3030 Midterm Exam Study

Define: homologs

matching chromosome pairs (NOT sister chromatids)

How many protein coding genes are in the human genome?

20,000

four levels of biological organization:

molecular, cellular, organism, population

Describe: PKU

phenylketonuria - presence of phenylalanine in urine

nonfunctional allele prevents breakdown of the amino acid phenylalanine

causes development problems

low-phenylalanine allows normal development

Describe the structure of a eukaryotic chromosome and a dyad

DNA is wrapped tightly around histones, pinched at centromere

Chromatids are attached by kinetochore complex of proteins wrapped around the centromere

Describe: three fields of genetics

Transmission genetics, founded on Gregor Mendel, inheritance patterns

Molecular genetics, DNA RNA and proteins

Population genetics, frequency of alleles in populations

Define: wild type

characteristic found in at least 1% of population

Define: mutant

rare characteristic found in >1% of population

Define: chromatin

complex of histones and DNA, decondensed chromosome

How and where do prokaryotic and eukaryotic chromosomes differ

eukaryotes: multiple linear chromosomes in nucleus

prokaryotes: single circular chromosome in nucleoid

Describe: preparation of karyotype

(drug that starts with ‘c’)

A blood sample is treated with colchicine to disrupt spindle formation

cells are suspended in hypotonic solution so they swell

cells are centrifuged

suspended in a fixative

stained

placed on slide

how do bacteria reproduce?

binary fission

Describe: binary fission

(protein that starts with F)

mother cell replicates entire chromosome

FtsZ assembles into a Z-ring that pinches cell into two (forms septum)

Describe: All parts of eukaryotic cell cycle in order

(and internal steps of mitosis)

= G0: non dividing state (like nerve cells)

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Interphase

= G1
— cell decides whether to continue dividing
— ‘restriction point’

= S (synthesis)
— chromosomes are replicated into sister chromatids

= G2
— cell gathers materials necessary for nuclear and cell division

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M-phase

= Mitosis
— Prophase; chromatids begin to condense / nuclear envelope breaks down / mitotic spindle forms

— Prometaphase; nuclear envelope gone / spindle microtubules grow / capture chromatids at kinetochore

— Metaphase; chromatids line up in middle ‘cell plate’

— Anaphase; chromatids separate into chromosomes / microtubules push apart / pull chromatids to polar ends

— Telophase; chromatids decondense into chromatin / nuclear envelope reforms / nuclei share one cytoplasm

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Cytokinesis
= contractile ring of actin and myosin form cleavage furrow in animals
= golgi-derived vesicles build a cell plate that grows outward to form new cell wall in plants

Define: autosome

any chromosome that is not a s_ chromosome

Define: synapsis

pairing homologous chromosomes during prophase I of meiosis; synaptomal complex

Define: bivalent

two paired homologs connected by a synaptomal complex containing four chromatids; tetrad

Define: tetrad

two paired homologs connected by a synaptomal complex containing four chromatids; bivalent

Define: chiasma

connection between homologs where crossing over occured

Define: reduction division

during Meiosis I when homologous chromosomes separate; 2n → 1n

Define: polar bodies

2 small extra cells that are produced during oogenesis

what ploidy are sporophyte and gametophyte generations?

sporophyte: diploid

gametophyte: haploid

how many sperm cells are produced during spermatogenesis?

4

how many cells are produced during oogenesis?

1 ova, 2 polar

how much genetic material do gametes hold?

half the usual amount (1n)

Define: isogamy, heterogamy

isogamous species produce male and female gametes that are similar

heterogamous species produce different male and female gametes

when does meiosis begin in the growth cycle?

meiosis begins after chromosomes are replicated in S phase

describe the main outcomes of meiosis I and meiosis II

meiosis I separates homologous chromosomes (reduction division)

meiosis II separates sister chromatids (like mitosis)

Describe: prophase I

much longer than prophase in mitosis

replicated chromosomes pair up with homologs → becomes bivalent, tetrad
= synaptonemal complex forms between homologs
= cohesins connect sister chromatids

= synaptonemal complex breaks down, chiasmata hold homologs together

what two structures hold together tetrads?

cohesins connect sister chromatids

synaptonemal complex connects homologs

Define: crossing over

when homologous chromosomes trade DNA at chiasmata

Describe: metaphase I

homologs line up at metaphase plate instead of chromatids

Define: independent assortment

homologs randomly line up at metaphase plate during metaphase I; alleles pass independently

Describe: meiosis II

essentially mitosis but with haploid cells

Describe: spermatogenesis

diploid spermatogonial cell → primary spermatocyte → (meiosis I) 2 secondary spermatocytes → (meiosis II) 4 spermatids → sperm cells

Describe: oogenesis

diploid oogonia → primary oocyte → (meiosis I) 1 secondary oocyte, 1 polar body → (meiosis II ONLY IF FERTILIZED) 1 egg cell, 2 polar bodies

Define: alternation of generations

plants alternate diploid sporophyte generations and haploid gametophyte generations

Define: monoclinous, monoecious, dioecious

monoclinous: single flower type with pollen and eggs

monoecious: multiple male and female flowers on one plant

diecious: separate male and female plants

Define: law of segregation

each parent only passes one of its two alleles in sexual reproduction

what are three sources of variation in meiosis?

crossing over, independent assortment, random fertilization

Define: random fertilization

any of millions of sperm can fuse with any possible egg

Define: testcross

crossing an individual with a dominant phenotype but unknown genotype to a homozygous recessive individual

homozygous dominant = all dominant offspring

heterozygous = 1:1 dominant and recessive offspring

Define: pedigree

a family tree used to follow inheritance of a trait

Define: genetic recombination

formation of new combinations of alleles; law of independent assortment

Define: pangenesis

Hippocrates’ thoery that seeds from all body parts combine to make offspring

Define: characteristic, trait

characteristic: a general feature like color (gene)

trait: a variation of a characteristic, like pink (allele)

Describe: monohybrid cross

two true-breeding parents (p-generation) make all heterozygote offspring (f1 generation)

f1 offspring self fertilize to make dominant/recessive homozygous offspring and heterozygous offspring (f2 generation)

what does ‘f’ stand for in crosses?

filial (generation)

Define: dihybrid cross

cross concerning two characteristics across generations

9:3:3:1 in heterozygous cross

Describe: multiplication method of phenotype frequencies

finding phenotype frequencies of characteristics separately and multiplying them together to find frequency of them together

Define: loss-of-function allele

when an allele causes non-function in the gene

what do squares and circles represent in pedigree charts?

squares represent males (sharp, structural, basis of reality, greater)

circles represent females (round, small, polka dot)

what is caused by the recessive allele of the CFTR gene?

cystic fibrosis

Define: recessive pattern

two unaffected parents with affected offspring are revealed to be heterozygous for the recessive allele

Define: dominant pattern

affected individuals must have inherited from an affected parent

Define: penetrance

the rate that individuals with a genotype show the associated phenotype

define: expressivity

the degree that a phenotype is expressed

Define: haploinsufficiency

one functional copy of an allele does not produce enough product for a normal phenotype

Define: hemizygous

having only one copy of a gene (X is hemizygous in XY individuals)

Define: pleiotropy

one gene that affects multiple traits

Define: epistasis

alleles of one gene alter the phenotype of another gene

why does a single dominant allele mask a recessive allele?

50% of the expression of the dominant allele is enough to express the phenotype

100% (AA) 50% (Aa) 0% (aa)

Define: genetic polymorphism

more than one wild-type allele in a population (more than one allele in <1%)

what three ways do dominant mutants occur?

gain-of-function: protein acquires new/increased/abnormal function

dominant-negative: mutant protein interferes with normal protein function

haploinsufficiency: a single allele (recessive) isn’t enough for normal phenotype

polydactyly is an example of…

haploinsufficiency

Define: norm of reaction

the full range of phenotypes a single genotype can produce according to different environments