BIO3 Exam 3 Study Guide

Mendelian genetics def

classic pattern of biological inheritance that shows how traits are passed down from parents → offspring through discrete units (genes)

has 3 laws: Mendel's law of dominance, independent assortment, & segregation

law of dominance def

states that when an organism inherits 2 diff alleles for a single trait (heterozygous genotype), one or more alleles will mask or hide the appearance of the other

law of independent assortment def

states that genes for diff traits separate independently, so inheriting one trait does not affect another—as long as they are on diff chromosomes

law of segregation def

states that allele pairs separate during gamete formation, so parents randomly pass only one copy of a gene to their offspring rather than both copies

gene def

specific segment of DNA that acts as the basic physical & functional unit of heredity

contains instructions to build specific proteins that determine specific traits

allele def

specific version of a gene; for every given trait, we inherit 2 alleles

if a gene is a category (ice cream), allele is an option (ice cream flavor)

dominant allele def

allele that is always expressed in the phenotype, even if you inherit only one copy; represented by capital letters

homozygous dominant (AA) def

having two copies of the same dominant allele at a locus

heterozygous (Aa) def

having two diff alleles at a locus (1 dominant & 1 recessive)

if you look at the pair as separate Xs (XX), one entire X carries the dominant allele, and the other entire X carries the recessive allele

recessive allele def

allele only expressed in the phenotype if two copies are inherited (one from each parent)

homozygous recessive (aa) def

having two copies of the same recessive allele at a locus

Mom's Chromosome (X): The left side (>) has an a, and the right side (

locus def

specific physical location of a gene on a chromosome

chromosomes come in homologous pairs, so we have 2 copies of every locus

alleles are located at exact same locus on both chromosomes

genotype def

genetic makeup (combo of inherited alleles)

ex: Aa, AA, aa

phenotype def

physical expression/observable trait of genotype

ex: eye color, height, hair type

Punnet square def

grid used to predict genetic outcomes of a cross between 2 parents, based on Mendel's laws of segregation & independent assortment

test cross def

method used to determine an unknown dominant genotype by crossing the organism with a homozygous recessive partner

if any offspring show the recessive trait, the unknown parent is heterozygous (Aa)

dihybrid cross def

breeding experiment that tracks inheritance of 2 diff traits simultaneously, demonstrating law of independent assortment

ex: crossing AaBb x AaBb

complex inheritance def

any pattern of genetic inheritance that does not follow standard Mendelian rules

ex: genetic linkage, incomplete dominance, codominance, multiple allelism, polygenic inheritance, pleiotropy, epistasis, environmental influences

genetic linkage def

form of complex inheritance where genes located close together on the same chromosome tend to be inherited together; an exception to law of independent assortment

can be broken by crossing over but is highly unlikely

incomplete dominance def

form of complex inheritance where neither allele is completely dominant, resulting in a heterozygous phenotype that is a blend of the two homozygous traits

ex: red x white snapdragons produce pink offspring due to red pigment being diluted by lack of white allele's pigment

codominance def

form of complex inheritance where both alleles are simultaneously & fully expressed in a heterozygous organism

ex: red x white cattle produce offspring with individual red hairs & white hairs growing side by side

multiple allelism def

form of complex inheritance where a single gene has 3+ possible alleles within a population

ex: human blood types have 3 alleles at the same exact gene locus

polygenic inheritance def

form of complex inheritance where a single physical trait is controlled by the combined effects of multiple diff genes, often located on separate chromosomes

ex: human skin pigmentation (melanin) & height exist on a continuous spectrum because they are governed by multiple genes

pleiotropy def

opposite of polygenic inheritance; form of complex inheritance where a single gene influences multiple, seemingly unrelated physical traits

ex: albinism is one gene mutation that affects skin color, hair color, eye color, & vision

epistasis def

form of complex inheritance where the expression of 1 gene is completely masked or modified by a separate gene at a diff locus

ex: lab dogs have genes that dictate the appearance of fur pigment, so even if a dog has a dominant gene for a fur color, it won't show up if they also have the gene that blocks pigment from manifesting

environmental influences def

form of complex inheritance where external environmental factors impact how a gene is expressed

ex: poor nutrition can stunt a person's genetically programmed height; sunlight, water, & soil acidity can alter a plant's size, color, or shape

epigenetics def

study of how behaviors & environmental factors cause reversible changes that affect how genes work, without altering the underlying DNA sequence.

blood types (ABO system)

multiple-allele & codominant system that determines blood type based on surface antigens

type A (AA, Ao): produces A antigens

type B (BB, Bo): produces B antigens

type AB (AB): produces both A & B antigens (codominance)

type O (oo): produces neither antigen (universal donor)

Rh gene def

protein on red blood cells inherited through simple dominance

Rh Positive (RR, Rr): Rh protein is present on blood cells.

Rh Negative (rr): Rh protein is completely missing

AB+ is universal blood recipient

autosome def

non-sex, homologous chromosomes 1-22 that carry genes for general body characteristics

sex chromosome def

23rd pair of chromosome that determines biological sex

female chromosome def

2 homologous X chromosomes

male chromosome def

1 X chromosome & 1 Y chromosome

SRY gene def

master switch gene in Y chromosomes that triggers the development of male physical traits

karyotype def

an individual's collection of chromosomes that are physically isolated, stained, & organized into a visual map

x linked genes def

genes located on the X chromosome; majority of those genes code for non-sex-related body functions

x linked recessive inheritance def

pattern of inheritance where a recessive mutation on the X chromosome always causes the disorder in males, while heterozygous females are typically unaffected carriers

hemizygous def

having only a single copy of a gene/chromsome segment instead of 2 copies; males are hemizygous for most genes located on the sex chromosome

X linked recessive traits are more commonly found in male offspring than in female offspring

pedigree def

genetic family tree that tracks the inheritance of a specific trait across multiple generations

types of chromosome structure alterations

deletion, duplication, inversion, translocation

deletion def

chromosome structure alteration where a fragment of a chromosome gets lost, resulting in that chromosome missing that gene

duplication def

chromosome structure alteration where a portion of a chromosome gets duplicated & reinserted into the same chromosome

inversion def

chromosome structure alteration where a portion of a chromosome is reversed

translocation def

chromosome structure alteration where a segment of a chromosome is moved to a diff, nonhomologous chromosome

cri du chat def

disorder caused by a deletion of a portion of chromosome 5 that can lead to severe intellectual disability, delayed development, & unusual facial features

chronic myelogenous leukemia def

blood cancer caused by translocation of a portion of chromosome 22 exchanged with chromosome 9, resulting in a shorter chromosome 22, causing uncontrolled cell cycle progression

nondisjunction def

abnormality in cell division where chromosomes fail to separate properly, resulting in daughter cells with too many or too few chromosomes

ex: down syndrome results from chromosome 21 failing to separate, creating a gamete with an extra chromosome

ex: nondisjunction occurring with chromosome 1 leads to a miscarriage

why is sex chromosome nondisjunction less severe than autosomal nondisjunction?

Y chromosome is tiny & carries few genetic instructions

X inactivation shuts down 1 of 2 X chromosomes, making females genetic mosaics & protecting body from toxic gene overload

mosaicism def

when an organism has 2+ genetically diff lines of cells caused by a mutation

abnormalities caused by abnormal numbers of sex chromosomes

turner syndrome (monosomy X), klinefelter syndrome (XXY), XYY syndrome, trisomy X (XXX)

turner syndrome (monosomy X) def

mutation where females only inherit 1 X chromosome → underdeveloped sex characteristics, infertility, short stature

klinefelter syndrome (XXY) def

mutation where males inherit 2 X chromosomes (rather than 1) → infertility, underdeveloped sex organs, feminine qualities, tall height, sometimes developmental delays

XYY syndrome def

mild mutation where males inherit 2 Y chromosomes → above average height, speech or motor delays, mild learning differences

trisomy X (XXX) def

mild mutation where females inherit 3 X chromosomes --> tall stature, mild/no developmental delays

amniocentesis def

type of fetal testing performed at ~15th week of pregnancy where amniotic fluid is drained & tested

chorionic villus sampling def

type of fetal testing at ~10th week of pregnancy where chorionic villus, made of fetal cells on bottom of placenta, is suctioned and analyzed

DNA structure

double helix polymer made of nucleotides; nucleotide consists of phosphate group, deoxyribose sugar (5-carbon), & nitrogenous base

purines def

one of the chemical families of the 4 nitrogenous bases in DNA/RNA; larger molecules composed of a double-ring structure

adenine & guanine

pyrimidines def

one of the chemical families of the 4 nitrogenous bases in DNA/RNA; smaller molecules composed of a single-ring structure

cytosine, thymine, & uracil (uracil replaces thymine in RNA)

how do adjacent nucleotides covalently bond to form a single DNA or RNA strand?

via a 3' to 5' phosphodiester bond

3' carbon of one nucleotide's sugar ring connects covalently to a phosphate group; that same phosphate group is already connected to the 5' carbon of the sugar ring directly below it

what indicator distinguishes DNA of diff organisms?

order & number of nucleotides

Erwin Chargaff

discovered that amount of adenine = thymine, and the amount of guanine = cytosine

also discovered that amount of bases differs between species

Rosalind Franklin

determined DNA has a helix shape and is uniform in diameter; Watson & Crick used her photos without permission to confirm DNA structure

anti-parallel strands def

structure where the 2 DNA strands run parallel to each other; one runs 5' → 3' & the complementary runs 3' → 5'

head = 5'

tail = 3'

complementary base pair def

matching rule between chemical bases that form rungs of the DNA ladder, where adenine always pairs with thymine and guanine with cytosine

A with T

G with C

semi-conservative replication def

how DNA copies itself during S phase of interphase by unzipping the original strand to serve as a template for the formation of new strands that are complementary to the template strands

every newly replicated DNA molecule consists of one old original strand & one brand-new strand

DNA duplication steps during interphase

1) origin of replication signals where copying process begins; helicase enzyme breaks up helix down the middle

2) helicase breaks hydrogen bonds connecting complementary bases to push the 2 DNA strands away from each other, creating replication bubbles at each origin point

3) primase enzyme leaves tiny RNA markers inside replication bubbles to signal where new strands should be built

4) DNA polymerase matches floating bases to old strands & helicase moves outward in both directions to widen bubbles; new strand only grows/is created from 5' → 3'

origin of replication def

sites (DNA sequence) where copying process of DNA strands begins

helicase enzyme def

enzyme that breaks up helix down the middle like a zipper

replication bubble def

unwound, open region of DNA created when helicase separates the 2 template strands at an origin of replication

primase def

enzyme that builds a short RNA primer (temporary starter flag) onto the template strand

DNA polymerase def

builder enzyme that matches free nucleotides to the template strand to synthesize the new complementary DNA strand

replication fork def

Y-shaped corners at either end of a replication bubble where the double helix is actively being unzipped

leading strand def

new strand of DNA built in 1 continuous strip that move toward the opening replication fork

lagging strand def

new strand of DNA built discontinuously in short, fragmented sections that move away from the opening replication fork

why is the lagging strand built discontinuously?

as helicase unzips the DNA, the DNA polymerase must wait for a section to open, attach at the fork, & build backward

when the fork opens more, DNA polymerase must detach and jump backward to start the process again

Ozaki fragments def

the individual, short segments of DNA created on the lagging strand each time DNA polymerase jumps backward and builds discontinuously away from the replication fork

DNA ligase def

the enzyme that glues Ozaki framents together to form a full strand

end-replication problem deff

biological constraint where the chromosome shortens with every replication cycle

final RNA primer at absolute tip of the lagging strand is removed → leaves blank space that DNA polymerase can't fill → a small piece of DNA is lost forever

telomere enzyme def

protective, repetitive caps of non-coding DNA buffers at the ends of chromosomes to delay the end-replication problem

normal shortening of telomeres limits cell division of mutated cells; cancer cells have abnormally long telomeres

progeria def

rapid aging mutation; kids with progeria have shorter telomeres than those of normal cells

telomerase enzyme def

enzyme that restores telomeres to their original length, discovered by Elizabeth Blackburn & Carol Greider

not typically present in adult somatic (body) cells

types of DNA repair systems

proofreading, mismatch repair, nucleotide excision

proofreading def

immediate, first line of DNA repair system that checks for mistakes, removing singular, incorrect bases before continuing on its check; catches 99% of immediate typos

mismatch repair def

2nd line of DNA repair system that identifies mispaired letters of freshly duplicated DNA, chopping incorrect sections off

DNA polymerase fills in the gaps & ligase glues the backbone shut

nucleotide excision repair def

type of DNA repair system that fixes physical damage (thymine dimers) caused by environmental factors, cutting out damaged sections before they are remade using the untouched strand as a guide

thymine dimer def

type of physical damage to DNA caused by UV radiation from the sun, which welds 2 adjacent thymines together into a knot

mutation def

errors in DNA sequences overlooked by repair systems & incorporated into DNA, forming mutations

DNA fingerprinting def

method of identifying unique patterns in DNA for each organism

gene expression def

process of instructions in DNA directing the synthesis of protein by the steps of transcription and translation

sequence of nucleotides in DNA specifies the order of amino acids in a protein (polypeptide chain)

types of RNA

mRNA (messenger), rRNA (ribosomal), tRNA (transfer)

mRNA def

temporary-single stranded copy of a specific gene from DNA that carries the copied message to the cytoplasm

rRNA def

structural, physical component of the ribosome itself that holds mRNA in place & chemically bonds incoming amino acids together to form a chain

tRNA def

RNA molecule that carries & delivers individual amino acids floating around the cell to the ribosome

tRNA structure

cloverleaf shape

attatchment site = top part that holds a specific amino acid

anticodon loop = bottom end has a sequence of 3 RNA letters (3-letter anticodon) meant to bind to its complementary match (codon) on the mRNA strand at the ribosome

transcription def

first stage of gene expression where a cell copies genetic message from DNA into temporary, portable mRNA

direction of synythesis moves from 5' → 3'

only the specific gene is transcribed, not the whole chromosome

promoter sequence def

specific sequence of DNA letters in transcription right before a gene starts transcribing

terminator sequence def

specific sequence of DNA letters in transcription at the end of a gene that stops RNA from being transcribed

steps of transcription

initiation, elongation, termination

initiation (transcription) def

enzyme RNA polymerase floats along DNA until it recognizes and binds to the promoter sequence, breaks the the 2 DNA strand, & unzips the double helix to expose the gene's hidden code