Chapter 3 – Cell Division and Inheritance Chromosomes All living things share a common heritage of genetic inheritance. To study how information is passed from generation to generation we must understand how reproduction occurs at the cellular level.

Genetics – This is study of how genetic information is passed from one generation to another. Genes – The most basic unit of information stored in the genetic material is called the gene. These units are what control the formation of proteins.

Chromatin – this is the combination of DNA and the histone proteins that are connected to it. In this state it is uncompressed and cottony. Nucleosome – As it wraps around the histones it forms bundles.

Sex Chromosomes – Sexually reproducing organisms have chromosomes that vary in size. Their presence produces the different genders of individuals.

Autosomes – All other chromosomes are in matched pairs and are called autosomes.

Diploid – When both members of a paired set of chromosomes are present the cell is said to be diploid. Haploid – Some organisms (male honeybees, rotifers) and cells produced during some parts of sexual reproduction have only one set of chromosomes.

Polyploidy – Even fewer organisms have more than one pair of chromosomes. Since irregular numbers of chromosomes often causes errors in sexual reproduction, many of these organisms are asexual.

Chromatid (sister chromatids) – Attached identical copies of chromosomes. Centromere – This is a part of the chromosomal DNA that connects copies.

The Cell Cycle This is the entire life cycle of a cell, from its formation until it reproduces.

Interphase – the vast majority of a cells life is spent growing and going about its regular processes food intake, waste removal and other biochemical processes.

Interphase has three main parts: G1 Phase – during this phase the cell grows to normal size following its formation from mitosis. S Phase – During this phase, the cell begins to copy its DNA in the chromatin form. This process is completed long before mitosis occurs. G2 Phase – This second growth phase occurs right before a cell begins mitosis. This growth supports the cells division into two parts.

Mitosis This is specifically the division of the nucleus and formation of two new nuclei. It is divided into 4 recognizable parts that aren’t distinct, but have certain hallmark events.

Prophase – During this phase DNA condenses and coils into chromosomes from the previously uncoiled cottony state. The nuclear membrane and nucleolus breaks apart. At the end of prophase the centriole pairs have moved to opposite poles and microtubules connect them.

Metaphase – During this phase the chromosomes line up along the equator of the cell. The centromeres divide, separating the sister chromatids into complete chromosomes.

Duplicated Chromosomes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Duplicated Chromosomes Fig. 3.4 3-4

Anaphase – During this phase the microtubules pull the pairs of chromosomes apart from their partners to separate ends of the cell, making two complete sets at each pole.

Telophase – During this phase a nuclear membrane begins to form around each set of chromosomes. The chromosomes uncoil. A new nucleolus is synthesized. The cell begins to pinch in the middle. Cytokinesis – This is the division of the cytoplasm of the cell. The new nuclei are separated into the two new halves.

Mitosis and Cytokinesis

Gametes – These are specialized haploid cells created through meiosis for the purposes of sexual reproduction.

Meiosis –forming haploid cells like mitosis, but two cell divisions. The names are similar to the mitotic analogues, but the two divisions are separated by using the Roman numerals I and II.

Prophase I – During this phase condensed DNA homologous pairs of chromosomes line up side by side. Metaphase I – The homologous pairs line up along the equator.

Anaphase I – Homologous pairs separate. Telophase I – Two new cells form, and each is haploid but has sister chromatid still attached.

Prophase II, Metaphase II, Anaphase II, Telophase II – Just like regular mitosis, the process continues, but this time with a haploid parent cell and haploid daughter cells.

Meiosis and Cytokinesis Fig. 3.6 3-6

Zygote – This is the diploid cell created from the fusion of a male and female gamete that occurs during fertilization in a process called syngamy.

Crossing Over – During prophase I, the homologous pairs are aligned perfectly, and segments can interchange between the pairs.

Synapsis and Crossing-Over 3-7

Spermatogenesis – The formation of four sperm cells from a male during meiosis.

Oogenesis – The formation of a single egg cell from a female during meiosis. The other three polar bodies are reabsorbed by the female body.

DNA – Deoxyribonucleic Acid. Stores the genetic information to make RNA. In the nucleus it is double stranded. RNA – Ribonucleic Acid. This chemical is actually involved in protein synthesis. In cells it is found in single strands.

Components of Nucleic Acids 3-8

Structure of DNA 3-9

Transcription – synthesis of RNA from a strand of DNA Transcription – synthesis of RNA from a strand of DNA. This RNA is essential in the process of translation.

Translation – formation of a protein from RNA at the ribosome Translation – formation of a protein from RNA at the ribosome. The RNA is responsible for aligning the amino acids in the protein

Events of Translation 3-14

Structure of Transfer RNA 3-13

Replication – Each strand of DNA acts a template to make two new identical semiconservative strands of DNA

Independent Assortment – during gamete formation pairs of factors (traits) segregate independently of one another.

Segregation – pairs of genes are distributed during gamete formation Segregation – pairs of genes are distributed during gamete formation. Fertilization results in random recombination of these genes. Mutation – a change in the nucleotide sequence in DNA resulting in a replacement, addition or deletion of nucleotides. This is always a random event!

Nondisjunction in Sperm Formation Fig. 315 3-15