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Cellular Reproduction. The Chromosome. Objectives. Identify four examples of cell division in eukaryotes and one example in prokaryotes Differentiate between a gene, a DNA molecule, a chromosome, and a chromatid. Differentiate between homologous chromosomes, autosomes , and sex chromosomes.
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Cellular Reproduction The Chromosome
Objectives • Identify four examples of cell division in eukaryotes and one example in prokaryotes • Differentiate between a gene, a DNA molecule, a chromosome, and a chromatid. • Differentiate between homologous chromosomes, autosomes, and sex chromosomes. • Compare haploid and diploid cells. • Predict how changes in chromosome number or structure can affect development
Formation of New Cells by Cell Division • About 2 trillion cells are produced by the human body every day. • ___________ is the process of making new cells. This division occurs at different times in the cell’s life and at different rates based on the type of the cell and the age of the organism. • There are many different kinds of cell division. Prokaryotes divide on way, eukaryotes divide another. Gametes, an organisms’ sex cells, are created in a third type of division. • Regardless of the type of division a cell undergoes, the information that tells the cell how to divide is located in the molecules of DNA present in the cell. Cell Division
Prokaryote Division • Prokaryote cells do not possess a nucleus to aid in cell division. The type of cell division they undergo is called _____________. • Binary Fission: A form of asexual reproduction that produces identical offspring with the same flaws and advantages as the parent organism. Binary Fission
Binary Fission • Binary Fission occurs in two steps: • The DNA inside the prokaryote cell is copied so that each of the offspring cells will have the complete genetic code. • The cell divides by adding new cell membrane to a point along the original cell membrane somewhere between the two DNA copies. As new material is added, the cell is constricted in the middle and each of the DNA copies is forced into one or other sides of the cell. Eventually the cell membrane can constrict no further and pinches off two form two new identical cells, each with an exact copy of the DNA of the original.
Eukaryote Cell Division Sexual • Eukaryotes (___________________) use _______ or ________ reproduction to make new individuals. In sexual reproduction, _____________ are combined in a process called ____________ to produce new offspring. • ___________ (body cells, skin cells, liver cells, etc.) reproduce by ________. • Gene: A segment of _______ that provides the code of information for a specific trait (ex. Hair color, eye color, skin tone, etc). • A single molecule of DNA has thousands ofgenes lined up like train cars. Protozoa, fungi, plants, and animals asexual Gametes (sperm or egg Fertilization Somatic Cells mitosis DNA
Eukaryote Duplication • The DNA coils and becomes visible before Mitosis. This familiar structure is called a ____________ and includes the DNA and the proteins it coils around. • Ordinarily chromosomes are hair-like structures coiled within the nucleus. When the cell is ready to divide, the chromosomes coil and twist into the characteristic double helix shape we associate with DNA. • Before the DNA can coil, it must be duplicated to insure that both offspring get the same information. The pair of copies of DNA are called Chromatids. They are attached to each other at the centers by a structure called a centromere. During the division process this structure will let go and each half of the chromatid will be pulled into one or the other offspring cells. chromosome
How Chromosomes Affect Development • Every human cell, except for sperm and egg cells, has _____ pairs, or ____ total chromosomes. • They differ in size, shape, and number of genes. • Together they control the entire development process of the organism. • ________________: Chromosomes that are similar in size, shape, and genetic content. • Each homolog of the pair comes from one parent. 23 46 Homologous Pairs
Chromosomes and Development • ________: A cell that has the full amount of chromosomes. For humans that is any cell that has 46 total. • ________: A cell that has only half the normal amount of chromosomes. For humans that would include sperm and egg cells. When two halves combine, they form a whole cell or diploid. • _________: A fertilized egg cell. The human zygote contains 46 chromosomes. Diploid Haploid Zygote
Sex Chromosomes • _________: Chromosomes that are not directly involved in determining the sex of an organism. • _______________: Chromosomes that directly determine the sex of an organism. In humans, and many other organisms, the sex chromosomes are referred to as X and Y. • The presence of a Y chromosome designates a male organism. • The sex of the offspring is determined by the father. Autosomes Sex Chromosomes
Changes in the Chromosome Number • Too many or too few chromosomes results in mutation. This is always bad. • _________: A micrograph of the chromosomes of a cell, arranged according to size. Karyotype
Numbers of Chromosomes • In mothers younger than 30, downs syndrome occurs only about 1 out of 1500 times. As they age, the odds increase. For a mother over 37, the incidence doubles to 1 out of 290. In mothers over 45 the risk can be as high as 1 out of 46. • All the eggs that a woman will ever produce are with her when she is born. As she ages, the eggs accumulate damage from things like smoking and diet to ambient background radiation.
Disjunction • What causes extra chromosomes is called ___________. • Disjunction: During sperm and egg formation, the homologous pairs of chromosomes disjoin or separate. If that fails to occur (nondisjunction) then one new gamete (sex cell) receives too many chromosomes and one receives too few. • _________: A condition that occurs when one gamete with too many chromosomes is fertilized by a normal gamete resulting in a zygote with too many chromosomes. In Downessyndrome, the nondisjunction occurs at chromosome 21. disjunction Trisomy
