BIO exam 3

chromatin

the building material of chromosomes (DNA + protein)

recombinant chromosomes

new DNA combinations created by crossing over

locus

a gene’s specific location on a chromosome

MPF

protein complex that triggers the jump from late interphase to mitosis

protein kinases

enzymes that activate or inactivate proteins by phosphorylation

mitotic spindle

microtubules and proteins that move chromosomes during mitosis (forms in prophase)

haploid

one set of chromosomes

diploid

two sets of chromosomes

true breeding

plants that always produce offspring with the same traits through self-pollination

law of segregation

alleles for one gene separate into different gametes

testcross

breeding an unknown genotype organism with a homozygous recessive to reveal its genotype

law of independent assortment

different genes separate independently of each other during gamete formation

complete dominance

when the dominant allele hides the recessive allele (Aa=AA)

monohybrid cross

a cross involving one trait

dihybrid cross

a cross involving two traits

main function of G1 interphase

metabolic activity and growth

main function of S interphase

metabolic activity, growth, and DNA synthesis

main function of G2 interphase

metabolic activity, growth, and preparation for cell division

G1 checkpoint

determines if a cell should divide or enter G0 (a nondividing state) to ensure the cell only divides when needed

M checkpoint

during metaphase ensures all chromosomes are properly attached to spindle fibers (prevents wrong number of chromosomes in daughter cells)

cytokinesis in animal cells

a cleavage furrow pinches the parent cell into two cells

cytokinesis in plant cells

forms a cell plate that creates a new cell wall between daughter cells

asexual reproduction

one parent creates genetically identical offspring

advantage: fast, only requires one parent

disadvantage: no genetic diversity

sexual reproduction

two parents create genetically diverse offspring

advantage: increases genetic variation

disadvantages: slower, requires two parents

homologous pairs (the two chromosomes of a pair in a karyotype) have the same…

length, centromere position, and staining pattern

karyotype

displays chromosome pairs arranged by size and shape

normal cells vs cancer cells

normal cells exhibit anchorage dependence (attached to a surface) and density-dependent inhibition (stop dividing), but cancer cells ignore the signals and divide uncontrollably

cancer development

cancer begins when a single cell loses cell cycle control, avoids the immune system, and undergoes uncontrolled division

benign tumors

abnormal cells remain at the original site

malignant tumor

cells undergo genetic changes that allow them to spread to new tissues and impair organ functions

three main sources of genetic variation that arise during meiosis

1. independent assortment of chromosomes (random orientation of homologous pairs)

2. crossing over (exchange of genetic material)

3. random fertilization (any sperm with any egg)

mitosis vs meiosis purpose

growth/development vs gamete production

mitosis vs meiosis number of divisions

1 vs 2

mitosis vs meiosis number of daughter cells

2 vs 4

mitosis vs meiosis genetic composition

identical vs non identical

mitosis vs meiosis chromosome number

diploid (46) vs haploid (23)

mitosis vs meiosis crossing over

does not occur vs does occur

mitosis vs meiosis homologous chromosomes

no vs yes

mitosis phases

prophase, prometaphase, metaphase, anaphase, telophase

meiosis phases

prophase I, prometaphase I, metaphase I, anaphase I, telophase I, prophase II, prometaphase II, metaphase II, anaphase II, telophase II

mitosis vs meiosis role in genetic variation

low variation vs high variation

what events are unique to meiosis (meiosis I) that do not occur in mitosis?

prophase I: crossing over occurs between homologous chromosomes

metaphase I: homologous pairs instead of individual chromsosomes line up together at the metaphase line

anaphase I: homologous chromosomes separate, but sister chromatids stay attached

recessive disorder example

cystic fibrosis

dominant disorder example

achondroplasia

recessive carrier genotype

Aa

recessive affected genotype

aa

dominant affected genotype

AA or Aa

how did Mendel explain that traits disappeared in the F1 generation and then reappeared in the F2 generation?

principle of dominance

F1 generation: recessive traits are masked by dominant alleles

F2 generation: the recessive trait reappears because the hidden allele is still present and can pair with another recessive allele

amniocentesis

test screening for genetic disorders by extracting amniotic fluid to analyze fetal cells (later in pregnancy)

chorionic villi sampling

test screening for genetic disorders by removing a small tissue sample from the placenta (earlier in pregnancy)

mendelian genetics

a dominant allele will always mask a recessive allele

punnett square with a Mendelian cross between two guinea pigs that are heterozygous for hair (include phenotype and genotype ratio)

H h

H HH Hh

h Hh hh

3 have hair : 1 hairless

1 HH : 2 Hh : 1 hh

non-Medelian trait

traits that do not follow the rule where one allele is completely dominant over another

incomplete dominance

neither allele is fully dominant causing a blend of traits (red +white = pink, RW)

codominance

both alleles are expressed equally causing both traits to show (black + white = speckled, C^BC^W)

pleiotropy

influence of a single gene on multiple, unrelated traits

polygenic traits

multiple genes work together to determine a single trait (height, skin tone)

snapdragons RR x rr Mendelian vs non-Mendelian

Mendelian: Rr is red

non-Mendelian: Rr is pink

epistasis

one gene controls the expression of another gene (ex. B=black wool, b = brown wool, C = pigment, c = no pigment)

wild type

the most common (“normal”) phenotype in nature

mutant type

any trait alternative to the wild type (caused by mutation)

nondisjunction

failure of chromosomes/chromatids to separate properly during meiosis or mitosis

SRY gene

the switch on the Y chromosome that triggers male development

antiparallel

DNA strands running in opposite directions (5’ → 3’ vs 3’ → 5’)

telomerase

an enzyme that extends the ends of chromosomes to prevent shortening

histones

small, positively charged proteins that DNA wraps around

transformation

when a cell takes up and incorporates foreign DNA from its environment

gene expression

the process by which DNA directs protein synthesis

codon

a 3-nucleotide sequence on mRNA (basic unit of genetic code)

Thomas Hunt Morgan and drosophila

proved that specific traits are linked to the X chromosome, confirming that genes occupy specific locations on chromosomes (trait-sex correlation)

X-inactivation in females

in females, one X chromosome is “shut off” in every cell to prevent them from having double the gene products compared to males

sex-linked disorders in males

males have more X-linked recessive disorders because they only have one X chromosome without the second X chromosome in females to mask it

aneuploidy

abnormal chromosome number

monosomy

missing one chromosome from a pair (turner syndrome)

trisomy

having one extra chromosome in a pair (down syndrome)

linked genes

genes located close together on the same chromosome that tend to be inherited together

recombination

the production of offspring with traits that differ from the parents

independent assortment Morgan vs Mendel

Morgan challenged this Mendelian law by showing that linked genes do not always sort independently

Frederick Griffith

discovered transformation: a heritable substance from dead pathogenic bacteria could transform harmless live bacteria

Hershey and Chase

proved DNA is the genetic material (not protein) by showing only phage DNA enters bacterial cells during infection

Erwin Chargaff

established Chargaff’s rules

1. DNA base composition varies by species

2. ratios of adenine = thymine and guanine = cytosine

Rosalind Franklin

used x-ray diffraction to confirm DNA has a helical shape with a sugar-phosphate backbone on the outside

Watson and Crick

disocvered the double helix structure by building models based on Franklin’s x-ray data and Chargaff’s rules (also A→T, G→C)

Meselson and Stahl

proved the semiconservative model of DNA replication using nitrogen isotopes

prokaryotes vs eukaryotes DNA replication

prokaryotes: circular, single replication origin, one replication bubble

eukaryotes: linear, multiple replication origins, multiple replication bubbles

helicase

untwists the double helix and separates parental strands

topoisomerase

relieves “overwinding” strain ahead of replication fork

primase

synthesizes an RNA primer to start replication (start flag)

DNA poly III

adds DNA nucleotides to the RNA primer (5’→3’ direction)

DNA poly I

removes RNA primers and replaces them with DNA

ligase

glue that joins okazaki fragments into a continuous strand

leading strand

synthesized continuously toward the replication fork (5’→3’)

lagging strand

synthesized discontinuously away from the replication fork in short segments called okazaki fragments