Alterations of C’some Structure & Number

8.19-8.23

1. Karyotype

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

2. Down Syndrome

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 defectsMothers over 35 have an

increased risk of having a child w/ down syndrome

3. Alterations in C’some Number

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

4. Abnormal C’some Num. of Sex C’somes

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’somesThe 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

5. Chromosomal Alterations

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