Chapter 15: The Chromosomal Theory of Inheritance (2)

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Chapter 15: The Chromosomal Theory of Inheritance (2)
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2011-02-01 21:56:21
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  1. Because the identity of the __ chromosomes in an individual could be inferred by observing the sex of the fly, the behavior of the two members of the pair of __ chromosomes could be correlated with the behavior of the two __ of the eye color gene.
    • sex x2
    • alleles
  2. In humans and other mammals, there are two varieties of sex chromosomes, designed __ and __.
    -- The __ is much smaller than the __.
    - A person with ___ is a female; a person with __ is a male.
    • X
    • Y
    • Y
    • X
    • two X chromosomes
    • an X and a Y
  3. Short segments at either end of the __ chromosome are the only regions that are homologous with corresponding regionsof the __.
    -- These ___ allow the __ and __ chromosomes in males to pair and behave like __ during meiosis in the __.
    • Y
    • X
    • homologous regions
    • X
    • Y
    • homologous chromosomes
    • testes
  4. In both teh testes and ovaries, the two sex chromosomes __ during meiosis, and each receives one.
    Egg= __
    Sperm= __
    • segregate
    • X
    • X and Y
  5. __ is a matter of chance- 50%
    sex determination
  6. There are three other chromosomal systems besides the human X-Y system.
    - name the first one in grasshoppers and cockroaches
    • X-0 (grasshoppers/roaches)
    • - only one type of sex chromosome, the X-Females are XX
    • -males are X0
    • -SEx of the offspring is determined by whether the sperm cell contains an X or no sex chromosome
  7. Name the chromosomal system in birds and fishes, etc.
    • Z-W
    • - sex chromosome in the egg determines the sex of offspring.
    • - Sex chromosomes are Z and W
    • - Females: ZW/ Males: ZZ
  8. Name the chromosomal system in bees and ants.
    • Haplo-diplo system
    • - no sex chromosoems.
    • -females develop from fertilized eggs and are diploid
    • -males- from unfertilized eggs are haploid- have no fathers
  9. In humans, the anatomical signs of __ begin to emerge when the embryo is about __ months old.
    - Before then, the rudiments of the __ are generic- they can develop into either __ or __, depending on whether a __ is present.
    • sex
    • 2
    • gonads
    • testes
    • ovearies
    • Y
  10. In 1990, a British research team identified a gene on the _ chromosome required for the development of the __.
    - __
    -- In the absence of __, the gonads develop into ovaries.
    -- The biochemical, physiological, and anatomical features that distinguish males and females are complex and many genes are involved in their development. In fact, __ codes for a protein that regulates other genes.
    • Y
    • testes
    • SRY- sex-determining region of Y
    • SRY
    • SRY
  11. Researchers have sequenced the human __ chromosome and have identified __ genes, which code for about __ proteins (some genes are duplicates). ABout 1/2 of these genes are expressed only in the testis, and some are required for normal __ functioning. In their absence, an __ individual is male, but doesn't produce normal sperm.
    • Y
    • 78
    • 25
    • testicular
    • XY
  12. In addition to their role as carriers of genes that determine sex, these chromosomes, especially X chromosomes, have genes for many characters unrelated to sex.
    -- A gene located on either sex chromosome is called a __, although in humans the term has historically referred specifically to a gene on the __ chromosome. __ in humans follow the same pattern of inheritance as the fruit flies eye-color.
    • sex-linked gene
    • X
    • sex-linked genes
  13. Fathers pass __ to all of their daughters but to none of their sons.
    In contrast, mothers can pass __ to both sons and daughters.
    sex-linked alles x2
  14. If a __ is due to a __ allele, a female will display the phenotype onyl if she is a __.
    Males don't use homo and heterozygotes. These use __.
    -- Any male receiving the __ from his mother will express the trait. For this reason, far more males than females have sex-linked recessive disorders.
    -- However, even though the chance of a female inheriting a double dose of the __ is much less than the probability of a male inheriting a single does, there are females with sex linked disorders.
    • sex-linked trait
    • recessive
    • homozygote
    • hemizygous
    • recessive allele
    • mutant allele
  15. __- affects about one of every 3500 males born in the US; characterized by a progressive weakening of the muscles and loss of coordination; affected individuals rarely live past their early 20s; researchers have traced the disorder to the absence of a key muscle protein calle ddystrophin and have mapped the gene for this protein to a specific locus on teh X chromosome
    Duchenne muscular dystrophy
  16. __- sex-linked recessive disorderdefined by the absence of one or more of the proteins required for blood clotting. When a person with this is injured, leeding is prolonged because a firm clot is slow to form. Bleeding in the muscles or joints, unlike a small cut, can be painful and can lead to serious damage
    hemophilia
  17. One X chromosome in each cell in females becomes almost completely inactivated during __.
    - As a result, the cells of females and males have the same effective dose (one copy) of these genes. The __ X in each cell of a female condenses into a compact object called a __, which lies along the inside of the nuclear envelope.
    - Most of the genes of the X chromosome that forms the __ are not expressed. In the ovaries, __ chromosomes are reactivated in the cells that give rise to eggs, so every female gamete has an __.
    • embryonic development
    • inactive
    • Barr body
    • Barr body
    • Barr-body
    • active X
  18. __ demonstrated that selection of which X chromosome will form the __ occurs randomly and independently in each embryonic cell present at the time of X __.
    -- As a consequence females consist of a mosaic of two types of cells: those with the __ derived from the father and those from the mother.
    • Mary Lyon
    • Barr body
    • inactivation
    • active X
  19. After an X chromosome is inactivated in a particular cell, all mitotic descendents of that cell have the same inactive X.
    - Thus, if a female is __for a __, about half her cells will express one allele, while the others wll express the alternate.
    • heterozygous
    • sex-linked gene
  20. In humans, __ can be observed in a recessive X-linked mutation that prevents the development of sweat glands. A woman who is eterozygous for this trait has patches of normal skin and patches of skin lacking sweat glands.
    mosaicism
  21. Inactivation of an X chromosome involves modification of the DNA, including attachmeent of __ groups to one of the __ of DNA __.
    • methyl
    • nitrogenous bases
    • nucleotides
  22. Researchers have also discovered an X chromosome gene called __ for __ that is active only on the __ chromosome.
    • XIST
    • X- inactive- specific- transcript
    • Barr body
  23. Multiple copies of the __ product of this gene apparently attach to the X chromosome on which they are made, eventually almost covering it.
    -- Interaction of this __ with the chromosome seems to initiate __, and regulation of this process by other genes is still being researched.
    • RNA
    • RNA
    • X inactivation

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