From Parents to Offspring Plants and Animals From Parents to Offspring

Inherited Traits inherited trait: a characteristic that is passed on from parent to offspring. Could be hair color, eye color, freckles, etc. Behaviors can also be inherited; dogs are born with the instinct to be able to swim, humans are not.

Inherited Traits Organisms receive half of their DNA from their mom and half of their DNA from their dad. This means that they cannot be identical to either parent. This also means that siblings cannot be identical to one another, except for identical twins.

Dominant vs. Recessive Traits Dominant trait: strong trait; will show in the offspring if they receive it from either parent. Recessive trait: weak trait; will show in the offspring only if they receive it from both parents.

Gregor Mendel Gregor Mendel was a monk and scientist. He studied pea plants and noticed that some grew tall and some stayed short, while other produced green peas and some produced yellow. He wanted to experiment to find out why these changes happened, so he began crossbreeding, or mixing, different types of pea plants together.

Gregor Mendel He began by crossing two tall pea plants. The first generation produced 100% tall plants. When these plants produced offspring, 75% were tall plants and 25% were short plants. What do you think this could mean?

Gregor Mendel Mendel made a hypothesis: he said that every trait is controlled by a set of factors (now called alleles). Each organism receives one set of factors from the mom and one set from the dad. The traits that an organism has depends on how these factors are passed on to them. Therefore, Mendel guessed that the short factor must have been hidden somewhere in the first generation.

Genes Gene: Mendel’s factors; contain DNA codes for all of an organism’s traits. They are found on chromosomes (inside the nucleus), and each gene has a specific location. The likelihood of certain genes being passed on can be calculated using a Punnett square.

Punnett Square In a Punnett square, one side (top) represents one of the parents, and the other side (left) represents the other parent. A dominant trait is represented with capital letters, and a recessive trait is represented with lowercase letters. If you have one dominant and one recessive factor for the same trait, then it is one capital and one lowercase letter. Punnett Squares

Punnett Square Let’s say that brown fur is dominant for a rabbit (B) and white fur is recessive (b). If the mother is dominant (BB) and the father is recessive (bb), what does that mean for the offspring?

Punnett Square Since all of the offspring would be mixed (Bb), they would all have brown fur. Remember, the recessive trait only shows if BOTH factors are lowercase. Suppose a rabbit with mixed factors (Bb) mixes with a rabbit that was recessive (bb). What does this mean for their offspring?

Punnett Square Since two of the offspring are mixed (Bb), those two offspring will both have brown fur. The other two offspring are recessive (bb), so those two will both have white fur. In other words, 50% will have brown fur and 50% will have white fur.