Inquiry Question: Why are some people tall and others short?
The characteristics of many living things, called traits, are passed along from the parents to their offspring during sexual reproduction.
At the end of this inquiry, you should be able to answer the following questions:
What is a heritable characteristic?
What is a non-heritable characteristic?
What is discrete variation?
What is continuous variation?
How is variation affected by the environment?
Pages 26 to 29 in your textbook will help you answer these questions about traits.
Background Information
Figure 1 – There are many different traits observed in a group of people.
Why are some people tall while others are short?
Are these traits inherited? What does this inquiry question have to do with purple cows?
Is there similarity between the colour purple and why some people are taller than others are? You know that sexual reproduction requires a female and male organism and that the process of fertilization produces an embryo with traits
from both organisms.
In a population of a species, similar physical traits are evident among them but these traits occur in various forms. Look at our own species, Homo sapiens; we all have eyes that are coloured but many shades of colour. Each
has his or her own genetic makeup that defines the person.
We receive this genetic make-up from the combination of both parents’ genes through the process of fertilization. These characteristics are called inherited traits, genetic traits, heritable traits, or physical characteristics. Inherited
traits in humans include such things as eye colour, hair colour, freckles or no freckles, curly or straight hair, attached or unattached earlobes, and ability or non-ability to roll the tongue. Heritable traits can be discrete or continuous.
Later in the lesson, these two variations of heritable traits are explained in more detail.
Seeing various forms of traits is interesting, but how did we get those traits? Traits that are inherited are passed from parents to offspring through sexual reproduction, but not all traits are inherited. Many traits are learned
from the environment in which we live, and these are
called non-inherited traits, acquired traits, or learned characteristics.
Watch
Watch the video "Inherited vs Acquired Traits" for a summary of the differences between what you're born with and what you learn.
How unique do you feel? Have people said that your smile, eyes, nose, or hair are just like those of another member of your immediate family or a close relative? To learn more about the uniqueness of inherited traits, watch the video "How special are your physical traits"?
Figure 2 – An attached ear lobe.
Figure 3 – An unattached ear lobe.
Heritable and Non-Heritable Traits
Heritable traits are the characteristics you have that were inherited from your parents. Genetic information found in the sperm and egg during fertilization provide the information for the heritable traits. Heritable traits include physical characteristics
like eye colour, height, and earlobe attachment (figures 1 and 2). Non-heritable traits are characteristics influenced by the environment. Examples of non-heritable traits include playing the piano, and ice skating.
Figure 5 – Red hair, freckles, and an inability to roll the tongue are all heritable traits.
Heritable Traits: Discrete and Continuous Variations
Heritable traits are in two categories: discrete or continuous variations. Discrete variations are distinct forms of a trait; either an organism has the characteristic or it does not. The environment does not affect the inheritance of these traits.
They are inherited. Check some traits below. Do you have any of these? What traits do your parents have? Are your parents’ traits similar to yours?
Heritable traits that are not discrete are then classified as having continuous variations. Characteristics of traits that have wide ranges show continuous variations. Some examples of heritable traits that demonstrate continuous variation
are height, hair colour, and size of feet. Often, these traits can be affected by the environment. For example, your weight is a heritable characteristic, but can be affected by the amount of exercise you get or your diet.
Non-heritable Traits
Although physical characteristics generally enable us to tell the difference between an inherited and non-inherited trait, much debate occurs about non-inherited traits. This is the nature vs. nurture debate. The expression of some traits is
influenced by the environment. For example, height and weight can be affected by diet. Scars or injuries can alter a person’s physical appearance. Studies of identical twins help scientists to understand more about this subject. Because identical
twins have the exact genetic makeup, scientists have studied twins raised in different environments to determine the affect of the environment on their physical appearance and personality traits.
Have you ever seen a purple cow? If purple was a heritable trait in cows we would see it sometimes when we look at a herd of cattle. And it seems silly to even think of being purple as a learned, non-heritable trait. After all, you can't learn
to be purple. Being purple sounds more like a heritable trait, but how can the genetics of a cow suddenly allow for a trait like purpleness to appear?
Watch
Watch "Twins: Is it all in
the Genes" to learn more about this topic of nature vs. nurture.
Do you understand the difference between inherited and non-inherited traits? Watch "Acquired and Inherited Traits" to deepen your understanding.
When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
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This practice work is not for marks, it is meant to help you check your
understanding. Check the answers AFTER doing the questions! Keep the
practice worksheet for study purposes. If you don't understand
something, contact your teacher!
