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

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Presentation on theme: "Chromosomal Mutations Changes in Chromosome Number or Structure Alterations of Inheritance Patterns by Gender."— 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 Polyploidy: one or more extra sets of chromosomes Aneuploidy: gain or loss of one chromosome or a small number of chromosomesAneuploidy: gain or loss of one chromosome or a small number of chromosomes

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

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

5 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) + Sperm with 1 copy of #21 (23 chromosomes) = Embryo with 3 copies of #21 (47 chromosomes) = Embryo with 3 copies of #21 (47 chromosomes) Down Syndrome Trisomy 21 Three copies of chromosome 21

6 Karyotype for Down Syndrome Eye fold Palm Crease Physical Features

7 Incidence of Down Syndrome Increases with Maternal Age Age of Mother (years) N u m b e r p e r B i r t h s

8 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. Polyploidy 2. Non-disjunction 3. Aneuploidy 4. Crossing-over 5. Trisomy

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

12 Human Chromosomal Aneuploids How can XYY Syndrome occur? One Copy of the X chromosome One Copy of the X chromosome Two Copies of the Y 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 InactivationInactivation 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. TheThe arrow shows a Barr body, or inactivated X. 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

15 Chromosome Structure Changes ChangeDescription 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 180 o )

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 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.Deletion 2.Duplication 3.Inversion 4.Translocation

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

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

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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