Chromosomal Mutations

Changes in Chromosome Number or Structure

Alterations of Inheritance Patterns by Gender

Alterations in Chromosome Number

• Polyploidy: one or more extra sets of chromosomes

• Aneuploidy: gain or loss of one chromosome or a small number of chromosomes

Aneuploidy• Arises by Non-disjunction• Non-disjunction = failure of homologues or

chromatids to separate during meiosis

Normal Meiosis

Non-disjunction in Meiosis I

Non-disjunction in Meiosis II

Human Chromosomal Aneuploids

Down Syndrome Trisomy 21

Edward Syndrome Trisomy 18

Patau Syndrome Trisomy 13

Autosomal Aneuploids

Trisomy: three copies of one chromosome

Human Autosomal Abnormality

How can Down Syndrome occur?

Eg. Egg with 2 copies of #21 (24 chromosomes) + Sperm with 1 copy of #21 (23 chromosomes) = Embryo with 3 copies of #21 (47 chromosomes)

Down Syndrome Trisomy 21

Three copies of chromosome 21

Karyotype for Down Syndrome

Eye fold Palm Crease

Physical Features

Incidence of Down Syndrome Increases with Maternal Age

10 20 30 40 500

100

200

300

400

Age of Mother (years)

Num

ber p

er 1

000

Birth

s

Applying Your Knowledge

A. Which one involves the loss of one chromosome?

B. Which one describes the failure of chromatids to separate in Anaphase II?

C. Which one involves the gain of an extra set of chromosomes?

D. Which is the most specific description for the cause of Down Syndrome?

1. Polyploidy2. Non-

disjunction3. Aneuploidy4. Crossing-

over5. Trisomy

Human Chromosomal Aneuploids

Sex Chromosome Aneuploids

Turner Syndrome 45, XO

Triplo-X 47, XXX

Klinefelter Syndrome 47, XXY

XYY Syndrome 47, XYY

Sterile female

Fertile female

Sterile male

Fertile male

Human Sex Chromosome Abnormality Turner Syndrome XO

One copy of XNo second sex chromosome

How can Turner Syndrome occur?Eg. Egg with 0 copies of X (22 chromosomes) +Sperm with 1 copy of X (23 chromosomes) = Embryo with 1 copy of X (45 chromosomes)

Karyotype for Turner’s Syndrome

Chromosome Structure Changes

Change Description Deletion Loss of a chromosomal

segmentDuplication Repeat of a chromosomal

segment Translocation Movement of chromosomal

segment to non-homologous chromosome

Inversion Reversal of a chromosomal segment (rotated 180o)

Chromosome Deletion in Humans

Cri-du-chat syndromeis correlated witha deletion at the endof chromosome 5.

Chromosome Duplication in Humans

Small duplications in chromosome 15 cause no symptoms

Large duplication (with inversion) causes seizures and mental retardation

Chromosome Translocation

in Humans

Reciprocal Translocation involves exchange between two non-homologous chromosomes

Reciprocal translocation between chromosomes 2 and 20 causes Alagille Syndrome

Chromosome Translocation in Humans

Robertsonian Translocation involves a fusion of the long arms of two different chromosomes

Translocation Down Syndrome involves a Robertsonian Translocation between chromosomes 14 and 21

Applying Your Knowledge

Which type of structure change a. represents an exchange between two

non-homologous chromosomes? b. represents a reversal of a chromosome

segment? c. represents a loss of a chromosomal

segment?

1. Deletion2. Duplication3. Inversion4. Translocation

Interaction between Gender and Heredity Sex-influenced characteristic

Determined by autosomal genesExpression differs by gender

bb

BB or Bb bb

BB or Bb

Example: Pattern BaldnessCaused by a dominant allele in males,

but a recessive allele in females

John Adams

John Quincy Adams