Chapter 14b: Chromosomal Theory of Inheritance

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31 Terms

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chromosome theory of inheritance

-proposed by Sutton and Boveri

-asserted that the genes are located on chromosomes and inheritance patterns are determined by chromosome behavior during Meiosis

<p>-proposed by Sutton and Boveri</p><p>-asserted that the genes are located on chromosomes and inheritance patterns are determined by chromosome behavior during Meiosis</p>
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sex linkage + chromosome theory

-supported by experiments on the sex chromosomes

-in some animals there were sex chromosomes called X and Y chromosomes (they determine the sex of offspring)

-found by Nettie Stevens

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X-linked

gene located on the X chromosome

<p>gene located on the X chromosome</p>
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Y-linked

gene located on the Y chromosome

<p>gene located on the Y chromosome</p>
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sex linked

genes being on either sex chromosome

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sex chromosomes

-pair during meiosis I (synapsis occurs but no recombination or crossing over)

-segregate during meiosis II

-gametes have either an X or Y chromosome

<p>-pair during meiosis I (synapsis occurs but no recombination or crossing over)</p><p>-segregate during meiosis II</p><p>-gametes have either an X or Y chromosome</p>
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homogametic

females since they only produce X gametes

<p>females since they only produce X gametes</p>
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heterogametic

-males produce half X gametes and half Y gametes

-50% of sperm contain X chromosome and 50% contain Y chromosome

<p>-males produce half X gametes and half Y gametes</p><p>-50% of sperm contain X chromosome and 50% contain Y chromosome</p>
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Thomas Morgan

-adopted fruit flies as model organisms

-used reciprocal cross to find that some patterns don't follow Mendelian behavior

-when the F1 and/or F2 ratios are different in recip. cross it means the genes are sex linked(X-linked in this case of fruit fly eye color)

<p>-adopted fruit flies as model organisms</p><p>-used reciprocal cross to find that some patterns don't follow Mendelian behavior</p><p>-when the F1 and/or F2 ratios are different in recip. cross it means the genes are sex linked(X-linked in this case of fruit fly eye color)</p>
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fruit flies

-diploid and have 4 pairs of chromosomes

-females have 4 homologous pairs and males have 3 because X and Y are not homologous

<p>-diploid and have 4 pairs of chromosomes</p><p>-females have 4 homologous pairs and males have 3 because X and Y are not homologous</p>
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inheritance for males

are hemizygous for genes on the X and Y chromosomes (heterogametic)

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inheritance for females

can be heterozygous or homozygous for X-linked genes (homogametic)

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wild type

most common phenotype in the natural population and typically the result of natural selection

<p>most common phenotype in the natural population and typically the result of natural selection</p>
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mutants

all other phenotypes besides wild type that arise by mutations

<p>all other phenotypes besides wild type that arise by mutations</p>
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mutation

a stable and heritable change in the nucleotide sequence and only mutations in gametes are heritable since mutations in somatic cells can't be passed down

<p>a stable and heritable change in the nucleotide sequence and only mutations in gametes are heritable since mutations in somatic cells can't be passed down</p>
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Y chromosome mechanism

presence of Y causes male development

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X chromosome - autosome balance

-number of copies of X determines sex

-Y chromosome may or may not be present but determines fertility

-1.0 ratio is female and 0.5 is male, in between is intersex

<p>-number of copies of X determines sex</p><p>-Y chromosome may or may not be present but determines fertility</p><p>-1.0 ratio is female and 0.5 is male, in between is intersex</p>
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turner syndrome

females with only one X sex chromosome who are short, often sterile, and have low sexual development

<p>females with only one X sex chromosome who are short, often sterile, and have low sexual development</p>
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klinefelter syndrome

A chromosomal disorder in which males have an extra X chromosome, making them XXY, XXXY, or XXYY instead of XY.

<p>A chromosomal disorder in which males have an extra X chromosome, making them XXY, XXXY, or XXYY instead of XY.</p>
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extra sex chromosomes are often result of...

nondisjunction in meiosis

<p>nondisjunction in meiosis</p>
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gene dosage

extra chromosomes increase the number of copies of the genes on them

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how can they tolerate extra Xs?

-shut off/inactivate all but one X during development(dosage compensation)

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Barr Body

an inactivated X chromosome that is condensed and sticks to nuclear envelope

<p>an inactivated X chromosome that is condensed and sticks to nuclear envelope</p>
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lyonization

-process that created Barr bodies and the chromosome is highly condensed -> heterochromatin

-happens during fetal development (day 16)

-each cell selects an X at random and descendants of cell will have same X shut off

<p>-process that created Barr bodies and the chromosome is highly condensed -&gt; heterochromatin</p><p>-happens during fetal development (day 16)</p><p>-each cell selects an X at random and descendants of cell will have same X shut off</p>
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mosaics

individuals whose somatic cells display two different genetic cell lines, each exhibiting a different karyotype. they must have two X chromosomes

<p>individuals whose somatic cells display two different genetic cell lines, each exhibiting a different karyotype. they must have two X chromosomes</p>
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testis-determining factor (tdf)

-causes fetal gonads to develop into testes

-testes then produce male sex hormones

-hormones direct the rest of the sex development

<p>-causes fetal gonads to develop into testes</p><p>-testes then produce male sex hormones</p><p>-hormones direct the rest of the sex development</p>
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X chromosome - autosome balancing system

-Y doesn't determine sex, it is determined by the # of X's

-ratio of copies of X to copies of each autosome

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males are homogametic in some organisms...

-in birds, butterflies, moths, and some fish

-they have two homologous sex chromosomes (ZZ)

-females are heterogametic (ZW) -> W causes female development

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dioecious

in plants some species have male and female individuals, "two houses"

<p>in plants some species have male and female individuals, "two houses"</p>
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monoecious

-in some plants the individuals are hermaphrodites, "one house"

-perfect flowers produce both male and female gametes together in the same flower

<p>-in some plants the individuals are hermaphrodites, "one house"</p><p>-perfect flowers produce both male and female gametes together in the same flower</p>
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environmental sex determination systems

Environmental conditions control sex of organism

•temperature during incubation controls sex of turtles

•presence of opposite sex

-some organisms (fish) can switch sex if few partners available

<p>Environmental conditions control sex of organism</p><p>•temperature during incubation controls sex of turtles</p><p>•presence of opposite sex</p><p>-some organisms (fish) can switch sex if few partners available</p>

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