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The words homozygous, heterozygous, and hemizygous are used to describe the genotype of a diploid organism at a single locus on the DNA. Homozygous describes a genotype consisting of two identical alleles at a given locus, heterozygous describes a genotype consisting of two different alleles at a locus, hemizygous describes a genotype consisting of only a single copy of a particular gene in an ...
Figure 1: Inheritance pattern of dominant (red) and recessive (white) phenotypes when each parent (1) is homozygous for either the dominant or recessive trait. All members of the F 1 generation are heterozygous and share the same dominant phenotype (2), while the F 2 generation exhibits a 6:2 ratio of dominant to recessive phenotypes (3).
When conducting a dihybrid test cross, two dominant phenotypic characteristics are selected and crossed with parents displaying double recessive traits. The phenotypic characteristics of the F1 generation are then analyzed. In such a test cross, if the individual being tested is heterozygous, a phenotypic ratio of 1:1:1:1 is typically observed. [7]
If both alleles are the same, the genotype is referred to as homozygous. If the alleles are different, the genotype is referred to as heterozygous. Genotype contributes to phenotype, the observable traits and characteristics in an individual or organism. [3] The degree to which genotype affects phenotype depends on the trait.
Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene (is heterozygous), but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that allele (is homozygous). Those who are heterozygous for the sickle cell allele produce both normal and ...
In the example pictured to the right, RRYY/rryy parents result in F 1 offspring that are heterozygous for both R and Y (RrYy). [4] This is a dihybrid cross of two heterozygous parents. The traits observed in this cross are the same traits that Mendel was observing for his experiments. This cross results in the expected phenotypic ratio of 9:3:3:1.
The phenotype of a homozygous dominant pair is 'A', or dominant, while the opposite is true for homozygous recessive. Heterozygous pairs always have a dominant phenotype. [11] To a lesser degree, hemizygosity [12] and nullizygosity [13] can also be seen in gene pairs.
If heterozygous, she is a carrier of the mutated allele because the disease is recessive. If homozygous, she has the disease. An affected father with an X-linked recessive trait will always pass the trait on to the daughter. Therefore, all daughters of an affected male are obligate carriers.