Biology Chapter 8 Study Guide

**Genes are located on chromosomes at a specific location called ________.**

Loci

**What is the structure of chromatin?**

Chromatin is a long DNA molecule that is attached to protein molecules called histones, when the cell is not dividing chromatin exists as a diffuse mass of long, thin fibers.

**What are diploid cells?**

A cell containing two homologous sets of chromosomes, one set inherited from each parent; a 2n cell.

**What are haploid cells?**

A cell containing a single set of chromosomes; an n cell.

**What are the 2 general phases of the cell cycle?**

The mitotic phase (M phase) and interphase.

**What are the 3 different structures of chromosomes?**

Chromatin, chromosomes, double helix.

**What are the phases of mitosis?**

Prophase, metaphase, anaphase, and telophase.

**What is the growth phase of a cell called?**

Interphase, more specifically the G1 phase, as that's when the cells matures the most.

**What happens when the cell cycle is not controlled?**

An abnormal mass of cells grows, resulting in a tumor.

**Be able to explain the difference between somatic cells and sex cells.**

Somatic cells are not involved in sexual reproduction, are diploid (have 46 chromosomes, 23 pairs), and reproduce using mitosis. Sex cells are involved in sexual reproduction as egg or sperm, are haploid (23 chromosomes), and reproduce using meiosis.

**What are homologous chromosomes?**

The two chromosomes that make up a matched pair in a diploid cell. They are of the same length, centromere position, and staining pattern and possess genes for the same characters at corresponding loci. Each pair is called a tetrad.

**With regards to chromosome number what is the difference between cells produced through mitosis and meiosis?**

Mitosis produces two identical daughter cells, whereas meiosis produces 4 different daughter cells.

**Be able to describe the phases of meiosis.**

Prophase 1 - homologous chromosomes pair up, called synapsis. Each pair is called a tetrad. 

Chromatids line up so corresponding genes genes line up next to each other, then they cross over and portions of broken chromatids will attach to adjacent chromatids. Results in genetic recombination. 

Metaphase 1- tetrads randomly line up on the equator of the cell. Spindle fibers attach to centromeres. 

Anaphase 1- each homologous chromosome moves to the opposite ends of the cell 

Telophase 1  - spindle fibers disappear 

Meiosis ll -  Same as mitosis but w/ the exception of no nuclear envelope 

**What is crossing over?**

Crossing over occurs when portions of broken chromatids attach to adjacent chromatids in homologous chromosomes. It results in genetic recombination..

**Be able to describe the differences between mitosis and meiosis.**

Mitosis is the process of dividing one parent cell into two identical daughter cells with one division. Whereas meiosis is the process of taking two gametes (egg and sperm) and merging their DNA through the process of fertilization. They will go through 2 divisions to create 4  unidentical daughter cells. 

**What four things is cell division used for?**

Reproduction, Repair, Growth, Renewal/Replace.

**Why is cell division simpler for prokaryotic cells?**

Because there aren't as many organelles to copy and prokaryotes only have 1 chromosome in the form of a circle.

**By what process do prokaryotes reproduce? Describe the process.**

They produce by binary fission. Binary fission is where the chromosome makes a copy of itself, then the cell doubles in size, a cell wall forms btw the chromosomes, and the cell divides.

**Explain the structure of DNA.**

DNA is composed of nucleic acids and contains genetic information. It is made up of a double helix.

**Why is chromatin made?**

Chromatin is made because double helixes are fragile and easy to break, so by creating chromatin, the double helix is more squished/twisted together, and as a result stronger and less prone to mistakes.

**What is the structure of chromosomes and how are they created?**

Chromosomes are created during cell division, when chromatin (DNA) condenses and twists around proteins called histones. They are only visible during cell division and are microscopic. 

**What are the three phases of  Interphase and what do they do?**

G1 phase  - grows the cell to maturity 

S phase - duplicating DNA

G2 phase - Preparing for mitosis, and copying organelles. Doubling in size 

**What happens in prophase?**

Chromatin coils into visible chromosomes 

Nuclear envelope disappears 

Spindle fibers form 

Spindle fibers attach to centromeres 

**What happens in Metaphase?**

The chromosomes line up in center of the cell 

**What happens in Anaphase?**

Sister chromatids separate 

Spindle fibers pull chromosomes to opposite poles

**What happens in Telophase?**

Chromosomes begin to unwind 

spindle fibers break down

Nuclear envelope reforms around each set of chromosomes

A new plasma membrane begins to form between two nuclei

**What happens in Cytokinesis?**

Cytokinesis is actual cell division 

The cytoplasm is pinched in half, creating a cleavage furrow 

Forms 2 new cells 

**Describe a benign tumor:**

A benign tumor is a mass of cells that continuously kept growing until they eventually stopped. This type of tumor stays at the original site of where it started growing. It is not dangerous and to us is just a mole on our skin.

**Describe a malignant tumor:**

A malignant tumor is a mass of cells that continues to divide. These tumors do not stay at the original site but spread. They are cancerous. 

**Which stage of meiosis most closely resembles mitosis?v**

The movement of chromosomes during meiosis II very closely matches mitosis (except with half as many chromosomes).

 **A cell from a diploid organism has the haploid number of chromosomes, but each chromosome has two chromatids. The chromosomes are arranged singly at the center of the spindle. What is the meiotic stage?**

Metaphase II (because the chromosomes line up two by two in metaphase I)

**How many autosomes are found in a human sperm cell? How many and which sex chromosomes?**

22 autosomes plus either an X or Y sex chromosome.

**Are all of your chromosomes fully homologous?**

If you were born female, yes. If you were born male, no, because you have a Y chromosome and an X chromosome, which are not homologous.

**Contrast cytokinesis in animals with cytokinesis in plants.**

In animals, cytokinesis involves a cleavage furrow in which contracting microfilaments pinch the cell in two. In plants, it involves formation of a cell plate, a fusion of vesicles that forms new plasma membranes and new cell walls between the cells.

**You view an animal cell through a microscope and observe dense, duplicated chromosomes scattered throughout the cell. Which state of mitosis are you witnessing?**

Prophase (because the chromosomes are condensed but not yet aligned).

**What is genetics?**

The study of heredity, pioneered by Gregor Mendel in his pea plant experiment.

**What is a gene?**

A segment of DNA that codes for a trait, located on chromosomes.

**What is the difference between a character and a trait?**

Character is a heritable feature that varies among individuals, such as flower color. A trait is each variant for a character, such as purple or white flowers.

**What plant did Gregor Mendel study and why?**

Garden Peas because they grow quickly and have lots of characters.

**How did Mendel ensure that each variety of garden peas was true-breeding for a particular trait?**

Self-fertilized the plant with that particular trait so that the offspring had that particular trait.

**What is a monohybrid cross?**

A cross between two individuals differing in a single character.

**What does the Law of Independent Assortment describe?**

Pairs of alleles segregate independently of one another during gamete formation.

**Each gene is composed of 2 ________.**

Alleles, which are the alternative forms of the trait of that gene.

**The inheritance when the  phenotype is in-between dominant and recessive is called _________.**

Incomplete dominance

**What does Mendel's Law of Segregation describe?**

A general rule in inheritance that individuals have two alleles for each gene and that when gametes form by meiosis, the two alleles separate, each resulting gamete ending up with only one allele of each gene. *Two alleles from the same gene must separate from each other.*

**Describe the difference between sexual and asexual reproduction.**

Sexual reproduction is between 2 organisms that both give DNA to the offspring, creating similar, but not identical offspring. Asexual reproduction is when a singular organism creates an identical copy of itself, this is without the need for 2 organisms. 

**Explain why cell division is necessary for growth, repair, and reproduction of organisms.**

Cells in organisms are constantly dying and getting damaged, it is necessary that cells continue to divide in order for the organism to sustain itself. It is also important because when reproduction starts, that is when DNA is copied and passed onto the offspring and the cycle continues. 

**Describe the events of binary fission.**

1. Binary fission is the cell division that happens in only prokaryotic cells. First, the chromosome takes a copy of itself, the cell grows to approximately twice its original size, a cell wall starts to form between the two chromosomes, and finally, the cell will divide into 2 identical daughter cells. 

**What type of reproduction does binary fission represent?**

Binary fission represents asexual reproduction because it is a complete copy of DNA. 

**What are the 2 different types of cell division in eukaryotic organisms?**

The two different types of cell division in eukaryotic cells are Mitosis and Meiosis. Mitosis is the division of a eukaryotic cell that results in two identical daughter cells, this represents a type of asexual reproduction. Meiosis is cell division into 4 haploid daughter cells called gametes that are used in sexual reproduction. These haploid daughter cells are not identical and only carry one set of genes. 

**Describe each phase of mitosis.**

In mitosis, we start with prophase(1st phase)which is when chromatin coils up into identifiable chromosomes, the nuclear membrane disappears, and the spindle fibers start to form and attach to the centromeres. In metaphase(2nd phase), the spindle fibers line up the chromosomes in the center of the cell across the metaphase plate. In Anaphase(3rd phase), the sister chromatids are separated and are pulled to each side of the cell. In Telophase(4th phase), the chromosomes begin to unwind, spindle fibers break down, the nuclear envelope starts to form around it, and a plasma membrane begins to form between the two developing cells. Cytokinesis(usually starts while telophase is occurring) is where the cell actually divides and forms two daughter cells. Mitosis is the first 4 phases, the Mitotic phase includes cytokinesis. 

What is chromatin?

The state in which DNA is normally found in nondividing cells, DNA is coiled around proteins called histones. 

**Describe the structure of a chromosome.**

A chromosome is strands of DNA wrapped around proteins and tightly condensed. They are most visible during cell division. 

**What is the difference between sister chromatids and chromosomes?**

Sister chromatids are the two copies of the DNA in which make up a chromosome. Two sister chromatids are linked together by the centromere that is then a chromosome. 

**What is the cell cycle defined as?**

The cell cycle is an ordered series of events that run from the instant a cell is first formed from a dividing parent cell until its own division into two daughter cells.

**Describe each phase of interphase**

In interphase, it is known as the growth phase in which cells spend the most time. The G1 phase is growth and maturity of the cell after its division, the S(synthesis) phase is when the cell is told to copy the DNA, and the final phase is the G2 phase when the cell is preparing for mitosis.

**What is the difference between plant and animal cell cytokinesis?**

The difference between plant and animal cell cytokinesis is that plant cells have a cell wall which does not allow the plant cell to create a cleavage furrow. Instead, the cell creates a cell plate between the two nuclei.

**What is the difference between somatic and sex cells?**

Somatic cells are the cells that make up the body and are 2n cells(diploid cells)(have 2 homologous sets of chromosomes. Sex cells, also called gametes, are n cells(haploid cells) because in order to reproduce sexually the chromosome number in sex cells must be reduced to half. 

**What is a pedigree?**

A pedigree is a recording of all your family members and their genotype for a specific trait, based on phenotype. 

**True or false: If both parents are dominant for a certain trait we are able to find out their specific genotype.**

False. Because a pedigree is based off of phenotype we are not able to find the specifics of their genotype if both of them are dominant. We are only able to know if one of their offspring is homozygous recessive.

**What is incomplete dominance?** 

When both sets of alleles are dominant, and both are partially expressed. Which results in the creation of a characteristic in the middle of the two parent alleles. 

**What is codominance and how does it differ from incomplete dominance?**

Codominance is when both dominant sets of alleles are expressed. Whereas in incomplete they are only partially expressed which makes a new characteristic, and in codominance you see the two separate characteristics. 

**What type of alleles are most genetic disorders?**

Homozygous recessive

**What is an example of a genetic disorder caused by a dominant allele? Explain.**

Huntington's disease. It is a lethal genetic disorder caused by dominant alleles and although rare, does not appear until 30-50 yrs old, so passed on unknowingly through reproduction.

**Explain what the lines, shapes and shades symbolize in pedigrees.**

Squares represent males and circles represent females. Shaded represents that the trait is expressed, unshaded means not expressed, and half shaded represents heterozygous. Vertical lines symbolize offspring (genetically related; siblings)  and horizontal lines represent the parents (reproducers). Horizontal rows represent a generation.

**Explain an example of incomplete dominance.**

If a white flower and red flower cross, a pink flower would be created. This is because the red allele codes for red pigment while the white allele codes for no pigment. So the offspring gets half of red pigment, resulting in a lighter shade of red, also known as pink.

**What is an example of a gene having more than 2 alleles?**

Blood types are an example, as there are 4 different types: A (AA/AO), B (BB/BO), O (OO), AB (Codominance of A+B)

**Explain why sickle cell anemia can be an example of codominance.**

It is a condition in which part (heterozygous) or all (homozygous) of red blood cells are shaped like a sickle. If only part of the red blood cells are shaped like a sickle, it represents codominance as the person lives with half sickle cells and half normal (not always equally half and half).

**Name and describe inheritance patterns.**

* Codominance: When a heterozygous gene will express both phenotypes equally. 
* Incomplete dominance: When heterozygous alleles are partially expressed resulting in an intermediate phenotype.
* Complete dominance: Phenotypes of the heterozygous and dominant homozygote are indistinguishable
* Multiple alleles: When a gene has more than 2 alleles.
* Polygenic inheritance: When a trait is controlled by multiple genes.

**Explain an example of polygenic inheritance.**

Eye color is controlled by multiple genes. There are different genes for different colors and genes that pick the phenotypic color. For example you may have genes for brown, green, blue and hazel eyes, but other genes pick green, so you will have green eyes.