genetics

The scientific study of heredity

true-breeding

A term used to  describe organisms that produce offspring identical to themselves if allowed to self-pollinate.

trait

A specific characteristic that varies from one individual to another.

hybrid

An offspring of crosses between parents with different traits.

 gene

A sequence of DNA that codes for a protein and thus determines a trait.

allele

One of a number of different forms of a gene.

segregation

A separation of alleles during gamete formation.

gamete

What is the principal of dominance?

The principle of dominance states that some alleles are dominant and others are recessive.

What happens during segregation?

alleles separate

During gamete formation, alleles are segregated from each other so that each gamete carries only a single copy of each gene.  Each F₁ plant produces two types of gametes --those with the allele for tallness and those with the allele for shortness. 

What are dominant and recessive alleles?

What did Mendel conclude determines biological inheritance?

Medel drew two condlusions:

1: That biological inheritance is determined by factors that are passed from one generation to the next.  (genes)

2. (the principle of dominance)  States that some alleles are dominant and others are recessive. 

probability

The likelihood that a particular event will occur; the probability that you can flip a coin 4 times and get a tails for each is 1/2 x 1/2 x 1/2 x 1/2 = 1/16.

Punnett square

A diagram showing the gene combinations that might result from a genetic cross.

homozygous

A term used to refer to an organism that has two identical alleles for a particular trait (AA or aa)

heterozygous

A term used to refer to an organism that has two different alleles for the same trait (Aa).

phenotype

The physical characteristics of an organism; the expression of a trait (pink, red, type O blood, tall)

genotype

The genetic makeup of an organism; the two alleles an individual has for a particular trait (AA, Aa, or aa)

How do geneticists use the principles of probability?

The principles of probabiltiy can be used to predict the outcomes of genetic crosses.

How are the principles of probability used to predict the outcomes of genetic crosses?

(If you flip a coin twice, you are likely to get one head and one tail.  Hoewever, you might also get two heads or two tails.  To be sure of getting the expected 50:50 ratio, you would have to flip the coin many times.)

The same is true of genetics.  The larger the number of individuals, the closer the resulting offspring numbers will get to expected values.   

independent assortment

The independent segregation of genes for different traits during the formation of gametes; today we know that these genes would be for traits on non-homologous chromosomes.

incomplete dominance

The situation in which one allele is not completely dominant over another; an individual with two different alleles for the trait (Aa) would have an intermediate phenotype

codominance

The situation in which both alleles of a gene contribute to the phenotype of the organism; AB blood type, black and white speckled chicken feather, roan cows

multiple alleles

Three or more alleles of the same gene in a population; rabbit coat color, eye color in humans, human blood type (A,B,O alleles), etc.

polygenic trait

A trait controlled by two or more genes in an individual; human skin color, human hair color, etc.

What is the principle of independent assortment?

Genes for different traits on different, non-homologous chromosomes can segregate independently during the formation of gametes.

What inheritance patterns exist aside from simple dominance?

Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

Meiosis

A process of reduction division

in which the number of chromosomes per cell

is cut in half through the separation

of homologous chromosomes

in a diploid cell; 4 genetically different

haploid cells result.

How is meiosis different from mitosis?

Mitosis results in the production

of two genetically identical diploid cells,

whereas meiosis produces four

genetically different haploid cells.

homologous

A term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent.

diploid

A term used to refer to a cell that contains both sets of homologous chromosomes (2N = 46 in humans); all body cells have this number of chromosomes, except gametes.

Haploid

A term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes (N = 23 in humans);

only found in sex cells 

meiosis

A process by which the number of chromosomes per cell is cut in half through the separation of homoologous chromosomes in a diploid cell.

tetrad

A structure containing 4 chromatids

that forms during meiosis I (prophase I).

crossing-over

A process in which homologous chromosomes exchange portions of their chromatids

during meiosis I (prophase I);

results in recombined gametes.

Describe the main results of meiosis.

Meiosis produces four

geneticlly different

haploid cells.

What structures actually assort independently?

It is the chromosomes, however, that assort independently, not individual genes.

gene map

A diagram showing

the relative locations of each known gene

on a particular chromosome.