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Material for Exam 1 in Genetics (BIO220) at AACC

theory of epigenesis

posits that an organism is derived from substances present in the egg that differentiate into adult structures during embryonic development

theory of preformation

stated that sex cells contain a complete miniature adult, perfect in every form, called a homunculus

cell theory

all organisms are composed of basic units called cells, which are derived from similar preexisting structures

idea of spontaneous generation

disproved idea of the creation of living organisms from nonliving components

idea of fixity of species

disproved notion that animal and plant groups have remained unchanged in form since the moment of their appearance on Earth

theory of natural selection

based on the observation that populations tend to consist of more offspring than the environment can support, leading to a struggle for survival among them. Those organisms with heritable traits that allow them to adapt to their environment are better able to survive and reproduce than those with less adaptive traits.

chromosome theory of inheritance

the idea put forward independently by Walter Sutton and Theodore Boveri that chromosomes are carriers of genes and the basis for the Mendelian mechanisms of segregation and independent assortment

genetics

branch of biology concerned with the study of heredity and variation

diploid (2n)

a condition in which each chromosome exists in pairs; having two of each chromosome

homologous chromosomes

chromosomes that synapse or pair during meiosis and that are identical with respect to their genetic loci and centromere placement (usually one maternal and one paternal in a set)

mitosis

a form of cellular reproduction producing two progeny cells, identical genetically to the progenitor cell, that is, the production of two cells from one, each with the same chromosome complement as the parent cell

meiosis

the process of cell division in gametogenesis or sporogenesis during which the diploid number of chromosomes is reduced to the haploid number

haploid (n)

a cell or organism having one member of each pair of homologous chromosomes. Also, the gametic chromosome number

mutation

any heritable change; source of all genetic variation

allele

alternative forms of a gene

phenotype

different observable features produced by different alleles

genotype

set of alleles for a given trait carried by an organism

bacteriophages (or phages)

a virus that infects bacteria, using it as the host for reproduction

nucleotide

building blocks of nucleic acids; a single phosphate linked to the 5' carbon of the ribose or deoxyribose sugar linked to a nitrogenous base

nitrogenous bases and pairing in DNA (4)

adenine, guanine, thymine, cytosine; A with T and C with G

transcription

process in which the nucleotide sequence in one strand of DNA is used to construct a complementary RNA sequence

mRNA

messenger RNA; an RNA molecule transcribed from DNA and translated into the amino acid sequence of a polypeptide

translation

synthesis of proteins under the direction of mRNA

proteins

polymers made up of amino acid monomers

Number of different amino acids commonly found in proteins?

20

genetic code

the deoxynucleotide triplets that encode the 20 amino acids or specify termination of translation

codon

a triplet of nucleotides that specifies a particular amino acid or a start or stop signal in the genetic code. 61 codons specify the amino acids used in proteins, and three codons, called stop codons, signal termination of growth of the polypeptide chain

tRNA

transfer RNA; recognize the information encoded in the mRNA codons and carry the proper amino acids for construction of the protein during translation

central dogma of genetics

DNA makes RNA which most often makes protein

enzymes

molecules that serve as biological catalysts, essentially causing biochemical reactions to proceed at rates necessary for sustaining life; largest category of proteins

restriction enzymes

cut any organism's DNA at specific nucleotide sequences, producing a reproducible set of fragments

vectors

In recombinant DNA, an agent such as a phage or plasmid into which a foreign DNA segment will be inserted and utilized to transform host cells

recombinant DNA

a DNA molecule formed by joining two heterologous molecules

clones

identical molecules, cells, or organisms derived from a single ancestor by asexual or parasexual methods

genome

complete haploid DNA content of a specific organism

biotechnology

commercial and/or industrial processes that utilize biological organisms or products

transgenic animals

animals that contain genes transferred from other animals, usually from a different species

DNA microarrays

an ordered arrangement of DNA sequences or oligonucleotides on a substrate (often glass)

gene therapy

the insertion of working copies of a gene into the cells of a person with a genetic disorder in an attempt to correct the disorder

genomics

the study of genomes (genomes-->the complete haploid DNA content of a specific organism)

proteomics

the study of the expressed proteins present in a cell at a given time

bioinformatics

the design and application of software and computational methods for the storage, analysis, and management of biological information such as nucleotide or amino acid sequences

model organisms

organisms used for the study of basic biological processes

gamete

a specialized reproductive cell with a haploid number of chromosomes

spores

produced by some bacteria, plants, and invertebrates, a unicellular body or cell encased in a protective coat. It is capable of surviving in unfavorable environmental conditions and gives rise to a new individual upon germinations. In plants, spores are the haploid products of meiosis

chromatin

the complex of DNA, RNA, histones, and nonhistone proteins that make up uncoiled chromosomes, characteristic of the eukaryotic interphase nucleus

plasma membrane

a phospholipid bilayer that surrounds a cell and serves as a barrier between the cell and its surroundings

cell wall

A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix

glycocalyx

covering over the plasma membrane, consisting of glycoproteins and polysaccharides, on most animal cells

eukaryotes

organisms having true nuclei and membranous organelles and whose cells demonstrate mitosis and meiosis

nucleus

the membrane-bound cytoplasmic organelle of eukaryotic cells that contains the chromosomes and nucleolus

chromosome

in prokaryotes, a DNA molecule containing the organism's genome; in eukaryotes, a DNA molecule complexed with RNA and proteins to form a threadlike structure containing genetic information arranged in a linear sequence and visible during mitosis and meiosis

nucleolus

the nuclear site of ribosome biosynthesis and assembly; usually associated with or formed in association with the DNA comprising the nucleolar organizer region

nucleolus organizer region (NOR)

areas of DNA that encode rRNA

prokaryotic cells

organisms lacking nuclear membranes and true chromosomes

nucleoid

area where genetic material is present in prokaryotic cells

cytoplasm

nonparticulate, colloidal material referred to as the cytosol, which surrounds and encompasses the cellular organelles

endoplasmic reticulum (ER)

a membranous organelle system in the cytoplasm of eukaryotic cells. In rough ER, the outer surface of the membranes is ribosome-studded; in smooth ER, it is not

mitochondria

generate large amounts of ATP; found in both plant and animal cells

chloroplast

a self-replicating cytoplasmic organelle containing chlorophyll

endosymbiotic theory

the proposal that self-replicating cellular organelles such as mitochondria and chloroplasts were originally free-living organisms that entered in to a symbiotic relationship with nucleated cells

centriole

a cytoplasmic organelle composed of nine groups of microtubules, generally arranged in triplets. Centrioles function in the generation of cilia and flagella and serve as foci for the spindles in cell division

spindle fibers

cytoplasmic fibrils formed during cell division that are involved with the separation of chromatids at the anaphase stage of mitosis and meiosis as well as their movement toward opposite poles in the cell

centromere

the specialized heterochromatic chromosomal region at which sister chromatids remain attached after replications, and the site to which spindle fibers attach to the chromosome during cell division. Also known as the primary constriction

Classifications of chromosomes based on centromere location (4)

-metacentric
-submetacentric
-acrocentric
-telocentric

Arms of chromosomes (2)

-p arm (think "petite") is shorter and shown on top
-q arm is longer and is shown below (think "q" is the letter after "p")

karyotype

the chromosome complement of a cell or an individual. Often used to refer to the arrangement of metaphase chromosomes in a sequence according to length and centromere position

sister chromatids

replica chromatids (two parts of each chromosome) that are connected by a common centromere

locus (pl., loci)

the site of place on a chromosome where a particular gene is located

biparental inheritance

one member of each homologous pair of chromosomes is derived from the maternal parent and one is derived from the paternal parent

sex chromosome

a chromosome, such as X or Y in humans, or Z or W in birds, which is involved in sex determination

zygote

single-celled fertilized egg

karyokinesis

nuclear division

cytokinesis

cytoplasmic division

cell cycle

events that occur from the completion of one division until the beginning of the next division

interphase stage of the cell cycle

interval between divisions

S phase

period during interphase during which replication of the DNA of each chromosome occurs

Stages of Interphase (4)

1) G1-Gap 1
2) [G0 stage-cells can withdraw from the cell cycle during G1]
3) S phase
4) G2-Gap 2

Events of Prophase in Mitosis (3)

1) chromosomes coil up and condense
2) centrioles divide and move apart
3) nuclear envelope breaks down and nucleolus disintegrates

centrosome

area of differentiated cytoplasm just outside of the nuclear envelope where centrioles are found

Events of Prometaphase in Mitosis (3)

1) Chromosomes are clearly double structures
2) Centrioles reach the opposite poles
3) spindle fibers form

Events of Metaphase in Mitosis (1)

Centromeres align on metaphase plate

metaphase plate

equatorial plane; midline region of the cell

kinetochore

a fibrous structure with a size of about 400 nm, located within the centromere. It appears to be the site of microtubule attachment during division

Events of Anaphase in Mitosis (1)

Centromeres split and daughter chromosomes migrate to opposite poles

daughter chromosome

name for chromatids after initiation of anaphase; formerly sister chromatids

Events of Telophase in Mitosis (6)

1) Daughter chromosomes arrive at poles
2) Cytokinesis commences
late telophase:
3) chromosomes uncoil to chromatin
4) nuclear envelope reforms
5) spindle fibers disappear
6) nucleolus begins to reform

cell plate

cell wall that is synthesized and laid down across the metaphase plate region during telophase in plant cells; becomes the middle lamella

cell furrow

complete constriction of the cell membrane in animal cells

cell division cycle (cdc) mutations

a class of cell division cycle mutations in yeasts that affect the timing and progression through the cell cycle

crossing over

genetic exchange between members of each homologous pair of chromosomes

Difference in behavior of homologous pairs in mitosis and meiosis?

In mitosis, homologous pairs of chromosomes behave autonomously during division; In meiosis, they form pairs and synapse

bivalent

synapsed structure including a homologous pair of chromosomes in zygotene (2nd) stage of meiosis prophase I; both members of each bivalent have replicated but the double structure is not yet visually apparent

tetrad

synapsed structure including a homologous pair of chromosomes that appears in pachytene (3rd) stage of meiosis prophase I, after the double structure of each homolog is evident

reductional division

number of centromeres is reduced by one-half; meiosis I

dyad

the products of tetrad separation or disjunction at meiotic prophase I; each dyad consists of two sister chromatids joined at the centromere

equational division

number of centromeres remains equal; meiosis II and mitosis

monad

the one chromosome left in each cell at the end of meiosis II after a dyad splits

synapsis

the pairing of homologous chromosomes at meiosis

Five Substages of Meiotic Prophase I

1) Leptotene stage
2) Zygotene stage
3) Pachytene stage
4) Diplotene stage
5) Diakenesis

Events during Leptotene Stage of Meiotic Prophase I (2)

1) Chromatin material begins to condense, and the chromosomes, though still extended, become visible
2) Chromomeres (localized condensations) are found along each chromosome

Events during Zygotene Stage of Meiotic Prophase I (4)

1) Chromosomes continue to shorten and thicken
2) Homology search occurs
3) Synaptonemal complex begins to form
4) Paired homologs are in the form of bivalents

Events during Pachytene Stage of Meiotic Prophase I (3)

1) Chromosomes continue to coil and shorten
2) Further development of the synaptonemal complex occurs
3) The double structure of each homolog is evident and paired homologs are in the form of tetrads

Events during Diplotene Stage of Meiotic Prophase I (2)

1) Within each tetrad, each pair of sister chromatids begins to separate
2) Earlier crossing over is evident through chiasmata

chiasma (pl., chiasmata)

area where nonsister chromatids remain in contact, thought to represent a point where genetic exchange occurred through the process of crossing over

Events during Diakenesis of Meiotic Prophase I (4)

1) Chromosomes pull farther apart but non sister chromosomes remain loosely associated through chiasmata
2) Terminalization occurs--chiasmata move towards the end of the tetrad
3) Nucleolus and nuclear envelope break down
4) two centromeres of each tetrad attach to the recently formed spindle fibers

disjunction

the separation of chromosomes during the anaphase stage of cell division

nondisjunction

a cell division error in which homologous chromosomes (in meiosis) or the sister chromatids (in mitosis) fail to separate and migrate to opposite poles; responsible for defects such as monosomy and trisomy

spermatogenesis

production of male gamete

oogenesis

production of female gamete

spermatogonium

undifferentiated diploid germ cell

primary spermatocyte

enlarged spermatogonium

secondary spermatocyte

product of first meiotic division in spermatogenesis

spermatids

product of second meiotic division in spermatogenesis

spermiogenesis

series of developmental changes that occur to spermatids

spermatozoa

sperm; product of spermiogenesis

ova (sing., ovum)

eggs

oogonium

diploid germ cell

primary oocyte

enlarged oogonium

first polar body

one of the products of meiosis I in oogeneis - contains half the chromosomes but little of the cytoplasm

secondary oocyte

product of first meiotic division in oogenesis

ootid

product of second meiotic division in oogenesis

second polar body

a small body containing the chromosomes discarded during the second meiotic division of an ovum

folded-fiber model

a model of eukaryotic chromosome organization in which each sister chromatid consists of a single chromatin fiber composed of double-stranded DNA and proteins wound like a tightly coiled skein of yarn

asexual reproduction

reproduction that does not involve the union of gametes and in which a single parent produces offspring that are genetically identical to the parent

autosomes

chromosomes other than the sex chromosomes. In humans, there are 22 pairs of autosomes.

binary fission

the division of a prokaryotic cell into two offspring cells

eukaryotes

organisms having true nuclei and membraneous organelles and whose cells demonstrate mitosis and meiosis

fertilization

process in sexual reproduction in which male and female reproductive cells join to form a new cell

gametogenesis

production of gametes

germ cells

the only cells that can undergo meiosis--spermatogonium & oogonium

homologues

two chromosomes that code for the same traits as itself; traits are same, but actual genes may be different

karyotype

the chromosome complement of a cell or individual. Often used to refer to the arrangement of metaphase chromosomes in a sequence according to length and centromere position.

mitotic spindle (apparatus)

the framework of microtubules that appears in cell division, and eventually attaches to and moves the chromatids apart

organelles

specialized structure that performs important cellular functions within a eukaryotic cell

prokaryotes

organisms lacking nuclear membranes and true chromosomes

somatic cells

all cells other than the germ cells or gametes in the organism

sperm cells

male reproductive cells

synaptonemal complex

an organelle consisting of a tripartite nucleoprotein ribbon that forms between the paired homologous chromosomes in the pachytene stage of the first meiotic division. May be essential for crossing over.

testcross

a cross between an individual whose genotype at one or more loci may be unknown and an individual who is homozygous recessive for the gene or genes in question

X-linked alleles

genes located on the X chromosome

Classification of chromosomes in a karyotype

1) size
2) banding pattern
3) centromere location

Summary of events of 5 periods of prophase I of meiosis

1) leptonena -- chromomeres (localized condensations)
2) zygonema -- bivalents
3) pachynema -- tetrad
4) diplonema -- chiasma
5) diakinesis -- terminalization (chiasmata move toward ends of tetrads)

ploidy

a term referring to the basic chromosome set or to multiples of that set

2 major differences btwn mitosis & meiosis

1) mitosis produces 2 diploid daughter cells; meiosis produces 4 haploid daughter cells
2) mitosis produces daughter cells that are genetically identical; meiosis produces daughter cells that are not genetically identical

3 ways chromosomes of a karyotype are classified

1) size
2) banding pattern
3) centromere location

karyokinesis

nuclear division

alleles

different versions of the same gene

homozygous

an individual with two identical alleles

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