Genetics (RS9)

germ cell mutation

a change in the DNA of a sex cell that can be passed on to future generations

autosomes

a chromosome trait that is NOT a sex chromosome. In a normal human there are 44 of these (22 pairs) in all cells but the gametes.

trisomy

a condition caused by nondisjunction during meiosis It results in three homologous chromosomes instead of two. In humans, the individual will have 47 chromosomes per cell (except the gametes) instead of 46. There are different types... ex) Edward's syndrome, Patau syndrome

monosomy

a condition caused by nondisjunction during meiosis. It results in only one chromosome instead of two. In humans the individual will have 45 chromosomes per cell (except in the gametes) instead of 46. ex) Turner's syndrome

Klinefelter's syndrome

a condition caused when a sperm, containing both X and Y chromosomes, fertilizes a normal egg (trisomy 23). The individual is a male who is sterile and often develops the secondary sex characteristics of a female. Intellectual disability is usually part of this syndrome.

gamete

a general name given to a sexual reproductive cell. female=egg, male=sperm

PKU (phenylketonuria)

a genetic disease cause by the lack of an enzyme (protein) that coverts phenylalanine to another amino acid. A build up of phenylalanine damages the brain and other organs if not detected. If the newborn is put on a special diet they will develop normally. Type of point mutation.

sickle-cell disease (anemia)

a genetic disease in which the red blood cells exhibit a sickle shape. There is one incorrect amino acid in the blood protein hemoglobin. When the cells become sickle-shaped, they clump together in the blood vessels and prevent blood from supplying oxygen to the tissues.

nondisjunction

a mutation caused when replicated chromosomes fail to separate during cell division. This results in a cell that contains too many or too few chromosomes.

diploid

a name given to the cell when it contains both chromosomes of a homologous pair. The normal number of chromosomes found in the somatic cells. 2N. In humans 2N = 46 chromosomes, or 23 pairs.

haploid

a name given to the cell when it contains only one chromosome of each homologous pair or 1/2 the normal number of chromosomes. N. The number of chromosomes found in the gametes. In humans N= 23 chromosomes.

karyotype

a picture of an individual's chromosomes where the chromosomes are arranged in homologous pairs

meiosis

a specialized type of nuclear division that reduces the chromosome number from diploid to haploid. Only occurs in the gametes.

somatic cells

all body cells but the gametes

Down's syndrome

also called trisomy 21 and caused by nondisjunction. It results in varying degrees of intellectual disability and physical deformity.

alleles

an alternative form of a gene that controls a particular trait. ex) the genes for brown and blue eyes are these for eye color

mutagen

an environmental factor that damages DNA and causes a mutation. ex) radiation

fraternal twins

individuals that develop at the same time from two different eggs fertilized by two different sperm. They do not have to look alike or be the same sex.

identical twins

individuals that develop from a single fertilized egg

homologous chromosome

one of a pair of chromosomes that are the same in size and arrangement of genes, but may differ in the genes that control the trait. In all normal cells (but the gametes) they occur in pairs.

point (gene) mutation

the change of a single nitrogen (N) base within a segment of DNA. ex) sickle-cell disease (anemia), PKU

crossing over

the exchange of genes by homologous chromosomes during meiosis. This may or may not cause defects in the zygote.

Law of Segregation

The principle that members of each pair of factors (genes) separate during gamete formation.

Law of Dominance

The principle that one factor (gene) in a pair may mask the other factor (gene) and prevent it from having an effect.