Mitosis, Meiosis, and Mendelian Genetics

Bio Quiz No. 2

What is the difference between MITOSIS and MEIOSIS?

Mitosis is a type of cell division that results in two genetically identical daughter cells, primarily for growth and repair, while meiosis is a specialized cell division that produces four genetically diverse gametes, essential for sexual reproduction.

What types of cells are involved in Mitosis?

Mitosis involves somatic cells, which are all body cells except for gametes, and is responsible for growth and repair in multicellular organisms.

What type of cells are involved in Meiosis?

Meiosis involves germ cells, which give rise to gametes through division to produce genetic diversity for sexual reproduction. Gametes are either sperm or egg cells.

Describe INTERPHASE:

Interphase is the phase of the cell cycle where the cell prepares for division, encompassing G1, S, and G2 phases, during which the cell grows, duplicates its DNA, and prepares for mitosis or meiosis.

Describe PROPHASE

Prophase is the first stage of mitosis and meiosis, where chromatin condenses into visible chromosomes, the nuclear envelope begins to break down, and spindle fibers start to form.

Describe METAPHASE:

Metaphase is the second stage of mitosis and meiosis, where chromosomes align at the cell's equatorial plane, ensuring proper letter distribution to daughter cells during division. Chromosomes are attached to the spindle fibers through their centromeres.

Describe ANAPHASE:

Anaphase is the third stage of mitosis and meiosis, during which sister chromatids are pulled apart to opposite poles of the cell, ensuring that each daughter cell receives an identical set of chromosomes. Spindle fibers shorten to allow this to happen.

Describe TELOPHASE:

Telophase is the final stage in mitosis and meiosis. The nuclear membrane begins to form, and the chromosomes begin to decondense back into expanded chromatin.

Describe CYTOKINESIS:

Parent cell cytoplasm divides to form two daughter cells (animal cells). In plant cells, a cell wall forms between the two cells instead.

In mitosis, how many chromatids are there BEFORE division (after the DNA has been copied)

92

Describe Prophase 1:

Parent is diploid. Pairs of homologous chromosomes form tetrads. These homologous pairs are close enough that they may swap/exchange alleles (called crossing over).

Describe METAPHASE 1:

Tetrads line up at the equator randomly. Maternal/paternal don’t have to be on the same sides.

Describe ANAPHASE 1:

Homologous pairs are pulled apart: random assortment (lottery of maternal/paternal genes).

Describe TELOPHASE 1:

Nuclear membrane reforms, chromosomes are still double stranded. 2 haploid cells.

Describe PROPHASE 2:

Cells only have 1 replicated chromosome. No tetrads, no crossing over. Nuclear membrane disappears again.

Describe METAPHASE 2:

Chromosomes line up, spindle fibers attach to centromeres.

Describe ANAPHASE 2:

Chromatids are pulled apart. Spindle fibers shorten and move to the poles.

Describe TELOPHASE 2:

Nuclear membrane reforms, chromosomes relax back into chromatin.

What is the result of MEIOSIS?

4 haploid daughter cells, all of which have different genes. Genetic diversity which strengthens a species

Chromosomal abnormalities can be either…

Structural, where the structure of the chromosomes is altered, or numerical, where there is an incorrect number of chromosomes present.

What causes structural abnormalities?

Deletion, Duplication, or Inversion/Translocation. They can be inherited or caused by agents such as radiation (x-rays, UV radiation), chemicals (toxic substances, mutagens), or viruses or environmental factors.

Describe numerical abnormalities:

Failure of chromosomes to separate properly during ANAPHASE 1 or ANAPHASE 2 of meiosis. If occurs in ANAPHASE 1, all cells will end up with an incorrect amount of chromosomes. If happens in ANAPHASE 2, only 2 cells end up with incorrect amount of chromosomes.

What is monosomy?

1 less chromosome, 45 total

What is trisomy?

1 more chromosome, 47 total

What are some examples of nondisjunction on autosomes?

Trisomy 21 (down syndrome), Trisomy 18 (Edward syndrome), Trisomy 13 (Patau syndrome). These are examples of non disjunction on AUTOSOMES.

What are some examples of nondisjunction on sex chromosomes?

XXY (Klinefelter syndrome), XYY (Jacobs syndrome), XXX (Triple X syndrome), X0 (Turner syndrome).

What is prenatal testing?

Maternal blood testing (blood is withdrawn between 15th and 22nd week), Ultrasound (sound waves produce visual scan of fetus), amniocentesis (sampling amniotic fluid with fetal cells), and chorionic Villi sampling (sample of placental tissue taken).

Who was Gregor Mendel?

Austrian Monk who studied math and botanist. Known as “father of genetics” for establishing patterns in how traits are inherited, known as mendelian genetics. He experimented with readily available pea plants that produced large amounts of offspring and observing several measurable traits, all with 2 alleles.

BONUS: What were the seven traits Mendel studied?

Flower colour, seed colour, pod colour, seed shape, pod shape, tall or dwarf, axial or terminal

What was the F1 generation?

Tall and short plant produced ALL TALL plants

What was the F2 generation?

Tall and Tall plant (F1) produced 3 tall, 1 short plant

What are alleles?

Specific version or variant of a gene.

Explain the process of crossing over.

Homologous chromosomes align precisely in tetrads, forming a synaptonemal complex, a protein structure that ensures accurate pairing of gene sequences. Holliday junction is formed to allow for reciprocal exchange of DNA segments. Produces recombinant chromatids.

Mendel’s Law of Segregation

The two alleles an organism carries for one trait separate during gamete formation, so each gamete receives only one allele. This separation occurs randomly.

Mendel’s Law of Dominance

If an organisms inherits two different traits for the same allele, the dominant trait will show up in the phenotype; dominant trait masks the recessive trait.

Mendel’s Law of Independent Assortment

The inheritance of an allele for one trait does not influence the inheritance of an allele for another trait. In other words, alleles of two or more genes separate independently when gametes are formed.

What is a germ cell?

A specialized cell that gives rise to gametes. These cells have heavily protected DNA that are usually safe from mutations in somatic cells; germ cells are found in gonads.

Female germ cell

oocyte

Male germ cell

Spermatocyte

Difference between oocyte meiosis and spermatocyte meiosis.

Oocyte produces only one large ovum and 2-3 polar bodies due to uneven cytokinesis. Only one viable gamete. Finite supply, as only 400 to 500 mature over a lifetime.

Spermatocytes produce four, genetically different, viable gametes. Millions produced daily throughout adult life.

What is a tetrad?

A pair of homologous chromosomes (four chromatids)

Why men are more likely to get x-linked traits/diseases

They only need one recessive trait to express it since they only have 1 X chromosome.

Examples of X-linked traits

Recessive:

Hemophilia, Duchenne Muscular Dystrophy

Other examples:

Red-green colour blindness

Turner Syndrome

Improper development of reproductive system, short stature, webbed neck. Only one X chromosome.

Klinefelter Syndrome

XXY. Slower cognitive development, taller height, breast development, less facial hair, less muscle mass, broader hips, longer legs with shorter torso.

Jacobs Syndrome

XYY. Minor symptoms, such as delayed development of speech and language skills and a taller stature, behavioral issues.

Triple X syndrome

Mild reproductive problems, slight developmental delay, taller stature, behavioural problems.

Down Syndrome

Trisomy 21. Flattened face, small nose, short neck, almond-shaped eyes, small wide hands with single crease in the palm. Developmental delays and intellectual disabilities.