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Biology Chapter 6: Meiosis
Terms in this set (36)
Body cells that make up most of your body tissues and organs
Cells in your reproductive organs that develop gametes
Sex cells with DNA that can be passed on to your children
Two chromosomes, one inherited from the mother and one from the father, that have the same length and general appearance. These chromosomes have copies of the same genes, although the two copies may differ.
Chromosomes that contain genes for characteristics not directly related to the sex of an organism.
Directly control the development of sexual characteristics. Humans have two very different sex chromosomes, X and Y.
It involves the fusion of two gametes, resulting in offspring that are a genetic mixture of both parents.
The fusion of an egg and a sperm. When fertilization occurs, the nuclei of the egg and sperm cell fuse to form one nucleus.
Means that a cell has two copies of each chromosome, one copy from the mother and one copy from the father.
Means that a cells has only one copy of each chromosome.
A form of nuclear division that divides a diploid cell into haploid cells.
The process of formation of the male and female gametes (sex cells). It includes both meiosis and other changes that produce a mature cell. In males this takes places in the testes / sperm. In females, this takes place in the ovaries / egg.
Haploid cells produced during meiosis, which are smaller in size compared to the gamete and will disintegrate. These cells have little more than DNA that is eventually broken down. In many species, including humans, the polar body produced by meiosis I does not undergo meiosis II.
Which cell type makes up the brain?
How many chromosomes does each body cell contain? Are your body cells genetically identical or different?
Each body cell contains 46 chromosomes. Your body cells are genetically different.
How have scientists ordered homologous chromosomes?
They have ordered them by size.
Are homologous chromosomes identical? Explain.
Homologous chromosomes are identical in length and appearance, however they may differ. This is because one is inherited from the mother and one is inherited from the father.
Why is it important that gametes are haploid cells?
It is important that chromosomes are haploids, because when the sperm and the egg fuse together the cell will have 46 chromosomes.
What is gametogenesis and where does it take place?
Gametogenesis is the process of formation and the male and female sex cells. It takes place in the testes for men and the ovaries for women.
What is a polar body? Can it be fertilized?
Polar bodies are haploid cells produced during meiosis, which are smaller in size compared to the gamete and will disintegrate. They cannot be fertilized.
Is the cell that results from fertilization a haploid or diploid cell?
It is a diploid cell
Explain the steps of meiosis I and meiosis II.
Meiosis is a form of nuclear division that creates four haploid cells from one diploid cell. The process involves two rounds of cell division called meiosis I and meiosis II. Each round of cell division has four phases. Before meiosis starts, DNA has already been copied. Meiosis does not occur in most body cells. In animals, meiosis occurs in the sex organs for sexual reproduction.
homologous chromosomes are separated from one another, producing two haploid cells with duplicated chromosomes.
Prophase I: Nuclear membrane breaks down, the centrosomes and centrioles move to opposite sides of the cell, and spindle fibers start to assemble, duplicated chromosomes condense, and homologous chromosomes pair up
Metaphase I: Spindle fibers align the homologous chromosomes along cell equator. Each side of equator has chromosomes (23) from both parents (some from the father and some from the mother). This mixes up the chromosomal combinations and helps maintain genetic diversity.
Anaphase I: Paired homologous chromosomes separate from each other and move toward opposite sides of the cell. Sister chromatids remain attached during meiosis
Telophase I: Nuclear membrane forms again in some species, spindle fibers disassemble, cell undergoes cytokinesis. The end result is two cells that each have a unique combination of 23 duplicated chromosomes coming from both parents.
Sister chromatids are separated (like in mitosis) but, the resulting cells are haploid cells rather than diploid cells
Prophase II: Centrosomes and centrioles move to opposite sides of the cell, and spindle fibers start to assemble.
Metaphase II: Spindle fibers align the chromosomes along the equator.
Anaphase II: Sister chromatids are pulled apart from each other and move to opposite sides of the cell.
Telophase II: Nuclear membranes form again around the chromosomes, spindle fibers break apart, and the cell undergoes cytokinesis.
What is the major difference between meiosis I and meiosis II
Meiosis has two cell divisions. Mitosis has only one cell division.
During meiosis, homologous chromosomes pair up along the cell equator. During mitosis, homologous chromosomes never pair up.
In anaphase 1 of meiosis, sister chromatids remain together. In anaphase 1 of mitosis, sister chromatids separate.
Meiosis results in haploid cells. Mitosis results in diploid cells.
How do homologous chromosomes differ from sister chromatids?
Homologous chromosomes are two separate chromosomes. Homologous chromosomes consist of one chromosome from the mother and the other one from the father. Homologous chromosomes are very similar to each other, but they are not copies of each other. Homologous chromosomes are divided in meiosis I. However, sister chromatids refers to the duplicated chromosomes that remain attached by the centromere. Sister chromatids are not divided until meiosis II.
Explain why an egg cell is so much larger than a sperm cell. How does a sperm cell's structure relate to its function?
The egg cell is so much larger than the sperm cell because the formation of the egg begins before birth inside the developing body of a female embryo, and is not finished until the egg is fertilized by a sperm many years later. The egg's size is due to its contribution of the organelles, molecular building blocks, and other materials an embryo needs to begin life. The sperm cell's main contribution to an embryo is DNA, but it must swim to an egg to fertilize it. The ability to move is critical, so the sperm cell develops a whip-like flagellum and compact head that is tightly packed with DNA. The neck region is packed with mitochondria that drive the cell. This structure allows the sperm to function and reach the egg for fertilization.
How does sexual reproduction create unique gene combinations?
The major advantage of sexual reproduction it that it leads to a great deal of genetic variation within a species. This variation results from the independent assortment of chromosomes during meiosis and the random fertilization of gametes. The random assortment of chromosomes in each homologous pair (tetrads) that line up and separate at metaphase I is a matter of chance, like the flip of a coin. Crossing over can produce a single chromosome that contains a new combination of genetic information from different parents, a result called genetic recombination, and adds to further genetic variation within a population of organisms.
Suppose two genes are very close together on a chromosome. Are the genes likely to be separated by crossing over? Explain.
If two genes are very close together on a chromosome, they are less likely to be separated during chromosomal crossover, and are said to be genetically linked. This genetic linkage is the tendency for genes located close together on the same chromosome to be inherited as a unit.
How does crossing over contribute to genetic diversity?
Crossing over during meiosis results in genetic diversity. Crossing over between homologous chromosomes creates a patchwork of genes from both parents. Crossing over can produce a single chromosome that contains a new combination of genetic information from different parents, a result called genetic recombination, and adds to further genetic variation within a population of organisms. Crossing over happens any time a germ cell divides and can occur many times within the same pair of homologous chromosomes.
What makes an individual male?
What makes an individual female?
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