Biology Study Guide- Laws of Segregation, Independent Assortment, and Dominance

What is a phenotype?

A description of actual physical characteristics of an organism. This includes straightforward visible characteristics like size and color, but also includes overall health, disease history, behavior, and general disposition. Most phenotypes are influenced by both genotype and by environment.

What is the difference between a dominant allele and a recessive allele?

A dominant allele is expressed even if an offspring inherits only one copy of that allele. For example, a person with one allele for brown eyes (dominant) and one allele for blue eyes (recessive) will have brown eyes. A recessive allele is one that only produces its characteristic phenotype if two copies of the allele are present. For example, a person with naturally blonde hair must have inherited the allele for blonde hair from both parents, as blonde hair is a recessive gene.

Who was the "father" of these laws?

Gregor Mendel, a 19th century friar who is considered the father of modern genetics.

How can two brown-eyed parents produce a blue-eyed child?

If you think of the allele for brown eyes as (B) and the allele for blue eyes as (b), it is possible that both parents have the phenotype "Bb", where the gene for blue eyes is present, but not expressed due to the dominance of brown eyes. Looking at these genotypes with a punnet square, it becomes clear that the offspring of the "Bb" parents have a 75% chance of having brown eyes, and a 25% chance of having blue eyes.

What does the Law of Dominance state?

Recessive alleles will always be masked by dominant alleles. Therefore, a cross between a homozygous dominant and a homozygous recessive will always express the dominant phenotype, while still having a heterozygous genotype.

What is the Law of Independent Assortment?

The Law of Independent Assortment states that alleles for separate traits are passed independently of one another from parents to offspring. That is, the biological selection of an allele for one trait has nothing to do with the selection of an allele for any other trait.

What are the major differences between the Law of Segregation and the Law of Independent Assortment?

The Law of Segregation discusses how alleles behave during meiosis. When sex cells are formed, they receive only one copy of an allele, and when fertilization occurs, the resulting offspring inherits one allele from each parent. The Law of Independent Assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene. Basically, it means that alleles for different traits are inherited independently... so, for example, the genes for blood type and hair color are independent, and what blood type allele an offspring inherits has absolutely nothing to do with what allele they inherit for hair color.

What is the Law of Segregation?

The Law of Segregation states that every individual organism contains two alleles for each trait, and that these alleles segregate (separate) during meiosis so that each gamete contains only one of the alleles.An offspring thus receives a pair of alleles for a trait by inheriting homologous chromosomes from the parent organisms: one allele for each trait from each parent.

What is a genotype?

The complete heritable genetic identity; it is a unique genome.

What does heterozygous mean?

When an individual has two different alleles. For example, if a rabbit has one allele for white fur and another allele for brown fur.

What does homozygous mean?

When an individual has two of the same allele. For example, a blue-eyed person would be homozygous, as they would have two copies of the allele for blue eyes.