4C2 Environmental factors influence the expression of the genotype in an organism

Environmental factors influence many traits both directly and indirectly Explain how the following environmental factors influence traits. ◦ Height and weight in humans ◦ Flower color based on soil pH ◦ Seasonal fur color in arctic animals ◦ Sex determination in reptiles

Height and Weight in Humans There's no one gene that makes a difference. There's many, many genes, dozens, perhaps hundreds … each of which has a small effect on the obesity in the population But which add up to a susceptibility when exposed to this environment we live in, for getting more overweight or not. No doubt that genetics, the DNA that we inherit from our parents, affects how much we weigh Also no doubt that the environment we live in affects how much we weigh. There's no nature vs. nurture. There's nature and nurture

Flower color based on soil pH Most major plant nutrients are more accessible at a pH of 6 to 6.5. A pH that is too high or too low can keep plants from absorbing nutrients from the soil. The nutrients are unavailable — or not absorbable — to the plant because of soil's chemistry. This problem can manifest itself in a variety of ways, but in the case of hydrangeas, the bloom color changes.

Color variation in hydrangeas is due to the presence or absence of aluminum compounds in the flowers. If aluminum is present, the color is blue. If it is present in small quantities, the color is variable between pink and blue. If aluminum is absent, the flowers are pink. Soil pH indirectly changes flower color by affecting the availability of aluminum in the soil. When the soil is acidic (pH 5.5 or lower), aluminum is more available to the roots, resulting in blue flowers

Seasonal fur color in arctic animals Many birds and mammals deal with loss of camouflage by producing different colors of fur or feathers depending on the time of year. In most cases, either changing amounts of daylight or shifts in temperature trigger a hormonal reaction in the animal that causes it to produce different biochromes.

Biochromes General appearance of an organism as determined by the quality and quantity of light that is reflected or emitted from its surfaces. Coloration depends upon several factors: the color and distribution of the organism’s biochromes (pigments) ◦ The relative location of differently colored areas ◦ The shape, posture, position, and movement of the organism ◦ The quality and quantity of light striking the organism.

Sex determination in reptiles Non-genetic sex determination occurs when the sex of an organism can be altered during a sensitive period of development due to external factors such as temperature, humidity, or social interactions. Temperature-dependent sex determination (TSD), where the temperature of the embryo’s environment influences its sex development, is a widespread non-genetic process of sex determination among vertebrates, including reptiles. All crocodilians, most turtles, many fish, and some lizards exhibit TSD.

One cause of TSD is the enzyme aromatase. Aromatase helps to convert sex steroids, a group of hormones that influence sex development and reproduction, from male sex hormones (androgens) to female sex hormones (estrogens). Individuals with low levels of aromatase during the thermosensitive period will develop male characteristics.

High levels of aromatase activity increase the production of female hormones, resulting in the development of female characteristics. While aromatase activity remains low for much of development in individuals that exhibit TSD, during the thermosensitive period, variations in temperature increase the activity of aromatase

An organism’s adaptation to the local environment reflects a flexible response of its genome Explain how darker fur in cooler regions of the body in certain mammal species. Adaptation is a process of members of a species passing on a superior trait that will enhance that species ability to survive within the genome it occupies. There are some animals that have darker fur color that serve to radiate heat away from the body, which serves as a cooling effect, making them better able to exist in hotter climates, such as tropical environments.

Adaptations give a species a "one-up" on other members of the same species without this specific adaptation. In the process of natural selection, the members of the species that are better able to deal with the physical factors placed upon them within their genome are more likely the ones to propagate the species These then pass their adaptive traits along to their offspring, who will in turn pass them on to their offspring.

Explain how alterations in timing of flowering due to climate changes Hotter springs, earlier blooms Researcher Ellwood and her colleagues gathered all of Thoreau's flowering records from several archives. They then compared flowering dates with spring temperatures for 32 different flowering plants. They found that as temperatures warmed over the last 161 years, the date of first blooms of the season crept forward, too — about 10 days earlier than when Thoreau first visited the site.

During the record-breaking years of 2010 and 2012, flowering happened a full 20 to 21 days earlier. The average spring temperature at Walden Pond has increased about 6 degrees Fahrenheit (3.4 degrees Celsius) since Thoreau's time.

Similarly, at another location, as average spring temperatures rose about 3 degrees Fahrenheit (1.7 degrees Celsius) over the last eight decades First flowering came a week early for the 23 species they studied. During the hottest years in the United States (2010 and 2012), flowering came 24 days earlier