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February 23, 2009 Objective: Discuss the effects of nondisjunction Drill: What is crossing over? What phase of meiosis does it occur?

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Presentation on theme: "February 23, 2009 Objective: Discuss the effects of nondisjunction Drill: What is crossing over? What phase of meiosis does it occur?"— Presentation transcript:

1 February 23, 2009 Objective: Discuss the effects of nondisjunction Drill: What is crossing over? What phase of meiosis does it occur?

2 Nondisjunction

3 Review: What is a mutation? Mutation: A change in the nucleotide sequence of DNA –A single nucleotide change can have serious effects

4 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

5 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

6 Nondisjunction

7 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)

8 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)

9 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

10 Karyotype A * Normal male

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

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

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

14 Karyotype E * Normal female

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


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