unit 4: Genetics & evolution

3 forms of DNA

1. DNA 2. Chromatin 3. Chromosome

Trophic level

an organism’s relationship to energy and means of consuming; grouped by shared characteristics

Gonads

organs that produce gametes (both XX and XY)

Ducts

tubes that deliver + store gametes (both XX and XY)

ovaries

XX: gonad; store follicles that contain dormant eggs (watiing to be stimulated by a hormone to release an egg to develop through meiosis0

uterus

XX: womb; site of pregnancy; where embryo develops; contains many blood vessels to nourish fetus; very muscular (allows for expansion)

after how long is an embryo called a “fetus”

8 weeks

Cervix

separation between uterus and vagina

vagina

muscular chamber; serves as birth canal; repository for sperm during sex

vulva

collective term for external genitalia; protects internal reproductive system

Fallopian tubes

connect ovary to uterus; location where sperm + egg meet (“fertilization”); ducts

Differences b/w mitosis and meiosis

• 4 non-identical cells vs 2 identical daughter cells

• Meiosis when homologous pairs align, they are stacked (not linear) → whole pairs are separated from each other during A1 (not separate chromatids until A2)

What types of cells can undergo Meiosis vs Mitosis

Meiosis: germ cells (produce sperm / egg)

Mitosis: somatic cells (typically body cells)

3 parts of a chromosome

Chromatid: identical half of chromosome

Centromere: point of attachment b/w sister chromatids ( attached to spindall fibers during cell division )

Telomere: protective caps on ends of chromatids

n [haploid #]

½ normal amount of DNA (found in gametes, 23 chromosomes; 23 unique chromatids)

2n [diploid #]

Normal amount of DNA, 46 chromosomes (23 homologous pairs); 46 unique chromatids

4n [tetraploid#]

Double normal amount of DNA, only during cell division, 46 chromosomes; 46 pairs of sister chromatids = 92 total chromatids

Heredity

Passing down traits through reproduction (sexual asexual) fromto parent offspring generation

Gene

Basic unit of heredity (section of DNA that codes for a particular protien) • proteins give individuals + cells (thrnough gene expression ) their unique characteristics

Allele

One of the possible forms a particular gene can take

Genotype

Coded DNA (alleles) an organism has

Phenotype

How the combo of alleles presents itself in the traits you have (physical traits / appearance)

Homozygous

When an organism has 2 of the same alleles for a given trait

Heterozygous

When an organism has 2 different alleles for a given trait

Mendel'S 4 principles of genetics

Factors, dominance, segregation, independent assortment

Mendel'S principle of factors

2 “factors” (alleles) control for each trait; 1 factor came from each parent

Mendel'S principle of dominance

• Options for each factor (allele) that determine characteristics

• Dominant →”masks” other traits (always expressed)

• Recessive → masked by dominant (only shows up when alone)

Mendel'S principle of segregation

Factors (alleles) of the parents split during reproduction merits bring factor from each parent) [get either, R or r from Rr in a parent)

Phases of the cell cycle

G0, Interphase (G1, S G2), Mitosis (PMAT), Cytokenesis

Cell cycle: G0 phase

regular cell activity

cell cycle: Interphase- G1 phase

cell grows in volume to prep for division; organelles duplicated + more cytoplasm

• 2n

• DNA in chromatin form

cell cycle: Interphase- S phase

DNA is duplicated (chromatin form)

• 4n

cell cycle: Interphase- G2 phase

cell keeps growing; centrioles form

• 4n

Cell cycle: Mitosis- Prophase

DNA goes to chromatid form (1 chromosome = 2 chromatids); nuclear envelope starts dissolving; centrioles start making spindle fibers (only in animal cells)

Cell Cycle: Mitosis- Metaphase

centromeres of chromosomes line up across middle of cell; spindle fibers attach to centromeres

• spindle fibers pushing against each other to elongate the cell

Cell cycle: Mitosis- Anaphase

sister chromatids separate; spindle fibers pull them to opposite sides of cells (phase ends when sister chromatids are in 2 equal groups at opposite ends of the cell)

• spindle fibers pushing against each other to elongate the cell

cell cycle: Mitosis- Telophase

nuclear envelope starts to reform; chromatids return to chromatin form

• spindle fibers pushing against each other to elongate the cell

Cell cycle: Cytokenesis

cell officially divides into 2 daughter cells

• 2n (each)

Mitosis

division of a cell into 2 identical daughter cells

Meiosis

Division of one cell into 4 non-identical daughter cells (n each)

• only for gametes

Chromosome condition for producing viable offspring

both parents must have same number of chromosomes (different species have different numbers which is why for ex a turtle cant breed with a duck)

Meiosis: Metaphase 1

Homologous pairs align (*stacked*) (random- top codes for different trait than bottom)

• 4n

Meiosis: end result of Telephase 1

top half now codes for different traits than bottom half → 2 non-identical daughter cells 2n each)

Meiosis: Metaphase 2

individual chromosomes, (each have two sister chromatids), align along the middle of the cell; spindle fibers attach (2n) x2

Meiosis: Anaphase 2

sister chromatids pulled to opposite ends of cell (2n) x2

name for general gamete production

gametogenesis

oogenesis

female gametogenesis: 1 cell → 4 gametes (1 viable egg + 3 polar bodies)

• occurs in the ovaries

oocyte

XX germ cell; dormant diploid or haploid (depending on stage) cell stored in every follicle of ovary

• ovulation: 1 oocyte stimulated every 28 days by FSH (follicle stimulating hormone) to start meiosis [at menopause FSH not signaling anymore]

• Primary oocyte = 2n, Secondary oocyte = n

testes

XY gonads; site of sperm formation; housed in scrotum (external)

• optimal temp. for sperm formation is 96 deg F (scrotum contracts / relaxes to maintain this temp)

Epididymis

stores sperm

vas deferens

duct that transports sperm from epididymus to urethra prior to ejaculation

glands in XY reproductive system (3)

Seminal vesicles, prostate, bulbourethral gland

• contribute semen (nourishing fluid) for sperm; balance acidity of vagina

• semen = 90% nourishing fluid, 10% sperm

spermatogenesis

XY gametogenesis; germ cells undergo meiosis to form 4 haploid sperm (gametes) ~ 10 days

• occurs in seminiferous tubules of testes (continuously replenishing cells)

• mature sperm become motile (flagella) and wait

differences in meiosis in oogenesis vs spermatogenesis

Oogenesis: unequal- one big haploid cell with most cytoplasm and organelles + 3 polar bodies

Spermatogenesis- 4 equally viable cells (just nucleus and mitochondria for energy)

grandmother hypothesis

menopause happens because older females put their energy towards ensuring their offspring survive so genes are passed on (instead of putting their energy towards reproducing)

Who is considered the “father of modern genetics” and what did he first experiment on?

Gregor Mendel; pea plants

Mendel’s principle of independent assortment

random chance of inheriting EITHER “factor” (allele) from parental generation

• each allele has an equal chance of passing on (“mix and match”)

• creates genetic diversity

heterozygous genotype

2 different alleles (Rr)

Homozygous genotype

2 of the same alleles (RR or rr)

Codominance

(Mendel Exception) 2 alleles equally dominant → both expressed at same time (ex. ermine chicken- 2 colors)

• BB = black; B¹B¹ = white → BB¹ = black + white (genotype considered heterozygous)

Incomplete dominance

(Mendel Exception) neither allele is completely dominant; heterozygous phenotype is a blend

• rr = red, r¹r¹ = white → rr¹ = pink

multiple alleles

(Mendel Exception) >2 possible alleles for a gene

• ex rabbits: (in order of dominance) R = full, r^ch = chinchilla, r^h = himalayan, r = albino

polygenic traits

(Mendel Exception) 2+ separate genes interact to determine one trait

• creates continuos variety (spectrum)

• ex: human height → if 7 genes code for heights there’s 128 combos for various heights

Linked genes

(Mendel Exception) genes that are structurally close on the same chromosome (less likely to be split)

• ex. blond hair + blue eyes linked

crossing over

(Mendel Exception) in meiosis during M1, parts of different chromosomes can be swapped → makes 4 different chromatids (increases genetic diversity)

• reason for “linked genes”

environmental influence

(mendel exception) environment (interactions/ signals) plays a role on gene expression

• ex: human height → more calories have led to taller heights

sex-linked traits

(mendel exception) 1 of the 23 chromosomes in gametes is a sex-linked chromosome → some traits are only linked to the sex chromosome (XX or XY)

• ex. colorblindness found on X chromosomes so men are more likely to have it (women less since if one X is not colorblind then it will dominate; men only have one X)

autosome

non-sex chromosome (humans have 22 pairs of autosomes and 1 pair of sex chromosomes)

karyotyping

pre-birth scan of chromosomes for genetic issues (can also tell sex)

population

organisms of the same species that interbreed and live in the same space at the same time

gene pool

combo of genes + alleles present in a population (not always expressed)

What were Darwin’s 5 observations for where species originate (defies “special creation”)

Diversity of life, fitness, diversity of fossils, environment changing, more variation in domestic environments

Darwin Observation: Diversity of life

organisms living in different geographic locations but similar habitats are similar;

differing species in close proximity (generally lots of diversity)

Darwin Observation: Fitness

everything is good at surviving (but in different ways) → driven by selection pressures; have adaptations to survive in their specific niche

Darwin Observation: Diversity of Fossils

some extinct species are similar to living ones in the same places (adaptation / evolution)

Darwin Observation: Environment is changing

causes adaptation (can be more/ less beneficial to survival) → die off or evolve

Darwin Observation: more diversity in domestic environments

due to domestic organisms (ex. dogs) not having to care for themselves / “survive” as much as wild organisms → more opportunity to breed

evolution

a change in a population’s genetic makeup (allele frequency) over time (millions of years)

• *idea that species come from ancestral (extinct) species

4 drivers of evolution

Natural selection, genetic variation / mutation, migration/ gene flow, drift

Natural selection

individuals with favorable traits survive / reproduce at higher rates than individuals with less favorable traits —> favors those with higher Fitness

• driven by competition + environmental change

• more survival = better change of passing down favorable traits

Directional natural selection

population trend shifts in one direction (towards one extreme)

stabilizing natural selection

mean/ avg trait is selected for

disruptive / divergent natural selection

both extremes selected for (leads to speciation) (both extremes beneficial)

artificial selection

taking the best (favorable traits) members of a population and breeding more (form of genetic modification)

Genetic mutation

the “raw materials” (including sexual reproduction) that allow for evolution (traits that can be selected for / against)

• mutation introduces new potential traits to species / populations → genetic variation

  • sexual reproduction allows for new gene combos → variation/ diversity

genetic migration

population’s genetics changed by individuals entering/ exiting the population

• maintains genetic diversity & similarities b/w populations

genetic drift

random change in population’s allele frequencies (based on luck, not fitness)- more common in smaller populations w/ less diversity (can lead to diversity loss)

Model 1: Founder effect- small group breaks away from larger population (allele frequency in smaller group is NOT representative of the larger group)

Model 2: Bottleneck effect: catastrophe → few species survive → smaller population = less genetic diversity = changes in allele frequencies

selection pressures that drive natural selection

environmental change, catastrophes, anthropogenic, predation, competition

3 types of mutation

Beneficial- good for fitness / survival

Harmful- bad for fitness / survival

Silent- no effect on phenotype (potentially harmful internally though)

what disproves “equal reproduction” (-reproduction not all based on fitness)

"good genes” hypothesis, sexual selection, intersexual selection, intrasexual selection, handicap hypothesis?

microevolution

short term changes in a population → changes in allele frequencies driven by 4 drivers of evolution

• NO new species

macroevolution

change at the species level or above → new species of taxonomic groups

• Drivers: natural selection, mutation, reproductive isolation, speciation

speciation

1 or more new species arise from an existing species

reproductive isolation

factors that prevent a species from breeding w/ each other

• prevents gene flow; creates greater variation

3 modes of speciation

allopatric, sympatric, parapatric

allopatric speciation

2 populations geographically isolated → gene flow reduced → speciation

sympatric speciation

(rare / hypothesized) populations not geographically isolated by stop breeding (often due to non-overlapping niches)

• strong selection for a specialized trait

parapatric speciation

no geographical barrier; populations isolated by distance so interbreed less→ less gene flow + diverse selection pressures

• hybrid zone

convergent evolution

unrelated organisms randomly adapt to similar pressures → evolve similar traits or characteristics independently

• Analogous structures- anatomical features in different species w/ similar functions (but unrelated species)ev

ecology

study of the relationship between living organisms and their environments (includes biotic + abiotic factors)