4/7 Genetic Principles: Mitosis, Meiosis, and Mendel's Laws

Mitosis

Maintains genetic consistency within an organism.

Meiosis

Generates diverse gametes to pass genetic information to the next generation.

Gametes

Contain half of the genetic material (except in fungi, which have a lot).

Single gene inheritance

Concept linked to genetic analysis today.

Two gene interaction/double interaction

Concept linked to genetic analysis on Wednesday.

Chi-square test

Used to test the ratio in the population on Friday.

Mutants

Any heritable variant observed in the same species that differs from the white type.

White type

The most common form of any trait of an organism, or the trait found in nature.

Genetics

The science studying variation.

Spontaneous mutation

A mutation that occurs naturally in nature.

Aphids Example

A professor's experiment in central California where aphids destroyed all but one variety of cow-peas, the remaining being a mutant resistant to aphids.

Alleles

Different versions of a gene; can be homozygous or heterozygous.

Homozygous

Individuals carrying the same version of a gene.

Heterozygous

Individuals carrying different versions of a gene.

Genotype

The genetic makeup of an organism; the type of allele of a gene in the organism (e.g., big E and small E).

Phenotype

Observable traits; what we can observe with our naked eyes, under a microscope, or by bioassay.

Gregor Mendel

Deduced the principles of genetics by breeding garden peas.

Model organism

Peas were an excellent choice due to short generation times and the ability to produce many seeds.

True Breeding Lines

Lines that, when crossed with themselves, produce offspring identical to the parents.

Replicability

Ensuring consistent results when repeating experiments.

Crossing tall plants

Yields all tall offspring.

Crossing short plants

Yields all short offspring.

Controlled Cross

A method where pollen from another plant is transferred onto the stigma of a flower after removing the male part to prevent self-fertilization.

Reciprocal Crosses

Experiments where the roles of the parents are reversed to observe if the progeny's appearance changes.

F1 Generation

The first filial generation resulting from a cross, which displays the dominant trait.

Alleles

Different versions of a gene.

Homozygous

Plants with two identical alleles.

Dominant Trait

A trait that will show in a heterozygote.

Recessive Trait

A trait that is hidden in a heterozygote.

Chromosome Segregation

The process during meiosis where alleles are located on homologous chromosomes and segregate into gametes.

Phenotype Prediction

The ability to predict the phenotype based on the genotype, especially for dominant traits.

Mendel's First Law

The Law of Segregation states that during meiosis, members of a gene pair segregate equally into gametes.

Parental Genotypes

The genetic makeup of parents, which can be homozygous dominant, homozygous recessive, or heterozygous.

Heterozygous

An organism that has two different alleles for a trait.

Homozygous Dominant

An organism that has two identical dominant alleles.

Homozygous Recessive

An organism that has two identical recessive alleles.

Small s Allele

The recessive allele for wrinkled seeds, which is hidden when paired with the dominant big S allele.

Big S Allele

The dominant allele for smooth seeds, which determines the visible phenotype in hybrids.

F1 Offspring

Offspring from true-breeding lines that are 100% heterozygous.

Gametes

Reproductive cells (sperm or eggs) that carry alleles.

Phenotype

The observable characteristics or traits of an organism.

Genotype

The genetic constitution of an organism, which may not always be directly observable.

Trait

A characteristic that is inherited and can be dominant or recessive.

Smooth Seed Phenotype

The visible trait expressed when at least one big S allele is present.

F1 Offspring

F1 offspring from true-breeding lines are 100% heterozygous.

Monohybrid Cross

A cross between two individuals that are heterozygous for the same gene.

Gamete Combinations

A heterozygous plant produces two types of gametes.

Punnett Square

The Punnett Square is a tool used to solve genetics problems.

Phenotype to Genotype

Given a recessive phenotype, the genotype can be determined directly.

Self-pollination

If a plant is homozygous dominant, the progeny will all look the same.

Test Cross

Cross the unknown individual with a homozygous recessive individual.

Homozygous Recessive

The homozygous recessive individual only has one phenotype.

Test Cross Purpose

A test cross is used to determine if an organism with a dominant phenotype is homozygous dominant or heterozygous.

Homozygous Dominant Test

If the plant in question is homozygous dominant (AA), then all gametes will carry the dominant allele (A).

Heterozygous Test

If the plant in question is heterozygous (Aa), then half of the gametes will carry the dominant allele (A), and half will carry the recessive allele (a).

Haploid Organisms

In haploid organisms, each individual has only a single set of chromosomes.

Single Allele Inheritance

Haploid organisms possess only a single allele for each gene.

Haploid Life Cycle

A haploid cell exists. Two haploid cells fuse to form a diploid cell.

Gene Segregation in Haploids

In haploid organisms, gene segregation is straightforward: the progeny segregate 50-50.

Dominant Phenotype

If an individual has at least one dominant allele, they will display the dominant phenotype.

Homozygous Dominant

Homozygous dominant individuals result from the combination of two dominant alleles.

Homozygous Recessive Phenotype

The phenotype of the progeny will reveal the genotype of the unknown parent.

Segregation in Diploids

Segregation in diploid organisms is more complicated than in haploid organisms.

Equal Frequency of Gametes

There are four possible combinations of male and female gametes, each occurring with an equal frequency of 25%.

Progeny Segregation

If heterozygous, the progeny will segregate.