Genetics is the study of heredity or passing on of traits from one generation to the next.
A trait is a physical characteristic an organism has
(something you can see). Examples are how tall a person is, the color of the seeds, and the shape of the seeds, the hair color and the eye color.
Gregor Mendel (1860’s) was an Austrian monk and a biologist. He experimented with pea plants to see how traits are passed from one generation to the next.

usually, pea plants fertilize themselves called self pollination
 however, Mendel cross-fertilized pea plants called cross pollination
P1 generation
(parental
F1 generation
(1st generation)
F2 generation
(2 nd generation)
generation)
TT x tt true breeding
Tt x Tt
all offspring tall & short plants were tall
TT x Tt x Tt x tt
3 tall offspring
1 short
(see text book Life Science page 586 Figure 23-3) true breeding (get the same)- organisms that produce offspring with the same traits as parents dominant (capital letter)- trait that is expressed or shown “mask” or hide other genes recessive (lower case letter)- trait that is seldom shown, usually hidden by dominant gene homozygous - means “same”, both genes are the same
(ex: TT or tt) heterozygous - means “different” genes in a pair (ex: Tt) hybrid -2 genes that are different for a trait (same as heterozygous)

~ traits, or characteristics are blended down from one generation to the next
~ the traits of an organism are controlled by genes
~ organisms inherit genes in pairs, one gene from each parent (law of segregation)
~ some genes are dominant, while other genes are recessive
~ dominant genes mark recessive genes when both are inherited by an organism
~ some genes are neither dominant or recessive, these genes blend together when they are inherited
~ law of independent assortment- each gene pair for a trait is inherited independently of the gene pairs for all other traits
~ co-dominant-

In some gene pairs the genes are neither dominant nor recessive
~ these genes exhibit incomplete dominance
~ Karl Correns discovered incomplete dominance
~ incomplete dominance-neither gene is dominant
(neither hides the other)
~ in his research, Correns discovered that when crossing true-breeding red (RR) four-o’clock flowers with truebreeding white (WW) four o’clock flowers, all offspring were pink. (blend red and white = pink)


Punnett square model showing Correns discovery of incomplete dominance using red and white four o’clock flowers.
R W
R RR RW
R R
W RW RW
W RW WW W RW RW
(genotype is the gene type or letter combo)
~ the genotype for red four o’clock flowers RR
~ the genotype for white four o’clock flowers WW
~ the genotype for pink four o’clock flowers RW

Phenotype is the physical look (ex: red, white, pink)
Chromosomes are rod shared structures found in the nucleus of every cell. The chromosomal theory is when genes are located on chromosomes and they are responsible for carrying the hereditary information. Walter Sutton developed this theory.
The main function of chromosomes is to control the production of protein. All organisms are made mainly of proteins.
Some functions proteins control are the size, shape any other physical characteristics of an organism. However, it is not really the chromosomes that control the production of proteins. Genes that are carried on the chromosomes actually control protein production.
~ In 1907, Thomas Hunt Morgan discovered sex chromosomes while studying male and female fruit flies.
~ females have two X chromosomes
~ males have one X and one Y chromosome

MODEL SHOWING SEX DETERMINATION
X X
X XX XX
Y XY XY
Mutations are a change in a gene or chromosome that may affect the organism. Hugo DeVries discovered the occurrence of mutations in nature. Mutations that affect only the organisms that carry it occur in body cells. These mutations cannot be passed on to the offspring. Mutations that can be passed on to the offspring causing a change in the next generation occur in sex cells. Most mutations are harmful! Often, they reduce an organism’s chance of survival or reproduction. One type of harmful mutation in humans is called sickle cell anemia (abnormally shaped blood cell that does not carry O
2 well. Some mutations are helpful and may result in desirable or beneficial characteristics. An example of a helpful mutation would be seedless oranges, katahdin potatoes (are resistant to diseases that kill other potatoes. Some mutations are neither harmful nor helpful but rather are neutral. Mutations may go undetected throughout the life of the organism.
Sometimes, a gene that is passed onto the next generation contains an error or possibly a mutation. This incorrect gene can cause harmful effects that medicine is today unable to correct.
Inherited diseases that are passed on from the parents to their offspring must be present (carried) on the sex chromosomes—in particular the X chromosomes! Because of this, females can often act as carriers for a particular trait. Being a carrier for a particular trait means that an individual has the genes for the disorder but does not show the trait or is affected by it.

The punnett square below shows the possible outcomes of offspring, when a normal male parent is crossed with a female parent who is a carrier of the inherited disease hemophilia.
XY = normal male
XX = normal female
X H Y = diseased male
X H X = carrier female
X H
X
X
X H X
XX
Y
X H Y
XY
Only 25% of the offspring will suffer from the disease.
(deoxyribonucleic acid)
DNA is the basic substance of heredity. James Watson Crick discovered DNA, it is found within the chromosomes and it is what makes up genes.
DNA STRUCTURE
~ DNA looks like a twisted bladder (helix)

the rungs of which determine the genetic traits that will be shown
~ below are the four nitrogen bases that make up the “rungs” of the ladder adenne
 
thymine guenine
 
cytosine
~ by changing the order of one “rung” of the ladder, a new gene is formed!

DNA REPLICATION
~ whenever cells divide, their genetic material must first be duplicated so that each cell has a copy of the hereditary information
~ the process of duplicating DNA is called replication.
During this process, the ladder divides down the middle (between nitrogen bases) and two new sides attach producing identical ladders.
NONDISJUNCTION
Nondisjunction means the failure of chromosomes to separate during meiosis
Down syndrome is one example of a condition resulting from the failure of chromosomes to separate during meiosis. Someone with down syndrome may suffer various degrees of mental retardation and have various physical problems.
Down syndrome is caused when an individual has an extra chromosome on the 21 st pair. To determine if an unborn child has the inherited disease, the mother would have a test called an amniocentesis.
A human has 46 chromosomes and 23 pairs.