Question

Describe how meiosis provides for genetic variability. If an animal had a haploid number of two (no sex chromosomes), how many genetically different gametes could it produce? (Assume no crossing over.) What if it had a haploid number of five?

Short answer

Meiosis contributes to genetic variability through independent assortment of chromosomes, producing different combinations of maternal and paternal chromosomes in gametes. An animal with a haploid number of two can produce 4 genetically different gametes (\(2^2 = 4\)), while an animal with a haploid number of five can produce 32 genetically different gametes (\(2^5 = 32\)), assuming no sex chromosomes and no crossing over.

Step-by-step solution

Understanding Meiosis and Genetic Variability

Meiosis is a type of cell division that produces four gametes, or sex cells, with half the number of chromosomes as the parent cell (referred to as haploid cells). Meiosis is crucial for sexual reproduction and introduces genetic variability through two key processes: independent assortment of chromosomes and, if allowed, crossing over between homologous chromosomes. In this exercise, we are only considering independent assortment as a source of genetic variability. Independent assortment occurs during meiosis I when the paired homologous chromosomes line up along the metaphase plate, and their orientation is random. This means each gamete produced can have a different combination of maternal and paternal chromosomes.

Calculating the Number of Different Gametes for Haploid Number of Two

By assuming no sex chromosomes and no crossing over, we can use the independent assortment principle to determine the possible number of genetically different gametes. For an animal with a haploid number of two chromosomes (n=2), there are two pairs of homologous chromosomes. The different combinations can be calculated using the formula: \(2^n\) where n is the haploid number In this case, \(2^2 = 4\) So, the animal with a haploid number of two can produce 4 genetically different gametes.

Calculating the Number of Different Gametes for Haploid Number of Five

Now, let's calculate for an animal with a haploid number of five chromosomes (n=5), assuming no sex chromosomes and no crossing over. Using the same formula: \(2^n\) In this case, \(2^5 = 32\) So, the animal with a haploid number of five can produce 32 genetically different gametes. In conclusion, meiosis contributes to genetic variability in organisms mainly through independent assortment of chromosomes and crossing over (though not considered in this exercise). An animal with a haploid number of two can produce 4 genetically different gametes, while one with a haploid number of five can produce 32 genetically different gametes.

Key concepts

Genetic Variability

Genetic variability is the diversity observed in the genetic makeup of individuals within a population. It is a critical factor in the continued survival and adaptation of species.
Meiosis, a specialized form of cell division, plays a pivotal role in generating genetic variability. This process involves two successive divisions that result in four gametes, each containing half the number of chromosomes compared to the parent cell.
During meiosis, genetic variability is introduced mainly through two mechanisms: independent assortment and crossing over.

• Independent Assortment: Refers to the random distribution of maternal and paternal chromosomes to gametes during meiosis.
• Crossing Over: Involves the exchange of genetic material between homologous chromosomes.

Because each gamete can possess a different combination of maternal and paternal chromosomes, the offspring produced from sexual reproduction are genetically unique, contributing to the genetic diversity of a species.

Independent Assortment

Independent assortment is one of the fundamental ways meiosis generates genetic diversity. This process occurs during the first division of meiosis, known as meiosis I. At this stage, homologous chromosomes pair up and align along the metaphase plate in a random orientation.
The key feature of independent assortment is that the way one pair of chromosomes lines up is independent of how other pairs line up. This random orientation leads to the production of gametes with a mix of chromosomes from both parents.

• This mechanism allows for various combinations of chromosomes to be passed down to the gametes, thus increasing the potential genetic variation in offspring.
• For instance, if an organism has a haploid number of two, it can produce 2^2 = 4 combinations of gametes based on independent assortment only.

Haploid Number

The haploid number, denoted as \(n\), is key to understanding genetic variability in meiosis. It refers to the number of distinct chromosomes found in a gamete. Haploid cells contain one set of chromosomes, as opposed to diploid cells, which contain two sets, one from each parent.
In sexual reproduction, gametes combine during fertilization to form a diploid zygote with a complete set of chromosomes. The variation present in the haploid gametes contributes to the genetic uniqueness of the offspring.

• For a haploid number of 2 (\(n=2\)), meiosis can result in \(2^n = 4\) different gametes.
• For \(n=5\), simplicity in calculation shows \(2^5 = 32\) different gametes.

These calculations illustrate the relationship between the haploid number and the potential for genetic diversity in offspring.

Gametes

Gametes are the reproductive cells crucial for sexual reproduction. In animals, gametes are sperm and eggs, each carrying half the genetic information of the parent organism. Gametes are produced through the process of meiosis, which ensures they contain a single set of chromosomes, or haploid number.
This reduction in chromosome number is vital as it allows for the restoration of the diploid state during fertilization when two gametes unite.

• The diversity of gametes, due to processes like independent assortment, enhances the genetic variability of populations.
• An increase in the number of possible gametes, calculated by \(2^n\), ensures a wide range of genetic combinations among offspring.

Chromosomes

Chromosomes are long, thread-like structures made of DNA and proteins. They carry genetic information that determines the traits of an organism. Each species has a characteristic number of chromosomes in its cells. For instance, humans have 46, or 23 pairs, in their diploid cells.
In the context of meiosis, chromosomes play a crucial part in genetic diversity.

• During meiosis I, homologous chromosomes undergo independent assortment, leading to numerous genetic combinations.
• This mixing of chromosomes ensures gametes have variation in the genetic information they carry, influencing genetic variability in the next generation.

Understanding chromosomes and their behavior during meiosis helps illustrate how genetic information is shuffled and shared in sexually reproducing organisms.