The Chromosome Theory of Inheritance wolf/power%20points/chapt04b_lecture.ppt.

The Chromosome Theory of The Chromosome Theory of InheritanceInheritance

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Outline of Chromosome Outline of Chromosome Theory of InheritanceTheory of Inheritance

Observations and experiments determined Observations and experiments determined the hereditary material in the nucleus on the hereditary material in the nucleus on the chromosomesthe chromosomes

Mitosis ensures that every cell in an Mitosis ensures that every cell in an organism carries same set of organism carries same set of chromosomeschromosomes

Meiosis distributes one member of each Meiosis distributes one member of each chromosome pair to gamete cellschromosome pair to gamete cells

Validation of the chromosome theory of Validation of the chromosome theory of inheritanceinheritance

Evidence that Genes Reside Evidence that Genes Reside in the Nucleusin the Nucleus

1667 – Anton van Leeuwenhoek1667 – Anton van Leeuwenhoek Semen contains spermatozoa (sperm Semen contains spermatozoa (sperm

animals)animals) Hypothesized that sperm enter egg to Hypothesized that sperm enter egg to

achieve fertilizationachieve fertilization 1854-1874 – confirmation of 1854-1874 – confirmation of

fertilization through union of eggs fertilization through union of eggs and spermand sperm Recorded frog and sea urchin Recorded frog and sea urchin

fertilization using microscopy and time-fertilization using microscopy and time-lapse drawings and micrographslapse drawings and micrographs

Evidence that Genes Reside Evidence that Genes Reside in Chromosomesin Chromosomes

1880s – innovations in microscopy and 1880s – innovations in microscopy and staining techniques identified thread-staining techniques identified thread-like structureslike structures

Follow movement of chromosomes Follow movement of chromosomes during cell divisionduring cell division

Mitosis – two daughter cells contained Mitosis – two daughter cells contained same number of chromosomes as parent same number of chromosomes as parent cell (somatic cells)cell (somatic cells)

Meiosis – daughter cells contained half Meiosis – daughter cells contained half the number of chromosomes as the the number of chromosomes as the parents (sperm and eggs)parents (sperm and eggs)

One Chromosome Pair One Chromosome Pair Determines an Individual’s Determines an Individual’s

SexSex Walter Sutton – Studied great lubber Walter Sutton – Studied great lubber

grasshoppergrasshopper Parent cells contained 22 Parent cells contained 22

chromosomes plus an X and a Y chromosomes plus an X and a Y chromosomechromosome

Daughter cells contained 11 Daughter cells contained 11 chromosomes and X or Y in equal chromosomes and X or Y in equal numbersnumbers

After After fertilization fertilization Cells with XX Cells with XX

were femaleswere females Cells with XY Cells with XY

were maleswere males

Great lubber grasshopper

(Brachystola magna)Fig. 4.2

Sex chromosomeSex chromosome Provide basis for Provide basis for

sex sex determinationdetermination

One sex has One sex has matching pairmatching pair

Other sex has Other sex has one of each type one of each type of chromosomeof chromosome

Photomicrograph of humanX and Y chromosome Fig. 4.3a

Sex Sex determination determination in humansin humans Children Children

receive only receive only an X an X chromosome chromosome from mother from mother but X or Y but X or Y from fatherfrom father

Fig. 4.3b

The number and shape of The number and shape of chromosomes vary from chromosomes vary from

species to speciesspecies to species

4623Humans

7839Dogs

1260630Ophioglossum reticulatum (fern)

2211Giant sequoia trees

2814Macaroni wheat

147Peas

126Drosophila virilus

105Drosophila obscura

84Drosophila melanogaster

2nnOrganism

Karyotypes can be produced by Karyotypes can be produced by cutting micrograph images of cutting micrograph images of

stained chromosomes and stained chromosomes and arranging them in matched pairsarranging them in matched pairs

Human male karyotype

Fig 4.6

Autosomes – pairs of nonsex chromosomesSex chromosomes and autosomes are arranged in homologous pairs

Note 22 pairs of autosomes and 1 pair of sex chromosomes

There is variation between There is variation between species in how chromosomes species in how chromosomes determine an individual’s sexdetermine an individual’s sex

__________________________________________________

Chromosome Females Males Organism__________________________________________________

XX-XY XX XY Mammals, DrosophilaXX-XO XX XO GrasshoppersZZ-ZW ZW ZZ Fish, Birds, Moths__________________________________________________

DiesNormal or nearly normal male

Normal male

Turner female

(sterile); webbed

neck

Kleinfelter male

(sterile); tall, thin

Normal female

Nearly normal

femaleHumans

DiesNormal male

Normal male

Sterile male

Normal female

Normal female

DiesDrosophila

OYXYYXYXOXXYXXXXX

Complement of sex chromosomesHumans – presence of Y determines sex

Drosophila – ratio of autosomes to X chromosomes

Meiosis contributes to Meiosis contributes to genetic diversity in two genetic diversity in two

waysways Independent assortment of Independent assortment of

nonhomologous chromosomes nonhomologous chromosomes creates different combinations of creates different combinations of alleles among chromosomesalleles among chromosomes

Crossing-over between homologous Crossing-over between homologous chromosomes creates different chromosomes creates different combinations of alleles within each combinations of alleles within each chromosomechromosome

Specific traits are Specific traits are transmitted with specific transmitted with specific

chromosomeschromosomes A test of the chromosome theory.A test of the chromosome theory.

If genes are on specific chromosomes, then If genes are on specific chromosomes, then traits determined by the gene should be traits determined by the gene should be transmitted with the chromosometransmitted with the chromosome

T.H. Morgan’s experiments demonstrating T.H. Morgan’s experiments demonstrating sex-linked inheritance of a gene sex-linked inheritance of a gene determining eye-color demonstrate the determining eye-color demonstrate the transmission of traits with chromosomestransmission of traits with chromosomes

1910 – T.H. Morgan discovered a white – 1910 – T.H. Morgan discovered a white – eyed male eyed male Drosophila melanogasterDrosophila melanogaster among among his stockshis stocks

Criss-cross Criss-cross inheritance inheritance of the white of the white

gene gene demonstrates demonstrates

X-linkageX-linkage

Fig. 4.20

X and Y linked traits in X and Y linked traits in humans are identified by humans are identified by

pedigree analysispedigree analysis X-linked traits exhibit five characteristics X-linked traits exhibit five characteristics

seen in pedigreesseen in pedigrees Trait appears in more males than femalesTrait appears in more males than females Mutation and trait never pass from father to Mutation and trait never pass from father to

sonson Affected male does pass X-linked mutation to Affected male does pass X-linked mutation to

all daughters, who are heterozygous carriersall daughters, who are heterozygous carriers Trait often seems to skip a generationTrait often seems to skip a generation Trait only appears in successive generations Trait only appears in successive generations

if sister of an affected male is a carrier. If if sister of an affected male is a carrier. If so, one half of her sons will show traitso, one half of her sons will show trait

Example of sex-linked Example of sex-linked recessive trait in human recessive trait in human pedigree – hemophiliapedigree – hemophilia

Example of sex-linked Example of sex-linked dominant trait in human dominant trait in human

pedigree – hypophosphatemiapedigree – hypophosphatemia

Fig. 4.23 b