BIOLOGY 12

CHROMOSOMAL MUTATIONS

referenced Horton High E-Biology

Chromosomal Mutations

changes in chromosomal number

changes in chromosomal structure

Chromosomal Number

monosomy occurs when and individual has only one of a particular type of chromosome

trisomy occurs when and individual has three of a particular type of chromosome

monosomy and trisomy occur in plants and animals generally lethal in the body cells of animals

nonlethal human monosomies and trisomies include the following:

Turner syndrome: monosomy where the individual has single X chromosome

Down syndrome is most common trisomy among humans; it involves chromosome 21

Chromosomal Number cont.

nondisjunction is the failure of chromosomes to separate it is more common during meiosis I than meiosis II it can occur in mitosis

polyploidy: offspring end up with more than two complete sets of chromosomes polyploidy does not increase variation in animals,

would likely be lethal polyploidy is a major evolutionary mechanism in plants successful polyploidy results in a new species

Chromosomal Structure

Disorders Down syndrome

most common autosomal trisomy, involves chromosome 21 Down syndrome child has tendency for leukemia, cataracts, faster

aging, and mental retardation

Turner (XO) syndrome females have only one sex chromosome, an X Turner females are short, have broad chest and webbed neck ovaries of Turner females never become functional; therefore, do not

undergo puberty

Klinefelter syndrome males have one Y chromosome and two or more X chromosomes affected individuals are sterile males; testes and prostate are

underdeveloped individuals have large hands and feet and long arms and legs

Disorders cont. Triplo-X females

have three or more X chromosomes there is no increased femininity; most lack any physical

abnormalities there is an increased risk of having triplo-X daughters of

XXY sons may experience menstrual irregularities, including early

onset of menopause

XYY males with Jacob syndrome have two Y chromosomes instead of one results from nondisjunction during meiosis II usually taller than average; suffer from persistent acne; tend

to have lower intelligence earlier claims that XYY individuals were likely to be

aggressive are not correct

Disorders cont.

Fragile X Syndrome X chromosome is nearly broken; most often

found in males as children: hyperactive or autistic; delayed

speech; account for part of higher proportion of males in institutions for mentally retardation

as adults: large testes, unusually protruding ears

occurs in females, but symptoms are less severe