9.4 Flashcards
What are genes?
Regions that the DNA on chromosomes is arranged in; they code for the formation of proteins, which carry out most of the work of cells.
Each chromosome consists of hundreds of genes, each playing a role in determining the characteristics and functions of the cell.
How many chromosomes does each human cell have?
Human body cells have 46 chromosomes, except for gametes. Each parent contributes 23, resulting in 23 pairs of chromosomes.
What are homologous chromosomes?
They are Chromosomes that make up a pair, each piece from a parent. Homologous chromosomes have the same length and centromere position and carry genes that control the same traits.
What are Gametes?
They are sex cells that have a single set of chromosomes.
What does the symbol n represent?
It represents the number of chromosomes that each parent contributes to a cell or the number of chromosomes in a single set. In humans, n is 23.
What is a haploid cell?
A cell that has only one set of (or n) chromosomes.
What is Fertilization?
The process by which one gamete combines with another gamete to form a diploid zygote.
What is a diploid cell?
A cell that contains paired chromosomes, one from each parent.
What are sex chromosomes?
One of the 23 pairs of chromosomes in a normal cell that determines an individual’s gender.
What are autosomes?
The 22 pairs of chromosomes in a normal cell that does not determine an individual’s gender.
What are the two types of sex chromosomes?
X and Y. Individuals with two X chromosomes are female. Individuals with X and Y are male.
What is meiosis?
A type of cell division that reduces the number of chromosomes and forms gametes.
What does meiosis do?
It halves the chromosome number through the separation of homologous chromosomes. A cell with 2n chromosomes will have gametes with n chromosomes after meiosis.
Where does meiosis occur?
Meiosis occurs in the reproductive structures of organisms that reproduce sexually.
What is crossing over?
A process during which chromosomal segments are exchanged between a pair of homologous chromosomes.
What happens to DNA in interphase 1 during meiosis?
Chromosomes replicate and chromatin condenses.
What happens to DNA in prophase 1 during meiosis?
Homologous chromosomes pair and crossing over occurs.
The nuclear envelope breaks down and spindles form.
What happens to DNA during metaphase 1 in meiosis?
Spindle apparatus attaches to centromeres. Homologous chromosomes line up at the equator.
What happens to DNA during anaphase 1 in meiosis?
Homologous chromosomes separate and move to opposite poles of the cell.
What happens to DNA during telophase 1 in meiosis?
Spindles break down, chromosomes uncoil to form two nuclei, and the cell divides.
What happens to DNA during prophase 2 in meiosis?
Chromosomes condense. Spindles form in each new cell. Spindle fibers attach to chromosomes.
What happens to DNA during metaphase 2 in meiosis?
Centromeres of chromosomes line up randomly at the equator of each cell.
What happens to DNA during anaphase 2 in meiosis?
Centromeres split. Sister chromatids separate and move to opposite poles.
What happens to DNA during telophase 2 in meiosis?
Four nuclei form around chromosomes. Spindles break down. Cells divide.
What are the final Products of meiosis?
Four cells have formed. Each nucleus contains a haploid number of chromosomes.
How does meiosis provide variation?
Depending on how chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.
What happens to DNA during asexual preproduction?
During asexual reproduction, chromosome number is maintained by mitosis.
The organism inherits all of its chromosomes from a single parent.
The new individual is genetically identical to its parent.
How do species reproduce in nature?
Bacteria reproduce asexually, whereas most protists reproduce both asexually and sexually.
Most plants and many of the more simple animals can reproduce both asexually and sexually.
What are Telomeres?
They are chromosomes that end in protective caps that consist of DNA associated with proteins.
Telomeres might be involved in aging and cancer.
What is a karyotype?
A karyotype is a type of micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.
What is nondisjunction and where does it occur?
Cell division during which sister chromatids fail to separate properly. Nondisjunction occurs in both autosomes and sex chromosomes.
What results from nondisjunction?
Nondisjunction can result in extra copies of certain chromosomes or only one copy of a particular chromosome in offspring.
In humans, alterations of chromosome numbers are associated with serious disorders, which are often fatal.
What causes down syndrome?
Down syndrome is the result of an extra chromosome 21 and is often called trisomy 21.
What is Turner’s syndrome?
An individual with Turner’s syndrome has only one sex chromosome. The condition results from fertilization with a gamete that had no sex chromosome.
What is Klinefelter’s syndrome?
An individual with Klinefelter’s syndrome has three sex chromosomes. This condition results from fertilization with a gamete that had two sex chromosomes.
What does meiosis form in plants?
Spores.
