bio quiz 4

lectures 11 - 13 ; inheritance, genetics, origin of life

what is a genotype of an organism?

set of alleles present (ex: AA, Aa, aa)

what is a phenotype of an organism?

observable trait determined by its genotype

what is a character of an organism?

observable heritable feature that may vary between individuals (ex: hair colour, flower colour)

what is a trait of an organism?

detectable variants in a character (ex: blond hair colour, red hair colour, purple flower colour)

what is the location at which a gene occurs on a chromosome called?

gene locus

what is it called when an organism has two of the same allele?

homozygous (ex: AA or aa)

what is it called when an organism has two different alleles?

heterozygous (ex: Aa)

who is credited with developing the formal explanation of how characteristics were passed from one generation to the next?

gregor mendel

what is a pure-breeding specimen?

specimen with a long lineage of displaying the same traits, likely are homologous for that trait

what is a monohybrid cross?

mix between two individuals with opposite homologous genotypes

what are the four main concepts to mendel’s model?

1. inherited characteristics are controlled by genes
2. each individual contains a pair of alleles for a gene
3. only one member of the pair appears in any one gamete (law of segregation)
4. at fertilization, the single alleles in the sperm and the egg combine, making the new individual’s pair of alleles

what is the F₁ generation?

offspring of the original cross

what is the F₂ generation?

offspring of the F₁ generation

what is a dihybrid cross?

mix of two individuals, focusing on two traits

what is the law of independent assortment?

each pair of alleles in a dihybrid cross are inherited independently and do not depend on each other

how do you calculate the number of possible gamete combinations given the genotype?

2^number of heterozygote genes

what is incomplete dominance?

neither allele involved is dominant to the other

what is codominance?

when heterozygotes simultaneously express both homozygous phenotypes

what is the difference between incomplete dominance and codominance?

incomplete dominance: heterozygous form is intermediate between the two homozygous forms (ex: red, pink, white)

codominance: both phenotypes of homozygotes are displayed at the same time (ex: blood groups; ABO)

why can humans only have two of the three alleles associated with blood type?

because we are diploid

what is epistasis?

certain alleles on one locus preventing or masking the expression of alleles on a different locus (ex: gene for pigment can be masked by gene for colour deposit)

what is pleiotropy?

a single gene affecting multiple phenotypes (often proteins in multiple tissues)

what is polygenetic inheritance?

many genes affecting the expression of one trait

what is sex-linked inheritance?

an allele found on an X chromosome determines a condition, biological females have two alleles (XX) while biological men only have one (XY), condition is found almost only in biological men

what does hemizygous mean?

biological men only have one X chromosome, and certain alleles are only found on that X chromosome. this one allele makes them hemizygous instead of hetero or homo

what is dosage compensation?

inactivation of one X chromosome in biological females to make the two X chromosomes equivalent to one in a biological male

what is a barr body?

a dense and metabolically inactive X chromosome, as a result of dosage compensation

what is polyploidy?

presence of multiple sets of chromosomes (triploid, tetraploid)

what is aneuploidy?

presence of a single extra chromosome or the absence of a single chromosome

what is disomy?

the normal number of sets of chromosomes in each cell

what is trisomy?

when there is an extra chromosome, making three of one kind

what is monosomy?

the lack of one member of a pair of chromosomes

from where does monosomy arise?

nondisjunction (failure to separate)

when does nondisjunction happen?

during anaphase I or II

what is a pedigree?

diagram of a family history concerning ancestral relationships and inherited traits

how can you tell if a condition is sex-linked?

only (or mostly) biological males affected

how can you tell if a condition is autosomal?

biological males and females affected equally (or roughly equally)

how can you tell if a condition is recessive?

it skips generations, then reappears

how can you tells if a condition is probably dominant?

it does not skip generations

what are the four main stages of the production of the first simple cells?

1. abiotic synthesis of monomers
2. joining of monomers into polymers (proteins and nucleic acids)
3. combination of polymers into protocells
4. development of hereditary mechanism (nucleic acid)

what was the first geological eon and what was it named after?

hadean, named after hades

what are the two hypothesis of how organic molecules were synthesized?

* panspermia (extraterrestrial origin)
* abiogenesis

what two scientists individually hypothesized that organic molecules could have evolved from abiotic matter?

Oparin and Haldane

what did Oparin and Haldane originally hypothesize?

* early atmosphere was reducing (electron-adding)
* energy for the synthesis of organic molecules could have come from lightening and intense UV radiation

what experiment demonstrated the possibility of organic molecules having been formed on earth in the early atmosphere?

miller-urey experiment

what are the two hypotheses of how and where the first polymers formed?

* volcanic activity could have generated a high enough temperature, monomers could have been splashed onto hot rocks, formed polymers, and then washed back into the ocean
* clay could cause polymers to form

what is the problem with the hypothesis that the first polymers were formed using volcanic activity and hot rocks?

the extremely high temperatures would cause the organic molecules to break down

what properties of clay allow for the possibility that the first polymers were formed on it?

* the clay wouldn’t have had to have been hot
* slight charge (attracts and holds molecules)
* contains metal ions (act as catalysts of dehydration reactions)
* can store energy and discharge it when clay changes temperatures or is dehydrated

what is a protocell?

the first membrane structure

in what structure were the first protocells?

bilayer

what would be the main consequence of protocell formation?

ability to control internal conditions, and to separate from external conditions

what was most likely the first genetic material?

rna (ribozymes)

why could rna have been the first genetic material?

unlike dna, rna can transcribe and replicate itself

why was it advantageous for anaerobic archaea living near cyanobacteria to live very close to aerobic bacteria?

the bacteria would consume all the oxygen nearby, making the oxygen levels tolerable for the anaerobic archaea to live in

when the anaerobic archaea enveloped aerobic bacteria, what did the bacteria become?

mitochondria

when the early protists (single-celled eukaryotes) took in cyanobacteria, what did the cyanobacteria become?

choloplasts

why did protists take in both aerobic bacteria and cyanobacteria?

to maximize possible energy intake

what evidence is there for the theory of endosymbiosis (archaea taking in bacteria)?

mitochondria and choloplasts:

* have their own circular dna (like prokaryotes)
* reproduce through binary fission (like prokaryotes)
* have ribosomes that resemble bacterial ribosomes
* share many genes with prokaryotes
* produce energy
* double membrane (inner membrane from original bacteria, outer membrane formed by archaea)

what is the sequence of major events in the origin of life?

1. origin of bacteria
2. origin of eukaryotes
3. origin of multicellular eukaryotes
4. origin of animals
5. colonization of land by vertebrates