Bio 120 chapters 12, 13, 14, and 15

Mitosis

Mitosis

a type of cell division that results in two daughter cells having the same number and kind of chromosomes as the parent nucleus

What are the two types of nuclear division?

Meiosis and mitosis

What is cytokinesis?

The cytoplasmic division of a cell at the end of mitosis or meiosis; brings about the separation into two daughter cells

Why do cells divide?

Reproduction Growth and development Repair/replace other cells

What are the important features of interphase in eukaryotic cells?

Cell acquires nutrients, creates and uses proteins and other molecules, and starts the process of cell division by replicating the DNA. Interphase is divided into three distinct stages, Gap 1, Synthesis, and Gap 2

Be able to draw out the cell cycle; draw out a cell in interphase and explain what’s happening in interphase.

What are the results of mitosis?

Two identical copies of a cell are formed. Increases the number of cells for growth and development

Chromatid

One of two strands of a copied chromosome

sister chromatids

Two chromatids that are joined together at their centromeres

Chromosome

threadlike structure of nucleic acids and protein found din the nucleus of most living cells, carrying genetic information in the form of genes

Homologous chromosome

same size/shape

Kinetochore

attach to chromosome and break chromatids

Mitotic spindle

A cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division

Centrosome

The organizing centers for microtubules involved in separating chromosomes during mitosis

Centromere

The region where the identical DNA molecules are most tightly attached to each other after chromosomes condense

What are the "phases" of mitosis?

Prophase Prometaphase Metaphase Anaphase Telophase and cytokinesis

Prophase

1. Chromatin condenses to form chromosomes: 2 sister chromatids attached with centromere and collusion

2. Nucleoli disappear

3. Mitotic spindle begins to form

Prometaphase

1. Nuclear Envelope ruptures

2. Spindle enters nuclear are: -Kinetochore fibers: attach to chromosome and break chromatids -Non-kinetochore fibers

Metaphase

Chromosomes align at the metaphase plate

Anaphase

1. Sister chromatids separate

2. Move toward opposite poles: -Pacman method -Walking/reeling in method

3. Cell elongates- stretches the cell to make it easier to divide

Telophase and Cytokinesis

1. Nuclear envelope reforms

2. Nucleoli reappear

3. Chromosomes uncoil (form chromatin)

4. Mitosis spindle disappears

5. Cytokinesis happens

How does cytokinesis differ in plant and animal cells?

Cleavage groove in animal cells Cell plate formation in plant cells

What triggers cell division?

1. Growth/development factors

2. Repair/replace other cells

3. Reproduction

How is mitosis regulated?

1. Checkpoints along the way act like stop signs

2. Really tight regulations that control growth

3. MPF (maturation-promoting factor)

What happens in meiosis?

-The process of nuclear division in which the number of chromosomes in the nucleus is cut in half, and 4 genetically different nuclei are produced -Organisms use meiosis when they’re making gametes

Phases of meiosis/major events

1. Pre-meiotic interphases: cell replicates DNA

2. Meiosis I (reduction division) Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis

3. Meiosis II (sister chromatids split) Prophase II Metaphase II Anaphase II Telophase and Cytokinesis

What are the 3 sources of genetic variation in sexually reproducing organisms?

1. Crossing Over

2. Independent assortment of chromosomes

3. Random fertilization of gametes

Compare mitosis and meiosis

look at image

Differences between mitosis and meiosis

look at image

Gametes

An organism's reproductive cells. Also referred to as sex cells

Haploid

Those that have only a single set of chromosomes (n). Haploid cells are formed through meiosis.

Diploid

Have two sets of chromosomes (2n). Undergo mitosis

Zygote

a diploid cell resulting from the fusion of two haploid gametes (male and female); a fertilized ovum

What do Mendel's laws of segregation and independent assortment state? When do these occur? (during meiosis)

Laws of segregation- the 2 alleles for each character segregate (separate) when gametes are made (Meiosis I)

Law of Independent assortment- During the formation of gametes, alleles of 1 gene segregate independently of the allele of a second gene.

Alleles

Different forms of a single gene. Account for variations in characters such as flower color

Genes

A unit of heredity which is transferred from a parent to offspring and is held to determine some characteristics of the offspring -Genes come in pairs. Organisms inherit 2 copies of a gene for the same character

Dominate

The allele that masks the expression of the other allele

Recessive

The allele that typically isn't expressed

Incomplete dominance

A heterozygous for a character doesn’t show a complete dominance/recessive relationship. Example: Pink genotype for snapdragons as a result form red and white mixing

Co-dominance

An organism is heterozygote for a character and both alleles affect the phenotype in separate, distinguishable ways. Example: Blood groups. I^a and I^b are both dominant and i is recessive

Pleiotropy

When a single gene has many phenotypic effects Example: Sickle cell disease (2 copies of the HbS allele)

What does the norm of reaction refer to?

Describes the pattern of phenotypic expression of a single genotype across a range of environments

What is X-inactivation?

When an Xist gene on one of the X chromosomes acts to inactivate the X chromosome early in embryonic development

Why are tortoise shell cats almost always females?

In order to be tortoise shelled, the cat's genotype has to be X^oX^b. So, has to have XX, which is unusual in males.

What important contribution to biology did Mary Lyon make?

She discovered the Barr body (x inactivation)

What is a Barr body?

In every female mammal, one of the X chromosomes that's inherited becomes inactivated

How many Barr bodies are found in females with a sex chromosome complement of XX? OR XXX?

XX- one

XXX- two

How do chromosomal nondisjunction and lagging result in abnormal chromosome numbers in cells?

The error in cell division results in a different end number of chromosomes

Nondisjunction

When chromosomes fail to separate properly during cell division (meiosis or mitosis)

Lagging

Delayed movement of a chromosome during anaphase

Aneuploidy in non-sex and sex chromosomes in humans

Non-sex: Fairly common and not an issue

Sex: Not as common, and can have devastating results

Alterations of chromosome structure

Trisomy: Extra chromosomes(s)

Monosomy: Missing a chromosome(s)

Polyploidy: Having a whole extra set of chromosomes (23)