heterozygous

Examples of heterozygous in the following topics:

• Sex Determination

  • Individuals homozygous for X (XX) are female, while heterozygous individuals (XY) are male.
  • Homozygous for Z (ZZ) results in a male, while heterozygous (ZW) results in a female.
  • The presence of X and Y chromosomes are one of the factors responsible for sex determination in mammals, with males being the heterozygous sex.
  • In birds, Z and W chromosomes determine sex, with females being the heterozygous sex.

• Lethal Inheritance Patterns

  • However, consider two heterozygous parents that have a genotype of wild-type/nonfunctional mutant for a hypothetical essential gene.
  • For crosses between heterozygous individuals with a recessive lethal allele that causes death before birth when homozygous, only wild-type homozygotes and heterozygotes would be observed.
  • People who are heterozygous for the dominant Huntington allele (Hh) will inevitably develop the fatal disease.

• Hardy-Weinberg Principle of Equilibrium

  • In our example, the possible genotypes are homozygous dominant (YY), heterozygous (Yy), and homozygous recessive (yy).
  • We do not know how many are homozygous dominant (Yy) or heterozygous (Yy), but we do know that 16 of them are homozygous recessive (yy).
  • The frequency of heterozygous plants (2pq) is 2(0.6)(0.4) = 0.48.
  • Therefore, 48 out of 100 plants are heterozygous yellow (Yy).

• The Punnett Square Approach for a Monohybrid Cross

  • A self-cross of one of the Yy heterozygous offspring can be represented in a 2 × 2 Punnett square because each parent can donate one of two different alleles.
  • Therefore, the two possible heterozygous combinations produce offspring that are genotypically and phenotypically identical despite their dominant and recessive alleles deriving from different parents.
  • Beyond predicting the offspring of a cross between known homozygous or heterozygous parents, Mendel also developed a way to determine whether an organism that expressed a dominant trait was a heterozygote or a homozygote.

• Mendel's Laws of Heredity

  • If the two alleles are different, the individual is called heterozygous.
  • In heterozygous individuals, the only allele that is expressed is the dominant.
  • He did this by cross-breeding dihybrids; that is, plants that were heterozygous for the alleles controlling two different traits.

• Epistasis

  • Homozygous recessive expression of the W gene (ww) coupled with homozygous dominant or heterozygous expression of the Y gene (YY or Yy) generates yellow fruit, while the wwyy genotype produces green fruit.
  • However, if a dominant copy of the W gene is present in the homozygous or heterozygous form, the summer squash will produce white fruit regardless of the Y alleles.

• Genes as the Unit of Heredity

  • There can be many alleles of a gene within a population, but an individual within that population only has two copies and can be homozygous (both copies the same) or heterozygous (the two copies are different) for any given gene.

• Mendel's Law of Segregation

  • For the F2 generation of a monohybrid cross, the following three possible combinations of genotypes could result: homozygous dominant, heterozygous, or homozygous recessive.

• Sex-Linked Traits

  • The F1 females are heterozygous (XWXw), and the males are all XWY, having received their X chromosome from the homozygous dominant P1 female and their Y chromosome from the P1 male.
  • The F1 generation would exhibit only heterozygous red-eyed females (XWXw) and only white-eyed males (XwY).

• Alternatives to Dominance and Recessiveness

  • Such heterozygous individuals are sometimes referred to as "carriers."