Genetics: Mendel's Laws, Punnett Squares, and Inheritance Patterns

Model Organisms

Non-human organisms studied to make discoveries & gain insight on other organisms.

Character

An inherited feature that varies among individuals (ex. plant height, flower color, etc.).

Traits

Different variants of a specific character (ex. short/tall plants & white/purple flowers).

P generation

Parent generation.

F1 generation

First filial generation.

F2 generation

Second filial generation.

Dominant Trait

A trait that is expressed even when one copy is present.

Recessive Trait

A trait that is expressed if no dominant alleles are present.

Law of Segregation

The two alleles for a heritable character segregate during gamete formation and end up in different gametes.

Gene

Segment of DNA that codes for a protein or RNA. Controls what characteristics are expressed.

Alleles

Variants/versions of a specific gene.

Dominant Allele

The allele that is expressed even when one copy is present e.g, in homozygous dominant PP or in heterozygous Pp.

Recessive Allele

The allele that is expressed if no dominant alleles are present.

Mendel's First Concept

Alternative versions of genes account for variations in inherited characters.

Mendel's Second Concept

For each character, an organism inherits two copies of a gene, one from each parent.

Mendel's Third Concept

If the two alleles at a locus differ, then one, the dominant allele, determines the organism's appearance; the other, recessive allele has no noticeable effect on the organism's appearance.

Mendel's Fourth Concept

The two alleles for a heritable character segregate during gamete formation and end up in different gametes.

Punnett Square

A tool that uses probability to help predict the characteristics of an offspring given the physical characteristics of the parents.

Genotype

The genetic makeup of an organism. An individual's inherited alleles make up its genotype.

Phenotype

The physical appearance or expression of an inherited genotype.

Probability

The chance or likelihood that an event will occur.

Homozygote

An organism that inherits two alleles of the same type (BB or bb). Or An organism that has a pair of identical alleles for a gene. PP or pp could be examples.

Heterozygote

An organism that has two different alleles for a gene, such as Pp.

Monohybrid Cross

A cross dealing with only one characteristic.

Key for Alleles

Use uppercase block print for dominant alleles (A) and lowercase script (a) for recessive alleles.

Alleles Representation

The dominant allele is represented with a capital letter (example: B) and the recessive allele is represented with the same letter as the dominant allele but in lower case (example: b).

Possible Genotypes

The three possible genotypes are BB, bb, Bb (the order that the alleles are listed does not matter, so bB is the same as Bb).

Homozygous Traits

Homozygous dominant traits (BB) and heterozygous traits (Bb) will express the phenotype in one way.

Homozygous Recessive Traits

Homozygous recessive traits (bb) will express the phenotype in another way.

Broad definition of evolution

Descent with modification.

Specific definition of evolution post-genetics understanding

Process by which species accumulate differences from their ancestors as they adapt to different environments over time.

Evolution

A change in the genetic composition of a population from generation to generation.

Allele frequency

A change in the allele frequency of a population from generation to generation.

Natural selection

Individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

Key features of natural selection

1. Individuals vary in their traits 2. Some of the variation is heritable - passed to offspring 3. More offspring are produced than survive to reproduce 4. Survival and reproduction are non-random; those with favorable traits reproduce most & pass their alleles to the next generation.

MRSA

Methicillin-resistant Staphylococcus aureus, a flesh-eating strain of bacterium.

Variations in MRSA

Resistant or not resistant to antibiotics.

Selection in MRSA

Presence of antibiotics.

Fitness in MRSA

Resistant bacteria have more chances to reproduce and have increased fitness.

Population evolution in MRSA

Resistant bacteria become more common.

Selection in Rock pocket mice

Presence of predators.

Fitness in Rock pocket mice

Dark colored mice on dark floor will avoid predation and will survive and reproduce more.

Population evolution in Rock pocket mice

Dark mice will become more common.

Natural selection process

Natural selection is a process of editing, not a creative mechanism.

Rapid evolution

In species that produce new generations in short periods of time, evolution by natural selection can occur rapidly in just a few years (S. aureus) or decades (soapberry bugs).

Dependence of natural selection

Natural selection depends on time and place; it favors characteristics in a genetically variable population that provide an advantage in the current, local environment.

Pathogen

bacteria, virus, or other microorganism that can elicit an immune response and can cause disease

Immune system

defense system of animals against pathogens, comprised of many cells and various tissues

Immunity

Resistance against pathogens

Innate immunity

nonspecific defense that mounts generic/similar response to pathogens

Adaptive immunity

acquired, specific defense against specific pathogens, confers long-term immunity

First line of defense (humans)

The outer covering of skin, linings of the digestive tract and airways, and secretions that trap or kill pathogens.

First line of defense (insects)

Exoskeleton as an external barrier and lysozyme enzymes within the digestive system.

Phagocytosis

The ingestion and breakdown of foreign substances, including bacteria

Lysosome

Contain hydrolytic enzymes called lysozyme that can destroy pathogens.

Barrier defenses (invertebrates)

Exoskeleton as an external barrier and lysozyme enzymes within the digestive system.

Physical defenses (invertebrates)

Exoskeleton as an external barrier

Chemical defenses (invertebrates)

lysozyme enzymes within the digestive system.

Cellular innate defenses (invertebrates)

Hemocytes that do phagocytosis

Barrier defenses (vertebrates)

can be physical, chemical or cellular

Physical defenses (vertebrates)

blocks the entry of many pathogens; examples include mucous membranes and the skin.

Chemical defenses (vertebrates)

Lysozyme in tears, Acidic pH in stomach. Complement proteins, pathogen recognition triggers the production and release of a variety of specific proteins that join to form membrane attack complex and can cause pores in the membrane of pathogens.

Cellular innate defenses (vertebrates)

phagocytic innate immune cells dedicated to detecting, devouring, and destroying invading pathogens. Includes macrophages, neutrophils and natural killer cells.

Immune cells in invertebrates

Hemocytes

Innate immune cells in vertebrates

macrophages, neutrophils and natural killer cells.

Function of Hemocytes in invertebrates

Hemocytes circulate within the hemolymph and carry out phagocytosis, the ingestion and breakdown of foreign substances, including bacteria. Some hematocytes deal with large unicellular parasites by forming a capsule around them. Some hemocytes produce a defense molecule that helps entrap larger pathogens. Many hemocytes also release antimicrobial peptides that disrupt the plasma membranes of fungi and bacteria.