Problem 9 - Campbell Biology

Question

Synthesis/Evaluation WRITE ABOUT A THEME: INFORMATION In sexually reproducing species, each individual inherits DNA from both parent organisms. In a short essay ( \(100-150\) words), apply this idea to what occurs when organisms of two species that have homologous chromosomes mate and produce ( \(\mathrm{F}_{\mathrm{l}}\) ) hybrid offspring. What percentage of the DNA in the \(\mathrm{F}_{1}\) hybrids' chromosomes comes from each parent species? As the hybrids mate and produce \(\mathrm{F}_{2}\) and later-generation hybrid offspring, describe how recombination and natural selection may affect whether the DNA in hybrid chromosomes is derived from one parent species or the other.

Step-by-Step Solution

Answer

Each \(\text{F}_{1}\) hybrid gets 50% of its DNA from each parent species. Over generations, recombination and natural selection will influence DNA proportions from each parent species in hybrids.

Step 1 - Introduce the Basic Concept

Begin by explaining the premise that each sexually reproducing individual inherits DNA from both parents. Mention the DNA contribution from both parent organisms to the offspring.

Step 2 - Explain the Formation of F1 Hybrids

Detail the scenario where organisms from two different species with homologous chromosomes mate and produce \(\text{F}_{1}\) hybrids. State that each \(\text{F}_{1}\) hybrid inherits 50% of its DNA from each parent species.

Step 3 - Describe the Genetic Composition of F1 Offspring

Explain that because the DNA inheritance from both parents is equal, each \(\text{F}_{1}\) hybrid will have chromosomes made up of approximately 50% DNA from one species and 50% DNA from the other species.

Step 4 - Discuss Recombination in Subsequent Generations

Describe how \(\text{F}_{1}\) hybrids, when mating, produce \(\text{F}_{2}\) offspring and beyond. Point out that recombination during meiosis can create new combinations of genetic material.

Step 5 - Explain the Role of Natural Selection

Discuss the role of natural selection in determining which genetic material persists in later-generation hybrids. Mention that natural selection may favor certain genetic combinations that are more advantageous for survival, leading to some genes becoming more prevalent over others.

Step 6 - Summarize Genetic Composition Over Generations

Summarize that over time, and several generations, recombination and natural selection will influence the proportion of DNA from each parent species in hybrid offspring. The outcome will depend on the selective disadvantages or advantages conferred by specific genetic combinations.

Key Concepts

Sexually Reproducing Species

All sexually reproducing species share common processes of genetic inheritance. When two organisms mate, each parent provides half of the genetic material to the offspring. This means that the offspring contains a mix of DNA from both parents. This combination of genetic material ensures genetic diversity, which is crucial for the survival and adaptation of the species. For example, humans get 23 chromosomes from their mother and 23 chromosomes from their father, resulting in a complete set of 46 chromosomes.

Homologous Chromosomes

Homologous chromosomes are chromosome pairs, one from each parent, that are similar in shape, size, and genetic content. These chromosomes carry genes for the same traits, but they might have different versions of these genes, known as alleles. When two different species with homologous chromosomes mate, their offspring will inherit a set of chromosomes from each parent. In the resulting F1 hybrids, each chromosome pair will contain one chromosome from the mother and one from the father, making up about 50% of the DNA from each parent species. This ensures that the offspring have a balanced mix of genetic material from both parent species.

Genetic Recombination

Genetic recombination occurs during meiosis, the process through which gametes (sperm and egg cells) are formed. Recombination involves the exchange of genetic material between homologous chromosomes. This shuffling of genes creates new combinations of alleles, increasing genetic diversity. In hybrid offspring, genetic recombination plays a significant role in the F2 and subsequent generations. As the hybrids reproduce, the new combinations of alleles may result in offspring with unique traits, which could affect their survival and reproductive success. This process continually reshapes the genetic landscape of the hybrids over generations.

Natural Selection

Natural selection is the process by which certain traits become more common in a population because they confer a survival or reproductive advantage. In the case of hybrid offspring, natural selection will favor the genetic combinations that are best suited to the environment. Over generations, some alleles inherited from one parent species may provide better survival advantages than those from the other parent species. Consequently, the frequency of these advantageous alleles will increase in the population. This selective pressure can shape the genetic makeup of the hybrid population, potentially leading to the dominance of certain traits or even the emergence of new species.

Hybrid Offspring

Hybrid offspring are the result of mating between two different species. The initial F1 hybrids inherit roughly 50% of their DNA from each parent species. However, as these hybrids reproduce over successive generations (F2 and beyond), the proportions of DNA from each species can change. Genetic recombination during meiosis introduces new allelic combinations, while natural selection influences which traits are passed on. This interplay between recombination and selection can lead to hybrids that are more suited to their environment, which can change the genetic landscape over time. Ultimately, the DNA of hybrid offspring will reflect a complex blend of their parental genes, shaped by these evolutionary forces.