Biology Exam 4

Lifes unique feature:

ability to reproduce

Reproduction is…

cell division

Cell division in single-celled organisms:

Cell division creates new organisms

Cell division in multicellular organisms:

Cell division causes embryonic development and growth

renews and repairs tissues

How does one parent cell give rise to two genetically identical daughter cells?

When the cell divides, it copies its DNA

Transmission of copied DNA causes heredity

Heredity =

the resemblance between parents and offspring

Where is DNA located in Eukaryotic cells?

Nucleus

All DNA in cell makes up the cells…

genome

Genome consists of either:

1. a single DNA molecule (Prokaryotes)

2. many DNA molecules (Eukaryotes)

Chromosome is composed of?

chromatin

DNA molecules are packaged into…

Chromosomes

Chromatin:

a complex of DNA and protein that condenses during cell division

DNA & Protein —> ? —> ?

DNA & Protein —> Chromatin (relaxed DNA) —> Chromosomes (Condensed in cell division)

Chromatin is what kind of DNA?

relaxed DNA

Chromatin is DNA in what stage?

in uncondensed form during DNA replication

Chromosomes are what kind of DNA?

Condensed DNA

Chromosomes are DNA in what stage?

condensed DNA in mitosis or meiosis

Chromatid:

1 DNA molecule wrapped around many proteins

one of two identical halves of a duplicated chromosome

Chromatids: after DNA replication is makes?

2 identical sister chromatids

Sister Chromatids:

DNA after replication ; identical copies of chromatin

1 Chromosome =

1 Chromatid

1 Chromosome replicated =

2 identical chromatids

Cohesins:

proteins holding sister chromatids together at centromere

Homologous Chromosomes

2 versions of each chromosome

same genes in same locations

same size

NOT identical → different versions of same genes

Are homologous chromosomes identical?

No

same type of chromosome but have different version of genes

Diploid:

cells with 2 versions of each chromosome

Haploid:

cells with only 1 version of each chromosome

Why homologous?

2 Parents

one homologue from mom and the other from dad

Egg and sperm

Diploid Zygote:

one homologue from egg

one homologue from sperm

formed after fertilization

Humans have how many chromosomes?

23 pairs of chromosomes

46 total chromosomes

Each sperm and egg carries how many chromosomes?

23 each

The 23rd chromosome =

Sex chromosome (X or Y)

What is M chromosome?

Mitochondrial DNA

Inherited solely from mother

Somatic Cells:

non-reproductive cells

diploid (two versions of each chromosome)

Gametes:

reproductive cells

sperm & eggs

haploid (1 version of each chromosome)

Cell division occurs through two main processes:

• Mitosis → makes regular body cells

• Meiosis → makes sex cells like sperm and eggs

Cell Cycle 2 Main Phases:

1. Interphase

2. M Phase (Mitosis or Meiosis)

Cell Cycle for Mitosis:

1. Interphase → cell grows, prep for cell division, chromosomes duplicate, DNA copied

2. Mitosis → chromosomes copies are separated and moved to opposite ends of cell

3. Cytokinesis → cell divides into two daughter cells, genetically identical to each other and parent

Interphase: 3 main stages

1. G1 phase

2. S phase

3. G2 phase

G1 phase:

metabolic activity and growth

no DNA replication

S phase:

metabolic activity, growth , and DNA synthesis

DNA replication

G2 phase:

metabolic activity, growth, and preparation for cell division

G0 phase:

non-dividing cells stay here

• muscle cells

• neurons

• red blood cells

• sperm, egg

Interphase:

longest part of cell cycle

preparing cell to divide

Mitotic (M) Phase: 2 main stages

1. Mitosis

2. Cytokinesis

Mitosis:

Single cell divides into two genetically identical daughter cells

Dividing sister chromatids from each chromosome into two separate daughter cells

Cytokinesis:

Division of cytoplasm to producing two daughter cells

• final step of cell division

Difference between mitosis and cytokinesis?

• Mitosis = divides the cell's nucleus and genetic material (DNA)

• Cytokinesis = divides the cytoplasm and physical cell body into two separate cells

5 Stages of Mitosis:

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase

IPPMAT (including interphase)

In interphase (S) when DNA is replicated DNA is in what form?

uncondensed chromatin form.

Prophase:

DNA condenses

• into chromosomes made of two identical sister chromatids joined at the centromeres

Spindle forms

• centrosomes move toward opposite ends (poles) of the cell, extending protein fibers that build the mitotic spindle

Prometaphase:

Nuclear envelope breaksdown

• absorbed by ER

Kinetochore formation

• proteins assemble at centromere of each sister chromatid (2 each facing opposite directions)

Kinetochore microtubule formation

Metaphase:

(Middle Alignment)

Chromosomes line up on metaphase plate

Anaphase:

(Apart)

Sister chromatids separate

Movement to poles

• once each individual chromatid is separated = a full chromosome

Telophase:

(Two New Nulcei)

Chromosomes arrive

• Two complete, identical sets of chromosomes reach opposite poles of the cell

Nuclei reform

• New nuclear envelopes build around each set of chromosomes, creating two distinct nuclei inside one elongating cell

DNA relaxes

• tightly packed chromosomes uncoil back into loose chromatin, and the mitotic spindle breaks down

Prokaryotes reproduce by…

Binary fission

• NO MITOSIS

Binary fission:

1. chromosome replication begins

2. one copy of origin is now at each end of cell

3. replication fisnihes

4. two daughter cells result

Heredity:

transmission of traits from one generation to the next

Meiosis: in relation to heredity

the cellular process underlying all patterns of heredity in sexual species

Meiosis is the mechanism of …

genetics

Genetics is the study of …

heredity

3 Main Stages of Meiosis:

1. Interphase

2. Meiosis 1

3. Meiosis 2

Gametes (sperm & eggs)→

carry genes, passing them from parent to offspring

Fertilization:

joining of two gametes to form zygote

Meiosis produces

gametes

Meiosis:

process separates homologous chromosomes to transform a diploid cell into haploid gametes

Diploid Cell:

2n

two sets of homologous chromosomes

• 2n = 46

Haploid Cell:

n

lack homologous chromosomes

• n = 23

Karyotype:

an ordered display of the pairs of chromosomes from a cell

Human Somatic cells have:

• 22 pairs of autosomes

• 1 pair of sex chromosomes

Sex Chromosomes:

• help determine sex of individual

• Females = pair of X

• Males = one X and one Y

Autosomes:

remaining 22 pairs of chromosomes

Sex Determination:

Default pathway = female

SRY Gene (sex-determining region Y)

• causes embryo to develop as male

SRY Gene:

• Initial trigger of male development

• Typically located in Y chromosome

• can be present but inactive

SRY Gene : Process

• SRY Trigger :: SRY gene on the Y chromosome turns on → synthesizes SRY protein

• SOX9 Activation :: This protein turns on the SOX9 gene (chromosome 17) → takes over as main builder

• Testes Formation :: SOX9 stimulates development of testes

• Hormone Release :: Testes secrete male hormones (androgens)

• Receptor Binding :: Hormones bind to Androgen Receptor Gene (on X chromosome)

What if SOX9 gene is non-functional?

SRY protein has no effect

• failure to build testes

• default to female

What if Androgen Receptor Gene is non-functional?

Testes still form

Develops as female

BUT no ovaries, uterus, or fallopian tubes

Biological Definition of Sex:

Females produce eggs

Males produce sperm

Sex is NOT defined by:

• Sex chromosomes

• Presence/absence of genitals

• Hormone levels

Sex:

physiological

• female → eggs

• male → sperm

Gender:

Behavioral & culturally defined

Meiosis does…

reduces number of chromosome sets from diploid to haploid

• 1 Diploid cells → 4 Haploid cells

Meiosis begins after ?

DNA chromosome duplication (like mitosis)

Meiosis 1 does ?

Separates homologous chromosomes

• chromosome reduction (key step of meiosis)

Meiosis 2 does ?

separates sister chromatids

identical to mitosis

Meiosis 1 : 4 phases

1. Prophase 1

2. Metaphase 1

3. Anaphase 1

4. Telophase 1 & cytokinesis

Meiosis 1 : 4 phases

1. Prophase 2

2. Metaphase 2

3. Anaphase 2

4. Telophase 2 & cytokinesis

Meiosis : Prophase 1 →

• chromatin condenses into chromosomes

• matching homologous chromosomes pair up tightly

• crossing over - swap DNA

• nuclear envelope breaksdown

• spindles form

Meiosis : Metaphase 1 →

Homologous chromosome pairs line up side-by-side along the center of the cell (metaphase plate)

Meiosis : Anaphase 1 →

• Spindle fibers pull the homologous chromosomes apart toward opposite poles of the cell

• The sister chromatids remain attached to each other at their centromeres

Meiosis : Telophase 1 & Cytokinesis→

• separated chromosomes arrive at opposite poles

• nuclear envelopes may briefly reform

• cytoplasm divides to create two haploid cells (each chromosome still consists of two joined sister chromatids)

• cleaves furrow

Prophase 1 why is it interesting in meiosis?

• crossing over

• synapsis → when homologous chromosomes pair up tightly (4 group)

• Chiasmata → bridge where DNA is exchanged and keep homologues together until Anaphase 1

Chiasmata:

formed in Prophase 1

Bridge where DNA is exchanged

Keep homologues together until Anaphase 1

Crossing Over:

in meiosis 1

produces recombinant chromosomes which combine DNA inherited from each parent

Comparison of Mitosis and Meiosis:

Mitosis -

• produces 2 genetically identical daughter cells

• diploid parent → diploid daughter cells

Meiosis -

• produces 4 genetically variable daughter cells

• diploid parent → haploid daughter cells

3 Events Unique to Meiosis:

all in meiosis 1

1. Synapsis & Crossing over in Prophase 1 ; also form chiasmata

2. Alignment of homologous pairs at metaphase plate in Metaphase 1

3. Separation of homologues in Anaphase 1

Mendel’s Pea Plant Expt:

conducted controlled crosses

Conclusions of Mendel’s Expt:

• traits transmitted from parent to offspring as genes

• every individual has 2 genes for each trait

• every individual passes only 1 gene for each trait to offspring

Why do individuals carry 2 genes for each character?

they are diploid

Why is only one gene from each parent transmitted to offspring?

meiosis