CHROMOSOMES & GENES

Gregor Mendel never knew where his ___________ were located. His work was largely disregarded because no one understood it until later.

1882 - ___________ observed chromosomes during mitosis.

1890's - ___________ hypothesized that chromosomes were responsible for heredity.

However, the real breakthrough did not come until 1903 when ___________ ___________ noticed the similarities between Mendel's work and his own observations of chromosomes in grasshoppers.

SUTTON'S OBSERVATIONS:

• 1. Chromosomes are found in ___________.
• 2. Pairs of chromosomes separate in ___________.
• 3. Sperm & egg cells contain ___________ a set of chromosomes each.
• 4. Sperm & egg cells are the only link between one ___________ and the next.
• 5. Since sperm & egg cells contribute to heredity ___________, and the sperm has much less cytoplasm, the hereditary factors must be in the nucleus.

Since organisms have more ___________ than chromosomes, scientists reasoned that each chromosome must carry hundreds or thousands of smaller parts that contain hereditary information.

The term "___________" was first used to describe these tiny particles of inheritance in 1909, by Wilhelm ___________.

We now know that genes are particular sections of ___________ molecules that carry the A,T,C,G codes for making the proteins that build our bodies.

The Chromosome Theory:

Hereditary factors, or genes, are carried on the chromosomes.

SEX CHROMOSOMES & SEX-LINKED TRAITS

___________ ___________ - discovered sex chromosomes.

Drosophila (___________ ___________) were used for genetic experiments because they were very small, easy to grow, and reproduce in only 2 weeks.

Fruit flies have only ___________ pairs of chromosomes.

In males, the members of this 4th pair are different. One is long and rod-shaped, the other is short and hook-shaped while in females the two are the same.

So we call the sex chromosomes in males; ___________ and ___________

We call the sex chromosomes in females; ___________ and ___________.

Sex chromosomes - the chromosomes that determine the sex of the individual (the x and y chromosomes).

___________ - all other chromosomes.

Sex-linked traits:

___________ ___________ discovered that the gene for eye color is located on the sex chromosomes (in most cases on the X chromosome).

Red eyes - ___________ in fruit flies

White eyes - ___________

Sex-linked recessive traits show up much more often in males than in females because they have only one X chromosome.

Common examples:

___________

___________ (free-bleeders)

GENE LINKAGE:

Morgan also showed that specific genes are located on ___________ autosomes, and that certain genes are found on the ___________ chromosomes.

Morgan crossed homozygous gray, long-winged fruit flies (GGLL) with black short-winged fruit flies (ggll).

The F₁ generation came out all ___________ and long-winged.

The F₂ generation came out different than expected, proving that the genes were inherited together, not separately.

CROSSING OVER:

In further studies Morgan found that linked genes could sometimes be inherited ___________. This could only happen if the genes from the two chromosomes had swapped places. This occurs during ___________ by a process called ___________. In crossing over, the ends of two identical sister chromatids break off and swap places as they are re-attached.

CHROMOSOME MAPPING:

One of Morgan's students realized that the farther apart genes are on the chromosome, the more likely they are to cross over. Therefore, if we know the frequency at which genes cross over we can estimate how far apart they are.

MUTATIONS:

A change in a gene is called a ___________. These are usually caused by mistakes in copying the genetic code during mitosis. Some mutations cause no effect, most are harmful, some are called "lethal mutations" because they result in ___________.

___________ mutations - a change in a single gene which may be due to:

• ___________
• ___________
• ___________

___________ mutations - involve changes in many genes usually due to breaks in chromosomes:

• ___________ mutations - missing sections
• ___________ mutations - sections are upside down
• ___________ mutations - sections are on the wrong chromosome

___________ Mutations - mutations in body cells

This type of mutation may cause harmful effects such as ___________.

Germ cell mutations - occur in reproductive cells.

These may occur during meiosis or later. These mutations will be transmitted to the offspring if it survives.

CAUSES OF MUTATIONS:

___________ - any substance that can cause mutations in cells

Known mutagens include:

• ___________
• ___________
• ___________
• ___________
• ___________
• ___________
• ___________