Chapter 9 Outline 9.1 Chromosome Mutations Include Rearrangements, Aneuploids, and Polyploids, 238 9.2 Chromosome Rearrangements Alter Chromosome Structure, 240 9.3 Aneuploidy Is an Increase or Decrease in the Number of Individual Chromosomes, 249 9.4 Polyploidy Is the Presence of More than Two Sets of Chromosomes, 255 9.5 Chromosome Variation Plays an Important Role in Evolution, 260

9.1 Chromosome Mutations Include Rearrangements, Aneuploids, and Polyploids Chromosome Morphology (position of the centromere on the chromosome): Metacentric Submetacentric Acrocentric Telocentric

Types of Chromosome Mutations Rearrangements: Aneuploidy Polyploidy

9.3 Chromosome mutations consist of chromosome rearrangements, aneuploids, and polyploids. Duplications, trisomy, and autotriploids are examples of each category of mutation.

9.2 Chromosome Rearrangements Alter Chromosome Structure Duplication

9.5 In an individual heterozygous for a duplication, the duplicated chromosome loops out during pairing in prophase I.

9.6 The Bar phenotype in Drosophila melanogaster results from an X-linked duplication. (a) Wild-type fruit flies have normal-size eyes. (b) Flies heterozygous and (c) homozygous for the Bar mutation have smaller, bar-shaped eyes. (d) Flies with double Bar have three copies of the duplication and much smaller bar-shaped eyes.

9.8 Unbalanced gene dosage leads to developmental abnormalities.

9.2 Chromosome Rearrangements Alter Chromosome Structure Deletions

9.9 In an individual heterozygous for a deletion, the normal chromosome loops out during chromosome pairing in prophase I.

9.2 Chromosome Rearrangements Alter Chromosome Structure Inversion (depends on the involvement of the centromere in the inversion): Paracentric inversion Pericentric inversion

9.12 In a heterozygous individual, a single crossover within a paracentric inversion leads to abnormal gametes.

9.13 In a heterozygous individual, a single crossover within a pericentric inversion leads to abnormal gametes.

9.13 In a heterozygous individual, a single crossover within a pericentric inversion leads to abnormal gametes.

9.14 Chromosome 4 differs in humans and chimpanzees in a pericentric inversion.

Translocation Nonreciprocal translocation Reciprocal translocation Robertsonian translocation

9.15 In a Robertsonian translocation, the short arm of one acrocentric chromosome is exchanged with the long arm of another.

9.16 In an individual heterozygous for a reciprocal translocation, crosslike structures form in homologous pairing.

9.17 Human chromosome 2 contains a Robertsonian translocation that is not present in chimpanzees, gorillas, or orangutans. G-banding reveals that a Robertsonian translocation in a human ancestor switched the long and short arms of the two acrocentric chromosomes that are still found in the other three primates. This translocation created the large metacentric human chromosome 2.

9.3 Aneuploidy Is an Increase or Decrease in the Number of Individual Chromosomes Causes of Aneuploidy: Deletion of centromere during mitosis and meiosis Robertsonian translocation Nondisjunction during meiosis and mitosis

9.19a Aneuploids can be produced through nondisjunction in meiosis I, meiosis II, and mitosis. The gametes that result from meioses with nondisjunction combine with a gamete (with blue chromosome) that results from normal meiosis to produce the zygotes. (a) Nondisjunction in meiosis I.

9.19b Aneuploids can be produced through nondisjunction in meiosis I, meiosis II, and mitosis. The gametes that result from meioses with nondisjunction combine with a gamete (with blue chromosome) that results from normal meiosis to produce the zygotes. (b) Nondisjunction in meiosis II.

9.19c Aneuploids can be produced through nondisjunction in meiosis I, meiosis II, and mitosis. The gametes that result from meioses with nondisjunction combine with a gamete (with blue chromosome) that results from normal meiosis to produce the zygotes. (c) Nondisjunction in mitosis.

Types of Aneuploidy Nullisomy: loss of both members of a homologous pair of chromosomes. 2n − 2 Monosomy: loss of a single chromosome. 2n − 1 Trisomy: gain of a single chromosome. 2n + 1 Tetrasomy: gain of two homologous chromosomes. 2n + 2

Concept Check 3 A diploid organism has 2n = 36 chromosomes. How many chromosomes will be found in a trisomic member of this species?

Concept Check 3 A diploid organism has 2n = 36 chromosomes. How many chromosomes will be found in a trisomic member of this species? 2n + 1 = 36 + 1 = 37

Effects of Aneuploidy in Plants

9.20 Mutant capsules in Jimson weed (Datura stramonium) result from different trisomies. Each type of capsule is a phenotype that is trisomic for a different chromosome.

Effects of Aneuploidy in Humans Sex-chromosome aneuploids: Turner syndrome. XO Klinefelter sydrome. XXY

Effects of Aneuploidy in Humans Autosomal aneuploids: Trisomy 21 – Down syndrome Primary Down syndrome, 75% random nondisjunction in egg formation Familial Down syndrome, Robertsonian translocation between chromosomes 14 and 21

9.21 Primary Down syndrome is caused by the presence of three copies of chromosome 21. Karyotype of a person who has primary Down syndrome. [L. Willatt, East Anglian Regional Genetics Service/Science Photo Library/Photo Researchers.]

9.22 The translocation of chromosome 21 onto another chromosome results in familial Down syndrome. Here, the long arm of chromosome 21 is attached to chromosome 15. This karyotype is from a translocation carrier, who is phenotypically normal but is at increased risk for producing children with Down syndrome. [Dr. Dorothy Warburton, HICCC, Columbia University.]

9.23 Translocation carriers are at increased risk for producing children with Down syndrome.

Effects of Aneuploidy in Humans Autosomal aneuploids: Trisomy 18 – Edward syndrome, 1/8000 live births Trisomy 13 – Patau syndrome, 1/15,000 live births Trisomy 8 – 1/25,000 ~ 1/50,000 live births Why is there a drastic decrease in frequency of these trisomic syndromes from chromosome 18 to chromosome 8?

Effects of Aneuploidy in Humans Autosomal aneuploids: Aneuploidy and maternal age Possible interpretation of this connection Uniparental disomy: Both chromosomes are inherited from the same parent. Mosaicism and nondisjunction in mitotic division

Down syndrome is caused by the presence of three copies of one or more genes located on chromosome 21. [Stockbyte.]

9.24 The incidence of primary Down syndrome and other aneuploids increases with maternal age.

9.4 Polyploidy Is the Presence of More than Two Sets of Chromosomes Autopolyploidy: From single species Allopolyploidy: From two species

9.26a Autopolyploidy can arise through nondisjunction in mitosis or meiosis.

9.26b Autopolyploidy can arise through nondisjunction in mitosis or meiosis.

9.28 Most allopolyploids arise from hybridization between two species followed by chromosome doubling.

9.5 Chromosome Variation Plays an Important Role in Evolution New and extra copies of genes give rise to new functions. New and extra sets of genes may give rise to new species.