Plant Sci, Genetics & Evolution

Lesson 8. Ch. 12, 13.

Genes

A segment of DNA that produces a functional product (protein/enzyme)

Alleles

Different forms of the same gene

Genes: Alleles

Cake Recipe: Flavor Variation of Recipe.

Analogy for the relationship between genes & alleles. If Genes are the recipe for a cake, an allele is a “chocolate” or “vanilla” version of that same recipe

Characters

Property of an organism (E.g. flower color, plant height)

Trait

A specific, observable variant of a character (e.g. red flower color. Tall height.)

Haploid (1n)

Contains one set of chromosomes, with one chromosome from each pair.

Diploid

Contains two sets of chromosomes, forming homologous pairs (one from each parent); Two letters, PP, Pp, pp

Mendelian inheritance Generations

P, F1, F2.

P Generation (Parental)

The starting generation in Mendel’s experiments, which were true-breeding (homozygous) for specific traits, such as yellow (YY) or green (yy) peas

F1 Generation (First filial)

The offspring of the P cross, which are heterozygous (Yy) and display the phenotype of the dominant allele only.

F2 Generation (Second Filial)

The offspring from the self-pollination or crossing of F1 individuals. This generation typically displays a 3:1 phenotypic ratio (dominant: recessive) and a 1:2:1 genotypic ratio (YY: Yy: yy) as the recessive trait re-emerges

Law of Segregation

During gamete formation, each parent passes only one of their two alleles to their offspring.

Law of Independent Assortment

Different traits are inherited independently of each other, assuming they are on different chromosomes.

Dominance

The dominant allele masks the recessive one in the generation. Written out as a capital allele: P

Traits can be _ or _

Dominant, Recessive

Alleles can be _ or _

Homozygous, Heterozygous

Genotype

Genetic makeup of an organism

Phenotype

Observable physical expression of the genes, influenced by genetics & environment

Particulate theory of inheritance

Traits are passed from parents to offspring through discrete, separable particles (now known as genes); Genetics passed down from generation to generation

Homozygous

Having 2 identical alleles (versions) of a specific gene inherited from both parents. Such as AA (dominant) or aa (recessive)

Heterozygous

Having two different alleles (versions) of a specific gene, one inherited from each parent. Such as Aa.

Recessive

A version of a gene that only expresses its associated phenotype when two copies are present, otherwise remains hidden or masked by the presence of a dominant allele. Written out as a lowercase allele: p

Mendelian Inheritance Criteria

1. The character is controlled by one gene

2. The gene has only two alleles

3. One allele is completely dominant

4. When two or more genes are involved, they are not linked.

Complex patterns of inheritance

1. Polygenic inheritance

2. Pleiotropy

3. Incomplete dominance

4. Linkage

5. Environmental influence

Polygenic inheritance

Multiple genes control one character

Pleiotropy

Single gene controls multiple characters

Incomplete dominance

neither allele for a trait is completely dominant, resulting in a heterozygous offspring with a blended or intermediate phenotype

Linkage

Genes occur on the same chromosome and are inherited together

Environmental influence

altering gene expression and phenotypic outcomes without changing the underlying DNA sequence.

Meiosis

Cell division essential for sexual reproduction. Divides twice and results in four haploid daughter cells

Mitosis

Cell division that creates identical body cells. Divides once, creates two diploid daughter cells.

Mnemonic device for Mitosis vs Meiosis

Mitosis: “My toesies are growing,” meaning mitosis is responsible for body cells replicating
Meiosis: “Meiosis made me,” meaning meiosis is responsible for creating sex cells

Meiosis I Phases

• Prophase I: Chromosomes condense, homologous chromosomes pair up (synapsis), and crossing over occurs, swapping genetic material.

• Metaphase I: Homologous pairs line up in the middle of the cell.

• Anaphase I: Homologous chromosomes are pulled apart to opposite poles.

• Telophase I & Cytokinesis: Two haploid daughter cells are formed, but chromosomes are still doubled.

Meiosis I - Reduction Division

Separates homologous chromosomes.

Meiosis II - Equational Division

Separates sister chromatids, similar to mitosis.

Meiosis II Phases

• Prophase II: Chromosomes condense again.

• Metaphase II: Chromosomes line up individually at the equator.

• Anaphase II: Sister chromatids are pulled apart.

• Telophase II & Cytokinesis: Four unique haploid daughter cells are produced.

Gene Expression

the fundamental process by which cells convert genetic information from DNA into functional products

Transcription

Synthesize or transcribe messenger RNA (mRNA) from a gene

Translation

Synthesize protein by translating mRNA information

Biopharming

Genetic engineers introduce “designer” genes into the plant genomes and use GM plants to produce proteins in large quantities

Natural Selection

• Individuals in a population vary in size because of their traits

• Only a small percentage of offspring will survive and reproduce

• Individuals compete for limited resources

• Individuals best adapted to an environment will survive and reproduce in greatest numbers

Evolution is the change in…

• genetic traits of a population where certain traits are inherited and increased in frequency by following generations

• allele frequencies from one generation to the next

What does Population Genetics study?

• All genes and their alleles occuring in all individuals of a population

• how often certain alleles occur

• how they change over time

• what might be the cause for the change in allele frequency

Fitness

The potential of an individual to reproduce and pass on its alleles to the next generation (How well it can sexually reproduce)

Adaptation

Describes a genetic trait that is passed on to the next generation and improves the survival and reproduction of an individual under certain conditions

Acclimation

An organism changes in response to slow changes in the environmental conditions but this does not affect evolution (does not influence genotypic changes).
Ex. Plant species expand their range, some plants become acclimated to higher elevations

Does acclimation influence the genotype of future generations?

No.

How can a population’s genetics change?

• Mutation

• Gene flow

• Genetic drift

• Nonrandom mating

• Natural selection

Mutations

Random changes in the genetic composition of an organism

Gene Flow

Occurs when individuals leave or join a population

What are changes in population defined by?

Shifts in allele frequency. The proportion of different gene variants within a population’s gene pool. Changes in population = changes in allele frequency

Genetic Drift

Caused by random events affecting genotypes of a population (bottleneck effect and founder effect)

Nonrandom mating

Occurs when individuals with certain phenotypic characteristics are preferred over other individuals without

Natural selection

Favors individuals in a population that are better adapted to their environment than others.

Types of Natural Selection

Stabilizing, Directional, Disruptive

Stabilizing Natural Selection

Normal distribution with both extremes removed

Directional Natural Selection

Normal distribution with one extreme removed

Disruptive Natural Selection

Bimodal distribution with average size removed

Microevolution

Changes in the gene pool of a population. Rapid.

Macroevolution

Small changes add up over many generations and results in the formation of new species. Over a long period of time.

Punctuated Equilibrium

Eldredge and Gould, an evolutionary theory stating that species experience long periods of stability (stasis) interrupted by brief, rapid bursts of change and speciation. Ex. Tolerant bent grass on mine tailings, herbicide-resistant weeds

Darwin

Slow and gradual change over time through natural selection

Adaptive Radiation

An evolutionary event when a species rapidly produces several new species with diverse adaptations. When plants or animals colonize an island or an area where they have no competitors. Ex. The Hawaiian silversword and 27 other species from a common tarweed ancestor
Two Criteria:
1. Emergence of many new species from a common ancestor in a short period of time. 2. Adaptation by natural selection.

Convergent Evolution

Unrelated organisms with similar appearance which developed independently

Co-Evolution

when two or more species are co-evolving they influence each other’s adaptations and become interdependent