Many traits in plants and animals are heritable can be passed down from one generation to the nextand genetics is the study of these heritable factors. Specific conditions and rare syndromes may have a genetic basis. Where this is the case, there will be a variety of causes.
Asparagus urine. Some people have a prominent dimple or crease in the front of the chin, called a cleft chin or "butt chin" ; others do not. This is sometimes said to be controlled by a single gene with two alleles, with cleft chin C dominant to smooth chin S.
Our proband is a year-old man, who is affected with soft cleft palate and hypernasality. A study of about six generations of this family pedigree shows that cleft palate has repeatedly occurred in males, with probably a X-linked recessive pattern of inheritance. Interestingly, the sister of the proband is affected with hypernasality and she has an affected son.
In humans, there are hundreds of genes located on the X chromosome that have no counterpart on the Y chromosome. The traits governed by these genes thus show sex-linked inheritance. This type of inheritance has certain unique characteristics, which include the following: 1 There is no male-to-male father-to-son transmission, since sons will, by definition, inherit the Y rather than the X chromosome.
Autosomal dominant inheritance means that the gene involved is not on one of the sex chromosomes and so males and females have the same chance of being affected. It also means that a person only needs to have one changed gene before they have the disorder. The normal gene is not able to make up for the gene with a change in it.
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Klinefelter syndrome is characterized by the presence of an extra one or more X chromosome in male individuals, giving a 47,XXY rather than 46,XY karyotype. Variants of Klinefelter syndrome can include three or more copies of the X chromosome and are typically more severe. Phenotypic manifestations include hypogonadism, gynecomastia after puberty, and infertility due to testicular failure.
In general, inheritance patterns for single gene disorders are classified based on whether they are autosomal or X-linked and whether they have a dominant or recessive pattern of inheritance. These disorders are called Mendelian disordersafter the geneticist Gregor Mendel. In autosomal dominant inheritance, only one copy of a disease allele is necessary for an individual to be susceptible to expressing the phenotype. Unless a new mutation has occurred, all affected individuals will have at least one parent who carries the disease allele.
What do you know about your family tree? Have any of your relatives had health problems that tend to run in families? Which of these problems affected your parents or grandparents?