IB HL BIO YR 1 UNITS EIGHT & NINE

reproduction

fundamental aspect of life

the way by which organisms pass on their genes to future generations

ensures the continuity of their species

asexual reproduction

involves one parent and multiple offspring

seen in bacteria, fungi, many plants, and some animals, but there are different methods

normally involves mitosis followed by cell division

ensures that a large number of offspring can be produced within a relatively short period of time

less costly in terms of energy and time

binary fission

type of asexual reproduction

an organism divides into equal halves

results in two separate organisms

budding

type of asexual reproduction

a new individual organism develops as an outgrowth or bud from the parent organism and eventually detaches

fragmentation

type of asexual reproduction

the parent organism breaks into fragments and each fragment develops into a new organism

parthenogensis

type of asexual reproduction

reproduction from an ovum without fertilization

sexual reproduction

two parents

union of specialized gametes, one from each parent

offspring are similar but not genetically identical to parents or each other

very expensive in terms of time and energy

fusion of two haploid gametes to form a diploid zygote

advantages to sexual reproduction

results in genetic variation

more genetic diversity

better adapted to a changing environment

higher survival rates

gametes

sex cells

fuse during fertilization

produced by meiosis

cell cycle

Sequence of events that a cell undergoes, including growth, DNA replication, nuclear and cytoplasmic division

Two Parts: Interphase & Mitotic Phase

centrosomes

a type of Microtubule Organizing Center that contains centrioles

in animal cells

organize spindle fibers

kinetochore

motor proteins that are located in the centromere region

helps spindle fibers to move the chromosomes

spindle fibers

made of microtubules

responsible for movement of chromosomes during mitosis

dna packaging

each cell contains 2 meters of DNA within nucleus

DNA must be packaged so it can fit

nucleosome

stretch of dna

wrapped around a core of 8 histone proteins (2 copies of each: H2A, H2B, H3, & H4) and a 9th hostine (H1) holds DNA around it

linker DNA

stretch of DNA not wrapped around histones

connect nucleosomes

chromatin

loosely packaged DNA found in non-dividing cells

chromosome

tightly wound DNA found in actively dividing cells

can be duplicated or unduplicated

makes genes inaccessible (no transcription/gene expression)

cell proliferation

the process by which a cell grows and divides to produce two daughter cells

cell proliferation in unicellular organisms

asexual reproduction because it makes a whole new cell/organism

reasons for cell proliferation in multicellular organisms

growth (increase size/complexity of organisms by making more cells, ex: embryotic development)

cell replacement (helps to maintain healthy tissues and replace dead cells that are lost)

tissue repair (wound healing requires more cells to be made)

gap one (G1)

first part of interphase

involves cell growth and normal metabolic functions (protein synthesis)

cells double in size

mitochondria and chloroplasts divide using binary fission

synthesis (s)

second part of interphase

DNA is replicated

semi-conservative

gap two (G2)

third (and final) part of interphase

continued growth

synthesis of microtubules and other proteins necessary for cell division

centrosomes are duplicated

mitosis

part one of mitoic phase

division of the nucleus

four phases: prophase, metaphase, anaphase, and telophase

prophase (mitosis)

chromatin condenses → duplicated chromosomes (replicated in s phase)

nuclear membrane breaks down

spindle fibers form

plant cells use microtubule organizing centers (MTOCs) to organize spindles

animal cells use centrosomes (special MTOCs) to organize spindles

MTOCs migrate to cell’s poles

metaphase (mitosis)

part two

duplicated chromosomes line up alone the metaphase plate (middle of the cell)

spindle fibers attach to chromosomes at the kinetochore

anaphase (mitosis)

part three

centromere splits

sister chromatids separate and move away from each other towards poles

spindle fibers cause this chromosome movement

telophase (mitosis)

part four

chromosomes decondense → chromatin (1/2 of the X)

nuclear membrane forms around the 2 new nuclei

spindle fibers disassemble

cytokensis (mitosis)

part five

division of cytoplasm

parent cell → two daughter cells

can be simultaneous with telophase

happens different in animals and plants

cytokenisis in animal cells

actin and myosin proteins form at the contractile ring (center of cell)

ring pinches the cell membrane in and forms a cleavage furrow

furrow depends and eventually splits cells

goes from outside in

cytokenisis in plant cells

vesicles with cell wall material assemble in the cell plate (center of cell)

grows outwards from middle and eventually forms a cell wall between the 2 daughter cells

goes from inside out

binary fission

type of cell division done by prokaryotes (and mitochondria and chloroplasts)

produces genetically identical cells so does not increase genetic diversity (except for mutations)

g1 checkpoint

determines if the cell will eventually go on through the rest of the cell cycle

go signal here means cell can continue

stop signal here means cell exits the cycle and enters g0

g0

occurs after stop signal at g1 checkpoint

phase where cell is not preparing to divide

some can re-enter cell cycle

others cant re-enter → terminal _____

g2 checkpoint

checks if the cell has grown enough, if DNA is fully replicated, and if the cell has produced enough energy/proteins/organelles/etc to prepare for cell division

go signal means cell can enter mitoic phase

m checkpoint

occurs during mitosis metaphase

checks to make sure all chromosomes have attached to spindle fibers and are lines up at metaphase plate

go signal means cell can enter anaphase

external regulators

signals at checkpoints

respond to events outside of the cell

often directs cell cycle to speed up or slow down

ex: grow factors, anchorage dependence, density dependent inhibition

growth factors

important group of external regulatory proteins

stimulate growth/division of cells

important for embryotic development and wound healing

anchorage dependence

cells must be attached to a substratum to divide

most animal cells

density dependent inhibition

crowded cells stop dividing

prevents excess cell division (and eventually cancer)

internal regulators

signals at checkpoints

respond to events inside cell

allows cell cycle to proceed only when certain events have occurred

ex: cyclins and CDKs

cyclins

family of proteins

regulate cell cycle by activating CDKS by binding to them and creating a _____-CDK complex

different ______ accumulate during different parts of the cell cycle which activate different CDKs at different times

cyclin dependent kinases (CDKs)

enzymes that (when activated) phosphorylate proteins to progress the cell cycle

always present

not always active

proto-oncogenes

genes that code for proteins that help promote cell growth and division

mutations to these can lead to uncontrolled cell division

oncogene

mutated proto-oncogen

can lead to proteins being over expressed → uncontrolled cell division → cancerous cell growth

tumor suppressor genes

genes that code for proteins that normally slow down/prevent cell division

mutations in these can lead to malfunctioning proteins → uncontrolled cell division

can trigger apoptosis

apoptosis

programmed cell death

caused by tumor suppressor genes

benign tumors

abnormal growth of cells that are not cancerous

grow slowly

well defined margins

don’t metastasize

could cause issues depending on size/location

treatment: surgery

malignant tumors

cancerous abnormal growth of cells

grow and divide more rapidly

lack well defined margins

undergo metastasis

treatment: surgery, radiation, chemotherapy

metastasis

the development of secondary malignant growths away from primary cancer site

primary tumor

original tumor

benign/malignant

secondary tumor

tumor that forms in new location after metastasis

only malignant

mitotic index (MI)

measure of proportion of actively dividing cells in a population

value is 0-1

more cell division = higher MI (doesn’t always mean cancerous, could be embryo development, epithelial cell or meristem cell)

cells in mitosis / total cells

purposes of reproduction

organisms pass genes on to future generations

ensure continuity of species

necessary for natural selection

asexual reproduction advantages

large # of offspring produced in little time (good in stable environments if organism is well adapted)

less time/energy/resources/complex

asexual reproduction disadvantages

doesnt increase genetic variation/diversity (if environment changes species could be wiped out)

bad mutations are widespread

sexual reproduction

production of genetically different offspring from 2 sources of genetic information

offspring inherit some genetic info from each source

occurs in multicellular plants/animals

sexual reproduction disadvantages

fewer organisms produced in a longer time

more time/energy/resources/complex

harder to do (gametes must fuse)

sexual reproduction process

1. production of gametes (meiosis)

2. fertilization (fusion of two haploid gametes → diploid zygote)

   1. development of offspring (cell proliferation)

sources of genetic variation

crossing over (MI)

independent and random assortment of homologous chromosomes (MI)

random fertilization (gamete fusion)

diploid cells

2 copies of each chromosome

ex: somatic cells

haploid cells

one copy of each chromosome

ex: gametes

duplicated chromosome

one chromosome in an X shape

sister chromatids attached at centromere

homologous chromosomes

chromosomes within a pair of diploid chromosome

same length/gene loci/centromere location

ex: human chromosomes 1-22

meiosis

gamete cell division

produces four unique haploid gametes

reproduction division

1 diploid → 4 haploids by separating homologous chromosomes

prophase I (meiosis I)

nuclear membrane breaks down

spindle fibers form

MTOCs move away from each other, towards opposite poles

chromatin condenses into duplicated chromosomes

homologous chromosomes pair up during synapsis → tetrads/bivalents

crossing over occurs

crossing over

non sister chromatids exchange equal length DNA segments

happens at the chiasmata

created recombinant chromatids

metaphase I (meiosis I)

tetrads line up at metaphase plate

independent assortment (random orientation towards poles)

spindle fibers attach to kinectochores

anaphase I (meiosis I)

homologous chromosomes separate (because of spindle fibers)

sister chromatids stay connected at centromere

telophase I (meiosis I)

homologous chromosomes reach cell’s poles

chromosomes decondense to chromatin

nuclear membrane forms around 2 new haploid nuclei

spindle fibers break down

cytokenisis I (meiosis I)

produces 2 daughter cells

Haploid with duplicated chromosomes

Non-identical (genetically unique)

interkenisis

post meiosis one

period of rest before meiosis two

no DNA replication

prophase II (meiosis II)

chromatin → chromosome

nuclear membrane breaks down

MTOCs move to opposite poles

spindle fibers form

no pairing of homo chromos

no crossing over

metaphase II (meiosis II)

spindle fibers attach to kinetochores and centromeres

duplicated chromosomes line up at metaphase plate (randomly orientated)

anaphase II (meiosis II)

centromerers split

sister chromatids split and move towards opposite poles because of spindle fibers

telophase II (meiosis II)

chromosomes reach opposite poles

chromosomes decondense to chromatin

nuclear membrane forms around 2 new haploid nuclei

spindle fibers break down

cytokinesis II (meiosis II)

produces a total of 4 daughter cells that are unique haploid gametes with unduplicated chromosomes

karyogram

image of an organisms chromosomesa

aneuploidy

presence of an abnormal number of chromosomes in a cell

caused by nondisjunction

ex: trisomy (3 copies of a chromosome), monosomy (one copy of a chromosome)

nondisjunction

created aneueploidy

failure of homologous chromosomes to separate during meiosis I or a failure of sister chromatids to separate during meiosis II

heredity

passing on of characteristics/traits from parents to offspring

why Mendel picked peas

sexually reproduce

can self pollinate

cross pollination can be controlled

short reproductive cycle

produce many offspring

alleles

different version of same gene

created by mutations to gene sequence (SNPs)

7 pea plant traits

flower/pod/seed color

seed/pod shape

flower position

plant height

true breeding

breeding between two homozygous organisms that are both dominant or both recessive

offsprings’ traits will always be the same

P generation

mendel’s experiment

2 true breeding plants with opposite traits

f1 generation

hybrids of p generation

all only exhibited 1 out of 2 versions of each trait

self pollinated to make f2 generation

f2 generation

exhibited both versions of traits in predictable ratios

mendel’s concepts

2 alleles within each organism, 2 copies of each gene (could be same or different allele)

each organism inherits 1 allele from each parent for each trait

dominant vs recessive alleles

law of segregation

law of independent assortment

law of segregation

alleles of each trait separate into each gamete

each gamete only gets one allele

b/c homologous chromosomes split in meiosis (unless nondisjunction)

genotype

combination of alleles for an individual

written with 2 letters for each trait to represent the 2 alleles on the homologous chromosomes

homozygous

2 copies of the same allele

can be dominant (AA) or recessive (aa)

heterozygous

1 copy of each allele

can only be dominant (Aa)

phenotype

expression of genes

physical characteristics

punnett square

statistical tool used to predict genotypic or phenotypic outcome

outside represents parents’ gametes

inside represents the possible offspring genotypes

recessive disorders

many are inherited in an autosomal recessive pattern

individual must be homozygous recessive to express it

ex: phenylketonuria (PKU)

phenylketonuria (PKU)

recessive disorder

caused by a mutation in a gene on chromosome 12

gene codes for PAH enzyme (converts Phe to Tyr)

mutation results in malfunctioning enzyme

Phe builds up to toxic levels and causes brain damage

carrier

someone who is heterozygous for a recessive disorder

law of independent assortment

each pair of alleles separates independently from each other

the way each tetrad lines up during metaphase I does not impact other tetrads