week 3 genetics

X-Y system

males are XY and females XX

X-O system

only one type of sex chromosome, females: XX , males :X

Z-W system

males ZZ and females ZW

haplo diploid system

females are diploid, males are haploid (bees and ants)


in humans absence of y makes the person


presence of y in humans makes person


3 genotypes in Drosophila

XO or XY

male Drosophila flies

Hermann Henking

firebug, discovery of the X chromosome

Nettie Stevens and Edmund Wilson

differences in types of sex chromosomes, discovery of Y chromosome (Tenebrio=mealworm)


XX or XO is biologically what in humanns


XX or XXY in humans is biologically

organisms cannot survive without an X chromosome

why is OY lethal?

error in meiosis

absence or addition of "X" id due to (well-tolerated0

no because they do not contain the same genetic info

are X and Y strictly homologous

yes (homologous pair)

do X and X pair during meiotic cell division

no because they do not have shared sequence homology

do x and y crossover?

X chromosome

contains many types of essential genes in humans (this is why lack of this chromosome is lethal)

tolerated but not lethal

an extra X chromosome in humans is

Y chromosome

chromosome that contain genes associated w/ sperm production and drives male sexual differentiation

NR0B1 gene

gene on X chromosome that produces DAX protein

DAX protein

produces ovary tissue

SRY gene

the sex determining region of the Y chromosome in males. Encodes the testis-determining factor, which turns the primordial gonads into the testes

TDF protein

inactivates DAX protein; testes determining factor; triggers testes to develop


sterile male in flies; Y still needed for sperm production, but sex would still be male

no so they produce twice gene product as XY or XO

Do flies perform X inactivation?


do flies use DAX or SRY system

Sxl transcriptional activator

X-linked gene in flies; forms protein homodimers


activates ovary formation in flies

sxl transcriptional inhibitor

autosome linked gene; forms heterodimer with activator


prevents ovary formation


needle puncture of the amniotic sac to withdraw amniotic fluid for analysis


forms of genetic testing for juveniles and adults; very easy way to test (buccal swab, saliva sample, hair sample, blood test)


before genetic testing, how did genetic counselors determine the genes and diseases people might have?


in genetics research, the individual displaying the trait or characteristic being studied

monogenic traits

Traits determined by a single gene.

pedigree male


pedigree female

Affected Female Pedigree

affected male

dead male/female

sex unspecified


consanguineous mating

mating between relatives

Carrier of x linked trait


non-identical twins

dizygotic twins

identical twins (monozygotic twins)

dominant traits

each affected indiv must have at least one affected parent; no carriers! unaffected indiv must be homozygous recessive

unaffected offspring

in a dominant trait, two two unaffected parents only produce

recessive traits

affected individual can arise from two unaffected parents (carriers); affected=homozygous recessive; must inherit two copies to show trait

recessive traits

often arise from consangineous mating

rescessive trait

generally occurs due to founder effect

founder effect

genetic drift that occurs after a small number of individuals colonize a new area (limited gene flow, consangineous mating); offspring more likely to inherit two copies of the recessive trait=>more people with the trait

X-linked inheritance

trait determined by gene located on X chromosome; males are only hemizygous


A gene present on the X chromosome that is expressed in males in both the recessive and dominant condition


males only inherit an X-linked gene from


more likely to be affected by x-linked gene

Y-linked inheritance

only males!


al male offspring of an affected father in y-linked genes are

recessive traits

tends to skip generations

dominant trait

does not skip generations

virus (infectious particles)

Cause disease in BOTH eukaryotes and prokaryotes
Transmit genetic materially horizontally
Ex. Retroviruses: Hepatitis B and HIV;
DNA integrates into host genome, stays FOREVER!!
Drive organismal evolution!


Prokaryotic organisms
Trade plasmid DNA
Allows rapid evolution within and between populations
Ex. Toxins shared between two different bacterial species
Development of antibiotic resistance (from plasmid genes!)


total set of chromosomes in the organism; contains all genes necessary for organism survival


A small ring of DNA that carries accessory genes separate from those of the bacterial chromosome; replicate independently


contain genes that give organism extra capabilities (virulence factors, antibiotic resistance, ability to metabolize more diverse groups ,help organism survive in changing conditions)

no, but they are extremely helpful

are plasmids essential to survival of bacteria

origin of transfer

the location on an F factor or within the chromosome of an Hfr strain that is the initiation site for the transfer of DNA from one bacterium to another during conjugation

origin of replication

a particular sequence in a genome at which replication is initiated

vertical transmission

parent to offspring; mitosis and meiosis; coupled w/ cell division; prokaryotes and eukaryotes

horizontal transmission

transmission of genetic material (DNA or RNA) between two organisms; NOT limited to cell division process; not limited to same spp; not limited to genomic DNA; Can be within a generation, within or between species, types of organisms, intentional or unint

conjugation, transformation, transduction

three versions of horizontal transmission


A temporary union of two organisms for the purpose of DNA transfer. involves sex pilus. between two live cells; can transfer antibiotic resistance

donor and recipient cells of same spp and sex pilus

conjugation requires

F+ cell

contains F factor as a plasmid

F- cell

does not have F plasmid anywhere

Hfr cell

a cell with the F factor integrated into the chromosome

F' cell

following unequal excision of F factor from chromosome, F' cells contain
extra genes from the donor cell's genome.
Have one full chromosome, F factor (as a plasmid), AND extra copies of
genomic DNA from donor cell
Creates partial diploid cells

transformation bacteria

artificially insert gene into competent bacteria; does not require live donor cell, only need live recipient cell

dna fragment

does not have an origin of replication,
so it must be integrated into chromosome (or existing plasmid);like in transformation; artificially done in test tube

Transduction in bacteria

DNA is transferred from a donor cell to a recipient via a bacteriophage

naked" donor DNA and competent recipient cell

what does transformation require

bacteriophage carrying bacterial DNA (but no viral DNA) from a previous infection and a recipient cell conducive to phage infection

what does transduction require