Inheritance Why we look the way we do.

We look the way we do because we inherit certain traits from our parents, from the texture of our hair to the color of our eyes. All these traits that make up how we look are carried in our DNA (deoxyribonucleic acid).

Where is DNA found? DNA is found in the nucleus of the cell.

The Role of Genes in Inheritance Chromatin is in the nucleus of a cell Chromatin forms into chromosomes during cell replication Chromosomes are partly composed of DNA Do NOT put this on internet! Source of photos: Mitosis Stages

What is DNA? DNA is genetic material DNA carries information about an organism that is passed from parents to offspring Some of the DNA in chromosomes consists of genes

A gene is found on a chromosome. A chromosome contains many genes.

What is a Gene? A gene is a section of DNA that controls a trait that an organism inherits Genes are like recipes. Just as a recipe contains instructions for preparing food, genes contain instructions for building and running cells.

Sexual Reproduction Two parents supply genetic material that determines the characteristics of their offspring. (In other words, each parent supplies genes that determine the traits of the offspring.) In sexual reproduction, the offspring will not be identical to the parents. (In asexual reproduction, which involves only one parent, you’ll remember, the offspring will be identical to the parent.) Where do we see asexual reproduction?

How are Traits Expressed in the Offspring? An offspring receives traits from both parents Dominant traits hide recessive traits. In other words, even if an offspring receives one dominant and one recessive trait, the offspring will express only the dominant trait. Recessive traits are only expressed when provided by both parents. In other words, the offspring must receive recessive traits from both the male and female parent. If either parent passes on a dominant trait, the recessive trait will be hidden!

Bent pinky Pinkies lean away from each other: dominant Pinkies lean toward each other: recessive

Thumbs: Straight thumb (dominant trait) vs Thumbs: Straight thumb (dominant trait) vs. Curved thumb (recessive trait) When viewed from the side as in the illustration below, curved thumbs can be seen as part of a circle.

Tongue Rolling Tongue Roller Not a Tongue Roller

Hairline Widow’s peak Straight hairline

Chin Cleft Chin No Cleft Chin

Long toes Second toe longest Big toe longest

Are you an alien?

Are any of these traits learned? Traits are inherited, not learned. Behavior is learned.

Inherited or Acquired? Behavior is the way animals act and react Instinct is a form of behavior animals are born with. Other animal behaviors are learned or acquired through experience or study. Birds know how to build a nest. That is an instinct. Birds learn how to fly. Their parents teach them. That is a learned or acquired behavior.

Instinct or Acquired? Birds fly south for the winter. Salmon swim miles upstream against strong currents to lay their eggs. A bee stings its enemies. An animal avoids an electrified fence. A caterpiller spins a cocoon. A raccoon stands perfectly still if it senses danger. S.M.Willingham

Instinct or Acquired? An armadillo jumps straight up when surprised. A child says “please” and “thank you” at appropriate times. A dog sits before getting a treat. A black bear hibernates in the winter. A robin gathers food to feed her young. A sea lion balances a ball on the tip of its snout A cat drinks water when it is thirsty. S.M.Willingham

DOMINANT OR RECESSIVE? FREE ATTACHED

Brown eyes are dominant. Colored eyes are recessive.

Genetic Traits Earlobes: Free ear lobes (dominant trait) vs Genetic Traits Earlobes: Free ear lobes (dominant trait) vs. Attached ear lobes (recessive trait) Free earlobes are those that hang below the point of attachment to the head. Attached ear lobes are attached directly to the side of the head.

Hand clasping Left thumb on top: dominant Right thumb on top: recessive

Dimples: Dimples (dominant trait) vs Dimples: Dimples (dominant trait) vs. No dimples (recessive trait) Dimples are natural dents in the face to the right or left of the mouth. If a person has only one dimple, they should be counted as having dimples.