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Chromosomal Mutations

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Presentation on theme: "Chromosomal Mutations"— Presentation transcript:

1 Chromosomal Mutations
Changes in Chromosome Number or Structure Alterations of Inheritance Patterns by Gender

2 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

3 Aneuploidy Arises by Non-disjunction
Non-disjunction = failure of homologues or chromatids to separate during meiosis Normal Meiosis Non-disjunction in Meiosis I in Meiosis II

4 Human Chromosomal Aneuploids
Autosomal Aneuploids Down Syndrome Trisomy 21 Edward Syndrome Trisomy 18 Patau Syndrome Trisomy 13 Trisomy: three copies of one chromosome

5 Human Autosomal Abnormality
Down Syndrome Trisomy 21 Three copies of chromosome 21 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)

6 Karyotype for Down Syndrome
Physical Features Eye fold Palm Crease

7 Incidence of Down Syndrome Increases with Maternal Age
100 200 300 400 10 20 30 40 50 Number per 1000 Births Figure: FIGURE 12.20 Title: Down syndrome frequency increases with maternal age Caption: The increase in frequency of Down syndrome after maternal age 35 is quite dramatic. Age of Mother (years)

8 Applying Your Knowledge
Polyploidy Non-disjunction Aneuploidy Crossing-over Trisomy Which one involves the loss of one chromosome? Which one describes the failure of chromatids to separate in Anaphase II? Which one involves the gain of an extra set of chromosomes? Which is the most specific description for the cause of Down Syndrome?

9 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

10 Human Sex Chromosome Abnormality
Turner Syndrome XO One copy of X No 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)

11 Karyotype for Turner’s Syndrome
Non-functional Ovaries From Adult Female with Turner’s Syndrome Normal uterus, tubes and ovaries

12 Human Chromosomal Aneuploids
How can XYY Syndrome occur? One Copy of the X chromosome Two Copies of the Y chromosome Eg. Egg with 1 copy of X (23 chromosomes) Sperm with 2 copies of Y (24 chromosomes) = Embryo with XYY (47 chromosomes)

13 X-Chromosome Inactivation in Females
Inactivation of one of the X chromosomes in each cell of an adult female balances the sex chromosome/autosome ratio. Either the maternal or paternal chromosome is inactivated. The arrow shows a Barr body, or inactivated X. The number of Barr bodies equals the number of X chromosomes minus one. female male

14 Applying Your Knowledge
Determine how many Barr bodies would be found in each cell of someone with: Turner Syndrome 45, XO Triplo-X 47, XXX Klinefelter Syndrome 47, XXY XYY Syndrome 47, XYY 2 1

15 Chromosome Structure Changes
Description Deletion Loss of a chromosomal segment Duplication Repeat of a chromosomal segment Translocation Movement of chromosomal segment to non-homologous chromosome Inversion Reversal of a chromosomal segment (rotated 180o)

16 Chromosome Deletion in Humans
Cri-du-chat syndrome is correlated with a deletion at the end of chromosome 5.

17 Chromosome Duplication in Humans
Small duplications in chromosome 15 cause no symptoms Large duplication (with inversion) causes seizures and mental retardation

18 Chromosome Translocation in Humans
Reciprocal Translocation involves exchange between two non-homologous chromosomes Reciprocal translocation between chromosomes 2 and 20 causes Alagille Syndrome

19 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

20 Chromosome Inversions Lead to Unbalanced Meiotic Products
A paracentric inversion does not include the centromere A pericentric inversion includes the centromere

21 Applying Your Knowledge
Deletion Duplication Inversion Translocation Which type of structure change represents an exchange between two non-homologous chromosomes? represents a reversal of a chromosome segment? represents a loss of a chromosomal segment?

22 Interaction between Gender and Heredity
Sex-influenced characteristic Determined by autosomal genes Expression differs by gender Example: Pattern Baldness Caused by a dominant allele in males, but a recessive allele in females John Adams bb BB or Bb bb BB or Bb John Quincy Adams

23 Interaction between Gender and Heredity
Sex-limited characteristic Determined by autosomal genes Expressed only in one gender Cock-feathered male Hen-feathered female Hen-feathered male Cock feathering, autosomal recessive Expressed only in males

24 Interaction Between Gender and Heredity
Genomic Imprinting Expression of autosomal genes differs depending on whether they are inherited from the male or female parent Prader-Willi Syndrome Deletion on chromosome 15 inherited from father Angelman Syndrome Deletion on chromosome 15 inherited from mother

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