BSC Test 2

cell cycle

an orderly set of stages from the first division of a eukaryotic cell to the time the resulting daughter cells divide.

The two major stages of the cell cycle

interphase and mitotic stage

Interphase

most of the cell cycle is spent here; cell performs its usual finctions; time spent here varies by cell type;

Mitotic Stage

includes mitosis and cytokinesis

Mitosis

cell division in which the nucleus divides into nuclei containing the same number of chromosomes

Cytokinesis

division of the cytoplasm

mitotic spindle

daughter chromosomes distributed by this to two daughter nuclei

What happens during mitosis?

Centromeres holding sister chromatids together separate
Sister chromatids separate
Each becomes a daughter chromosome
Daughter chromosomes of each type distributed to opposite daughter nuclei

Prophase

Nuclear division about to occur.
Nucleolus disappears
Nuclear envelope fragments
Spindle begins to assemble
Two centrosomes move away from each other.
In animal cells, microtubules form star

Metaphase

Chromosomes pulled around by kinetochore fibers and connect to spindle fibers
Forced to align across the equatorial plane of the cell

Anaphase

Centromere dissolves, releasing sister chromatids
Sister chromatids separate at the centromere.
Now called daughter chromosomes
Pulled to opposite poles along kinetochore fibers
Poles move farther apart

Telophase

The spindle disappears.
New nuclear envelopes form around daughter chromosomes.
There are now two clusters of daughter chromosomes.

Early Prophase

Nucleolus has disappeared, and duplicated chromosomes are visible.
Centrosomes begin moving apart, and spindle is in process of forming.

Metaphase

Centromeres of duplicated
chromosomes are aligned at the metaphase plate (center of fully formed spindle).
Kinetochore spindle fibers attached to the sister chromatids come from opposite spindle poles.

Anaphase

Sister chromatids part and become daughter chromosomes that move toward the spindle poles. In this way, each pole receives the same number and kinds of chromosomes as the parent cell.

Telophase

Daughter cells are forming as nuclear envelopes and nucleoli reappear.
Chromosomes will become indistinct chromatin.

What order is mitosis?

prophase, metaphase, anaphase, telophase

What are the substages of interphase?

G1 Phase, S Phase, G2 Phase,

S Phase

DNA replication takes place.
Proteins associated with DNA are synthesized.
Chromosomes enter S phase with 1 chromatid each.
Chromosomes leave S phase with 2 identical chromatids (sister chromatids) each.
Sister chromatids remain attached until they are separated during mitosis.

G2 phase

located between DNA replication and onset of mitosis.
Cell synthesizes proteins, including microtubules, necessary for division.

G1 phase

The first gap, or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis begins.

Before mitosis begins

Chromatin condenses (coils) into distinctly visible chromosomes.
Each species has a characteristic chromosome number.

At the End of S Phase

Each chromosome internally duplicated
Consists of two identical double

Centromere

Area where the chromatids of a chromosome are attached

Diploid (2n)

includes two sets of chromosomes of each type.

Humans have \___ different types of chromosomes.

23

Each type represented twice in each body cell

diploid

Only sperm and eggs have one of each type

Haploid

parts of a chromosome

Abnormal growth of cells is called

Tumor

Tumors that are not cancerous, are encapsulated

benign

tumors that are cancerous, not capsulated

malignant

Development of Cancer

Tends to be gradual and multistep
May take years before cell is obviously cancerous

What are the characteristics of cancer cells?

Lack differentiation
Have abnormal nuclei
Do not undergo apoptosis

binary fission

Splitting in two
Two replicate chromosomes are distributed to two daughter cells.
Produces two daughter cells identical to original cell—asexual reproduction

Gametes

The only haploid part of the life cycle is the

Gametogenesis

Meiosis occurs only during

Spermatogenesis

All four cells become sperm.

Oogenesis

One of the four nuclei receives the majority of the cytoplasm.

synapsis

homologous chromosomes pair up in

Meiosis I

Chromosomes are replicated prior to it. Homologous chromosomes pair up in synapsis. Homologous pairs align themselves against each other, side by side at the metaphase plate.
The two members of a homologous pair separate.
Each daughter cell receives one duplicated chromosome from each pair.

Meiosis II

DNA is not replicated between meiosis I and meiosis II.
Sister chromatids separate and move to opposite poles.
The four daughter cells contain one daughter chromosome from each pair.
Each daughter chromosome consists of a single chromatid.
The daughter cells are haploid.

Meiosis I consists of

Prophase I, Metaphase I, Anaphase I, Telophase I

Prophase I

A spindle forms.
The nuclear envelope fragments.
The nucleolus disappears.
Each chromosome is duplicated (consists of two identical sister chromatids).
Homologous chromosomes pair up and physically align themselves against each other side by side (synapsis).
Synapsed homologs are referred to as a bivalent (two homologues) or a tetrad (four chromatids).

Metaphase I

Homologous pairs are arranged at the metaphase plate.
Bivalents are aligned at the spindle independently of one another.

Anaphase I

Homologous chromosomes of each bivalent separate from one another.
Homologues move towards opposite poles.
Sister chromatids do not separate.
Each is still a duplicated chromosome with two chromatids.

Telophase I

Daughter cells have one duplicated chromosome (n) from each homologous pair.

Interkinesis

Two haploid (n) daughter cells, each with one duplicated chromosome of each type
Interkinesis is similar to mitotic interphase, except
It is usually shorter.
DNA replication does not occur.

Meiosis II

(mitosis of two haploid cells) and gamete formation

Prophase II

chromosomes condense

Metaphase II

Chromosomes align at metaphase plate
They are no longer in homologous pairs.

Anaphase II

Centromere dissolves
Sister chromatids separate and become daughter chromosomes that are not duplicated.

Telophase II and Cytokinesis

Four haploid (n) cells all genetically unique
Gametes containing a mixture of maternal and paternal genes

how many chromosomes are in each cell at the end of meiosis

46

Euploidy

the correct number of chromosomes in a species.

Aneuploidy

is a change in the chromosome number.

Monosomy

only one of a particular type of chromosome

Trisomy

three of a particular type of chromosome

Autosome

any chromosome other than a sex chromosome (X or Y).

Incomplete penetrance

The dominant allele may not always lead to the dominant phenotype in a heterozygote.
Many dominant alleles exhibit varying degrees of penetrance.

points of the law of segregation

Each individual has a pair of factors (alleles) for each trait.
The factors (alleles) segregate (separate) during gamete (sperm & egg) formation.
Each gamete contains only one factor (allele) from each pair of factors.
Fertilization gives the offspring two factors for each trait.
Results of the monohybrid cross: All F1 plants were tall, disproved blending hypothesis

The process of meiosis explains Mendel's \______ and why only one allele for each trait is in a gamete.

Law of Segregation

points of the law of independent assortment

Each pair of factors segregates (assorts) independently of the other pairs.
All possible combinations of factors can occur in the gametes.

Dominant allele

masks the expression of the recessive allele

recessive allele

represents a "loss of function."

Homozygous

identical alleles (TT \= tall) (tt \= short)

Heterozygous

different alleles (It \= tall plant)

Genotype

It refers to the two alleles an individual has for a specific trait.

Phenotype

It refers to the physical appearance of the individual.

Monohybrid

Chose varieties that differed in only one trait
(P

Dihybrid

A dihybrid cross uses true

testcross

determines the genotype of an individual having the dominant phenotype

Punnett Square

Table listing all possible genotypes resulting from a cross
All possible sperm genotypes are lined up on one side.
All possible egg genotypes are lined up on the other side.
All possible zygote genotypes are placed within the squares.

pedigree

shows why hemophilia is referred to as "the royal disease."

Autosomal dominant.

An individual with AA has the disorder.
An individual with Aa has the disorder.
An individual with aa does NOT have the disorder.

autosomal recessive.

An individual with AA does NOT have the disorder.
An individual with Aa does NOT have the disorder, but is a carrier.
An individual with aa DOES have the disorder.

carrier

an individual who carries one deleterious allele for an autosomal recessive disorder

ABO blood types

The alleles:
IA antigen on red blood cells, anti

Codominance

A condition in which neither of two alleles of a gene is dominant or recessive.

incomplete dominance

Situation in which one allele is not completely dominant over another allele

incomplete dominance points

Heterozygote has a phenotype intermediate between that of either homozygote.
Homozygous red has red phenotype.
Homozygous white has white phenotype.
Heterozygote has pink (intermediate) phenotype.
Phenotype reveals genotype without a testcross.

Pleiotropy

occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits.

Polygenic Inheritance

Occurs when a trait is governed by two or more sets of alleles.
Each dominant allele has a quantitative effect on the phenotype.
These effects are additive.
It results in continuous variation of phenotypes within a population.
The traits may also be affected by the environment.

X

linked

X

linked disorders

DNA contains

adenine, guanine, cytosine, thymine

the two nucleotides with pyrimidine bases

Thymine (T) and Cytosine (C)

double helix

Shape of DNA similar to a twisted ladder

RNA nucleotides are of four types

Uracil (U), Adenine (A), Cytosine (C), Guanine (G)

Uracil (U) replaces

Thymine (T) in DNA

pre

mRNA transcript

RNA polymerase

connects the loose RNA nucleotides together.

Pre

mRNA is composed of exons and introns.

Exons

Coding segments of eukaryotic DNA.

Introns

Noncoding segments of nucleic acid that lie between coding sequences.

Pre

mRNA is composed of exons and introns.

DNA replication

the process of copying a DNA molecule.

Semiconservative replication

Each strand of the original double helix (parental molecule) serves as a template (mold or model) for a new strand in a daughter molecule.

temple

mold or model

Messenger (mRNA)

takes a message from DNA in the nucleus to the ribosomes in the cytoplasm