Unit 8- Reproduction

8b- Mutations

Bellwork1) Meiosis can be broken up into _______ phases.

2) By the end of Meiosis _______ haploid cells are formed.

3) Meiosis produces genetically (different or identical) cells.

4) Mitosis produced (different or identical) cells.

5) Haploid cells have (paired or unpaired) chromosomes?6) Give me an example of a haploid cell (n).

7) A cell with paired chromosomes is _________, or 2n.

8) Give me an example of a cell with paired chromosomes.

Mutations

• A mutation is the alteration of an organism's DNA. – Can range from a change in one base pair to the insertion

or deletion of large segments of DNA

• Mutations can result from a malfunction during the processes of mitosis or meiosis.

• They can also result from exposure to a physical or a chemical agent- a mutagen.

Mutations

• Most mutations are automatically repaired by the organism’s enzymes & therefore have no effect. – However, when the mutation is not repaired, the

resulting altered chromosome or gene structure is then passed to all daughter cells of the mutant cell• May have negative, positive, or no consequences for

the cell, organism, or future generations.

Somatic vs Sex Cell Mutations• If the mutant cell is a somatic cell, the daughter cells can be

affected by the altered DNA, but the mutation will NOT be passed to the offspring of the organism– These mutations can contribute to the aging process or the

development of many types of cancer.

• If the mutant cell is a sex cell (like egg and sperm), the altered DNA will be transmitted to the embryo and may be passed to subsequent generations. – Gamete cell mutations can result in genetic disorders. – If the mutation affects a single gene, it’s known as a gene mutation. – If the mutation affects a group of genes or an entire chromosome, it is

known as a chromosomal mutation.

Chromosomal Mutations• Chromosomal mutations can happen when

chromosomes break and do not repair correctly.

pg. 239

Chromosomal Mutations• Mutations can also occur during meiosis. • Nondisjunction- a chromosome fails to separate

from its homologue during meiosis– Results in one gamete receiving an extra copy of a

chromosome, and another gamete receiving no copy. Normal Example

Nondisjunction Examples

Types of Nondisjunction• In normal fertilization, a zygote would get one

copy of a chromosome from each parent resulting in one pair of each type of chromosome (humans: 23 pairs)

• Monosomy – when the zygote gets a copy of a chromosome from only one parent so it is missing one chromosome– Most zygotes with monosomy do not survive– One exception is Turner’s Syndrome

• Females have only one X chromosome instead of two• These people will still have female sexual characteristics

but they will generally be underdeveloped

Types of Nondisjunction

• Trisomy –The zygote gets 1 copy of a chromosome from one parent and 2 copies from the other parent – Down Syndrome (Trisomy 21) – This person has three

copies of the 21st chromosome. This can lead to mental retardation, susceptibility to certain illness or diseases, and a shorter life span

– Klinefelter's syndrome (XXY) – This person has two copies of the X chromosome as well as a copy of the Y chromosome. This person will be male but may suffer from underdeveloped testicles and infertility.

Identifying Chromosomal Disorders

• To determine whether or not an organism has the proper number of each chromosome, one can look at a karyotype

• To make a karyotype a photograph is taken of the paired chromosomes during metaphase

• These pairs are cut out & arranged in a chart according to length & location of centromere

• Once arranged, it is easy to see if there are any extra or missing chromosomes

This individual has an extra Y

chromosome

Checkpoint1) What are causes of mutations?– A physical or chemical mutagen (environmental

exposure)– Something goes wrong in mitosis or meiosis

2) Mutations (can/cannot be) passed on to daughter cells.– They can be passed on to daughter cells

3) If mutations happen in __________ cells, they can be passed on to offspring and subsequent generations.Reproductive cells (egg/sperm)

4) Give me an example of a chromosomal mutation.

Unit 8- Reproduction

8c- Cell Development

Cell Development• In the development of most multicellular organisms, a single

cell (fertilized egg) gives rise to many different types of cells, each with a different structure & function.– The fertilized egg gives rise to a large number of cells through

mitotic cell division, but the process of cell division alone leads to increasing numbers of identical cells.

– With cell division, the cells increase in number but also undergo differentiation, a process through which a cell becomes specialized in order to perform specific tasks.

– Various types of cells (such as blood, muscle, or epithelial cells) arrange into tissues which are organized into organs, and, ultimately, into organ systems.

Differentiation• Nearly all of the cells of a multicellular organism

have exactly the same chromosomes and DNA.– During the process of differentiation, only specific

parts of the DNA are activated; the parts of the DNA that are activated determine the function & specialized structure of a cell.

– Because all cells contain the same DNA, all cells initially have the potential to become any type of cell.

• Once a cell differentiates, the process cannot be reversed.

Stem Cells

• Stem cells are undifferentiated cells that have 2 important characteristics:– They are unspecialized cells that are capable of

renewing themselves by cell division. – Under certain natural or experimental conditions

they have the ability to differentiate into one or more specialized cells.

SciShow- Stem Cells- 3:47

Animal Stem Cells

• Human embryonic stem cells are derived from a 5-day old embryo. – They have the capacity for long-term self-renewal in

laboratory culture. – They can develop into any type of specialized cell in the

body. • Adult stem cells are undifferentiated cells found in

certain organs and differentiated tissue with a limited capacity for both self renewal (in the laboratory) and differentiation.

Importance of Stem Cells • Stem cells are important to the living organism.

– In 3-5 day old animal embryos they give rise to the entire body of the organism, including all of the many specialized cell types and organs such as the heart, lungs, skin, sperm, eggs, and all other tissues.

– In some adult animal tissues, such as bone marrow, groups of stem cells generate replacements for cells that are lost through normal wear and tear, injury, and disease.

Other Important Uses of Stem Cells

• Scientists use stem cells to study normal growth, development, and differentiation. – Can help identify causes of

cancer and birth defects that result from abnormal development

• Stem cells are currently used to screen new medicine for safety in humans.

Nat Geo- The Skin Gun 3.5min

Other Important Uses of Stem Cells

• Cell-based regenerative therapies are treatments in which stem cells are induced to differentiate into specific cell types required to repair damaged or destroyed cells or tissues. – Demand for organs & tissues needed for transplantation is

greater than the supply. – Stem cells offer a renewable source of replacement cells &

tissues such as:• Bone tissue from bone marrow cells• Spinal cord after injury• Cells of the pancreas that produce insulin to treat diabetes.

Pros & Cons: Human Embryonic vs Adult Stem Cells for Cell-Based Therapies

• The number of types of cells they can become:– Embryonic stem cells can become all of the types of cells in the

body. – Adult stem cells are thought to be limited to the types of cells in

the tissue that they are found.• Ease of growth in laboratory culture.

– Embryonic stem cells can be easily grown in culture & can divide indefinitely producing large numbers of cells for research.

– Adult stem cells are difficult to isolate from the original tissue & are difficult to grow in culture.

Pros & Cons: Human Embryonic vs Adult Stem Cells for Cell-Based Therapies

• Potential for rejection by the human immune system. – It is unknown how the immune system might react to embryonic

stem cells. – Scientists think that adult stem cells are less likely to be rejected

by the immune system because a patient’s own cells can be used.

Plant Stem Cells

• Virtually all of a plant’s tissues are descended from small groups of stem cells located in the actively growing tips of the roots and shoots.

• Plant stem cells have the capacity to grow into any type of plant organ, tissue, or cell.

• Plant stem cells have the capacity for nearly unlimited self-renewal.

• Many important compounds are derived from plants such as medicines, pigments, perfumes, and insecticides. – Stem cell technology offers the potential to produce these

chemicals under controlled conditions.