Key Concepts in Genetics and Evolution

Hereditary

The transfer of traits (genetic information) from parents to offspring.

Genetics

The study of heredity.

Father of Modern Genetics

Gregor Mendel.

Common garden pea

The plant with which Mendel worked.

Chromatin

The hereditary material that is associated with proteins.

Chromosome

A large structure composed of coiled DNA that contains genes.

Gene

A sequence of DNA that codes for a trait.

Alleles

The alternate forms of a gene.

Locus

The location of a gene on a chromosome.

Homozygous

If both of the alleles are the same.

Heterozygous

If the two alleles are different.

Phenotype

The observable expression of an allele combination or the physical appearance.

Genotype

The allele combination in an individual or the set of alleles.

Dominant alleles

Always expressed in the phenotype if they are present in the genotype and have the ability to mask another allele.

Recessive alleles

Expressed only in the absence of a dominant allele and are masked by dominant alleles.

Wild type

The most common phenotype or allele in a population.

Mutant type

The phenotype or allele that results from a mutation.

Punnett square

A tool used to determine the possible outcomes of a cross between two individuals.

Probability

The likelihood that a specific event will occur.

One factor cross

A cross between 1 pair of traits.

Two factor cross

A cross between 2 pairs of traits.

Test cross

Crosses an individual with an unknown dominant genotype with a recessive individual.

Principle of segregation

Allele pairs will separate when gametes form.

Principle of independent assortment

Allele pairs separate independently of other allele pairs.

Phenotypic ratio

The ratio representing the phenotypes of the offspring.

Incomplete dominance

Neither allele is dominant over the other allele.

Multiple alleles

Means that there are more than 2 allele choices.

Full color

CHCH or CHCch or CHCh or CHCa

Chinchilla

CchCch or CchCh or CchCa

Himalayan

ChCh or ChCa

Albino

CaCa

Codominance

Both alleles are dominant and must be expressed fully.

Human blood type

Alleles A and B are dominant to each other; A & B are codominant over O which is recessive.

Type A

IAIA or IAIo; Can receive blood from A & O.

Type B

IBIB or IBIo; Can receive blood from B & O.

Type AB

IAIB; Can receive blood from AB, O, A, B.

Type O

IoIo; Can receive blood from O.

23rd pair

Determines gender/sex.

Sex chromosomes

The pair of chromosomes that determine gender/sex.

XX

Female.

XY

Male.

Autosomes

The other 22 pairs of chromosomes that determine everything else.

Probability of a girl

50%.

Probability of a boy

50%.

Male parent

Determines gender chromosomally.

Sex-linked traits

Traits located on the X chromosome.

Inheritance of sex-linked traits

Most are inherited recessively.

Females and X chromosomes

Females have 2 X chromosomes and are less likely to inherit sex-linked traits.

Males and X chromosomes

Males have 1 X chromosome and are more likely to inherit sex-linked traits.

Passing male children sex-linked traits

Responsible by the female (Mom).

Carrier

An individual that is carrying one allele for a recessive trait but does not have the trait.

X inactivation

One X chromosome in females will be inactivated, meaning the genes are turned off.

Random X inactivation

In some cells the paternal X is turned off and in some the maternal X is turned off.

Barr body

The inactivated X.

Pleiotropic gene

A gene that has multiple phenotypic expressions leading to many wide-ranging symptoms that may seem unrelated.

Examples of pleiotropy

Marfan syndrome & porphyria.

Environmental influence

The environment can modify the expression of a trait, usually involving temperature.

Example of environmental influence

Siamese cat is darker in the colder areas of its body like tail, face, feet & white in warmer areas like the body.

Polygenic traits

Inheritance in which several genes affect a trait, creating many different phenotypic expressions.

Example of polygenic traits

Skin color.

Epistasis

Occurs when one gene masks the expression of another gene.

BBee

Produces a yellow lab with dark facial features.

Autosomal recessive diseases

Caused by recessive alleles; 2 alleles are needed to receive one of these diseases.

Carriers for autosomal recessive diseases

Yes, individuals can be carriers.

Albinism

Gene on chromosome 11; No pigmentation in skin, hair, eyes.

Cystic fibrosis

Gene on chromosome 7; Lung infections & congestion; issues with digestion.

Phenylketonuria

Gene on chromosome 12; Build-up of metabolic byproducts causes mental deficiencies.

Sickle cell anemia

Gene on chromosome 11; Joint pain, spleen damage, high risk of infection.

Tay-Sachs

Gene on chromosome 15; Build-up of byproducts causes nervous system degeneration.

Autosomal dominant diseases

Caused by dominant alleles; individuals cannot be carriers.

Achondroplasia

Gene on chromosome 4; Dwarfism with short limbs & normal size head & trunk.

Familial hypercholesterolemia

Gene on chromosome 2; High cholesterol & heart disease.

Huntington's Disease

Gene on chromosome 4; Progressive uncontrollable movements & personality changes; begins in middle age.

Marfan syndrome

Gene on chromosome 15; Long limbs, sunken chest, lens dislocation, spindly fingers, weakened aorta.

Neurofibromatosis

Gene on chromosome 17; Brown skin marks; benign tumors.

Polydactyly

Unknown mechanism; Extra fingers, extra toes, or both.

Familial hypercholestermia

High cholesterol & heart disease

Muscular dystrophy

Rapid muscle degeneration early in life

Fragile X

Mental retardation

Hemophilia

Uncontrollable bleeding

Red-green color blindness

Reduced ability to distinguish between red & green

Nondisjunction

Non-separation of chromosome pairs during meiosis

Monosomy

A zygote created with 1 chromosome instead of its pair

Trisomy

A zygote created with 3 chromosomes instead of its pair

DNA

Deoxyribonucleic acid

RNA

Ribonucleic acid

Nucleotide

Composed of 3 parts: sugar, phosphate group, nitrogen base

Nitrogen bases in nucleotides

5; uracil, thymine, adenine, cytosine, guanine

Purines

Nitrogen bases with a structural formula that contains 2 rings; examples are adenine & guanine

Pyrimidines

Nitrogen bases with a structural formula that contains 1 ring; examples are thymine, cytosine, uracil

Double helix

The spiral shape of DNA composed of 2 strands of nucleotides

Hydrogen bonds

The bonds that hold nitrogen bases to each other in DNA

Complementary base pairing

A purine must always be bonded to a pyrimidine; adenine is paired with thymine using 2 hydrogen bonds, cytosine is paired with guanine using 3 hydrogen bonds

DNA replication

Copying of DNA producing 2 identical copies

Interphase (S)

The phase during which DNA replication occurs before mitosis & meiosis

Helicases

Enzymes that break hydrogen bonds holding the 2 strands of DNA together.

Leading strand

One parent strand of DNA that is continuously synthesized during replication.

Lagging strand

The other parent strand of DNA that is synthesized in short segments during replication.

RNA primase

The enzyme that builds the RNA primer.

RNA primer

Attracts DNA polymerase to the replication site.