Chapter 5

Heredity

Define heredity.

The passing of traits from parent to offspring.

The different forms of a trait that a gene may have are called____.

Alleles

As a result of meiosis, every sex cell has _____ allele for each trait. During fertilization, each parent donates _____ chromosome. This results in the _____ alleles for the trait in the new individual.

OneOne Two

The study of how traits are inherited through the interaction

of alleles is _____________.

Genetics

Who was the Austrian monk known as the “father of genetics” because of his

experiments with pea plants?

Gregor Mendel

Mendel was the first scientist to study how ________ are passed from one generation to the next, and he was first to use the mathematics of __________ to

explain heredity.

Traits

Probability

One of the things that made Mendel’s results so accurate is that he used large

numbers of plants. He studied almost __________ pea plants over a period of _____ years.

30,000

8 years

When Mendel crossed two homozygous plants with different expressions of a trait, for example, GGXgg (homozygous green pea pods X homozygous yellow pea pods, he found that the pea pods all looked like one of the parents. These new plants were called __________.

hybrids

Gg

Distinguish between alleles that are dominant and alleles that are recessive.

Dominant: A trait that covers over, or dominates, another form of that trait. (R)

Recessive: A trait that is covered over, or dominated, by another form of that trait. (r )

Explain the use of a Punnett square.

A Punnett Square is a tool that can be used to predict the probability of certain traits in offspring. It shows the different ways the traits can combine.

In a Punnett square, ________ are used to represent the alleles. An upper case letter stands for a ________ allele. A lower case letter stands for a_________ allele.

Letters

Dominant (T)

Recessive (t)

From the letters on a Punnett square, one can determine the genotype and phenotype of an organism. Contrast genotype and phenotype.

Genotype

The genetic makeup of an organism.

(RR)

Phenotype

The way an organism looks and behaves as a result of its genotype.

(Round seeds)

Most cells in your body have two alleles for every trait, one allele from the male parent and one allele from the female

parent. These alleles are located on __________ within the nucleus of cells.

Chromosomes

An organism with two alleles that are the same can be described as __________.

Homozygous

(BB)

An organism that has two different alleles for a trait can be described as

__________.

Heterozygous

(Bb)

When making a Punnett square, explain where the letter representing the alleles for

each parent are written.

The two letters for one parent are written along the top of the grid, one letter per box.

The two letter for the second parent are written down the side of the grid, one letter per box.

Law of Segregation

When chromosomes separate during meiosis, alleles separate so that offspring receive one allele from each parent.

Law of Independent Assortment

When chromosome pairs separate during meiosis, they separate independently of other chromosome pairs.

Law of Dominance

Traits are controlled by alleles, and alleles can be either dominant or recessive.

When purebred red four o’clocks were bred with purebred white four o’clocks, the offspring were pink. When offspring of two homozygous parents show and intermediate phenotype, this inheritance is called _____________________.

Incomplete Dominance

Define multiple alleles, and give one example of a multiple allele in humans.

A trait that is controlled by more than two alleles.

Example: human blood type

How many alleles for blood types are there? Identify them.

Three

A, O, B

Identify the blood type that is an example of codominance.

AB

Explain how a parent with type A blood and a parent with type B blood could have a child with type O blood.

Both parents must be heterozygous and carry the recessive allele for type O blood.

AO, BO

Define polygenic inheritance and name three examples of polygenic inheritance.

When a group of gene pairs act together to produce a trait.

Examples: eye color, hair color, skin color, height

Your ___________ plays a role in how some of your genes are expressed or whether they are expressed at all. For example, a person who is at risk for skin cancer might limit his or her exposure to the sun.

environment

When a gene undergoes a change that results in a trait being expressed differently or when

an error occurs when the DNA is copied inside the cell, such changes and errors are

called __________________.

mutation

Identify one example of a chromosome disorder, and briefly explain characteristics of this disorder.

Down’s Syndrome: Occurs when three copies of chromosome 21 are produced. Individuals with this disorder can be short, exhibit learning disabilities, and have heart problems.

Explain how an individual would get a recessive genetic disorder.

Both parents would have the recessive allele responsible for the disorder, and each parent would pass the allele for the disorder to the child.

Identify two examples of recessive genetic disorders.

Cystic Fibrosis

Sickle Cell Anemia

Scientists identified one pair of genes that determine the sex of an organism. They labeled the pair _______ in females and _____ in males. The __________ always determines the sex of the offspring because he can contribute either an _____ or a _____ during fertilization.

XX

XY

Male

X

Y

An allele inherited on a sex chromosome is called a ________________.

sex-linked gene

Color blindness is an example of a _________________ because this trait is a recessive allele carried on the _____ chromosome.

Sex-linked disorder

X

Explain why males are more often color blind than females.

Males only have one X chromosome so a male with this allele on his X chromosome is colorblind.

A __________ can be used to trace a trait through several generations.

Pedigree

Define genetic engineering.

Biological and chemical methods to change the arrangement of a gene’s DNA to improve crop production, produce large volumes of medicine, and change how cells perform their normal functions.

Which type of genetic engineering involves inserting a useful section of DNA into a bacterium?

Recombinant DNA

__________ can be used to produce insulin for diabetic patients, to produce growth hormone for dwarfism, and to produce

chemicals to treat cancer.

Recombinant DNA

___________ is a type of genetic engineering in which a normal allele is

placed in a virus. The virus then delivers the normal allele to a target cell. The

normal allele replaces the defective one.

Gene Therapy

Gene therapy has been used to control ________________ and some kinds of

_________.

Cystic Fibrosis

Cancer

Explain why stores usually label foods that have been genetically engineered.

Consumers should have a choice whether or not they buy genetically engineered foods. The long-term effects of consuming genetically engineered foods are not known.

One flower is heterozygous red (Rr), and it is crossed with a homozygous white flowwer (rr). What is the probability of one of their offspring

being white?

R r

r

r

rr

rr

Rr

Rr

50%

In a certain species of plant, purple (P) is dominant to white (p). If a homozygous purple plant (PP) is crossed with a homozygous white (pp), what percentage of the offspring will be purple?

P P

p

p

Pp Pp

Pp Pp

100%

In a certain species of pine trees,short needles (S) are dominant to long needles (s). If a heterozygous short needled pine tree is crossed with another heterozygous short needled pine tree, what is the probability that a long needled pine would be an offspring?

S s

S

s

SS Ss

Ss ss

25%

Study for the test!