biology - UNIT 6: Genetics

Prophase 1

Chromosomes condense. Homologous chromosomes line up at the center of the cell and crossing over occurs. spindle fibres begin to show from centrosomes. synapsis occurs.

Metaphase 1

Homologous chromosomes randomly assemble at the metaphase plate. independent assortment occurs

Anaphase 1

Spindle fibres pull the homolous chromosomes apart. The sister chromatids are still attached.

Telophase 1 and cytokenisis

Sister chromatids arrive at the poles of the cell and begin to decondese. A nuclear envelope forms around each nucleus and the cytoplasm.

divided by cleavage furrow. result is 2 haploid cells.

Prophase 2

Sister chromatids condense. a new spindle begins to form. dissolution of the nuclear membrane

Metaphase 2

sister chromatids line up at the metaphase plate.

anaphase 2

sister chromatids are pulled apart into sepearate single chromosomes then uncoil into chromatin

Telophase 2 and cytokenisis

chromosomes arrive at the poles of the cell and decondense. nuclear envelopes surround the 4 nuclei.

cleavage furrows divide two cells into 4 haploid cells.

Diploid cells

2n - cell with two pairs oc each set of chromosomes.

Haploid cells

n - cell with one set of chromosomes

Zygote

A fertilized egg

Independent assortment

Chromosomes will split into daughter cells

Cross over

homologous chromosomes exchange genes

interphase

cell prepares for the next round of meiosis by duplicating chromosomes.

recombinant dna

Combination of two

asexual reproduction

• Asexual reproduction does not involve sex cells or fertilisation

• Only one parent is required so there is no fusion of gametes and no mixing of genetic information

• As a result, the offspring are genetically identical to the parent and to each other (clones)

• Asexual reproduction is defined as a process resulting in genetically identical offspring from one parent

• Only mitosis is involved in asexual reproduction

sexual reproduction

The formation of gametes involves meiosis. process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other.

as each gamete comes from a different parent, there is variation in the offspring

• The gametes of animals are the sperm cells and egg cells

Synapsis

The process of chromosome forming a tetrad (4 sister chromatids).

Internal fertilization and internal development

the process of fertilization that occurs inside the body of an individual. It occurs mostly in land animals. Requires union of gamete cells.

When embryo/fetus develops inside an animal's body.

ex: mammals

advantages: high chance of survival, more aftercare and less number of young

disadvantages: only happens in mammals, longer time taken for development of fetus or gamete.

External development and fertilization

a mode of reproduction in which a male organism's sperm fertilises a female organism's egg outside of the female's body. Nearly all fish reproduce this way, so do oysters.

When the embryo/fetus develops outside an animal's body.

ex: happens in amphibians and fish

advantages: time of development is shorter comparent to internal development (7days to 2 months)

disadvantages: aftercare period is low, resulting lesser chance of survival, number of young is too high contributing to low survival rate.

DNA REPLICATION - Semi Conservative process

DNA replication containing one original strand and one newly synthesized strand (the new strand is the template strand), ensures the fidelity of genetic information across generations by the combination of old and new dna replication.

Helicase

unwinds the DNA strands so two strands are sepearated

DNA Polymerase

an enzyme responsible for synthesizing new DNA strands by adding nucleotides to the growing chain during DNA replication.

What is DNA proofreading?

As DNA polymerase adds nucleotides to the new DNA strand, it proofreads the bases added. If errors occur, mismatch repair will take place. Enzymes remove and replace the incorrectly paired nucleotide

Transcription

The process during which a gene is copied to synthesize mRNA

Where does transcription occur?

nucleus (it has to occur in the nucleus because a DNA limitation is that DNA cannot leave the nucleus)

Translation

The process of reading instruction on an RNA molecule to put together amino acids that make a protein.

Where does translation occur?

ribosomes

RNA polymerase

the enzymes that transcribes a DNA sequence into RNA molecules

mRNA

synthesized during transcription from a DNA template. mRNA carries information from the DNA (@ the nucleus) to the ribosomes in the cytoplasm for translation

tRNA

brings specific amino acids to the ribosome for translation (protein productions)

Transcription Base Pairs (DNA—>mRNA)

A=U, C=G, T=A

Start codon

AUG—>Met

Stop Codons

UAA, UAG, UGA

The large ribosomal unit has three sites:

A site: amino acid site (holds the next tRNA carrying an amino acid)

P site: polypetide site (holds tRNA carrying growing poplypeptide chain)

E site: exit site

Large Scale Mutations

Chromosomal Changes (Ex: Trisomy 21/Down Syndrome)

Nondisjunction

Can lead to a large scale mutation ( a mutation that affects chromosomes). Nondisjuction are when chromosomes do not separate properly in meiosis.

Example: down syndrome

G, C have how many hydrogen bonds? Adenine, uracil, thymine?

3, 2

Prokaryotic vs. Eukaryotic transcription

prokaryotes use the same rna polymerase to trancribe all genes. while eukaryotic cells use multiple versions of mRNA and DNA to transcribe.

Prokaryotic transcriptions takes place in the cytoplasm while eukaryotic transcription in the nucleus.

Gene expression is present in both but on a larger scale in eukaryotic cells.

mRNA vs. DNA

mRNA contains an extra nitrogenous base called uracile which forms a pair with Adenine and lacks thymine.DNA is double stranded while mRNA is single.

Difference is important because the structure of mRNA complements the process of translation in a eukaryotic cell as well as DNA .

What might happen if a codon sequence is changed on mRNA?Whys accuracy important?

If the accuracy of codon sequences on mRNA is inaccurate, mutations take place thus resulting in a change in the amino acid sequence.

Mistake of DNA polymerase enzyme during DNA replication, effect?

Mismatching a base pair during DNA replication and not being able to correct through proofreading, the mistake will follow through during the whole process of protein synthesis resulting in wrongly transcribed mRNA and a wrong amino acid sequence. - mutation as a result

when does protein synthesis occur

before mitosis - interphase S.

What is DNA replication?

The process of replicating a double-stranded DNA molecule into two identical DNA molecules.

process of DNA replication

1. Double helix unwinds,

2. DNA helicase unzips the DNA so two strands are separated,

3. DNA polymerase attaches itself to the strand and adds complementary free nucleotides to both strands forming two brand new identical molecules,

4. twist to form two identical to original DNA double helix.

DNA Structure

made up of nucleotides containing phosphate, deoxyribose sugar, nitrogenous bases with complementary pairs and hydrogen bonds between each.

rungs are antiparallel, (ends of the strands are opposites)

translation

• mRNA then moves out of the nucleus and attaches to a ribosome

• The ribosome ‘reads’ the code on the mRNA in codons

• Each codon codes for a specific amino acid

• In this way the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein

• Once the amino acid chain has been assembled, it is released from the ribosome so it can fold and form the final structure of the protein

transcription - making the mRNA molecule

• DNA unwinds into two sepearate strands. one is used to make mRNA

• An enzyme called RNA polymerase is used to add complementary nucleotides to the new mRNA strand. mRNA is made.

• mRNA leaves nucleus through nuclear pores

• mRNA reaches ribosomes through the cytoplasm.

spermetogenisis

process of creating sperm

oogenisis

process of creating eggs.

main organs of the female reproductive system

uterus, fallopian tubes, ovaries, vagina

Main organs of the male reproductive system

allele

a variant form of a gene that determines didferent expressions of a trait.

result of meiosis

4 genetically unique daughter cells each of which contain half the number of chromsomes the parent cell contains.

meiosis I vs. meiosis II

meiosis I results in two daughter cells with 2 chromatid each while meiosis II results in 4 genetically variant daughter cells with 1 chromatid each.