Unit 3 Meiosis and Mitosis Quiz
Genetics
- Genetics is the field of biology that involves the study of how genetic information is passed from one generation of organisms or cells to the next generation.
- Genetic info is passed from parent cells to daughter cells in the form of DNA
The Cell Cycle
- All somatic cells (body cells excluding sex cells) go through the cell cycle
- Three functions of the cell cycle are: growth, repair, and maintenance to replace dead cells
- Cell division only accounts for a small portion of the cell cycle
- Three stages to the cell cycle are: interphase, mitosis (cell division), and cytokinesis.
Interphase
- The stage between nuclear divisions, interphase, is marked by a period of rapid growth (G1), the replication of chromosomes (S or synthesis), and finally another period of growth (G2)
- Genetic material is referred to as chromatin
- Each single strand of DNA (chromatid) duplicates and becomes double stranded
- Each double stranded pair is attached at the centromere, and are known as sister chromatids.
Prophase
- Chromatin condenses into chromosomes
- Since DNA is duplicated in interphase, the identical chromosomes (now called sister chromatids) are attached in the middle by a centromere
- Nuclear membrane disappears
- Nucleolus disappears
- centrioles (in animal cells only) move to opposite sides of the cell
Metaphase
- Sister chromatids are guided to the middle of the cell (equatorial plate) by the spindle fibres and are lined up.
- Spindle fibres come out of the centrioles and are attached to the centromere.
Anaphase
- Centromere divides and chromatids move to opposite ends of the cell (sister chromatids are now referred to as chromosomes)
- Spindle fibres shorten and chromosomes are pulled to opposite ends of the dividing cell
Telophase
- Chromosomes reach opposite ends, they begin to expand and lengthen, and a nuclear membrane begins to reform
- Spindle fibres dissolve, nucleolus reappears
- Cytokinesis (division of the cytoplasm) occurs. Cell now enters G1 of interphase. This is called cleavage of the cell. In plant cells, a cell wall reforms.
Structure of DNA
- DNA is made up of two strands that form a spiral shape called a double helix
- During interphase, DNA exists as chromatin but once mitosis begins, it condenses into chromosomes
- The building blocks of DNA are called nucleotides. A nucleotide consists of:
-Sugar
-Phosphate
-Nitrogenous base
Nitrogenous Bases
- Adenine (A)
- Thymine (T)
-Cytosine (C)
- Guanine (G)
A and T always pair together, C and G always pair together
Pairing of Chromosomes
- Humans have 46 chromosomes (23 pairs)
- One pair is called the sex chromosomes (XX -girl or XY - boy), and the other 22 pairs are called autosomes
Karyotype Charts
- A karyotype is a photograph of a person's chromosomes.
- Chromosomes are paired from largest to smallest, with the sex chromosomes placed last.
- A normal human karyotype has 23 pairs of chromosomes. Any deviation from that indicates a chromosomal disorder/condition.
Sexual and Asexual Reproduction:
- Reproduction that requires only one
parent and leads to the production of
genetically identical offspring is called
asexual reproduction.
Ex: Bacteria
- Humans reproduce through sexual
reproduction, which involves two parents
and leads to the production of offspring.
Haploid and Diploid Cells:
- Male and Female reproductive cells are referred to as Gametes
- The process of combining gametes is called fertilization.
- The fusion of these cells result in a Zygote
- a zygote contains 46 chromosomes from both parents
- In humans, the male gamete is the sperm cell and the female
gamete is the egg cell or ovum.
Homologous Chromosomes and Genes:
- Homologous chromosomes: pairs of chromosomes that appear similar,
but are not identical to each other.
- They carry genes for the same traits at the same location. You get one
from mother, other from father.
- Genes are sections of DNA that contain genetic information for the
inheritance of specific traits
Meiosis I
Prophase I: homologous chromosomes line up side by side. (Synapsis). segments of the chromosomes may be exchanged.
Metaphase I: homologous chromosomes line up along the equator of the
cell. The spindle fibres attach to the centromere.
Anaphase I: homologous chromosomes separate and move to opposite poles of the cell. Do not split chromosome number is reduced from 2n (diploid) to n (haploid).
Telophase I: begin to uncoil and the spindle fibres disappear. nuclear membrane forms.
Meiosis VS Mitosis
Mitosis: creates 2 identical diploid daughter cells, and to create all somatic (body cells) cells (not sex cells)
Meiosis: creates 4 non-identical haploid daughter cells, and used to create sex cells (egg and sperm). Ensures genetic variation.
Gametogenisis
Spermatogenesis:
- Process of producing male gametes (sperm cells) in mammals
- Occurs in testes
Oogenesis
- Process of producing female gametes (egg cells or ova) in
mammals
- Occurs in ovaries
- Of the four cells that are formed, only one is a viable mature egg. The others are non-functional polar bodies
How is Genetic Variation Ensured During Meiosis?
- Purpose of meiosis is to form genetically different
haploid gametes
- 2 ways this occurs:
Crossing Over - exchange of genetic bits between homologous chromosomes during prophase I
Independent Assortment - the random lining up of homologous chromosomes in metaphase I and the subsequent separation of them.
- 2n possibilities (8,388,608) different haploid cells can form
Errors During Meiosis
The two processes that produce genetic variation, independent assortment and crossing over, also provide the potential for chromosomal abnormalities.
Two types of chromosomal error
1. Changes in chromosome structure:error during crossing over
- Deletion: a piece of a chromosome is deleted
- Duplication: a section of a chromosome appears two or more times in a row
- Inversion: a section of a chromosome is inverted
- Translocation: a segment of one chromosome becomes attached to a
different chromosome
2. Changes in chromosome number: called non-disjunction, when homologous chromosomes or sister chromatids do not separate during anaphase I or II.
Trisomies and Monosomies:
- Monosomy: gamete is missing one chromosome, ex. Turner syndrome
- Trisomy: gamete contains an extra chromosome, ex. Down, Edward, Klinefelter, Triple X.