Introduction to Mendelian Genetics and Inheritance Patterns, Cell Division: Mitosis and Meiosis Explained

Gregor Mendel

Austrian Monk who experimented with pea plants and discovered genetics.

Genetics

The study of heredity.

Filial - F1 generation

First offspring producing a specific trait or possible combination.

Alleles

Different forms of a gene for a particular trait - a variation of a gene, or a different version of a DNA sequence at a specific location on a chromosome.

Homozygous

2 identical alleles for the same gene.

Heterozygous

2 different alleles for the same gene.

Dominant trait

A gene that shows up even when another gene is present completely masks the effect of another allele when present in an individual.

Phenotype

The observable characteristic determined by the dominant allele.

Law of dominance

In a pair of contrasting traits, one trait (the dominant trait) will mask the other (the recessive trait) in the first generation (F1) of offspring.

Recessive traits

A characteristic that's only expressed when an individual inherits two copies of the recessive allele for that trait.

Genotype

Determined by the alleles, or variant forms of a gene, that are inherited from parents.

Punnett square

Chart that helps to visualize the combinations of alleles that are possible.

Hybrid

An organism with two different alleles for a particular trait.

Second filial - F2 generation

Second offspring producing specific traits.

Law of segregation

Alleles for each trait segregate (separate) during the formation of gametes.

Generation

Born and living at the same time.

Incompetence dominance

Mixing or blending of traits.

Law of Independent Assortment

The inheritance of one gene does not influence the inheritance of another gene.

Dihybrid

Heterozygous for two traits.

Linkage

Does not follow the law of independent assortment (located on the same chromosome).

Recombination

Exchanging alleles 'crossing over'.

Chromosome Theory of inheritance

Chromosomes are the carriers of genetic information and that their behavior during cell division (specifically meiosis) explains Mendelian inheritance patterns.

Sex chromosomes

Chromosomes that determine an organism's sex.

Sex linked trait

Located on the x chromosome.

Pure

All squares the same.

Allele frequency

The extent in which a certain allele exists in a population.

Carrier

Both parents must carry the recessive allele.

Codominance

Both alleles for a trait are equally expressed in the phenotype of a heterozygous individual.

Sickle Cell

Weakens a person, however keeps a person immune to malaria.

Multiple allele inheritance

More than two different alleles of a gene for a particular trait.

Blood type

Different combinations of alleles.

Pleiotropy

Genes influencing not just one trait but several unrelated traits.

Polygenic inheritance

Traits controlled by many different genes.

Hemophilia

Blood clotting disorder (bleed to death).

Color blindness

Recessive but must be carried by mother for male to get it.

Eugenics

Sequencing of human genome to increase the ability for a desirable gene to increase within a population.

Pedigree charts

Study of genetic traits in a human population.

Chromosomes

Condensed Chromatin just before cell division - made from DNA and histones, 23 pairs of sex chromosomes which means 46 chromosomes.

Chromatid

A chromosome duplicates just before cell division into two identical DNA and protein structures.

Chromatin

A substance found in the cell nucleus that's composed primarily of DNA and proteins.

Centromere

The point where the spindle attaches to, part of the chromosome that helps the cell divide its DNA.

Cell cycle

Consists of 3 stages.

Interphase

Has 3 parts - Gap 1 (G1), Synthesis (S), Gap 2 (G2) - DNA replicates and cells grow normally.

Mitosis

Cell division that results in two daughter cells each having the same number of chromosomes.

Prophase

Centrosomes start to go to opposite sides, Chromatin starts to coil into visible chromosomes, nucleus disappears.

Metaphase

Spindles attach to the chromosomes at their centromeres and align them into the equatorial plane.

Anaphase

Centromeres split in half and pulls chromatids towards centrosomes.

Telophase

Chromatids are their own chromosomes, unwind back into chromatin, nucleus begins to reform.

Cytokinesis

Membrane completely pinches off and cytoplasm divides among daughter cells.

Necrosis

Cell death from trauma or injury.

Apoptosis

Programmed cell death when no longer needed.

Checkpoints

Cell checks whether it is ready to continue the cycle, controlled by proteins.

G1 phase

Checks for proper growth and nutrients.

S phase

Halts the cycle until it is done duplicating the DNA.

G2 phase

Checks for DNA damage and can repair or go into apoptosis.

M phase

Monitors spindle formation and does not continue until the chromosomes are correctly attached.

Mutation

If it happens and the cell is not discarded, it may die or proceed abnormally.

Heredity

Transmission of characteristics from parents to offspring through genes.

Genes

Units of genetic information in the chromosomes of the cells (DNA).

Mitosis

Cell division that forms two new daughter cells having identical characteristics and carrying on the same functions as the parent cell.

Asexual reproduction

Only one organism is required to reproduce by creating new cells.

Differentiation

When cells are called out to carry on specific functions specializing organs and components of tissues.

Sexual reproduction

Two organisms needed for reproduction, one male and one female.

Somatic Cells

Body cells that differentiate and have 46 chromosomes (every cell other than a Gamete).

Germ cells

Precursor to egg and sperm that goes through meiosis.

Gamete Cell

Is egg or sperm, has 23 chromosomes in each and only for reproduction.

HAPLOIDS

½ set of chromosomes (23) gametes - sperm or egg (n).

DIPLOIDS

1 full set of chromosomes (46) after fertilization (2n).

Zygote

After fertilization (single fertilized egg) the combined gametes have 46 chromosomes.

Meiosis

Begins with either Spermatocyte (pre-sperm) or Oocyte (pre-egg) also called REDUCTION DIVISION.

Spermatocyte

Formation of sperm cells in testes.

Oocyte

Formation of egg cells in ovaries.

Homologous pair

Same size, same shape and genetic information - One from mother and one from father.

Crossing over

Recombination of alleles in homologous chromosomes causing genetic variety in gametes.

Synapsis

Genetics information exchanges in pairing of homologous chromosomes.

Recombination of genes

Biological variation.