genetics exam 3

chromatin

DNA that’s packaged by proteins called histones; can exist in varying degrees of folding/compaction

eukaryotic cells only

condensation

the process of compacting and organizing chromatin during cell division

histones

basic proteins that package and compact DNA into structural units

nucelosomes

a complex of eight histone proteins

euchromatin

looser and more open; higher levels of transcription

heterochromatin

more compacted, much less transcription (genes are silenced)

histone acetylation

a reversible process where acetyl groups are added to lysine residues on histone tails; regulates gene expression and chromatin structure, causing the chromatin to become more open

RNA interference(RNAi)

a biological process in which small pieces of RNA can shut down protein translation by binding the mRNAs that code for those proteins

double-stranded RNA (dsRNA)

required for silencing

short interfering RNA (siRNA)

20-22 nucleotides with a 3’ overhang; enters the RNA induced silencing complex and unzips the dsRNA

mRNA degredation

after the single-stranded mRNA finds a complementary strand, it gets cut up by siRNA, causing its degredation

Is transcription active or inactive in euchromatin?

euchromatin is transcriptionally active

In what way does acetylation alter transcription activity?

Acetylation promotes transcription by neutralizing the positive charge of histone tails, weakening their interaction with DNA and making chromatin more accessible to transcription machinery.

true-breeding

pollination results in 100% of the parent phenotype for all filial levels

alleles

alternative forms (variants) of a gene

trait

a specific characteristic or feature of an organism that’s genetically determined

homozygous

genotype with two alleles that are the same (SS, ss)

heterozygous

genotype with two alleles that are different (Ss)

dominant trait

a trait that is displayed by an individual that is heterozygous

recessive trait

a trait that is not displayed by an individual that is heterozygous

monohybrid cross

a genetic cross between two true breeding individuals that differ in only one trait; allows for the study of the inheritance patterns of a single gene

dihybrid cross

a genetic cross between two individuals with two observed traits that are controlled by two distinct genes

test cross

a genetic cross of an individual organism of dominant phenotype but unknown genotype and an organism with a homozygous recessive genotype/phenotype

law of segregation (Mendel’s 1st law)

• during gamete formation, the two alleles for one trait seperate from one another

• at fertilization, only one allele is inherited from each parent, and allele choice is random

law of independent assortment (Mendel’s 2nd law)

during gamete formation, alleles for different traits assort independently

product rule

for independent events A and B, the probability of both A and B occuring is the product of their individual probabilities [p(A and B) = p(A) x p(B)]

sum rule

the probabi;ity of either event A or event B occurring is the sum of their individual probabilities [p(A or B) = p(A) + p(B)]

family pedigrees

a visual representation of a family’s genetic history highlighting relationships and patterns of inheritance for specific traits and conditions

hallmarks of pedigrees for dominant traits

• dominant traits can be displayed by an individual who is heterozygous or homozygous

• affected individuals always have an affected parent

• trait shows up at every generation - vertical pattern

hallmarks of pedigrees for recessive traits

• affected individuals are always homozygous

• affected individuals can have two unaffected parents

• when rare, recessive traits can appear without family history - horizontal pattern

“carrier” for an allele

an individual who has a particular allele; term most often used for individual who has the allele but does not show the trait

At a biochemical level, how can we explain the smooth or wrinkled pea phenotypes? Why is the smooth trait dominant and the wrinkled trait recessive?

The S (smooth) allele allows for translation of SBE1 which builds up branched starch in the organism, allowing it to retain water better. The s (wrinkled) allele does not allow for formation of branched starch and is therefore unable to retain water as well.

Heterochromatin is…

a. more condensed

b. less condensed

a. more condensed

A short interfering RNA (siRNA) triggers RNAi. This molecule is…

a. single-stranded, antisense

b. single-stranded, sense

c. double-stranded

c. double-stranded

According to Mendel, a parent possess how many “particles” (alleles) of information for a trait?

a. 1

b. 2

c. 3

b. 2

According to Mendel, how many alleles for a trait does a parent pass along to their child?

a. 1

b. 2

c. 3

a. 1

True or False

Heterochromatin is an open structure that leads to transcription activation.

False

True or False

Euchromatin does allow for gene transcription.

True

True or False

DNA is wrapped around proteins called nucleosomes.

True

How many histone proteins compose a nucleosome?

a. 2

b. 6

c. 8

d. 10

c. 8

True or False

Histone tails are acetylated to convert heterochromatin into euchromatin.

True

True or False

Fire and Mello’s experiment concluded that double-stranded RNA stimulates gene silencing.

True

What is a structural characteristic of siRNA?

a. 20-22 nucleotides long

b. double-stranded RNA

c. 3’ overhang

d. all of the above

d. all of the above

True or False

In RNAi, short interfering RNAs are designed to complement the target sequence/gene they must silence.

True

In eukaryotic genomes, regions of _____ are transcriptionally active while regions of _____ are transcriptionally silent.

a. heterochromatin, euchromatin

b. euchromatin, heterochromatin

c. none of the above

b. euchromatin, heterochromatin

True or False

We would expect histones with euchromatin to be acetylated.

True

Which of the following is NOT a method of eukaryotic gene regulation?

a. histone acetylation

b. chromatin compaction

c. RNA interference

d. all of the above are methods of eukaryotic gene regulation

d. all of the above are methods of eukaryotic gene regulation

In eukaryotes, histone acetylation leads to:

a. no change in chromatin organization

b. chromatin condensation

c. chromatin decondensation

c. chromatin decondensation

Which of the following is true of a short interfering RNA (siRNA)?

a. short length (19-22 nt)

b. 3’ overhangs on each end

c. RNA-RNA base-pairing

d. all of the above

d. all of the above

The molecule that triggers RNA interference is:

a. single-stranded sense RNA

b. single-stranded antisense RNA

c. double-stranded RNA

d. none of the above

c. double-stranded RNA

True or False

In eukaryotes, some mRNAs are not translated because they are silenced by RNA interference.

true

chromosome

a thread-like structure made of DNA and protein

haploid

a cell containing one of each chromosome (1n)

diploid

a cell containing two of each chromosome (2n)

homolog (or pair of homologs)

pairs of chromosomes that have the same genes in the same order, but may have different alleles of those genes

chromatid

one of the two identical halves of a homologous pair that has been replicated in preparation for cell division

sister chromatids

the two identical copies of a single replicated chromosome that are formed during DNA replication; separated during cell division

centromere

constricted regions on chromosomes that serve as the attachment point for spindle fibers and linking sister chromatids

chromosome arm

two arms on a chromosome that are separated by the centromere

crossover

exchange of the arms of the chromosomes between two homologous chromosomes’ non-sister chromatids; meiosis only

Cohesin protein

a protein that holds together the two chromosomes of a sister chromatid (shown in yellow on slides)

Separase enzyme

“pac-man” enzyme that cuts cohesin once spindle tension is present

segregation

meiosis reduces the chromosome number by half, allowing for only one homolog per gamete

spindles

attach to the centromere and pull sister chromatids and individual chromosomes apart during mitosis and meiosis

microtubule organizing centers

a cellular structure that nucleates and organizes microtubules

S phase

part of the cell cycle where DNA replication occurs, ensuring each daughter cell receives a complete set of chromosomes

mitosis

a type of cell division that produces two identical daughter cells from one parent cell; maintains chromosome number; haploid and diploid cells can unde

meiosis I

sister chromatids exchange arms (crossovers) between homologs; each pair of homologs attached to both poles and aligned at cell equators; regulated cutting of cohesin at arms via separase enzyme

meiosis II

sister chromatids align at equator and separate

daughter cell

either of the two cells formed when a cell undergoes mitosis

gamete

eggs and sperm; a haploid cell

What is segregated at mitosis?

sister chromatids

Describe the products of mitosis (include picture)

two genetically identical daughter cells

What is segregated at each phase of meiosis? What are the products of meiosis?

1) homologous pairs separate producing two haploid cells

2) sister chromatids separate to produce four haploid daugter cells

What happens in meiosis that allows a doubly heterozygous parent to produce gametes with all possible combinations?

Crossovers and alternative alignments

This trait must be…

a. dominant

b. recessive

c. could be either

b. recessive

Both parents must be…

a. homozygous

b. heterozygous

c. could be either

b. heterozygous

The probability of producing a Smooth pea from a cross between heterozygous parents is…

a. 0.25

b. 0.50

c. 0.75

d. 1.00

c. 0.75

True or False

Alleles are alternative forms of genes.

true

In eukaryotes, how many total alleles does an individual possess per trait?

a. one

b. two

c. three

d. four

b. two

In eukaryotes, how many total alleles does an individual receive from a parent?

a. one

b. two

c. three

d. four

a. one

What term refers to the combination of alleles that an individual possesses?

a. phenotype

b. genotype

b. genotype

True or False

A phenotype corresponds to an observable trait or characteristic.

true

True of False

If an individual has a homozygous genotype, that means both alleles are different.

false

Which law explains how members of different gene pairs are independently assorted into each gamete?

a. Mendel’s first law

b. Mendel’s second law

b. Mendel’s second law

Which of the following statements explains Mendel’s first law?

a. two alleles for one trait will separate from each other

b. only one allele is randomly inherited from each parent

c. both statements are correct

d. neither statement is correct

c. both statements are correct

True or False

In dominant traits, a heterozygous individual WILL display the trait.

true

True or False

Wild-type traits will always be dominant.

false

True or False

An autosomal trait is a trait located on a sex chromosome.

false

Which of the following is a hallmark of recessive traits in pedigrees?

a. affected individuals are always homozygous

b. affected individuals may be heterozygous or homozygous

a. affected individuals are always homozygous

Which of the following is another hallmark of a recessive trait in pedigrees?

a. affected individuals always have an affected parent

b. affected individuals can have two unaffected parents

b. affected individuals can have two unaffected parents

Pedigrees that express a dominant trait display

a. vertical pattern

b. horizontal pattern

c. no pattern

a. vertical pattern

hallmarks of X chromosome-linked traits

an allele located on the X chromosome

• affected father will never pass to sons

• affected father will pass allele to all daughters

• males only have 1 x-linked allele so they will display the recessive trait

parental type

progeny with the same allele combination as either parent

recombinant type

progeny with a different allele combination than both parents

recombination frequency (RF)

measures the likelihood of two genes being separated during meiosis

RF = (# recombinant progeny / # total progeny) x 100

unlinked and linked genes

when two alleles are linked, they tend to be inherited together

rule for linked genes: # parental > > > # recombinant

map unit

measure of distance between two genes on the chromosome

1% RF = 1 map unit

single crossover

double crossovers