Nondisjunction GT pg.363-364 (Section 13.10) chromosomal mutation, p.408 (Last paragraph)?? Reg- p. 401, top 374

Objective: Discuss the effects of nondisjunction Answer: What is crossing over? What phase of meiosis does it occur?

Review: What is a mutation? Mutation: A change in the nucleotide sequence of DNA A single nucleotide change can have serious effects Mutation: A change in DNA A single nucleotide change (insertion, deletion, substitution) could lead to the production of a different protein A change in the nucleotide sequence of DNA (mutation) at even one location, can have serious effects.

Chromosomal mutation A chromosomal mutation involves a change in the structure or number of chromosomes 4 types of chromosomal mutations: Deletion: loss of all or part of a chromosome Duplication: extra copy of all or part of a chromosome Inversion: reverses the direction of parts of a chromosome Translocation: part of one chromosome breaks off and attaches to another chromosome Translocation- Found in a form of leukemia. Mutation called the Philadelphia chromosome- parts of chromosomes 9 and 22 break off and are translocated (exchanged position)

Nondisjunction Other types of chromosomal mutations alter the number of chromosomes found in the cell. Nondisjunction: The failure of homologous chromosomes or sister chromatids to separate during meiosis. Produces gametes that have too many or too few chromosomes Normal meiosis Reg book: “not coming apart”

Nondisjunction

Disorders due to Nondisjunction In humans, a zygote with 45 chromosomes has only one copy of a particular chromosome monosomy In humans, a zygote with 47 chromosomes has three copies of a particular chromosome trisomy Example Down syndrome (trisomy 21)

Nondisjunction in the Sex Chromosomes Nondisjunction can also affect the sex chromosomes, where there can be too many or too few X or Y chromosomes (XX- normal female, XY-normal male) Examples of disorders: XXY (Klinefelter’s syndrome) XO (Turner’s syndrome)

Karyotype Karyotype: a picture of chromosomes in a dividing cell that are arranged in pairs by size. First 22 pairs are autosomes Last pair are the sex chromosomes

Karyotype A * Normal male

Karyotype B * Normal female

Karyotype C * Turner’s syndrome * Only 1 sex chromosome (X)- XO * Webbed neck, short stature, and infertility * Female

Karyotype D * Cri du chat syndrome * Deletion of short arm of chromosome 5 * Distinctive cry, low birth weight, respiratory problems, may have a shortened lifespan * Female X Y

Karyotype E * Klinefelter’s syndrome * 2 X chromosomes and 1 Y (XXY) * Tall, sterile, feminine characteristics, sometimes mentally retarded * Male

Karyotype F * Down syndrome * 3 copies of chromosome 21 (Trisomy 21) * Mental retardation, characteristic facial features, short stature, and heart defects * Male