SBI3U - Genetics

Allele

a Specific form of a gene

amniocentesis

long thin needle is used to remove some amniotic fluid from sac surrounding newborn | karyotype produced from cells in fluid

Asexual Reproduction

The production of offspring from a single parent; the genetic makeup of the offspring is identical to that of the parent

Autosomal Inheritance

inheritance of alleles located on autosomal (non-sex) chromosomes.

autosomes

non-sex chromosomes

cell cycle

a continuous sequence of growth and division in cells

chromatid

one of two 'sisters'; makes up half of a chromosome

Chromatin

The tangled strands of DNA and protein within a eukaryotic nucleus

chromosome

thread-like structures made up of DNA located in the nucleus of a cell

Cloning

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

Codominance

a situation where both alleles are expressed fully to produce offspring with a third phenotype.

co-dominance

there is more than one dominant allele and both are expressed at the same time, but don't dominate over one another

Complete Dominance

a situation where an allele will determine the phenotype, regardless of the presence of another allele

crossing over

the exchange of chromosome segments between homologous pairs during synapsis

cytokinesis

the cytoplasm is divided to form 2 distinct cells with one nucleus in each

daughter cell

the genetically identical cell produced through mitosis

deletion

a portion of the chromosome is lost. Viruses, irradiation, and chemicals can cause pieces of chromosomes (containing genes) to be broken off

Dihybrid Cross

a cross that involves two genes, each consisting of heterozygous alleles.

dihybrid cross

observing two traits in one cross

diploid cell

contain 2N chromosomes | 46 in humans

DNA

Deoxyribonucleic acid; present in nearly all living cells, main constituent of chromosomes, the carrier of genetic information

dominant

characteristics that are always expressed in an individual

double helix

the shape of DNA; two spirals

Down Syndrome

trisomy 21 | mental disabilites

duplication

when a gene sequence is repeated one or more times within one or several chromosomes. Even though it is normal for some genes to be repeated thousands of times, there appears a point where too many repeats affect the functioning of the gene.

F1 generation

first filial generation

F2 generation

second filial generation

Fertilization

The formation of a zygote by the joining together, or fusion, of two gametes

Gamete

A sex cell; includes sperm cells in males and egg cells in females

gametogenesis

the production of gametes (sex cells) in animals

gene cloning

the use of DNA manipulation techniques to produce multiple copies of a single gene or segment of DNA

Gene

A unit of heredity that is transferred from parent to child, and determines some of the child's characteristics

Genetic Screening

tests used to identify the presence of a defective allele that results in a genetic disorder.

Genetics

The study of heredity and the variation of inherited characteristics

genotype

the actual alleles an individual has for a trait eg Rr, Ss, bb, DD

haploid cell

contains N chromosomes | 23 in humans

Heredity

The passing of physical or mental characteristics from one generation to the next

heterozygous

an individual who has two different alleles for a gene

characteristics

Homologous Chromosome

Matching pairs of chromosomes, similar in size and carrying information for the same genes.

homozygous

an individual who has two identical alleles for a gene

Incomplete dominance

a situation where neither allele dominates the other and both have an influence on the individual; results in partial expression of both traits.

independent (random) assortment

chromosomes are randomly arranged, causing different combinations of gametes

Interphase

The portion of the cell cycle between mitotic divisions when the genetic material (in the form of chromatin) is duplicated

inversion

a certain gene segment becomes free from its chromosome momentarily before being reinserted in the reverse order

karyotype

the chromosomes of an individual that have been sorted and arranged according to size and shape

Law of Independent Assortment

The inheritance of alleles for one trait does not affect the inheritance of alleles for another trait.

Law of Segregation

A scientific law stating that organisms inherit two copies of genes, one from each parent, and organisms donate only one copy of each gene to their gametes because the genes separate during gamete formation

meiosis

produces gametes (sex cells) which have half the number of chromosomes and which are genetically unique

Mitosis

The process by which a eukaryotic cell divides the genetic material in its nucleus into two new identical nuclei

monohybrid cross

studying only one trait

Monosomy

a chromosomal abnormality in which there is a single chromosome in place of a homologous pair

multiple alleles

there are more than two alleles eg blood IA, IB, i

Mutation

a change in the genetic code of an allele; the change may have a positive effect, a negative effect, or no effect.

Non-disjunction

The failure of homologous chromosomes to move to opposite poles of the cell during meiosis; results in an abnormal number of chromosomes in the daughter cells

nucleotides

building blocks of DNA; consist of a sugar, phosphate, and nitrogenous base

oogenesis

the production of mature egg cells

Ova

Female sex cells (egg cells)

Pedigree

a diagram of of an individual's ancestors used in human genetics to analyze the Mendelian inheritance of a certain trait; also used for selective breeding of plants and animals.

phenotype

the expression of a genotype in an individual eg black hair, purple flowers

polar body

in oogenesis, every time splitting occurs one half has less cytoplasm and dissolves

pole

the end of a cell where the chromatids gather during telophase

Principle of Dominance

When individuals with two contrasting traits are crossed, one trait is always dominant over the other.

Probability

the likelihood that an outcome will occur if it is a matter of chance

Punnett Square

a diagram that summarizes every possible combination of each allele from each parent; a tool for determining the probability of a single offspring having a particular genotype

purebred

only have one type of allele; will only produce children of that type

recessive

characteristics that are latent (present but inactive) in an individual

reproductive cloning

the process of producing genetically identical organisms

sex chromosomes

XY | determine sex

sex-linked inheritance

inherited genes located on the X chromosome

Sexual Reproduction

The production of offspring from the fusion of cells (usually from two different parents); the genetic makeup of the offspring is different from that of either parent

Sister Chromatid

The identical copy of a single chromosome that remains attached to the original chromosome at the centromere

spermatogenesis

the production of mature sperm cells

Synapsis

The physical pairing up of homologous chromosomes during prophase 1 of meiosis.

Test Cross

a cross used to determine the genotype of an individual expressing a dominant trait

Tetrad

A pair of homologous chromosomes, each with two sister chromatids.

therapeutic cloning

the process of replacing an egg cell's nucleus with the nucleus from a somatic donor cell to produce a cell line of genetically identical cells

traits

distinguishing characteristics that make a unique individual

translocation

part of one chromosome changes places with another part of the same chromosome or with part of another non-homologous chromosome

Trisomy

A chromosomal abnormality in which there are three homologous chromosomes in place of a homologous pair

ultrasound

sound waves sent through amniotic fluid | 3D black-and-white image produced

X-linked

phenotypic expression of an allele that is found on the X chromosome.

Y-linked

phenotypic expression of an allele that is found on the Y chromosome.

Zygote

A cell produced by the fusion of two gametes