7.4 and 7.5: Heredity and Evolution Unit

What would happen if organisms of a certain species were not able to reproduce? That species would not be able to exist for more than one generation. Reproduction allows species to exist from one generation to the next by passing on genetic information.

All organisms must reproduce, but not all organisms reproduce the same way. Some organisms reproduce through asexual reproduction. Asexual reproduction is when one organism produces offspring that are identical to itself. There is only one parent in asexual reproduction, so an offspring receives all of its genes from one parent. Some advantages of asexual reproduction are it is efficient and often reproduction is quick. Disadvantages include no variation and no adaptability over generations.

Mold can reproduce asexually through the use of spores.

Asexual reproduction is common among unicellular organisms. However, most multicellular organisms reproduce sexually. Sexual reproduction is when two parents each contribute a sex cell to a new offspring. Sexual reproduction involves meiosis. Offspring that are produced through sexual reproduction are not genetically identical to either of their parents because they receive half of their genes from each parent.

Emperor penguins, like most birds, reproduce sexually.

Natural selection is the process where an organism with helpful traits is likely to have more offspring than an organism without helpful traits.

Armadillos, pill bugs, and tortoises all developed shells to keep them safe. For all three organisms, the hard shells are a useful trait that helps keep them alive. They developed the shells through the process of natural selection.

Adaptations cannot happen without variation among a population of organisms. Variation is the difference in traits among members of the same species.

All of these kittens have different traits even though they are all of the same species. This difference in traits is called variation.

Variations happen in a population because of mutations. A mutation is a change in an organism's genes. When an organism's genes change, its traits can change as well. Mutations can happen before birth or during an organism's life.

Finch beaks come in many sizes and shapes. Mutations to the genes controlling beak size and shape caused these differences.

Mutations can be good, bad, or neutral. Good mutations help an organism survive in its environment and can lead to adaptation.

This viper's poisonous venom is an adaptation that came from a good mutation.

Bad mutations can cause an organism to have a shorter life.

Sickle cell disease changes the shape of red blood cells and can lead to medical problems.

When different species evolve from a common ancestor, we call it common

descent. Paleontologists have found evidence of common descent in the fossil

record. This evidence has helped scientists develop the theory of evolution.

Fossils are important for estimating when and how species change over time. We

can use fossils to compare the anatomy of different groups of animals to

determine how they are related, when they lived, and when they became extinct.

Comparative embryology is the study of similar patterns among embryos. Some

of these similarities are only present in the embryo form and not in their adult

form. For example, all animals that have a backbone have gill slits and tails at

some point in their embryonic development. As the animal grows, these

characteristics disappear in animals that live on land, but are still present in the

animals that live in or around water. Organisms that share traits are more closely

related. These similarities in embryonic development show how some animals

may share a common ancestor.