BIOLOGY - UNIT 5: GENETICS: GOD'S PLAN OF INHERITANCE

Turner's syndrome

(XO) An abnormality in females where one of the sex chromosomes is missing leaving a total of 45 chromosomes; produced by nondisjunction.

Klinefelter's Syndrome

(XXY) An abnormality affecting males where there is an extra X chromosome due to nondisjunction.

chromosome

A "threadlike" molecule in the nucleus, composed of DNA. A chromosome possesses one allele for a given trait, therefore chromosomes occur in pairs. Each originates from the male and female gamete (parent).

mutation

A change in the genetic information code.

crossing over

A condition where non-sister chromatid of homologous chromosomes exchange genes.

chromatid

A double-stranded chromosome following replication attached by a centromere.

deoxyribose

A five-carbon sugar.

holandric gene

A gene located on the Y chromosome in XY species.

recessive

A gene or trait which is masked when a dominant allele is present.

trait

A genetic characteristic of the individual.

DNA

A giant molecule consisting of the sugar deoxyribose, phosphates and nitrogen bases; contain the coded genetic information.

DNA

A giant molecule consisting of the sugar deoxyribose, phosphates and nitrogen bases; contains the coded genetic information.

Punnett square

A grid system used to predict possible combinations of genes due to random fertilization.

hemophilia

A hereditary condition for bleeding due to the inability to clot properly.

guanine

A nitrogen base found in DNA and RNA; normally pairs with cytosine.

cytosine

A nitrogen base found in DNA or RNA; pairs normally with guanine.

thymine

A nitrogen base found in DNA; normally pairs with adenine.

adenine

A nitrogen base occurring in DNA and RNA; pairs normally with thymine.

RNA

A nucleic acid similar to DNA using ribose for the sugar and the nitrogen base uracil in place of thymine.

spindle fibers

A number of threadlike filaments formed between poles of the cell during cell division to which the centromeres of chromosomes attach; used to pull chromosomes apart and segregate them during anaphase.

pure-bred

A phenotype (trait) resulting from homozygous genes from the offspring of true breeding.

gene

A portion of DNA which codes a specific hereditary trait.

hypothesis

A proposed explanation for an observation which has not been experimentally tested.

gamete

A reproductive cell produced by the male or female parent, which contains the haploid number of chromosomes.

Y chromosome

A sex chromosome found in males; influencing the degree of maleness.

X chromosome

A sex chromosome; in human males only one is present and in females two are present.

centromere

A structure on the chromosome that holds a pair of chromatids together during replication.

meiosis

A type of cell division used to produce gametes and there is a reduction in the chromosome number from the diploid to the haploid number.

gene pool

All of the genes present in a specific population.

allele

Alternative forms for a specific gene.(either dominant or recessive)

law

An explanation for events which is supported by the results on many experiments by a large number of investigations.

sickle-cell anemia

An hereditary form of anemia.

Rh factor

An inherited protein found on the surface of the red blood cell membrane.

hybrid

An offspring from a cross between parents which has different phenotypes for a specific trait.

autosome

Any pair of chromosomes other than the sex chromosome.

diploid

Both members of a pair of chromosomes are present.

dihybrid cross

Breeding of individuals which have genes for two different characteristics.

tetrad

During metaphase I the two pairs of chromatids of the homologous pair of chromosomes comes together; crossing-over can occur at this time.

nondisjunction

Failure of chromosomes to segregate during the formation of gametes, resulting in extra or a shortage of chromosomes in the gamete.

F1 generation

First filial generation; the first generation from a given cross.

cotyledon

First leaf or leaves produced from the seed.

sex-linked

Genes which are carried on the X chromosome.

gene frequency

How common the gene is in the population.

dominant

In a pair of genes, one may prevent the allele from being expressed.

haploid

One member of a pair of homologous chromosomes is present, such as in a gamete.

sex-chromosome

One of the chromosomes which determine the sex of the individual.

nitrogen base

One of the three major types of chemicals making up a nucleotide in DNA; either guanine, cytosine, adenine, or thymine; the sequence of three codes for an amino acid.

polar body

One of three small cells produced during oogenesis, each contain the haploid number of chromosomes.

oogenesis

Process of development of haploid female gametes.

pedigree

The ancestral history of an individual; a chart showing the history of a trait in the family.

chromosome theory

The behavior of chromosomes explains the inheritance of genes.

incomplete dominance

The blending of two traits in a heterozygous individual.

test cross

The breeding of an individual which possesses the dominant trait to a homozygous recessive for that trait.

monohybrid cross

The breeding of two organisms which differ in a single trait.

nucleotide

The combination of phosphate, sugar, and nitrogen bases in DNA or RNA; the combination of three nucleotides codes a specific amino acid.

codominance

The condition in heterozygotes where both members of an allelic pair contribute to phenotype producing a mixture of phenotypic traits.

Down's Syndrome

The condition of mongoloid idiocy caused by the presence of an extra chromosome 21.

theory

The form of the hypothesis after it has been tested and found to be supported by the data collected as the explanation for the observation.

genotype

The genes present in an organism.

one-gene-one-enzyme concept

The genetic code of the gene is responsible for the production of a specific enzyme, which regulates the metabolic pathways in the cell during meiosis; the combination of chromosomes in a gamete is due to chance.

sickle-cell trait

The heterozygous condition which is generally phenotypically indistinguishable for normal person; in conditions of low oxygen some cells sickle. An example of incomplete dominance and environmental influence on gene expression.

self-fertilization

The organism, which possesses both male and female gametes, brings the two genetically identical gametes together to produce offspring.

phenotype

The outward appearance of the organism which is the product of gene action.

P1 generation

The parental generation for a given cross.

linkage

The presence of different genes on the same chromosome.

true-breeding

The process of crossing two organisms, both having homozygous genes for the same trait. i.e. (ZZ x ZZ) or (zz x zz).

spermatogenesis

The production of haploid male gametes by the male parent.

Prophase I

The stage in the first meiotic division where the doubled chromosomes become visible and nuclear membrane disappears.

Metaphase I

The stage in the first meiotic division where the homologous chromosomes line up as a pair, forming a tetrad of chromatids, at the equator of the cell.

Anaphase II

The stage in the second meiotic division where sister chromatids of a chromosome split and migrate to opposite poles.

Metaphase II

The stage in the second meiotic division where the chromatid pair lines up at the equator of the cell.

Telophase I

The stage of the first meiotic division where the cell divides into two cells each containing one member of each pair of homologous chromosomes.

Telophase II

The stage of the second meiotic division when the cell divides into two cells with each being haploid; these cells become the gametes.

Anaphase I

The stage on the first meiotic division when the homologous chromosomes move to opposite poles but the sister chromatids remain together.

population genetics

The study of a hereditary trait in a large population.

pollination

Transfer of pollen, male gamete, in plants to the stigma which contains the female gamete.

deviation

Variation from the predicted values.

multiple alleles

Where more than two alternatives for a gene exist.

heterozygous

Refers to a pair of genes for a specific trait in an organism which are different.

homozygous

Refers to a pair of genes in an organism which are identical in the way they influence a trait.

F2 generation

Second filial generation; the second generation resulting from interbreeding or fertilization from other F1 members.