome 21 is tripled.
18 Down’s SyndromeTrisomy 21, one of the most common causes of mental retardation is due to an extra chromosome 2`. This results in a number of characteristic features, such as short stature, broad hands, stubby fingers and toes, and a wide rounded face. Individuals with this syndrome have a high incidence of heart defects and lukemia. The average risk of having a child with Down’s syndrome is 1 in 750 live births. Mothers in their early twenties have a risk of 1 in 1,500, women over 35 have a risk factor of 1 in 70.
19 Edward’s SyndromeTrisomy 18 produces severe mental retardation and a highly characteristic pattern of malformations such as elongated skull, a narrow pelvis, rocker bottom feet. Nearly all babies born with this syndrome die in early infancy. The frequency of this syndrome is 1 in 5,000 live births.
20 Patau SyndromeThis syndrome (trisomy 13) causes severely abnormal cerebral functions and virtually always leads to death in early infancy. This baby has very pronounced clefts of the lip and palate, broad nose, small cranium and nonfunctional eyes. Heart defects and severe mental retardation are also part of the clinical picture. The frequency is 1 in 15,000 live births.
21 Nondisjunction occurs when homologous chromosomes do not separate Nondisjunction occurs when homologous chromosomes do not separate. The result may be abnormal numbers of chromosomes in the gametes. Nondisjunction is the most common error in meiosis.
22 Turner Syndrome (XO)This is a result of nondisjunction in meiosis. These girls appear normal before puberty, but as they grow secondary sex characteristics do not develop and no ova are produced. The frequency of this syndrome is 1 in 2,500 live births.
23 Klinefelter Syndrome (XXY) This is a result of nondisjunction in meiosis. The frequency of this condition is 1 in 1,000 live male births. Characteristics include a tall stature and sterility. Men appear normal in other ways.
24 Jacobs (XYY)A chromosome aberration which is caused by nondisjunction of the Y chromosome during the second phase of meiosis. Occurrence is 1 in 1,000 live male births. Men with this abnormality are tall and have low mental ability.
25 Triple XOccurs at a frequency of 1 in 1,000 female live births. No specific abnormalities are associated with this condition. The vast majority of women with this condition are normal mentally and physically and are fertile.
26 Genetic tests are now available for hundreds of disorders making it possible to determine whether prospective parents risk passing such genes to their children. DNA testing can pinpoint the exact genetic basis of a disorder making it possible to develop more effective treatment for individuals affected by genetic disease.
27 Beneficial mutations may produce proteins with new or altered activities that can be useful to organisms in different or changing environments.