Sources of Genetic Variation

Flashcards covering the fundamentals of genetic variation, including inheritance terms, the role of mutation, the process of meiosis, and the differences between sexual and asexual reproduction.

How are the terms heredity, genetics, and traits defined?

Heredity is the passing on of characteristics; genetics is the study of heredity; and traits are specific characteristics (e.g. eye colour).

What is the difference between a gene and an allele?

A gene is a section of DNA that holds the code for a specific trait, while an allele is an alternative version of a gene.

What is a locus?

A locus (plural: loci) refers to the specific location on a chromosome where a gene is found.

What is chromatin composed of?

Chromatin is made up of DNA tightly bound to proteins called histones.

Define the term diploid.

Diploid refers to cells containing pairs of chromosomes: one set from the mother (maternal) and one set from the father (paternal).

What are homologous chromosomes?

Homologues are the two members of a chromosome pair that carry the same genes, though not necessarily identical alleles.

What structure joins two sister chromatids together after DNA replication?

The two chromatids are joined together by a centromere.

Distinguish between continuous and discontinuous variation.

Continuous variation shows a complete range of measurements from one extreme to another (e.g. height), while discontinuous variation falls into distinct categories (e.g. fixed or free ear lobes).

What is a mutation?

A mutation is a permanent change in the base sequence of DNA.

Why are mutations considered the ultimate source of genetic variation?

They are the only process that can create entirely new alleles.

Identify the three main sources of variation within a gene pool.

1. Mutation; 2. Sexual Reproduction (Meiosis, mate selection, random fertilisation); 3. Environment.

How can the environment affect an organism's phenotype?

Factors such as food availability, light intensity, and disease may alter the expression of the genotype, modifying the expected phenotype.

Contrast somatic and gametic mutations.

Somatic mutations occur in body cells and cannot be passed to the next generation; gametic mutations occur in reproductive cells and can be passed on to offspring.

What are mutagens and what are some examples?

Mutagens are substances or factors that increase the rate of mutation, such as UV light, radiation (X-rays), and chemicals in cigarettes.

What are the four main types of block (chromosomal) mutations?

Deletion, Inversion, Translocation, and Duplication.

What are the three types of gene (point) mutations?

Insertion, deletion, and substitution of bases (adenine, guanine, cytosine, and thymine).

What is the primary purpose of meiosis?

To produce male and female gametes (sperm and ova) with half the original number of chromosomes for sexual reproduction.

How many chromosomes are found in human body cells versus human gametes?

Human body cells contain $46$ chromosomes, while gametes contain $23$.

What is independent assortment in meiosis?

The random lining up of homologous pairs at the cell equator, which leads to over $8$ million possible combinations of alleles in human gametes.

Describe the process of crossing over.

Homologous chromosomes exchange sections of DNA at points called chiasma, creating new combinations of alleles.

What are 'recombinants' in the context of meiosis?

Recombinants are gametes produced with a different combination of alleles than the parents due to crossing over.

Define segregation in meiosis.

The separation of allele pairs so that each gamete receives only one allele for each gene.

What is the result of fertilization?

A male gamete (sperm) joins with a female gamete (ovum) to form a diploid zygote.

What mathematical formula represents the possible combinations of chromosomes in gametes?

$2^n$, where $n$ is the number of chromosomes per gamete.

What is the major advantage of sexual reproduction over asexual reproduction?

Sexual reproduction produces genetic variation, which may help the species survive environmental changes or disease.

What are clones?

Offspring produced by asexual reproduction that are genetically identical to the parent and each other.