Lectures 18-21: Mitosis, Meiosis, Heredity, Evolution, and Speciation

Comprehensive practice flashcards covering mitosis, meiosis, cancer, heredity terminology, Mendelian principles, mechanisms of evolution, and speciation models based on Lectures 18-21.

What is DNA and what determines which proteins are produced?

DNA is a molecule that contains genetic (hereditary) instructions for producing proteins (or heritable traits). The sequence of nitrogenous bases (nitrogen-containing bases) determines which proteins are produced.

How are chromosomes, genes, and alleles defined and distinguished?

A chromosome is a DNA molecule. A gene is a DNA segment containing instructions for producing a particular protein (or heritable trait). An allele is an alternative form or variant of a gene (based on differences in nitrogenous base sequences) that causes variation in a heritable trait within a population or species.

What are homologous chromosomes, and how are they characterized in diploid ($2n$) cells?

Homologous chromosomes occur in pairs, are the same size and shape, and have the same genes (though not necessarily the same alleles).

Which amino acids do the nitrogenous-base sequences 'G-C-G' and 'A-C-G' code for?

'G-C-G' codes for the amino acid arginine, while 'A-C-G' codes for the amino acid cysteine.

What is the difference between an individual's genotype and phenotype?

Genotype is the sequence of nitrogenous bases (or the resulting allele/alleles for a trait). Phenotype is the observable form of a heritable trait, which is determined by the genotype.

Which eukaryotic cell types reproduce by mitosis, and what type of reproduction does this represent?

Every eukaryotic cell type reproduces by mitosis with the exception of germ cells (which produce gametes). Mitosis represents asexual reproduction and produces somatic cells (body cells) in multicellular organisms.

What is the primary outcome of mitosis in terms of daughter cell quantity and genetic composition?

Two daughter cells are produced from one parent cell, and each daughter cell is genetically identical to the parent cell (unless a mutation occurs during cell division).

What are the four sequential steps of the mitosis process?

1. Chromosomes of the parent cell replicate into sister chromatids, remaining attached at the centromere.
2. Replicated chromosomes align at the center of the nucleus, and the nuclear membrane dissolves.
3. Replicated DNA copies (sister chromatids) separate, and the cell divides (cytokinesis).
4. Two daughter cells are produced, each being a genetic copy of the parent.

How does cancer develop in relation to mitotic cell division?

Cancer is caused by uncontrolled mitotic cell divisions that produce a tumor (an abnormally large cell mass). This occurs when the regulation of the cell division rate stops working, resulting from damage to DNA.

What are free radicals, and how do antioxidants protect cells from them?

Free radicals are reactive oxygen-containing molecules produced as by-products of cellular respiration. Antioxidants are molecules that neutralize free radicals, thereby preventing these unstable molecules from damaging DNA.

What are carcinogens?

Carcinogens are cancer-causing environmental pollutants.

Where does meiosis occur in eukaryotic organisms, and what are its outcomes?

Meiosis occurs in germ cells (cells in the testes and ovaries), producing male (sperm) and female (egg) gametes. It produces 4 daughter cells from 1 parent cell, where each daughter cell is haploid ($n$) with half as many chromosomes as the diploid ($2n$) parent cell.

In what two ways does meiosis contribute to producing genetically distinct offspring?

1. Crossing over of homologous chromosome segments during meiosis.
2. Independent assortment of egg- and sperm-derived chromosomes to daughter cells during meiosis.

What is the process of meiosis from chromosome replication to daughter cell formation?

1. Chromosomes replicate into sister chromatids attached at the centromere; nuclear membrane dissolves.
2. Crossing over occurs (exchange of segments between homologous chromosomes).
3. Independent assortment occurs (chromosomes line up in the middle, and one of each pair is randomly pulled to an opposite pole).
4. Parent cell divides (cytokinesis), reducing chromosome number by $50\%$ (haploid; $n$).
5. Replicated chromosomes align at the center, and sister chromatids separate.
6. Daughter cells divide, producing 4 haploid ($n$) daughter cells with 1 copy of each chromosome.

How is the original chromosome number restored in sexually-reproducing organisms?

The original chromosome number is restored by the fusion of gametes (sperm and egg) during fertilization, forming a zygote.

What is heredity?

The transmission of genetic info from one generation (parent, parent cell) to the next (offspring).

What is the difference between homozygous and heterozygous genotypes?

A homozygous diploid organism has two copies of the same allele (e.g., RR or rr), whereas a heterozygous diploid organism has two different alleles of a gene (e.g., Rr).

Under what genotypic conditions are dominant and recessive alleles expressed in the phenotype?

A dominant allele (R) phenotype is observed in both homozygous dominant (RR) and heterozygous (Rr) genotypes. A recessive allele (r) phenotype is observed only in the homozygous recessive (rr) genotype.

What is Mendel's Principle of Segregation?

The principle stating that each allele segregates into a separate gamete during meiosis, meaning one chromosome from each pair is distributed to each gamete.

What are linked genes, and how does crossing over affect them?

Linked genes are alleles located on the same chromosome that tend to be transferred to the same gamete during meiosis. Crossing over results in some linked alleles being separated and distributed to different gametes.

What are the five main lines of evidence for evolution listed in the lecture?

1. Gradual change in a trait over time (based on the fossil record).
2. Similarities in traits of extant species (structural homology) implying common ancestry.
3. Embryo similarities among extant species (developmental homology) implying common ancestry.
4. Genetic similarities among extant species (genetic homology) implying common ancestry.
5. Evolution directly observed (artificial selection and emergence of drug- and pesticide-resistant populations).

What is artificial selection?

A change in phenotype and genotype frequencies in a population that is under human control.

What is a mutation, and why is it essential to evolution?

A mutation is a structural change in genetic information (a change in the nitrogenous-base sequence of DNA is a point mutation). It is the mechanism by which new alleles originate, serving as the raw material for evolution.

When does natural selection occur, and what is its consequence on a population over time?

Natural selection occurs when individuals with an adaptive phenotype produce the most surviving offspring. As a consequence, adaptive phenotypes (and the alleles coding for them) become or remain more common in the population over time.

How are biological fitness and adaptation defined in evolutionary biology?

Biological fitness refers to individuals having high reproductive success and contribution of alleles to the next generation. An adaptation is a heritable phenotype that increases fitness.

What specific examples of adaptation and natural selection are noted in the lecture?

Antibiotic resistance in Mycobacterium tuberculosis, pesticide resistance in insects and 'weeds', and change in beak size in the ground finch.

What is genetic drift, and in what type of populations is it especially important?

Genetic drift is a change in allele frequencies in a population due to chance. It is a potentially important mechanism of evolution in small populations.

What is the difference between the founder effect and a genetic bottleneck?

A founder effect occurs when a new population is formed by a few individuals. A genetic bottleneck occurs when a large population is reduced to a small number of individuals.

Why does genetic drift increase extinction risk and lead to inbreeding depression in small populations?

The loss of alleles reduces evolutionary potential. Inbreeding depression occurs because harmful alleles are likely to occur at abnormally high frequencies, leading to a high frequency of individuals that are homozygous for a harmful allele.

What is gene flow (allele flow), and what are its evolutionary consequences?

Gene flow occurs when individuals immigrate or emigrate to a new population. Its consequences include increased genetic similarities between populations and increased genetic diversity within a population through the addition of alleles.

What three concepts or criteria are used to identify and distinguish species?

1. Reproductive isolation (biological species concept)
2. Morphological differences (morphospecies concept)
3. Genetic differences (phylogenetic species concept)

What is speciation?

The emergence of new species from an ancestral species.

What is allopatric speciation, and which evolutionary processes contribute to it?

Allopatric speciation occurs in geographically isolated populations. Contributing evolutionary processes include the absence of gene flow, mutations, and natural selection (specifically directional selection).

What is directional selection, and why do allele frequencies shift differently in isolated populations?

Directional selection is natural selection in which allele frequencies (and phenotypes resulting from them) shift in one direction. Frequencies shift differently because alleles adaptive in the environment of one population may not be adaptive in the other.

What is sympatric speciation, and which evolutionary processes contribute to it?

Sympatric speciation occurs without geographic isolation of populations. Contributing evolutionary processes include mutations and natural selection (specifically disruptive selection).

What is disruptive selection?

Natural selection in which the most common (and most adaptive) alleles for a trait occur at opposite ends of a frequency distribution.