CONNECT!

•What are these things?

•Why are they called “mutants”?

•What is a mutation?

B. MUTATIONS

• changes in the genetic material

• If these mutations occur in sex cells, they may be transmitted to the next generation

• Mutations occurring in body cells may be perpetuated in the individual, but will NOT be passed on to offspring

2 Types of Mutations

1. Chromosome

2. Gene

Chromosomal Alterations(mutations)

are changes in the number of chromosomes or in the structure of chromosomes

• The effects of chromosomal changes are often visible in an organism because many genes are involved.

Chunk!

• Define mutation.• Mutations in certain kinds of cells will be passed

on to offspring. What are these cells?• Mutations in these cells are NOT passed on to

offspring. What are these cells?• Name two types of mutations.• What is a chromosomal alteration?• Why are chromosomal alterations often visible?

THINK!

• Do eggs and sperm have the same number of chromosomes as a regular body cell?

• Why/why not?

Body Cells

• Body cells have the full amount of chromosomes for the species. This is called the diploid (2n) number. The n refers to the # of different chromosomes, while the 2 indicates that there are 2 homologous chromosomes of each #.

• For example, human body cells have a diploid number of 46 chromosomes. This means that each body cell has 23 pairs of homologous chromosomes.

Diagram of Human Diploid Number

Why is this diploid? What kinds of cells are diploid?

Human Karyotype

Chromosome Number

• Meiosis is a special cell division that occurs in the gonads of sexually reproducing organisms to produce gametes (sex cells or sperm and egg).

• Meiosis cuts the number of chromosomes in half, so it is referred to as reduction division.

• The gametes are haploid (half the normal chromosome number of body cells).

Meiosis produces variation in gametes

GONADS

MAKE

HAPLOID

GAMETES

BY

MEIOSIS

What is the function of gametes?

• Sperm and egg join in the process of fertilization to form a zygote, which restores the species chromosome number for body cells.

Reproduction•How many chromosomes in the mother cell at far right?

•How many chromosomes are in the father cell at far right?

•How many chromosomes are in the egg and sperm cell at far right?

•Why are body cells called diploid?

•Why are sperm and eggs called haploid?

•What restores the diploid number of chromosomes?

DISJUNCTION

• If there is a junction between two ATV trails, what does that mean?

• So, disjunction means…?

• Normally during meiosis, homologous chromosomes separate from each other;

this separation is known as disjunction

• Sometimes, a pair of homologous chromosomes fails to separate from each other, which results in gametes with more or less than the normal chromosome number; when chromosomes do not separate, it is called nondisjunction.

• How many chromosomes are in the cell on the left?• This is the normal # for this species. What is the term for the normal

# of chromosomes in a body cell?• What mistake occurred in the middle cell?• The gametes should all be haploid, which means a chromosome #

of ___ for this species.• How many of the gametes have the proper # of chromosomes?• What is this type of mistake called?

Chunk!

• If gametes from nondisjunction are involved in fertilization, the resulting zygote may have more or less than the normal 2n chromosome number.

• For example, in humans, Down’s Syndrome usually results from possessing an extra 21st chromosome. This is caused by nondisjunction of chromosome # 21 during meiosis in one of the parents.

More examples of Nondisjunction

Changes in Chromosome Structure

• This occurs when chromosomes randomly break and re-attach

Navel orange

The mutation causes the orange to develop a second orange at the base of the original fruit, opposite the stem, as a conjoined twin in a set of smaller segments embedded within the peel of the larger orange. From the outside, it looks similar to the human navel, thus its name.

Because the mutation left the fruit seedless, and therefore sterile, the only means available to cultivate more of this new variety is to graft cuttings onto other varieties of citrus tree. Two such cuttings of the original tree were transplanted to California in 1870, which eventually led to worldwide popularity.

Today, navel oranges continue to be produced via cutting and grafting. This does not allow for the usual selective breeding methodologies, and so not only do the navel oranges of today have exactly the same genetic makeup as the original tree, and are therefore clones, in a sense, all navel oranges can be considered to be the fruit of that single over-a-century-old tree.

Chunk!• If gametes from nondisjunction are involved in fertilization, what is the result?

•Give an example in humans.

•What are some types of changes in chromosome structure?

JFF!