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In genetics, the terms homozygous and heterozygous are essential to understand when dealing with dominant and recessive traits. Homozygous means the individual has two identical alleles for a particular gene. This could be two dominant alleles (like HH for a hairy dog) or two recessive alleles (like hh for a hairless dog). On the other hand, heterozygous refers to an individual having two different alleles - one dominant and one recessive, such as Hh, which results in a hairy dog because the dominant allele masks the recessive one.

Understanding whether a trait is homozygous or heterozygous helps us predict the phenotype, or observable characteristics, of an organism. Knowing the genotype of the organism can tell us if it is likely to express a dominant or recessive trait. This is crucial in determining trait inheritance and performing genetic analysis.

A test cross is a genetic technique used to determine the genotype of an organism displaying a dominant trait. By crossing an individual with a known genotype (homozygous recessive) with one of unknown genotype that shows the dominant trait, we can reveal whether the unknown genotype is homozygous or heterozygous.

In our example with the rat terriers, performing a test cross involves mating the hairy terrier (unknown genotype) with a hairless terrier (homozygous recessive, hh). The pattern of the offspring will shed light on the genetic makeup of the hairy parent.

• If all offspring are hairy, the rat terrier parent is homozygous dominant (HH).
• If there are both hairy and hairless offspring, the parent is heterozygous (Hh).

Test crosses can be a powerful way to uncover unseen genetic information.

Genetic traits are characteristics determined by genes, which are units of heredity carried on chromosomes. Each trait comes in two forms called alleles – dominant and recessive. The expression of these traits depends on the combination of alleles an individual inherits from its parents.

For our rat terriers, hair presence is a dominant genetic trait, while being hairless is recessive. Genetic traits can influence various features in organisms, from physical attributes to behavioral patterns. Understanding genetic traits, and how they are passed down, helps in fields like animal breeding, agriculture, and human medicine.

Dominant and recessive terms describe how likely an allele is to appear in an organism's phenotype when paired with other alleles. A dominant allele, like the one for hair in rat terriers, will override a recessive allele in heterozygotes, those that have two different alleles (Hh). This means that even with just one dominant allele, the dominant trait is expressed.

Recessive alleles, on the other hand, only show up in the phenotype if there are two identical recessive alleles present (hh). If there is even one dominant allele, it masks the recessive trait.

The knowledge of dominant vs recessive is vital when predicting inheritance patterns and understanding how specific traits can be passed on in families or species.