SBI3U Biology - Unit 2

Cell Theory

1. All living things are made of cells

2. Cells are the basic functional unit of life

3. All cells emerge from pre-existing cells

Mitosis

A type of cell division involving the asexual reproduction of cells, where the nucleus is divided into two different cells. The two main reasons for mitosis are growth and repair.

Somatic Cells

The cells in which mitosis occurs

Gamete Cells

The cells in which meiosis occurs, also known as sex cells

Diploid Number

A number that represents two sets of chromosomes, 46

Haploid Number

The number that represents one set of chromosomes, 23

Fertilization

The process of which two gamete cells, one sperm and one egg, come together as two haploid cells to produce one zygote

Zygote

A diploid created after the fusion of a sperm cell and an egg cell. The cells will then become the embryo, and will undergo mitosis.

Meiosis

A type of cell division where one parent cell will reduce into four genetically different daughter cells. The diploid number is reduced to the haploid number of chromosomes.

Homologous Chromosomes

Two chromosomes that are very similar to each other

Bivalent

A pair of homologous chromosomes

Synapsis

The state of which two homologous chromosomes are paired

Tetrad

Four strands of chromatids on a pair of homologous chromosomes

Chiasmta

Areas of overlap of the tetrad

Crossing Over

The exchange of genetic material between the chromatids on the tetrad

Prophase I

In this stage, the nuclear membrane and nucleolus dissolve. Additionally, the chromatin condenses to form chromosomes. Afterwards, each chromosome finds its homologous chromosome and they synapse to form a bivalent. Occasionally, chiasmata is visible in this stage, and crossing over may occur. Lastly, the centrioles move to opposite poles to prepare for metaphase I.

Metaphase I

In this stage, the homologous chromosomes line up in the equator of the cell, and spindle fibers begin to form from the centrioles, grabbing onto each chromosome.Anap

Anaphase I

In this stage, each homologous chromosome is pulled apart from the chromosome it was originally synapsed with by the spindle fibers.

Telophase I

In this stage, nuclear division has taken place with homologous chromosome separated. Cytokinesis occurs at the same time.

Meiosis I

The separation of homologous chromosomes

Meiosis II

The separation of sister chromatids, very similar to mitosis

Prophase II

In this stage, the chromosomes stay thickened, and the centrioles move to opposite sides again. The nuclear membrane and the nucleolus also begin to dissolve.

Metaphase II

In this stage, the sister chromatids line up in the middle of the equator

Anaphase II

In this stage, the chromosomes are split up into two sister chromatids, as they are each pulled to opposite sides by the spindle fibers.

Telophase II

In this stage, cytokinesis occurs, the nuclear membranes reform around four genetically different daughter cell, and the nucleolus reappears.

Sperm Cells

The gametes of males.

Ova

The gametes of females.

Oogenesis

The process of creating ova. Out of the four daughter cells, only one will mature to be a true egg, while the remaining three are polar bodies

Polar Bodies

The cells that nourish the ova.

Spermatogenesis

The process of making sperm. Out of the four daughter cells, all four will mature to be functional sperm cells.

Genes

Segments of DNA found on a chromosome which code for a particular trait

Loci

A position on a chromosome where a particular gene is located.

DNA

A tightly coiled double helix structure that are made up of genes. They have a deoxyribose sugar and phosphate backbone, held together by phosphodiester bonds.

Nitrogenous bases

The “rungs” of the DNA structure. The four nitrogenous bases are: adenine (A), thymine (T), cytosine (C) and guanine (G). A can only bond with T, and C can only bond with G. They are bonded together with hydrogen bonds.

Nucleotide

A subunit making up DNA. They are composed of a sugar, a phosphate, and a nitrogenous base. The sugar and phosphate are held together by a phosphodiester bond.

Replication

The copying of the DNA strands. It involves the breaking down of a DNA into two RNA strands, where one of the RNA strands synthesizes a complementary strand, and is said to be semi-conservative. DNA replication required a DNA parent template, a supply of nitrogenous bases, several enzymes (8-12) and ATP.

Uracil

A nitrogenous base found only in RNA, after being converted from thymine.

Codon

A segment containing three nitrogenous bases in an RNA, which translate to a particular amino acid.

Mutation

An error that occurs in the copying of DNA.

Nondisjunction

A chromosomal error that occurs when homologous chromosomes or sister chromatids fail to separate during cell divison

Erwin Chargaff

A scientist who discovered that, in DNA, adenine pairs with thymine and cytosine pairs with guanine

Watson & Crick

Two scientists who theorized that the DNA was shaped like a double helix

Rosalind Franklin

A scientist who confirmed that the DNA was shaped like a double helix

Joachim Hammerling

A scientist who discovered that genetic material was contained within the nucleus

Hershey & Chase

Two scientists who discovered that DNA was passed on to future generations

Identical Twins

The result of a zygote being split up into two, containing equal genetic material

Fraternal Twins

The result of two different zygotes being fertilized at the same time

Asexual Reproduction

The production of offspring from a single parent, where the genetic makeup of the offspring is identical to that of the parent. Mitosis is an example of asexual reproduction

Sexual Reproduction

The production of offspring from the fusion of two sex cells. The genetic makeup of the offspring is different from that of either parent.

Cloning

The process of producing one individual that is genetically identical to another, using a single cell or tissue

Genetically Modified Organisms

An organism in which the genetic material has been altered using genetic engineering techniques

Alcohol

A substance used during the extraction of DNA to help precipitate DNA out of solution

Detergent

A substance used during the extraction of DNA that is used to break down the fat and proteins that make up the cell membrane

Salt

A substance used during the extraction of DNA that causes the phosphate ends of the DNA to come closer together which will make it easier to precipitate out of solution

Transcription

The conversion of DNA into RNA, so it can leave the nucleus and carry information to the ribosomes.

Translation

The coding of RNA into their amino acids.

Gregor Mendel

A monk in the early 1800’s who studied pea plants to learn about genetics. He is said to be the father of genetics.

Characteristic

A feature of an organism, which is typically more broad, such as height

Trait

A specific form of a characteristic, typically more specific, such as tall or short

Pure Bred Stock

Plants that have displayed the same trait for a characteristic for several generations

Genotype

Traits that are represented by two letters, such as “TT”

Homozygous

A trait that is expressed by two of the same sized letter, such as TT or tt.

Heterozygous

A trait that is expressed by two different sized letters, such as Tt.

Phenotype

Traits that are represented by a description, such as “tall”

Alleles

The alternate forms of a gene, expressed as T or t.

Hybrid

An organism that results between 2 pure bred’s crossing, resulting in a heterozygous offspring,

Mendel’s First Law

"The Law of Segregation,” which states that the alleles must separate during a cross.

Incomplete Dominance

A case where neither allele controlling the trait is dominant, resulting in a blending of the two traits. Expressed by a prime: “R and R’.” A good example is flower colour.

Co-Dominance

A case where both alleles for a trait are dominant. They are expressed by two capitals for each trait: “RW.” A good example is feather colour in chickens and coat colour in cattle.

Multiple Alleles

A case where a gene has more than two alleles. Expressed by and I, followed by a superscript of the trait. A good example is human blood.

Mendel’s Second Law

“The Law of Independent Assortment,” which states that different traits are inherited separately from each other.

Sex-Linkage

A case where some diseases arise from a defective gene on the sex chromosomes,

Carrier

A female who carries a defective gene, but her functioning X chromosome masks the effect of the other.

Pedigree

A family tree that displays the history of a particular disease in a family.

Cystic Fibrosis

A recessive disorder due to an allele on chromosome 7, which tends to reduce life expectancy.

Down’s Syndrome

A non-disjunctional disorder, as the result of a trisomy on chromosome 21. It becomes much more prevalent in women who are older than 40.

Hemophilia

A sex-linked disorder in which the patient is unable to clot blood properly.

Sickle Cell Anemia

A recessive/sex-linked disorder that is most prominent in Africa.

Albanism

A sex-linked, as the result of a mutation of chromosome 11. There is a lack of coloration due to a lack of melanin.

Klinefelter’s Disorder

A non-disjunctional disorder in the sex chromosomes such that the person is XXY.

Retinitis Pigmentosa

A sex-linked disorder with a mutation on the X chromosome, which can lead to blindness.

Hypercholesterolemia

A dominant disorder affecting chromosome number 5, which can lead to early heart attacks due to a lack of receptors for LDL cholesterol.

Muscular Dystrophy

A sex-linked disorder, which is a severe form of Duchenne’s syndrome. Boys have muscle weakness, and often results in respiratory problems, and eventually death.

Phenylketonuria

A recessive disorder affecting chromosome number 12. Patients require a special diet, and can lead to death if not diagnosed early.

Tay Sachs

A recessive disorder where the brain and spinal cords deteriorate at around 8 months old. Most die by 5 years old. Particularly common in Ashkenazi & Jewish people.

Red-Green Color Blindness

A sex-linked disorder which is prevalent in boys. Patients lack ability to distinguish red and green coloration.

Trisomy

A condition where one set of chromosomes has three copies, instead of two.

Monosomy

A condition where one set of chromosomes has one copy, instead of two.

Karyotype

An illustration of the chromosomes in the nucleus of a cell during the metaphase I stage.

Colchicine

A chemical used to freeze the chromosomes during metaphase I when karyotyping.

Amniocentesis

A technique of assessing the chromosomal status of a fetus, where a needle is inserted into the sac surrounding the fetus to extract fetal cells, that can be used to create a karyotype. This procedure is usually done at 16 weeks of pregnancy.

Chorionic Villus Sampling (CVS)

A technique of assessing the chromosomal status of a fetus, where cells are removed from the chorion, that can be used to create a karyotype. This procedure is usually done at 9 weeks of pregnancy.