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Chapter 15 notes The Chromosomal Basis of Inheritance.

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Presentation on theme: "Chapter 15 notes The Chromosomal Basis of Inheritance."— Presentation transcript:

1 Chapter 15 notes The Chromosomal Basis of Inheritance

2 Concept 15.1 In 1902 Sutton noted the parallels between the behavior of chromosomes and the behavior of Mendel’s factors. Chromosomal theory of inheritance: genes have specific loci on chromosomes, and the chromosomes undergo segregation and independent assortment

3 Concept 15.1

4 Morgan traced a gene to a specific chromosome - Morgan used Drosophila “fruit flies” for his experiments - only 4 pairs of chromosomes - wild type flies have red eyes - white eyes is a mutant phenotype

5 Concept 15.1 - Morgan mated the white-eyed male to a red-eyed female - all F 1 offspring were red-eyed - The F 2 offspring were not 3:1; instead all females were red-eyed while half of the males had red and half had white eyes - eye color was linked to the fly’s sex

6 Concept 15.1 Genes located on sex chromosomes are called sex-linked genes - Morgan’s evidence that a specific gene is carried on the X chromosome helped confirm the chromosomal theory of inheritance.

7 Concept 15.1

8 Concept 15.2 linked genes: genes that are located on the same chromosomes and tend to be inherited together - linked genes deviate from expected Mendelian ratios -ex. in flies body color and wing shape are inherited together

9 Concept 15.2

10 Genetic recombination: the production of new combinations of traits inherited from two parents yellow-round x green-wrinkled YyRr x yyrr Parental types: when the offspring phenotypes are identical to the parents - ex ¼ YyRr, ¼ yyrr

11 Concept 15.2 Recombinants: when the offspring phenotypes are new combinations ex ¼ Yyrr, ¼ yyRr When 50% of all offspring are recombinants, we say there is a 50% frequency of recombination - 50% frequency is observed for genes located on different chromosomes

12 Concept 15.2 Geneticists can use recombination data to map a chromosomes genetic loci Genetic map: an ordered list of the genetic loci along a particular chromosome Linkage map: a genetic map based on recombination frequencies

13 Concept 15.2 Map of body-color (b), wing-size (vg) and cinnabar (cn) - cn and b is 9% - cn and vg is 9.5% - b and vg is 17%

14 Concept 15.2

15 Concept 15.3 Sex-linked genes have unique patterns of inheritance - fathers pass sex-linked alleles to daughters, but not sons - mothers pass sex-linked alleles to both sons and daughters

16 Concept 15.3 Because males only have one locus, they cannot be heterozygous Sex-linked disorders in humans - muscular dystrophy: 1/3500 males in the US - hemophilia: absence of proteins for blood clotting

17 Concept 15.3

18 Concept 15.4 Nondisjunction: the members of a pair of homologous chromosomes do not move apart properly during meiosis I or II. - gametes are (n+1) or (n-1) if they have too many or too few chromosomes

19 Concept 15.4 Aneuploidy: having an abnormal chromosome number Trisomic: a chromosome in triplicate (2n+1); ex. trisomy 21 (Down’s syndrome) Monosomic: if a chromosome is missing (2n-1)

20 Concept 15.4

21 Polyploidy: organisms that have more than two complete chromosome sets - triploidy (3n) - tetraploidy (4n) Polyploids are more normal in appearance than aneuploids

22 Concept 15.4

23 Breakage of a chromosome can lead to four types of changes in chromosome structure Deletion: occurs when a chromosomal fragment lacking a centromere is lost during cell division

24 Concept 15.4 Duplication: a fragment becomes attached as an extra segment to a sister chromatid Inversion: a chromosomal fragment can reattach to the original chromosome in reverse order Translocation: the fragment joins a nonhomologous chromosome

25 Concept 15.4

26 Alterations in chromosome number and structure are associated with several human disorders - Down syndrome: 1/700 children born; extra 21 st chromosome - Klinefelter syndrome: XXY male - Turner syndrome: XO female

27 Concept 15.4



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