Karyotype- magnified images of chromosomes that are arranged in order A human karyotype

Mistakes during meiosis lead to gametes that have an incorrect dumber of c’somes or have major changes in the structure of the c’some

Called trisomy 21 b/c instead of two num 21 c’somes there are three Usually human embryos w/ an abnormal amount of c’somes are self aborted. Down syndrome produces mild to severe mental retardation It is characterized by: increased susceptibility to many diseases higher frequency of some birth defects Mothers over 35 have an increased risk of having a child w/ down syndrome

Meiosis occurs over & over again in our testes and ovaries to produces gametes w/o error Nondisjunction- occurs when homologous chromosomes fail to separate. The result is abnormal c’some number

Abnormal numbers of sex c’somes (X or Y) do not affect the survival of the individual Y chromosomes is very small has fewer genes than other c’somes The Y chromosome mostly affects maleness, which noes not dictate survival Cells can tolerate only one copy of a functioning X c’some in each cell b/c the other copies are usually inactivated in each cell

Klinefelter Syndrome (XXY)

Turner Syndrome (X0) Only one X c’some in each cell

Abnormalities in chromosomes structure can cause disorders Deletion- involve the loss of all or part of a chromosome

Duplication- produce extra copies of parts of a chromosome.

Inversion- reverses the direction of parts of chromosomes

Translocation- occurs when part of one chromosome breaks off and attaches to another