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Randa, Bio100

  • B.

    2nd Law: Law of Independent Assortment

    • --

      based upon experiments with 2 traits at a time: dihybrid cross

Law states: alleles for different genes sort independently during meiosis

Note: crossing over during meiosis genetic recombination

  • --

    Application: see if two traits are related (linked) or independent Chromosomes and Exceptions to Mendelian Genetics

    • IV.

      Sex Determination and Associated Traits

A. Sex chromosomes

X and Y

  • B.

    Sex-linked traits (X-linked traits)

    • --

      associated with X chromosome, not Y Therefore, recessive traits tend to be expressed more in males.

  • e.

    g., hemophilia; red-green color blindness

  • C.

    X-inactivation

In early development, one X chromosome randomly “shut off” per cell

    • e.

      g., calico cats

  • V.

    Other Exceptions to Mendelian Genetics

  • A.

    Incomplete dominance

heterozygote has phenotype intermediate between homozygotes

B. Codominance If heterozygous, more than one allele expressed at a time

  • e.

    g., ABO blood groups

  • C.

    Polygenes

alleles at different loci in luence a single trait

    • e.

      g., skin color in humans – additive effect

  • D.

    Lethal Alleles

    • e.

      g., recessive alleles that cause death of the embryo or fetus

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