Bio 211 Exam 4

What happens during interphase?

Cell growth and the copying of chromosomes for cell division

Interphase is ___ of the cell cycle

90%

What are the phases of interphase?

G1 phase, S phase, G2 phase

Which phase are chromosomes duplicated in?

S phase

What are the subphases of the Mitotic phase?

Mitosis and Cytokinesis

Geneome

All DNA in a cell

Chromosomes

Packaged DNA molecules, DNA + histone protiens

Chromatin

complex of DNA and protein that condenses during cell division

Somatic cells

Non-reproductive cells with two sets of chromosomes, undergoes mitosis

Gametes

Reproductive cells with half as many chromosomes, undergoes meiosis

Sister chromatids

Joined copies of the original chromosome, attached by cohesins

Centromere

Narrow "waist" of a duplicated chromosome, where spindle fibers attach

Mitosis

Division of genetic material in the nucleus

Prophase

Chromosomes condense to form sister chromatids
Nuclear envelope breaks down
Spindle fiber attaches to chromatids

Metaphase

Lining up on the plate in the middle of the cell

Anaphase

Separation of sister chromatids

Telophase

Nuclear envelope returns, chromosomes condense

Cytokenisis

Division of the cytoplasm

Sequential events of the cell cycle are directed by:

Cell cycle control system

The cell cycle control system is regulated by

Internal and external controls

Where are the checkpoints?

G1, G2, and M phases

G1 Checkpoint

Checks for nutrients, growth factors, DNA damage

G2 Checkpoint

Checks for cell size, DNA replication

M checkpoint

Checks for chromosome spindle attachment

What happens if a cell does not receive the go-ahead signal?

Exits the cell cycle and switches into G0 phase

Regulatory proteins involved in cell cycle control

cyclin, cyclin dependent kinases (Cdks)

Activity of a Cdk rises and falls with:

Changes in concentration of its cyclin partner

Maturation-promoting factor (MPF)

Cyclin-Cdk complex that triggers a cell's passage past the checkpoint in the M phase

Internal signal: cells will not begin anaphase until

All chromosomes are attached to the spindle at the metaphase plate

External control factors

Growth factors
Density dependent inhibition
Anchorage dependence to divide

Growth factors

Released by certain cells to stimulate other cells to divide

Density dependent inhibition

Crowded cells will stop dividing

Anchorage dependence to divide

Cells must be attached to a substratum to divide

Cancer cells...

Do not respond normally to the body's control mechanisms

Cancer cells may

Not need need growth factors
Make their own growth factors
Convey a growth factor's signal without the presence of the growth factor
Have an abnormal cell cycle control system

Transformation

A normal cell is converted to a cancerous cell

Tumors

Cancer cells that are not eliminated by the immune system
Masses of abnormal cells within otherwise normal tissue

Benign Tumors

Abnormal cells remain only at the original site

Malignant tumors

Cells invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body

Genes

Units of hereditary, made up of segments of DNA

DNA is wrapped around ___ so that it can fit into the nucleus

Histone proteins

Somatic cells

All cells in the body except gametes

Locus

A gene's specific position along a chromosome

Karyotype

Ordered display of the pairs of chromosomes from a cell

Homologous chromosomes

Two chromosomes in a pair, which are the same length and shape and carry genes controlling the same inherited characteristic

Diploid cell (2n)

Two sets of chromosomes, 46 for humans

Each replicated chromosome consists of:

two identical sister chromatids

Haploid Cell

A gamete (sperm or egg) contains a single set of chromosomes, 23 for humans

Fertilization

the union of gametes

Zygote

Fertilized egg, has one set of chromosomes from each parent
Produces somatic cells by mitosis and develops into an adult

Meiosis takes place in two consecutive cell divisions:

Meiosis I and Meiosis II

The two cell divisions in meiosis result in

Four daughter cells

Each daughter cell has ___ as many chromosomes as the parent cell

Half

Sister chromatid cohesion

Sister chromatids are closely associated along their lengths

Meiosis I

Separates homologous chromosomes

Prophase I

Chromosomes have been replicated, homologous chromosomes found each other
Crossing over occurs

Chiasmata

X-shaped regions that are sites of crossovers

Synaptonemal complex

Zipper-like structure that holds homologous together tightly

What happens during synapsis?

DNA breaks are repaired, joining DNA from one non-sister chromatid to the corresponding segment of another

Metaphase I

Law of Independent Assortment
Homologous pairs line up at the metaphase plate

Anaphase I

Separation of homologs

Meiosis II

Separate sister chromatids

Anaphase II

Sister chromatids separate

Three mechanisms that contribute to genetic variation

Independent assortment of chromosomes
Crossing over
Random fertilization

Independent Assortment

Each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs

Number of combinations possible when chromosomes assort independently into gametes

2^n

Recombinant chromosomes

Produced by crossing over, which combine DNA from two parents into a single chromosomes

How does crossing over contribute to genetic variation?

Combines DNA from two parents into a single chromosome

How does random fertilization contribute to genetic variation?

Any sperm can fuse with any ovum

Character

A heritable feature that varies among individuals

Trait

Each variant for a character

Advantages of Using Peas

Short generation time
Large numbers of offspring
Mating could be controlled

Mendel used pea varieties that were:

plants that produce offspring of the same variety when they self-pollinate

P-generation

true-breeding parents

F1 Generation

hybrid offspring of the P generation

F2 Generation

F1 individuals self-pollinate or cross- pollinate with other F1 hybrids

Law of Segregation

When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly

The Law of Segregation contradicted the:

blending model of inheritance

#1 of Mendel's 4-part hypothesis on inheritance

Alternative versions of genes account for variations in inherited characters

#2 of Mendel's 4-part hypothesis on inheritance

For each character, an organism inherits two alleles, one from each parent

#3 of Mendel's 4-part hypothesis on inheritance

If the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance

#4 of Mendel's 4-part hypothesis on inheritance

Law of Segregation
the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes

Homozygous

An organism with two identical alleles for a character

Heterozygous

An organism that has two different alleles for a gene

Phenotype

Physical Appearance

Genotype

Genetic makeup

Crossing two true-breeding parents differing in two characters produces

dihybrids in the F1 generation, heterozygous for both characters

dihybrid cross

a cross between F1 dihybrids

What can a dihybrid cross determine?

whether two characters are transmitted to offspring as a package or independently

Mendel developed the Law of Independent Assortment by using a

dihybrid cross

Law of Independent Assortment

each pair of alleles segregates independently of each other pair of alleles during gamete formation

The Law of Independent Assortment only applies to genes

different, nonhomologous chromosomes

Genes located near each other on the same chromosome...

tend to be inherited together

Complete dominance

phenotypes of the heterozygote and dominant homozygote are identical

Incomplete Dominance

the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties, blending

codominance

two dominant alleles affect the phenotype in separate, distinguishable ways

Inheritance of characters may deviate from simple Mendelian patterns when:

alleles are not completely dominant or recessive
a gene has more than two alleles
one gene produces multiple phenotypes
multiple genes influence one phenotype

epistasis

a gene at one locus alters the phenotypic expression of a gene at a second locus
ex. in labs, one gene determines hair pigment color and another determines whether or not the pigment is depositied

Quantitative characters

Characters that vary in the population along a continuum

Quantitative variation usually indicates

polygenic inheritance