What is an example of a heterozygous trait, homozygous recessive and homozygous dominant trait?

Homozygous refers to the state or condition that occurs when an individual inherits the same DNA sequence for a certain gene from both biological parents. When a particular gene has identical alleles (versions) of chromosomes inherited from both parents, the gene is homozygous. A homozygous trait is referred to by two capital letters (XX) for a dominant trait, and two lowercase letters (xx) for a recessive trait.

Biological parents pass on versions of genes to their children. These versions are referred to as alleles. When the alleles are identical, the gene is said to be homozygous. This can lead to a person exhibiting homozygous traits. There are many examples of homozygous genes.

Homozygous genes can impact the appearance of a person’s eyes as well as medical conditions related to the eyes.

• The dominant trait for eye color is brown, represented by BB. All other eye colors - blue, grey, green, and hazel - are recessive traits, represented by bb. A homozygous brown-eyed person would have the BB gene, while a homozygous blue-eyed person would have the bb gene.
• An individual has the dominant SS gene, a homozygous gene that results in farsightedness. However, his friend has the homozygous gene ss for the recessive trait, which is normal sight.
• An individual possesses normal vision due to the homozygous VV gene. On the other hand, his friend possesses the recessive vv gene, which results in his colorblindness.

Homozygous genes can manifest in certain factors that impact a person’s appearance, including hair and skin.

• Having freckles is the dominant trait for melanin deposits on the cheeks and body. A homozygous freckled person would have the FF gene, while someone with the homozygous gene of the individual without freckles would be represented by ff.
• Having dimples on the cheeks is a dominant trait, with the homozygous DD gene causing them. However, the recessive trait is distinguished by the symbol dd; individuals with this homozygous gene will not have dimples.
• A full head of hair is a dominant feature, with the homozygous gene of HH. However, the recessive trait - baldness - can be manifested in an individual with the homozygous recessive gene, or hh.
• Curly hair is a dominant trait, with the homozygous HH gene causing the condition. Its recessive trait, represented by the homozygous gene hh, is straight hair.

Homozygous genes can predispose a person to develop or have immunity to certain medical conditions.

• One girl's blood clots normally, so her homozygous gene is the dominant CC. A boy in her class has hemophilia, which is present in the recessive gene cc.
• The dominant trait for hearing and speaking is being able to speak normally, which is the result of the SS homozygous gene. However, an individual with the homozygous recessive trait, ss, is unable to speak or hear properly and is instead deaf and mute.
• One person is immune to poison ivy, which is represented by the dominant PP trait; while another is not immune to poison ivy, which is represented by the recessive trait distinguished by the symbol pp.

Homozygous genes can impact a person’s musculoskeletal system, impacting factors related to their movement and appearance.

• One gentleman can bend his joints in funny ways because he possesses the dominant JJ gene for double-jointedness. Another gentleman does not possess this gene - instead, he has the recessive jj gene which means his joints bend normally.
• A boy is born with an extra finger on each hand due to the dominant gene EE, while another newborn with the recessive homozygous ee gene has the normal number of fingers on her hands.
• Unattached earlobes is a trait that is the result of a dominant gene UU, while an individual with the recessive homozygous gene uu actually has attached earlobes.

While the basic homozygous definition simply describes the word as being a descriptive term for a cell that has two identical copies of a gene, the scientific definition is a bit more complex:

“Having the same alleles at a particular gene locus on homologous chromosomes”

In order to interpret the scientific definition, a person will need to know the meaning of some other key scientific terms.

• allele - different forms or versions of genes
• chromosomes - structures that carry genetic information (passed from biological parents to offspring)
• homologous - similar in structure
• locus - a particular site or location

Why do siblings look different even when they have the same parents? The difference lies in their genes – and specifically, whether they have homozygous or heterozygous traits. Keep reading to learn what the difference between these traits are, and what exactly they can determine.

To understand homozygous and heterozygous traits, you need to know about the basics of genetics and genotypes. All genotypes consist of two alleles – one from the first parent, and one from the second parent. The combination of these alleles determines whether the offspring exhibits homozygous or heterozygous traits.

The difference between these traits is:

• Homozygous traits have two copies of the same allele.
• Heterozygous traits have one dominant allele and one recessive allele.

Whether a trait is homozygous or heterozygous determines how the offspring exhibits that trait. If both parents have a trait, their offspring is more likely to have it as well. However, only a look at the individual’s DNA can determine their likelihood of exhibiting a particular trait.

Homozygous means “same genes received during the zygote period of development.” An individual with homozygous traits received one copy of each allele from each parent. These alleles can either be dominant or recessive.

You may see homozygous traits in the following situations:

• Both parents have two dominant alleles for black hair (B), so their offspring receive only dominant alleles (BB) and have black hair.
• Parents of a child with recessive type O (oo) blood each have type O blood.
• A litter of purebred Golden Retriever puppies receive the same genes for leg length and fur color from each of their purebred parents.
• Parents who are carriers of genetic mutations on dominant alleles (Dd) have a stronger likelihood of having a child that exhibits a genetic disorder (DD).
• Flowers that each have ten petals create seeds that will sprout flowers with ten petals each.
• Both parents pass on the recessive trait for poor eyesight (e), so the child will also have poor eyesight (ee).

Homozygous traits don’t always mean that offspring look exactly like their parents. However, if a parent has homozygous traits, it’s more likely that their offspring will resemble them. Check out more examples of homozygous traits with an educational article.

Genetics get a bit more complicated when it comes to heterozygous, or “different genetic” traits. Offspring who receive a dominant allele from one parent and a recessive allele from the other parent will exhibit heterozygous traits. That’s why siblings with the same parents sometimes look very different from each other: they received different combinations of genes.

Here are some examples of how offspring can exhibit heterozygous traits:

• A parent provides the dominant allele for black hair (B), and the other parent provides the recessive allele for blonde hair (b). The offspring has black hair (Bb) because they exhibit the dominant gene only.
• One parent has two dominant alleles for type A (AA) blood, and the other parent has one dominant allele (B) and one recessive allele (o) for type B (Bo) blood. One child has type AB (AB) blood but their sibling has type A blood (Ao) because they received one dominant A allele and one recessive O allele.
• A litter of puppies with a Golden Retriever mother and a Great Dane father exhibit a variety of traits. Some puppies have shorter legs from their mother’s recessive alleles, while others are very tall because of their father’s dominant alleles.
• One parent is a carrier for a genetic mutation on a dominant allele (Dd), but the other parent only has recessive alleles for that chromosome (dd). The child receives one recessive allele from each parent (dd) and neither carries nor exhibits the genetic disorder.
• Two flowers with ten petals but different genotypes (PP and Pp) produce seeds for flowers with the dominant allele for ten petals and flowers with the recessive allele for nine petals.
• One parent has poor eyesight (ee), but the other has a dominant allele for strong eyesight (Ee). Their offspring range in eyesight ability (ee and Ee).

As you can see, heterozygous traits allow for greater genetic variation. They can also protect offspring from gene mutation and possibly harmful genetic disorders. The alleles that offspring receives from its parents can determine what happens to its genetic line for generations to come.

Life seems so random and unpredictable sometimes. However, understanding the study of genetics helps us understand more about how life works. To learn more about the details of genotypes and genetic traits, read an article that details the occurrence of codominance in genetics. Then, explore some examples of inherited traits.