Notes on Genetics
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 All living organisms inherit genes from their parents. Genes contain the code for traits.
The passage of genetic instructions from one generation to the next is called heredity.
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DNA
carries genetic instructions. DNA is found in the nucleus of
every cell in the body.
Inherited traits like eyecolor, skin color, the length of a dog’s tail and ears, the color of
corn kernels on an ear of corn, naturally curly hair.
Not Inherited: tricks a dog has learned, a fire scar on a tree, the ability to speak English,
the liking for pizza, the ability to read.
Genes: are made of DNA and contain the instruction book for traits. Genes are found on
chromosomes. Genes are in the nucleus of all cells in the body.
Sexual reproduction: occurs when two parents contribute genetic material to offspring.
Sexual reproduction results in greater variety in the offspring. In one family with two
parents, for example, two children could have curly hair, one child could have wavy hair,
and one child could have straight hair. The Advantage of sexual reproduction is that
it makes a species more able to adapt to environmental changes because of the variety of
individuals. If the environment became very cold, for example, individuals with a lot of
body hair might have a better chance for survival. Sexual reproduction causes more
variety of individuals, so some might be better able to survive and live long enough to
reproduce and pass on their traits to their offspring. In humans, a fetus (developing
offspring) receives 46 total chromosomes, or 23 pairs of chromosomes.
Asexual reproduction: cloning. One parent creates an identical offspring. For example,
a paramecium, which is a single-celled organism living in pond water, becomes 2 new
paramecia. The genetic material of the new paramecia is usually identical to the original
paramecium. Hydra are pond organisms that also reproduce asexually, creating offspring
that are genetically identical to the parent. The advantages of asexual reproduction are
that it produces offspring quickly, and organisms that reproduce asexually do not have to
search for mates. A drawback of asexual reproduction is that environments sometimes
become less suitable for certain kinds of life. Offspring formed by asexual reproduction
are all the same. If they cannot adjust to changes in the environment, they will all die.
Mutations are unexpected traits that occur from changes in the genetic material of the
DNA.