Science 10 Genetics

DNA

Deoxyribonucleic Acid

Nucleotide

Building block of DNA made of sugar, phosphate, and nitrogen base

Polymer

Molecule made of many repeating units (monomers)

Monomer

Single unit that makes up polymers

Hydrogen bond

Weak bond that holds DNA strands together

Adenine

Nitrogen base that pairs with Thymine (2 hydrogen bonds)

Thymine

Nitrogen base that pairs with Adenine (2 hydrogen bonds)

Cytosine

Nitrogen base that pairs with Guanine (3 hydrogen bonds)

Guanine

Nitrogen base that pairs with Cytosine (3 hydrogen bonds)

Double helix

Shape of DNA made of two twisted strands

Sugar-phosphate backbone

Structure forming the sides of the DNA ladder

Nitrogen bases

Molecules that form the rungs of the DNA ladder (A, T, C, G)

Gene

Segment of DNA that codes for one protein

Genetic code

Order of nucleotides that provides instructions to make proteins

Chromosome

Structure of DNA and proteins (histones) found in the nucleus

Histone

Protein that DNA coils around to reduce tangling

Complementary base pairing

A pairs with T, and C pairs with G

Triplet

Three bases that code for one amino acid

Amino acid

Building block of proteins

Gene regulation

Process of turning genes on or off

Stem cell

Cell that has not activated all genes yet

Trait

Characteristic controlled by DNA

Genetics

Study of heredity and variation of traits

Environment

Factor that influences an individual's appearance along with genes

Clone

Organism genetically identical to another

Deoxyribose

Sugar in DNA that is missing one oxygen atom

Phosphate

Part of DNA that connects nucleotides together

Protein

Molecule made from genes; forms muscles, enzymes, hormones, etc.

Chromosomes in humans

46 total (23 pairs)

Parent chromosomes contribution

Each parent contributes 23 chromosomes

Intron

Non-coding part of DNA used for regulation and control

Exon

Coding part of DNA that exits nucleus to make proteins

Backbone of DNA

Made of sugar and phosphate

Rungs of DNA

Made of nitrogen bases

DNA function

Controls traits and codes for proteins

Number of human genes

About 20,000

Stomach cell function

Makes enzymes and mucus (example of specialized cell)

Skin cell function

Makes protective proteins (different genes active)

Cloning fact

When original dies, clone dies too because DNA is identical

Book analogy

Chromosome = book, Gene = chapter, Nucleotide = letter

1 gene = 1 protein

Each gene provides instructions for a single protein

Heredity

Passing of traits from parents to offspring

Homozygous

Identical alleles (same genes) for a particular trait (e.g., purple-purple or white-white)

Heterozygous

Two different alleles for a particular trait (e.g., purple-white)

Allele

Genetic option or variant of a trait (different forms of the same gene)

Trait inheritance

Each trait is controlled by two genes—one from mom and one from dad

Genotype

The genetic makeup of an organism (the two alleles present for a trait)

Phenotype

The physical appearance or expression of a trait

Environment and phenotype

The environment can change how a phenotype appears

Gregor Mendel

Austrian monk who first described the laws of inheritance

Mendel's experiment years

Between 1856 and 1863, Mendel tested over 28,000 pea plants

Mendel's pea traits

Studied seven traits, each controlled by a single gene with only two alleles

Pure generation

True-breeding (homozygous) generation created by Mendel

Parental generation

The first generation Mendel used in his experiments

F1 generation

Offspring from crossing pure yellow and pure green peas (all yellow)

Punnett square

Grid used to predict genetic probabilities of offspring

Mendel's conclusion

Traits are inherited; genes have multiple forms (alleles); some are dominant and some recessive

Dominant allele

Stronger allele that masks the effect of a recessive allele

Recessive allele

Weaker allele that is only seen when no dominant allele is present

Incomplete dominance

Neither allele is dominant; two alleles blend to form a new intermediate phenotype (e.g., pink flowers, wavy hair)

Codominance

Both alleles are expressed equally in the phenotype (e.g., speckled or roan chickens)

Dominant example

Yellow pea color dominates green pea color

Recessive example

Green pea color appears only if no yellow gene is present

Law of inheritance

Mendel's principle that traits are passed from parents to offspring through genes

Multiple allelism

When a gene has more than two alleles, producing many phenotypes

Human blood types

Classification of blood based on surface antigens on red blood cells (A, B, O, AB)

Type A blood

Has A antigens on red blood cells; allele IA; can pair with O

Type B blood

Has B antigens on red blood cells; allele IB; can pair with O

Type O blood

Has no antigens on red blood cells; allele i; recessive to A & B

Type AB blood

Has both A and B antigens; genotype IAIB; universal recipient

Recessive allele example

i allele in blood type O

Antigens

Proteins on the surface of red blood cells that determine blood type