Genetic Definitions

Question 1

Gene

Answer 1

A gene is the basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as instructions to make molecules called proteins. However, many genes do not code for proteins. A gene is a section of DNA that contains the instructions for making proteins that are passed down from parents to their children.

Question 2

Locus or Gene loci:

Answer 2

The position of a gene on a particular chromosome is called the locus (plural = loci)

Question 3

Genotype

Answer 3

The set of genes an organism has. Sometimes, genotype refers to the entire genome of an organism and sometimes it refers to the alleles carried at a particular locus.

Question 4

Phenotype

Answer 4

The physical features of an organism. Phenotype may refer to any aspect of an organism’s morphology, behaviour, or physiology. An organism’s phenotype is affected by its genotype and by its environment.

Question 5

Heredity

Answer 5

A property of systems in which intrinsic characteristics are passed from parent to offspring. This results in offspring that resemble their parent more than they resemble randomly chosen individuals of the population. In biology, heredity occurs largely through transmission of the genetic materials DNA and RNA. However, epigenetic heredity also occurs.

Question 6

Dominant

Answer 6

Gene version with an effect that is observed even when paired with a non-identical gene version in the same individual.

Question 7

Recessive

Answer 7

Gene version with an effect that is only observed when it is found paired with an identical version in the same individual.

Question 8

Heterozygous

Answer 8

An individual carrying two different gene versions for a particular gene (e.g., Aa as opposed to AA).

Question 9

Homozygous

Answer 9

An individual carrying two identical gene versions for a particular gene (e.g., AA as opposed to Aa).

Question 10

Allele

Answer 10

One possible variant of a gene, Different forms of a gene.

Question 11

Complete dominance

Answer 11

Complete dominance is a form of dominance in heterozygous condition wherein the allele that is regarded as dominant completely masks the effect of the allele that is recessive. For instance, an individual carrying two alleles that are both dominant (e.g. AA), the trait that they represent will be expressed.

Question 12

Incomplete dominance

Answer 12

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. This results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles.

Question 13

Codominance

Answer 13

Codominance happens when two traits are independently and equally expressed

Question 14

Polygenic traits

Answer 14

A polygenic trait is one whose phenotype is influenced by more than one gene. Traits that display a continuous distribution, such as height or skin colour, are polygenic.

Question 15

Monohybrid cross

Answer 15

A monohybrid cross is a mating between two individuals with different variations at one genetic chromosome of interest.

Question 16

Dihybrid cross

Answer 16

Dihybrid cross is a cross between two different lines (varieties, strains) that differ in two observed traits. In the Mendelian sense, between the alleles of both these loci there is a relationship of complete dominance - recessive.

Question 17

Punnett Squares

Answer 17

The Punnett square is a diagram that is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach. The diagram is used by biologists to determine the probability of an offspring having a particular genotype.

Question 18

Epistasis

Answer 18

The masking of one gene by another. For example, a gene causing baldness would mask the effect of a hair-colour gene

Question 19

Pedigree

Answer 19

A diagram showing the lineage or genealogy of an individual and all the direct ancestors, usually to analyse or follow the inheritance of trait.

Question 20

Chromosomes

Answer 20

Condensed DNA wrapped around histone proteins.

Question 21

Genomes

Answer 21

The total genetic information in an organism.

Question 22

Karyotype

Answer 22

An image of all the chromosomes of an organism.

Question 23

Homologue - Homologous chromosomes

Answer 23

2 chromosomes with the same size and length, the same centromere position, and they share the same genes at the same gene loci.

Question 24

Autosome

Answer 24

Any chromosome that is not a sex chromosome

Question 25

Nitrogenous base

Answer 25

adenine (A) connects with thymine (T); guanine (G) connects with cytosine (C)

Question 26

Haploid

Answer 26

A cell with a single set of chromosomes

Question 27

Diploid

Answer 27

A cell with a single set of chromosomes.

Question 28

Histone

Answer 28

A protein that has DNA wrapped around creating chromosomes.

Question 29

Telomere

Answer 29

The ends of a chromosome.

Question 30

Sex chromosome

Answer 30

23rd pair are the sex chromosomes, The X and the Y chromosomes are called sex chromosomes

Question 31

Nucleic acid: compound

Answer 31

Nucleic acid is compound, such as DNA or RNA, built from nucleotide sub-units

Question 32

Nucleotide

Answer 32

Nucleotide are made up of Sugar, Phosphate group and Nitrogenous base

Question 33

Somatic cell

Answer 33

Somatic cells are the cells in the body other than sperm and egg cells (which are called germ cells). In humans, somatic cells are diploid, meaning they contain two sets of chromosomes, one inherited from each parent.

Question 34

Chromatid

Answer 34

A chromatid is one of the two identical halves of a chromosome that has been replicated in preparation for cell division. The two “sister” chromatids are joined at a constricted region of the chromosome called the centromere.

Question 35

Sister chromatids

Answer 35

Sister chromatids the identical daughter strands of a replicated chromosome

Question 36

Short arm of chromosome

Answer 36

Short arm of chromsome - aka ‘p arm’ – this is the section of the chromosome that is shorter in length

Question 37

Long arm of chromosome

Answer 37

Long arm of chromosome - aka ‘q arm’ – this is the section of the chromosome that is longer in length homologous chromosomes

Question 38

Aneuploidy

Answer 38

Aneulploidy is when a cell or organism varies in the usual number of chromosomes in its genome by the addition or loss of a chromosome

Question 39

Polyploidy

Answer 39

Polyploidy when an organism contains additional sets of chromosomes in its genome more common in plants - one advantage of polyploidy includes increased size and hardness in certain types of fruit

Question 40

Monosomy

Answer 40

Monosomy is one missing chromosome (2n-1) e.g. turner syndrome - single chromosome X, fused neck

Question 41

Trisomy

Answer 41

Trisomy is one extra chromosome (2n+1) e.g. down syndrome - extra copy of chromosome 21, delayed physical growth e.g. Klinefelter syndrome - extra X chromosome in males (XXY), small testes

Question 42

Tetrasomy

Answer 42

Tetrasomy is two extra chromosomes (2n+2) e.g. Tetrasomy X - two extra copies of the X chromosome, mild delay in physical development