Exam 3

Question 1

single-factor vs two-factor cross

Answer 1

single-factor: mating and then looking at one factor (tall or short, white or black fur), lead to discovery of law of segregation
two-factor: mating and then looking at two factors (pod color and size), lead to discovery of law of independent assortment

Question 2

what is the law of segregation?

Answer 2

the two copies of a gene separate from each other during transmission from parent to offspring, homozygous parents in P generation produce offspring in F1 generation which only show the dominant trait, but offspring of F1 generation (F2) show to recessive trait again with one out of four being recessive

Question 3

what is the law of independent assortment?

Answer 3

during gamete formation, the segregation of any pair of alleles is independent of the segregation of other pairs (alleles of other genes), heterozygous P generation

Question 4

what is true-breeding?

Answer 4

plants that produce the same traits when self-fertilized or when bred with the same trait

Question 5

what do the letters inside and outside of a punnet square represent?

Answer 5

outside: parental genotype/alleles
inside: diploid offspring

Question 6

how do you determine inheritance probabilities for monohybrid crosses?

Answer 6

monohybrid cross ratio is 3 dominant : 1 recessive so 3/4 chance of being dominant 1/4 chance of being recessive, multiply either 1/4 or 3/4 by itself for each number of offspring depending on dominant or recessive trait (chance of first 2 offspring inheriting dominant trait is 3/4 (3/4) = 9/16

Question 7

how can you determine if a trait is recessive or dominant in a pedigree?

Answer 7

dominant: doesn’t skip any generations, affected offspring will have at least one affect parent, unaffected offspring from two affected parents must be dominant
recessive: can skip generations, two unaffected parents have a 25% chance of having an affected offspring, two unaffected parents with affected offspring must be recessive

Question 8

how can you determine if a trait is x-linked from a pedigree?

Answer 8

only females are affected if father is affected, daughters and sons can be affected when mother is affected, daughters affected if both parents are affected but all sons are affected when mother is affected

Question 9

how can you determine if a trait is autosomal (not sex-linked) from a pedigree?

Answer 9

unaffected son results from an affected mother or an affected son from an unaffected mother

Question 10

what is dosage compensation?

Answer 10

mechanism that keeps levels of expression of X chromosome genes in balance with those of autosomal genes
for both sexes, all mechanisms act on the x chromosomes in some way

Question 11

what are the different types of sex determination?

Answer 11

behavioral: clownfish, sex determined by behavioral interactions, females dies and male becomes female while a juvenile becomes male
temperature-dependent: reptiles and fish, male: 30 C female: above or below 30 C
haplo-diploid: bees, sex determined by number of sets of chromosomes, male: haploid (16) female: diploid (32)
Z-W: birds, male: ZZ female: ZW
X-O: insects, male XO female: XX

Question 12

what does the Sry gene control?

Answer 12

male development in mammals, located on the Y chromosome

Question 13

how does inactivation work?

Answer 13

during embryonic development one of the X-chromosomes is targeted for inactivation, inactivates starting from the xic and moving towards both ends, Xist gene encodes an RNA that coats X-chromosome and recruits proteins that promote its compaction into a Barr body, the inactivated X-chromosome remains inactivated through subsequent cell divisions

Question 14

what is the Lyon hypothesis?

Answer 14

the idea that female mammals inactivate one of their X chromosomes in each somatic cell, one X is chosen at random in different cells early in development, then maintained leading to variegation

Question 15

how many Barr bodies would you find in individuals with Klinefelter syndrome, Turner syndrome, or triple X syndrome?

Answer 15

Klinefelter: XXY, one Barr body
Turner: X0, no Barr bodies
Triple X: XXX, two Barr bodies

Question 16

what is incomplete dominance vs over-dominance vs co-dominance?

Answer 16

incomplete: heterozygotes exhibit a phenotype intermediate between the phenotypes of the homozygotes (homozygotic white and red flowers make heterozygotic pink flowers)
over: when a heterozygote is more vigorous than the two homozygotes (also called heterozygote advantage, sickle cell)
co: heterozygote has a different phenotype (IA and IB co-express to make AB blood type)

Question 17

what are lethal vs conditional lethal vs semi-lethal alleles?

Answer 17

lethal: mutations of essential genes that have the ability to cause death
conditional: alleles kill an organism only under certain environmental conditions
semi: kill only some individuals in a population, environmental factors and other genes may help prevent the detrimental effects of semi-lethal genes

Question 18

what is sex-influenced vs sex-limited inheritance?

Answer 18

sex-influenced: an allele is dominant in one sex but recessive in the other (sex influence is associated with heterozygotes)
sex-limited: traits that occur in only one of the two sexes

Question 19

what are the three explanations for over-dominance/heterozygote advantage?

Answer 19

1. disease resistance
2. homodimer/heterodimer formation
3. variation in functional activity

Question 20

what is incomplete penetrance?

Answer 20

the term indicates that an allele does not always “penetrate” into the phenotype of the individual (if 60% of heterozygotes carrying a dominant allele exhibit the trait, the trait is 60% penetrant)

Question 21

what is epistasis?

Answer 21

when a gene can mask the phenotypic effects of another gene

Question 22

what is complementation?

Answer 22

when wild-type offspring are produced from a cross between parents that both display the same recessive phenotype (CCpp and ccPP both encode for white, they make a CcPp offspring which encodes for purple)

Question 23

what is variable expressivity?

Answer 23

how affected an individual may be affected by the mutation

Question 24

what is pleiotropy?

Answer 24

multiple effects of a single gene on the phenotype of an organism (due to gene effecting function in multiple ways, being expressed in multiple cells type, or expressed at different stages of development)

Question 25

if for a particular gene, individuals are never found to be homozygous for a particular allele, this is most likely
an example of what?

Answer 25

a lethal allele

Question 26

what is extranuclear vs epigenetic vs simple mendelian inheritance?

Answer 26

extranuclear/cytoplasmic: traits inherited through genes that are not in the nucleus, but are in organelle genomes (mitochondria and chloroplasts)
epigenetic: modification to a gene that changes gene expression, but is not permanent over the course of generations, not a change in the DNA sequence itself
mendelian: inheritance patterns that
obey the Laws of Segregation and Independent Assortment

Question 27

where is extra-nuclear DNA located in mammalian cells and what type of inheritance is observed with extra-nuclear DNA?

Answer 27

mitochondria, cytoplasmic inheritance

Question 28

what is genomic imprinting and how does it relate to monoallelic expression?

Answer 28

genomic imprinting is when expression of a gene depends on whether it is inherited from the male or the female parent, monoallelic expression is when offspring express either the maternally-inherited or the paternally-inherited allele but not both

Question 29

what is heteroplasmy?

Answer 29

mix of wild-type and mutant in one
cell, associated with chloroplasts

Question 30

what is endosymbiosis?

Answer 30

the symbiotic relationship where one organism lives inside another species (ex. theory that mitochondria and chloroplasts originated from bacteria that took up residence within primordial
eukaryotic cells)

Question 31

what is maternal effect?

Answer 31

when only the genotype of the mother controls phenotype of offspring (gg female mating with Gg male will result in all offspring having recessive phenotype)

Question 32

what is gene linkage?

Answer 32

two or more genes on the same chromosome that are transmitted to the next generation together

Question 33

what does chi square analysis do?

Answer 33

used to determine if the outcome of a cross is consistent with linkage or with independent assortment

Question 34

an organism that contains patches of tissue that vary for a specific characteristic is an example of what type of recombination?

Answer 34

mitotic recombination

Question 35

what is genetic linkage?

Answer 35

when genes are linked close together on a chromosome and therefore are transmitted together as a unit, this results in offspring having very similar traits to the parents

Question 36

where is crossing over more likely to happen?

Answer 36

on genes that are far apart on the same chromosome

Question 37

what is the map distance and how do you find it?

Answer 37

map units = (number of recombinant offspring divided by total number of offspring) x 100, a map distance of X indicates that X% of the offspring exhibit recombination between the two genes

map distance is the relative distance between two genes

Question 38

in mapping experiments with three genes what is the frequency with which different phenotypes occur in the F2 generation?

Answer 38

parental phenotypes occur most frequently
double crossover phenotypes occur least frequently
single crossover phenotypes occur with “intermediate” frequency

Question 39

what are variations in chromosome structure important for?

Answer 39

evolution, they may result in production of abnormal offspring, and they may alter the phenotype of an organism

Question 40

how can chromosomes be identified?

Answer 40

by location of the centromere, banding patterns, and size of the chromosome

Question 41

what are deletion vs translocation vs inversion vs duplication chromosome mutations?

Answer 41

deletion: portion of the chromosome is missing
translocation: segment of one chromosome becomes attached to a non-homologous chromosome (simple is one way transfer, reciprocal is two way transfer)
inversion: change in the direction of part of the genetic material along a single chromosome
duplication: portion of the chromosome is repeated

Question 42

what causes chromosome deletions and duplications?

Answer 42

deletions: caused when a chromosome breaks and a fragment is lost
duplications: usually caused by abnormal events during recombination such as crossing-over between misaligned chromosomes

Question 43

what is non-disjunction?

Answer 43

failure of the chromosomes to segregate properly in anaphase

Question 44

what is aneuploidy vs polyploidy vs euploidy vs alloploidy?

Answer 44

aneuploidy: variation in the number of particular chromosomes within a set (trisomy (2n+1), monosomy (2n-1))
polyploidy: variation in the number of complete sets of chromosomes (triploid (3n), tetraploid (4n))
euploidy: refers to having the normal number of chromosomes
allopolyploidy: an individual having two or more complete sets of chromosomes derived from different species (allotetraploid = two complete sets of chromosomes from two different species)

Question 45

which vigorous allopolyploid plant causes serious problems in Washington State by clogging the Columbia River estuary?

Answer 45

spartina anglica, a super weed