Bennett Biology - Genetics

gene

Section of DNA on a chromosome that codes for a protein.

alleles

One version of a gene. You have one on a chromosome from Mom, the other on the chromosome from Dad. They are represented by capital or lower case letters.

dominant allele

A version of a gene where you only need one copy in order to express that trait. Represented by a capital letter.

recessive allele

A version of a gene that is not expressed if paired with a different type of allele. Represented by a lowercase letter.

homozygous

Two of the same alleles. If it is two upper case, the trait is dominant, if it is two lower case, the trait is recessive; (RR/rr)

heterozygous

A genotype with two different alleles. One capital next to a lower letter; the capital is dominant and is next to a recessive allele; (Rr).

homozygous recessive

Two copies of the recessive allele make up the genotype. When there are two lower case letters together.

homozygous dominant

Two copies of the dominant allele makes up the genotype. There are two upper case letters.

genotype

The genetic makeup; the alleles a person has.

phenotype

How the genotype is expressed in the individual.

Punnett square

A tool that is used to determine the likelihood of offspring traits.

genotypic ratio

Counting the relative number of squares that have the same letter combination.

phenotypic ratio

Counting the relative number of squares that have different physical appearances.

karyotype

The number and visual appearance of the chromosomes in the cell nuclei of an organism or species-- used to identify chromosomal abnormalities.

trisomy

A condition in which an extra copy of a chromosome is present in the cell nuclei, causing developmental abnormalities.

complete dominance

The dominant allele will take over the appearance of the recessive allele when there is an uppercase and a lower case together.

incomplete dominance

Two alleles blend together, giving a heterozygote a blended phenotype.

codominance

Two alleles share dominance by both expressing themselves.

polygenic inheritance

Traits controlled by more than one gene.

X chromosome

Females have two; many genetic diseases are carried on the x chromosome

Y chromosome

only found in males, smaller than the X chromosome.

pedigree chart

Way of identifying inheritance patterns in genetic diseases and disorders in a family. No color in shape = normal, half color in shape= carrier, color in shape = disease

sex-linked traits

Gene found on the X chromosomes; traits more common in males since males only have one copy of the gene. (if they receive the recessive allele they have no dominant allele to mask it).

crossing over

Creates variations between gametes, homologous chromosomes mix genes in prophase I of meiosis.

diploid

A cell that contains two copies of every chromosomes. All "autosomal" cells.

haploid

A cell that contains half the number of chromosomes of the body cell. Sex cells-- sperm and eggs.

gamete

Sex cell; an egg or a sperm cell.

46

Human diploid number.

23

Human haploid number.

blood types

A, B, AB and O. Type O is the universal donor and AB blood is known as the universal recipient.

sickle cell anemia

An autosomal recessive disorder that causes abnormal hemoglobin, resulting in some red blood cells assuming an abnormal sickle shape.

cystic fibrosis

Autosomal recessive disorder that affects the lungs and digestive system of the individual.

Huntington's disease

A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.

hemophilia

An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured.

red-green color blindness

A common, recessive sex-linked genetic trait.