Untitled Deck Flashcards
(24 cards)
What is the process called when a sperm and egg unite to form a new individual?
fertilization
What is meiosis?
nuclear division that precedes the formation of gametes (egg and sperm) and results in a halving of chromosome number.
What determines the sex of the individual?
Sex Chromosomes
What is a gene?
a section of DNA that influences hereditary traits.
What are alleles?
different versions of a specific gene.
What are homologous chromosomes?
carry the same genes in the same locations, but each one may contain different alleles.
What are organisms whose cells contain just one of each type of chromosome called?
haploid (n)
What does the haploid number n indicate?
number of distinct types of chromosomes present.
What does a cell’s ploidy indicate?
number of each type of chromosome present.
What are organisms called that contain two versions of each type of chromosome?
diploid (2n)
What do diploid cells have?
one paternal chromosome and one maternal chromosome.
What are organisms with three or more versions of each type of chromosome called?
polyploid (3n, 4n, etc.)
What are the two cell divisions in meiosis called?
meiosis I and meiosis II.
What is the outcome of meiosis?
a reduction in chromosome number.
For this reason, meiosis is known as a reduction division.
What is the ploidy of the original cell and the daughter cells in most plants and animals?
The original cell is diploid and the four daughter cells are haploid.
What happens when two haploid gametes fuse during fertilization?
A full complement of chromosomes is restored. The cell that results from fertilization is diploid and is called a zygote.
What is the composition of homologous chromosomes?
maternal + paternal
What happens during prophase I?
• The homolog pairs come together through synapsis.
• Synapsis forms tetrad consisting of two homologs.
• The chromatids of the homologs are called non-sister chromatids.
• Chromatids exchange or crossing over between non-sister chromatids occurs where chiasmata are formed during this stage.
What happens during prometaphase?
• The nuclear membrane breaks down.
• The spindle fiber microtubules attach to the kinetochore proteins.
• The homologous chromosomes are held together at the chiasmata.
What happens during metaphase?
• The tetrads line up at the metaphase plate.
What happens during anaphase?
• The paired homologs separate and begin to migrate to opposite poles.
• The sister chromatids remain tightly bound together at the centromere.
What happens during telophase?
• The homologs finish migrating to the poles of the cell.
• In some organisms, the chromosomes ‘decondense’ and nuclear envelopes form. Then the cell divides through cytokinesis.
• In other organisms, cytokinesis occurs without reformation of the nuclear envelopes.
What is asexual reproduction?
offspring produced are clones
What is sexual reproduction?
offspring produced are the fusion of gametes, have a chromosome makeup different from that of one another and from that of either parent.
