SBI3U - Unit 2 - Definitions

Genetics

Genetics

The study of heredity and variation of living organisms and how genetic information is passed from one generation to the next

Somatic Cell

A plant or animal diploid cell that forms the body of the organism; excludes reproductive cells

Interphase

The stage of the cell cycle during which a cell carries out its normal functions, grows, and makes copies of its genetic material in preparation for the next stage of the cycle

Mitosis

The stage of the cell cycle where a cell's nucleus and genetic material divide

Prophase

The stage where the cell's chromatin condenses into chromosomes, the nucleus and nucleolus disappear, and spindle fibres form from the centrosomes and move towards the poles

Chromosome

A structure in the nucleus that contains DNA

Sister Chromatid

One of two chromosomes that are genetically identical and held together at the centromere

Centromere

The region where two sister chromatids are held together in a chromosome

Spindle Fibre

A microtubule structure that facilitates the movement of chromosomes within a cell

Centrosome

A structure that helps to form the spindle fibres

Metaphase

The stage where the spindle fibres from each pole attach to the centromere and guide the chromosome to the equator of the cell

Anaphase

The stage where each centromere splits apart, and sister chromatids, now individual chromosomes, are separated to opposite poles so that each pole has a complete set of DNA

Telophase

The stage that begins when chromosomes reach the opposite ends of the cell, where chromosomes start to unwind, spindle fibres break down, and the nucleus and nucleolus reform

Cytokinesis

The stage of the cell cycle that involves the division of the cell cytoplasm and creation of two new daughter cells

Genome

The complete DNA sequence of an organism

Sex Chromosome

An X or Y chromosome, which determines the genetic sex of an organism

Autosome

A chromosome that is not involved in determining the sex of an organism

Homologous Chromosome

A chromosome that contains the same sequence of genes as another chromosome

Gene

A functional part of a chromosome that contains information for inheritance, governs the expression of a trait and is passed on to offspring; it has a specific DNA sequence

Allele

A different form of the same gene

Karyotype

A photograph of pairs of homologous chromosomes in a cell

Asexual Reproduction

Reproduction that requires only one parent and produces genetically identical offspring

Sexual Reproduction

Reproduction that requires two parents and produces genetically distinct offspring

Gamete

A male or female haploid reproductive cell

Zygote

A cell formed by the fusion of two gametes in fertilization

Fertilization

The joining of male and female haploid cells

Diploid

A cell that contains pairs of homologous chromosomes, represented by 2n

Haploid

A cell that contains half the number of chromosomes as the parent cell, represented by n

Meiosis

The cellular process that produces cells containing half the number of chromosomes as the parent cell (genetic reduction) and are genetically unique through combinations of alleles (genetic recombination)

Interphase Before Meiosis

Cells that will divide by meiosis will proceed through growth and synthesis, and replicate their chromosomes, so that the meiosis begins with duplicated chromosomes

Prophase I

Each pair of homologous chromosomes condense and line up side by side in synapsis, where genetic information is exchanged through crossing over

Tetrad

Two chromosomes or four chromatids

Chiasma

The site where chromosomes cross over

Metaphase I

The pairs of homologous chromosomes (tetrads) line up along the equator of the cell, and spindle fibres attach to the centromere of each homologous chromosome

Anaphase I

The homologous chromosomes separate and move to opposite poles, which turns a diploid cell into a haploid cell

Telophase I

Homologous chromosomes begin to uncoil and the spindle fibres disappear, the nuclear membrane forms, and two haploid cells form through cytokinesis

Prophase II

The nuclear membrane disappears and spindle fibres reappear

Metaphase II

A haploid number of chromosomes line up at the equator

Anaphase II

Sister chromatids are pulled apart at the centromere by the spindle fibres towards opposite poles of the cells

Telophase II

The nuclear membrane and nuclei reform

Spermatogenesis

The process of producing male gametes in mammals

Oogenesis

The process of producing female gametes in mammals

Independent Assortment

The orientation of each chromosome in a homologous pair to one pole, which can result in a variation of possible gametes containing a combination of maternal and paternal chromosomes

Crossing Over

The exchange of chromosomal segments between a pair of homologous chromosomes during prophase I

Deletion

A piece of a chromosome is deleted

Duplication

A section of a chromosome appears two or more times in a row

Inversion

A section of a chromosome is inverted

Translocation

A segment of one chromosome becomes attached to a different chromosome

Non

disjunction - The failure of homologous chromosome pairs or sister chromatids to separate during the anaphase stages in meiosis

Monosomy

The loss of a chromosome in an autosome as a result of non-disjunction

Trisomy

The gain of an extra chromosome in an autosome as a result of non-disjunction

Down Syndrome

Trisomy 21, and includes intellectual disabilities and a short stature

Edward's Syndrome

Trisomy 18, and includes intellectual and physical disabilities and facial abnormalities

Patau's Syndrome

Trisomy 13, and includes intellectual and physical disabilities, many organ defects, and a large triangular nose

Klinefelter's Syndrome

XXY, and includes sexual immaturity

Jacobs' Syndrome

XYY, and may be taller than average

Metafemale

XXX, and includes menstrual irregularity

Turner's Syndrome

XO, and includes a short stature and underdevelopment sexually

Hayflick Limit

The limit of the life span and amount of division of different types of body cells

G1 Checkpoint

Checks for DNA damage, cell size, nutrients and proteins for growth

G2 Checkpoint

Checks for successful DNA replication

Metaphase Checkpoint

Checks that chromosomes are correctly attached to spindles

Apoptosis

Programmed cell death, where suicide genes produce proteins that kill the cell

Necrosis

Cells die from damage through toxic chemicals or physical forces

Cancer

Cells divide uncontrollably as a result of DNA mutation and damage, where the genes that control checkpoints stop working

Tumor

A mass of cells that keeps growing and dividing without any obvious function

Benign Tumor

A tumor that physically crowds surrounding tissue, but does not affect it

Malignant Tumor

A tumor that interferes with the functioning of surrounding cells and outcompetes them

Metastatic Tumor

When cancer cells break off from a tumor and travel through blood and lymph to form a secondary tumor somewhere else in the body

Mutation

A random change in the DNA code

Trait

A specific characteristic or feature exhibited by an organism

True Breeding

Organisms that exhibit the same traits, generation after generation

Cross

The fertilization of a female gamete of specific genetic origin with a male gamete of a specific genetic origin

P Generation

In breeding, the organisms initially crossed and are typically true breeding

F1 Generation

The offspring of a cross of the P generation

F2 Generation

The offspring of a cross between the F1 generation

Mendelian Ratio

An approximate ratio of 3:1 for dominant to recessive phenotypes in a monohybrid cross between two heterozygous parents

Monohybrid Cross

A cross of two individuals that differ by one trait

Theory of Particulate Inheritance

Recessive genes can be discretely inherited through generations, which causes traits to go unexpressed in the F1 generation, but reappear in the F2 generation

Law of Segregation

Traits are determined by pairs of alleles that segregate during meiosis so that each gamete receives one allele

Law of Independent Assortment

During gamete formation, the two alleles for one gene segregate or assort independently of the alleles for other genes on other chromosomes

Dominant

The form of a trait that always appears when an individual has an allele for it

Recessive

The form of a trait that only appears when an individual has two alleles for it

Genotype

The combination of alleles for any given trait, or the organism's entire genetic make-up

Heterozygous

An organism that has two different alleles of a gene

Homozygous

An organism that has two identical alleles of a gene

Phenotype

The physical and physiological traits of an organism

Test Cross

A cross between a parent of an unknown genotype and a homozygous recessive parent

Dihybrid Cross

A cross of two individuals that differ in two traits due to two different genes

Continuous Variation

Multiple allele pairs spread throughout the chromosomes

Polygenic Traits

Traits controlled by multiple alleles

Codominant Gene

Two different alleles at a locus are responsible for different phenotypes, and both alleles affect the phenotype of the heterozygote

Incomplete Dominance

The phenotype of a heterozygote is a blend of both the dominant and recessive traits

Sex Linked Gene

A gene coded on a sex chromosome

Hemizygous

If there is only one copy of a gene for a particular trait, such as X-linked genes in males

Lethal Allele

A mutated gene that is capable of causing death

Wild-Type Allele

The non-mutant form of a gene, encoding the normal genetic function

Complementary Genes

Genes can only be expressed in the presence of other genes

Epistasis

One gene masks the expression of a different gene for a different trait