Bio HL1 Test 5 - Kim

organisms with a different chromosome number could struggle during meiosis due to

inability to produce homologous chromosomes, resulting in no or infertile offspring; e.g. horse (64) + donkey (62) → infertile mule (63)

chromosomes are not indicative of

genetic complexity

changes in chromosome number are

rare

most eukaryotes have ____ # of chromosomes

even

even number of CHR is a result of

sexual reproduction—fusion of gametes (n) → zygote (2n)—actual CHR number is unimportant, as long as all species have same #

Genome

total genetic info of a cell or organism

genome is measured using nuclear DNA content of

a haploid cell (gamete), as mass in picograms, as number of base pairs in megabase pairs

genome contains genes, or functional units; members of same species have same

genes; in same order, on same CHR, allowing crossing over during meiosis which increases diversity

diversity exists in alleles

through variation of genes, differing in one or few bases

single-nucleotide polymorphisms

main factor that causes uniqueness in humans

genome size—larger genomes carry more non functional DNA; in humans,

half of the human genome contistrs of transposons, refered to as “junk DNA”

base sequence

varies in number and types of genes—greater difference exists in populations that diverged longer ago, sequence of vital genes w/ stable functions won’t change (Cytochrome C)

Karyotype

Individual’s complete set of chromosomes

Karyogram

Picture of a karyotype—induce and arrest mitosis during metaphase, and stain chromosome to be photographed—chromosomes are arranged by homologous pairs with sex chromosomes last

centromere position

centromere is special DNA that holds chromatids, and p arm is shorrter and q arm is the longer arm, genes are found at specific loci or position

binding pattern—determined by base sequence

specific genes can be identified by:

chromosome number, arm letter (p or q), and G band number

goals for genome sequencing

determine evolutionary origins

trace diverging pathways from common ancestors

conserve and protect biodiversity

understand pathogenic bacteria

control and prevent infectious disease

sequence as many individual human genomes

develop personalized medicine

knowing SNPs can predict health problems and prescribe better drugs

diploid organisms

sexually reproducing organisms

diploids are produced through

zygotes, through mitosis

to prevent CHR number from doubling each generation, meiosis is

reduction division by cutting CHR in half in gametes (2n → n)

Meiosis has TWO cellular divisions:

Meiosis 1 separates homologous chromosomes (2n → n)

Meiosis 2 separates sister chromatids (n → n)

Formation of zygote via fertilization restores

diploid number

Haploid vs Diploid

Haploid: Nucleus, cell or organism with a single set of CHR that are non-homologous—gametes or sex cells from meiosis

Diploid: Nucleus, cell, or organism with TWO sets of CHRs that are homologous (one from each parent), body or somatic cells derived by mitosis.

homologous chromosomes

CHR that carry matching genes, containing two alleles, one from each parent; homologous=same information

Maternal and paternal CHR pair

Same size, bonding pattern, centromere position, same genes at same loci, alleles may differ, separated during meiosis, follows interphase where DNA is replicated, consists of two divisions, interkinesis (second growth) occurs between the two phases without DNA replication

Prophase I

CHR condense, nuclear membrane disappears, homologous CHR connect at chiasma to form bivalents, crossing over occurs

Metaphase I

Spindles connect to CHR at centromeres, align bivalents along equator

Anaphase I

Spindles contract and split bivalent, homologous CHR move to opposite poles

Telophase I

CHR decondense, nuclear membrane reforms, cytoplasm divides (cytokinesis) via cleavage furrow, produces two haploid daughter cells

Prophase II

CHR condense, nuclear membrane disappears, no crossing over

Metaphase II

Spindles connect to CHR at centromeres, align them along equator

Anaphase II

Spindles contract and split sister chromatids, now CHR moves to opposite poles

Telophase II

CHR decondenses, nuclear membrane reforms, cytoplasm divides (cytokinesis) via cleavage furrow, produces four haploid daughter cells

recombination in meiosis

meiosis reshuffles alleles to produce new combinations, mutation can change base sequences to make new alleles, recombination together with mutation creates homologous CHR that are similar but not identical

Genetic diversity in meiosis is created thru

crossing over and random orientation of bivalents

crossing over (prophase I)

homologous CHR undergo synapsis to become bivalents (tetrads), exchanges CHR btwn non-sister chromatids, held together at chiasmata, produces new allele combinations, occurs at random positions, at least one crossover occurs per bivalent, but often more than one

bivalent

two homologous CHR crossing over

bivalents aligning randomly at equator in Metaphase I determines

which alleles enter which gamete in anaphase I, position of one bivalent doesn’t affect other bivalents

cytokinesis

division of cytoplasm btwn two daughter cells, beginning after nuclear division

cytokinesis in animals

actin and myosin form a ring around the cell’s equator, constricts to form a cleavage furrow, use centripetal force, forming periphery, moving towards center, once furrow meets, mother cell pinches apart in two

cytokinesis in plants

microtubules form phragmoplast, made of microtubules and actin, across equator, vesicles fuse together and form early cell plate, contains pectin and other cellulose precursors for cell wall, vesicle membranes form two layers and connect to membranes of daughter cells, creating middle lamella that cements two cell walls together

asexual budding in yeast

after nuclear division, small outgrowth forms, receiving a nucleus and small amnt of cytoplasm with essential organelles

oogenesis in humans

requires two divisions, creates one large cell and one small polar body; large cell becomes mature oocyte (egg) and ensures that fertilized ovum has sufficient resources to undergo embryonic development, polar bodies degenerate via apotosis—smaller cells survive only if they receive a nucleus and essential organelles like mitochondria

nondisjunction

CHR fail to seperate properly, producing gametes with aneuploidy

if during Ana I, 4 daughter cells affected

If during Ana II, 2 affected

If these gametes form a zygote, resulting offspring will have aneuploidy

Missing CHR often results in

Extra results in

Cell death due to lack of essential genes

Can be lethal, but also can survive w/ conditions like down syndrome

Down Syndrome (trisomy 21)

One parent has two copies of CHR 21, fertilization produces a zygote w/ 3 copies of CHR 21, leads to palmar crease, short stature, intellectual disability, and heart defects

Klinefelter Syndrome (XXY)

Taller than average, longer legs and shorter torso, broader hips than other boys, absent or delayed puberty, small dih and balls, enlarged breast tissue

Turner’s syndrome (XO)

Only viable monosomy, short, wide neck, broad chest, moles, arms that flare at elbows

DNA replication

Production of new, identical DNA to existing DNA

Replication is needed for

Reproduction - offspring need copies of parental DNA

Growth and tissue replacement - both require cell division and DNA must be replicated

Semiconservative model

Both original strands serve as templates for the new, produces DNA with one original parent strand and one new daughter strand, allows every new strand to be identical to old

Complimentary base pairing

Only complimentary bases (A-T, C-G) can be added to new strand, hydrogen bonds cannot form btwn non-complimentary bases, this is how polymerase recognizes and replaces mispairings

All nucleotides have ___ covalent bonds

2, except for those at ends

New nucleotides bind to

3’end, while phosphate groups are found at 5’ end

Deoxynucleoside Triphosphates (dNTPs)

Free floating dNTPs have 3 floating phosphates, DNA polymerase cleaves 2 phosphates and uses the NRG to form a phosphodiester bond at 3’ end

DNA polymerase needs a ___ ___ to attach dNTPs

3’ end

DNA polymerase can extend, but not

initiate replication (new DNA grows in 5’ to 3’ direction)

Helicase

seperates and unwinds DNA by breaking hydrogen bonds btwn nitrogenous bases, occurs at origins of replication, creates replication forks, two parental strands serve as templates

DNA primase

lays down short RNA primers (10-15 bp), provides a 3’ for DNA Polymerase III to bind to and add nucleotides

DNA Polymerase III

binds to a template strand at 3’ end of RNA primer, NEEDS a 3’ end, can extend but not initiate

covalently bonds complimentary DNA nucleotides, new chain grows in 5’ to 3’ direction, forms phosphodiester bonds btwn deoxyribose sugar of one nucleotide and phosphate of another

cleaves two phosphates off of dNTPs and uses the energy to create bonds

proofreads each nucleotide

DNA Polymerase I

functions as both an exonuclease and polymerase, removes RNA primers and replaces them with DNA nucleotides, cannot make 3’ to 5’ links, leaves a gap where a sugar-phosphate bond would be

DNA Ligase

covalently bonds sugar-phosphate backbone to form a continuous strand, also joins Okazaki Fragments

replication involves leading and lagging strand:

Leading: makes DNA continuously, grows towards replication fork (5’ → 3’), finishes faster, needs only one RNA primer

Lagging: Makes DNA discontinuously, grows away from fork, has to backtrack to add nucleotides, as fork moves away and exposes more of the template strand, produces Okazaki fragments, needs primers every 100-200 nucleotides

DNA proofreading

Occurs immediately after a wrong base has been added, once recognized, DNA Polymerase III moves back one nucleotide and inserts correct base

Polymerase Chain Reaction (PCR)

Automated method of DNA replication, generates large amounts of specific DNA in a short period of time, requires initial small quantity of DNA

Materials: DNA of interest, DNA primers, free nucleosides (dNTPs), Taq polymerase (derived from a hot spring bacteria), can function in high temp without denaturing

Temperature dependent PCR procedures

Denature - 95 deg C, separates DNA strands by breaking H-bonds

Anneal - 55 deg C, allows primers to bind

Elongate - 72 deg C, optimal temp for Taq polymerase, assembles new DNA strands

Gel electrophoresis

Separates DNA fragments according to length, place samples into wells in agar gel, neg charged phosphates travel towards positive electrode, shorter strands have less resistance to gel and travel farther, different sizes separate into bands as they travel in different speeds, gel is treated with dye to make bands (DNA) visible, banding pattern determined by DNA sequence and type of restriction enzyme used, size of DNA fragment is determined by comparing to known marker (ladder)

Satellite DNA

non-coding regions, or junk DNA, contains short tandem repeats (STRs), short sequences of DNA repeated a varied amount of times

STRs (short tandem repeats)

people vary in number and location, creating unique DNA profile (banding pattern), 13 or more STRs used in DNA profiling, excised using restriction enzymes and separated using gel electrophoresis

DNA profiling

collect DNA from blood or semen, amplify via PCR, cut all samples w/ same restriction enzyme, different STRs generate different fragment lengths, separate with gel electrophoresis, compare profiles (banding patterns)

Forensic investigation

To convict, a suspect’s DNA must 100% match DNA from crime scene, population size is considered when determining uniqueness of a profile

Paternity testing

Children inherit their chromosomes from both parents, all DNA fragments of a child must match either that of the mother or father

Asexual Reproduction

Involves one parent

Uses mitosis

Offspring are genetically identical

Adapted to stable ENV.

e.g. binary fission, budding, vegetative propagation

Asexual reproduction advantages

Produces genetically identical offspring by individuals that are adapted to an existing environment

Rapid reproduction (no mate needed), requires less energy

Sexual reproduction

Involves two parents (M and F), involves meiosis and fertilization

Offspring are genetically unique

May be better adapted to changing ENV.

e.g. internal or external fertilization, pollination

Sexual reproduction advantages

produces offspring with variation which increases adaptability to ENV changes

Reproductive system

Organ system responsible for creating offspring and passing on genetic information

Structures differ by gender unlike other systems

male reproductive system

testis—produces sperm and testosterone

epididymis—stores sperm until it matures and is ejaculated

scrotum—skin fold that holds testes at a lower body temp, allows sperm to survive

vas deferens (sperm duct)—muscular duct that propels sperm during ejaculation

seminal vesicle and prostate gland—secretes fluids with nutrients, prostaglandin and anticoagulating enzymes to form semen

bulbourethral gland—secretes alkaline fluid that neutralizes acidity in urine

penis—enters vagina for semen ejaculation

urethra—transfers semen and urine out of body via the penis

Female reproductive system

ovary—produces egg and estradiol/progesterone

fimbria—tissue that sweeps released oocyte into oviduct

oviduct/fallopian tube—carries oocyte/embryo to uterus, site for fertilization

uterus—muscular organ where embryo develops

endometrium—inner lining of uterus, thickens in prep. of implantation, lost during menstruation

cervix—neck of uterus, protects fetus during pregnancy, dilates for childbirth

vagina—birth canal

vulva—outer area that protects internal reproductive organs

puberty

biological transition from childhood to adulthood marked by secondary sexual characteristics and reproductive maturity, regulated by hypothalamus-pituitary-gonadal (HPG) axis

hypothalamus secretes increasing amounts of gonadotropin-releasing hormone (GnRH) in childhood

stimulates anterior pituitary to release gonadotropins (luteinizing hormone—LH, and follicle-stimulating hormone—FSH)

Sex hormones in puberty

Estrogen and progesterone (both from ovaries):

Development of secondary sex characteristics (body hair, breast development), regulation of menstrual cycle

Testosterone (from testes):

Development of secondary sex characteristics (facial/body hair, muscle mass, deep voice), growth of testes and penis, initiation of sperm production

menstrual cycle

produces an ovum (egg) which allows pregnancy, begins in puberty and ends in menopause, lasts for ~28 days

Ovarian cycle—follicular phase (Days 1-14)

purpose: growth and maturation of follicles

FSH stimulates follicle growth → releases estradioll

estradiol releases more FSH and begins LH (positive feedback), which inhibits FSH at higher levels (not yet)

Ovarian cycle—ovulation (Day 14)

purpose: release of oocyte from follicle

LH surge causes ovulation, positive feedback with FSH/LH ends when follicle ruptures, inhibits FSH (negative feedback)

Ovarian cycle—luteal phase (15-28)

purpose: LH converts ruptured follicle into corpus luteum

corpus luteum → progesterone + some estrogen

progesterone thickens and maintains endometrium (inner lining of uterus)

with estradiol, inhibits FSH/LH (negative feedback), prevents development of new follicles

Uterine cycle—menstrual phase (1-5)

purpose: drop in progesterone and estrogen sheds endometrium

if fertilization doesn’t occur, corpus luteum → corpis albicans

no corpus luteum → less progesterone and increased FSH which begins cycle

Uterine cycle—proliferative phase (6-14)

purpose: regrow endometrial lining

if fertilization occurs, embryo releases hormones to sustain the corpus luteum

corpus luteum → progesterone → thickens and maintains endometrium for pregnancy

Uterine cycle—secretory phase (15-28)

purpose: endometrium prepares for implantation

increase blood supply and glandular secretion, progesterone maintains uterine lining

gametogenesis

process in which diploid cells become haploid (n) gametes

in males, sperm is made through spermatogenesis

in females, egg is made through oogenesis

BOTH involve mitosis/meiosis differentiation

spermatogenesis

production of spermatozoa (sperm)

location: seminiferous tubules of the testes

spermatogenesis as a continuous process

during puberty, spermatogonia (2n germ cells) continuously undergo mitosis

grows/matures into primary spermatocytes (2n)

after meiosis I, forms two secondary spermatocytes

after meiosis II, forms four spermatids

during differentiation, acquires a tail and becomes spermatozoa

detach from Sertoli cells (mother cells that provide nutrients for spermatids) and move out of testes

Oogenesis

Production of ova/ovum (egg)

location: ovaries

Oogenesis as a discontinuous process

Before birth, oogonia (2n) continuously undergo mitosis

grows/matures into primary oocytes

enters prophase I and pauses until puberty

during puberty, one primary oocyte completes meiosis I during each menstrual cycle

forms one larger secondary oocyte (n) (all cytoplasm)

enters meiosis II and pauses until fertilization

forms one smaller polar body, eventually degenerates due to unequal division of cytoplasm

during ovulation, secondary oocyte is released and enters oviduct

if fertilized, meiosis II is completed

forms ovum and another polar body via unequal division of cytopasm

differences between male and female gametes

Males: millions of sperm (small, motile), produced in testes via spermatogenesis, released continuously

Females: limited numbers of ova (large, sessile), produced in ovaries via oogenesis, released cyclically

Gamete structure and adaptations (M)

M: sperm is streamlined for motility, head—haploid nucleus, acrosome with enzymes to degrade jelly coat of egg, paired centrioles needed by zygote to begin mitosis, minimal cytoplasm, midpiece—large amounts of mitochondria to fuel movement via ATP, tail—large flagellum for motility, made of microtubules

Gamete structure and adaptations (F)

Egg contains a large amount of cytoplasm with nutrients, zona pellucida—follicular layer that provides structural support, cortical granules—released during fertilization to prevent polyspermy

Hormone regulation (M/F)

M: testosterone regulates spermatogenesis and secondary sexual characteristics (muscle, body hair)

F: estrogen and progesterone regulate ovarian and menstrual cycles and secondary sexual characteristics (breast development)

Reproductive roles (M/F)

M: produce and deliver sperm for fertilization

F: produce eggs, provide site for fertilization, and support embryo development

Fertilization

fusion of haploid sperm and egg to form a diploid zygote

Sperm transport and capacitation

transport—sperm travels through female reproductive tract (vagina → cervix → uterus 0 → fallopian tubes)

capacitation—membrane undergoes biochemical changes that enhance sperm’s motility and ability to penetrate egg, enzymes in female reproductive tract heighten sperm’s permeability to Ca2+