Life Science Study Sheet



ife Science Study Sheet

Modern Genetics Study Sheet

Know this information

(Also: Study the

vocabulary sheet

, your

homework answers

, and


.) Be sure to know

how to "read" a pedigree

. Know the

meanings of the symbols

used (circles, squares, shading, lines, etc.)

Section 1. Human Inheritance








Some human traits are controlled by

a single gene that has more than two alleles or forms.

These three or more forms of a single gene are called

multiple alleles

. Human blood type is an example of at trait controlled by multiple alleles.

Polygenetic traits are traits produced by multiple genes.

Skin color, eye color, and height are examples of polygenetic traits. These genes act together as a group to produce a single trait.

Traits are often influenced by the organism’s environment

. Height is an example of a trait that can be modified by an organism’s environment. If a proper amount of food is available, a person will probably reach his/her potential height.

If nutrition is poor the person may end up shorter that his/her potential height.

Males have one X chromosome and one Y chromosome. Females have two X chromosomes. (

Male = XY; Female = XX


The X and Y chromosomes are the 23 rd

pair of chromosomes in the human genome.

These chromosomes are called the sex or gender chromosomes


Males are more likely than females to have a

sex-linked trait

controlled by a recessive allele such as colorblindness. This is because the Y chromosome is shorter that the X chromosome. If the X chromosome has a defective gene, and there is no homologous gene on the Y chromosome to override it, the male will have the condition caused by the defective gene.



is a


that shows several generations of a family. Geneticists use pedigrees

to trace the inheritance pattern of a particular trait through a number of generations of a family.

Section 2. Human Genetic Disorders




Genetic disorders are abnormal conditions that are caused by mutations

or changes in an organism’s DNA in a gene or chromosome. In some cases, these mutations can be passed on from one generation to the next.

Commonly known genetic disorders include

cystic fibrosis, sickle-cell anemia, hemophilia,


Down syndrome.

There are many others that are not well known to the general public such as

Williams disorder


Turner syndrome.


is a

test used to diagnose genetic disorders

. During amniocentesis a small amount of fluid (amniotic fluid) surrounding the developing fetus is extracted and analyzed to see if any abnormalities are present in the fetus’s chromosomes.




is another tool used to diagnose genetic orders. A sample of DNA is taken from a white blood cell. The chromosomes are photographed, organized in pairs, and examined for abnormalities.

Genetic counselors

are professionals who help couples understand their chances of having a child with a genetic disorder.

Section 3. Advances in Genetics








Selective breeding

is the process of

selecting a few organisms with desired traits to serve as parents of the next generation

. Farmers and animal breeders have used selective breeding to improve plants and animals for thousands of years.


is a technique used to

produce an organism that is genetically identical to the organism from which it was produced.

The process involves removing the nucleus from an egg cell, replacing it with the nucleus of the organism to be cloned, then placing the egg cell with the new nucleus into compatible female organism for gestation.

Genetic engineering

involves the

transfer of a gene from the DNA of one organism into another organism

. Genetic engineering can be used to produce medicines and to improve crops. Genetic engineering is responsible for tomatoes with fish genes that can resist cold, and goats that produce spider silk or medicine in their milk!

Gene therapy


the insertion of working copies of a gene into the cells of a person with a genetic disorder

in an attempt to correct the disorder. Results have been mixed regarding the success of this strategy for curing diseases.

DNA fingerprinting

can be used to help determine whether material found at a crime scene came from a particular suspect. DNA can be extracted from urine, semen, saliva, blood, hair, and skin cells. DNA "fingerprints" are images of sequences of DNA. No two individuals, except for identical twins, have the same

DNA sequences.

Polymerase Chain Reaction

(PCR): A method used by scientists to increase the amount of DNA. This is important when only a small amount of DNA from blood or saliva is found at a crime scene. PCR allows forensic scientists to provide enough DNA to test.

The goal of the

Human Genome Project

was to

identify the DNA sequence of every gene in the human genome

. This has been accomplished. Scientists are working on or have completed the genomes of other species such as bacteria, fungi, many plants and some animals – many invertebrates and some vertebrates like dogs, mice, etc.