Patterns of Reproduction Notes

Patterns of Reproduction

Guiding Questions

• How do organisms reproduce and transfer genes to their offspring?
• How do offspring produced by asexual reproduction and sexual reproduction compare?
• Why do different offspring of the same parent usually look different?

Vocabulary

• Asexual reproduction: A reproductive process that involves only one parent and produces offspring that are genetically identical to the parent.
• Sexual reproduction: Reproduction where two parents combine their genetic material to produce a new organism that differs from both parents.
• Fertilization: The process in sexual reproduction where an egg cell and a sperm cell join to form a new cell.
• Trait: A specific characteristic that an organism can pass to its offspring through its genes.
• Gene: A sequence of DNA that determines a trait and is passed from parent to offspring.
• Inheritance: The process by which an offspring receives genes from its parents.
• Allele: A different form of the same gene.

Asexual and Sexual Reproduction

• Living things reproduce to pass on their genes to the next generation.
• Two main methods of reproduction: asexual and sexual.

Asexual Reproduction

• Involves only one parent.
• Offspring are genetically identical to the parent.
• Simplest form of reproduction.
• Examples: sponges, corals, certain jellyfish.
• Fragmentation: A new organism forms from a piece of the original (e.g., sea star).
• Budding: A new animal grows out from the parent until it fully matures and breaks off (e.g., sponges, some sea anemones).

Sexual Reproduction

• Two parents combine their genetic material.
• Offspring display a variety of traits and are not exact copies of each other.
• Involves an egg cell and a sperm cell joining in fertilization.
• Sperm cells (from the father) contain half of the father's chromosomes.
• Egg cells (from the mother) contain half of the mother's chromosomes.
• Fertilization results in a full set of chromosomes in the new cell.
• Offspring receive a combination of specific characteristics (traits) from each parent.
• Variations: Differences among offspring depend on which genes were passed on from each parent.

Comparing Types of Reproduction

Asexual Reproduction:

• Advantages: Don't have to find a mate; can produce many offspring quickly.
• Disadvantage: All offspring have the same genetic makeup, which is problematic if the environment changes.

Sexual Reproduction:

• Advantages: Greater genetic variation, increasing the chances of survival in a changing environment.
• Disadvantage: Need to find a mate, which can be difficult for animals in remote areas.

Math Toolbox: Gestation

Gestation is the time period between fertilization and birth.

Inheritance of Traits

• Inheritance: Offspring receive genes from parents.
• Genes are located on chromosomes and control traits.
• Each trait is described by a pair of genes (one from each parent).
• Allele: A different form of the same gene.
• Combination of alleles determines the offspring's traits.
• Dominant allele: If inherited from either parent, that trait will always show up in the offspring.
• Recessive allele: Trait will show only if offspring inherits recessive alleles from both parents.

Examples

• Fur color in mice: offspring may be brown, white, or combinations depending on inherited genes.
• Two brown-eyed people may have a blue-eyed child if they both carry the recessive blue-eye allele.

Incomplete Dominance

• Mixing of colors or sizes occurs.
• Occurs when a dominant allele and recessive allele are inherited.
• Offspring will have a mixture of these two alleles.
• Example: Gray fleece in sheep results from dominant white-fleece allele and recessive black allele.

Codominance

• Both alleles are expressed at the same time, without blending.
• Example: Roan color pattern in cattle, horses, and dogs (dominant white-hair allele and dominant solid-color allele).

Multiple Alleles

• One trait has more than two alleles.
• Example: Human blood type (A, B, O alleles).
• A and B are codominant; O is recessive.
• Each person receives two of the multiple alleles from each parent.

Polygenic Inheritance

• Traits are controlled by more than one gene.
• Different genes are expressed together to produce the trait.
• Example: Human height.

Genes and the Environment

Acquired Traits

• Traits you inherited can be affected by your experience.
• For example, humans are born with the capacity to learn languages, but the language you learn depends on your environment.

Environmental Factors

• Organisms interact with their environment regularly.
• Gene expression determines how inherited traits appear.
• The environment can lead to changes in gene expression.
• Chemicals in tobacco smoke or exposure to UV radiation may change how certain genes behave.
• These changes may cause cancer and other diseases.
• Changes in genes caused by environmental factors are not always passed on to offspring; the change must occur in sex cells (egg or sperm).