landmark discoveries in DNA (lecture 1)

Question 1

Gregor Mendel 3 laws of inheritance w/ definitions

Answer 1

1. law of segregation - traits are inherited by via a pair of gene (two alleles), parental alleles are randomly separated to the sex cells so that sex cells only contain one allele of the parent’s pair. Offspring then inherit one gene copy from each parent.
2. law of independent assortment - inheritance of different traits is not dependence on inheritance of another as genes for different traits are sorted separately from one another
3. law of dominance - an organism with alternate forms of a gene (one on each allele) will express the form that is dominant.

Question 2

Define allele

Answer 2

Chromosomes are found in pairs, each gene in a diploid organism has two alleles, one on each chromosome of the pair. Alleles are variants of a gene located the same place on different chromosomes (on the same place of each of our two chromosomal copies , except for the sex chromosomes).

Question 3

Chromosome

Answer 3

a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

Question 4

diploid

Answer 4

containing two complete sets of chromosomes, one from each parent.

carrying two copies of a gene means you are diploid for that gene

Question 5

haploid

Answer 5

having a single set of unpaired chromosomes

Question 6

genotype

Answer 6

genetic makeup of an organism determined by the pairs of alleles in our DNA

Question 7

filial 1

Answer 7

F1 generation, first generation offspring of original parents

Question 8

heterozygote

Answer 8

organism that inherits two different alleles for a given gene (inherited one copy of each allele from parents, parents had different alleles from one another)

Question 9

homozygote

Answer 9

organism that inherits two alleles of the same type for a given gene (inherited a copy of the exact same allele from each parent)

Question 10

are gametes haploid or diploid?

Answer 10

haploid, they only contain one copy of each gene/one chromosome/one set of alleles

Question 11

do heterozygotes or homozygotes produce gametes with either allele?

Answer 11

heterozygotes, homozygotes would produce gametes with only one allele (no option for “either” as there is no “either”)

Question 12

autosome

Answer 12

Any chromosome that is not a sex chromosome

Question 13

locus

Answer 13

place on a chromosome where a gene has its place

Question 14

according to chromosome theory of inheritance (Thomas Hunt Morgan, 1910), genes on separate chromosome behave how?

Answer 14

independently from one another

Question 15

according to chromosome theory of inheritance (Thomas Hunt Morgan, 1910), genes on the same chromosome behave how?

Answer 15

as if they are linked, but genetic linkage is not absolute

Question 16

Why is genetic linkage not absolute?

Answer 16

offspring may show new combos of alleles not seen on the parent chromosome when crossing over/recombination occurs

Question 17

what drives the frequency of recombination between two genes? (how often do two genes on the same parental chromosome end up on different chromosomes in F1?)

Answer 17

the distance separating genes on the chromosome

Question 18

general recombination

Answer 18

Recombination that occurs anywhere along two homologous DNA molecules is called during meiosis (during the production of gametes)

The mechanism of general recombination ensures that two DNA double helices undergo an exchange reaction only if they contain an extensive region of sequence similarity (homology).

Question 19

sister chromtids

Answer 19

two copies of one chromosome produced during mitosis, looks like an x and centromere is in center holding it together

Question 20

one gene-one enzyme hypothesis

Answer 20

Idea proposed by Beadle and Tatum (1941) that each gene encodes a separate enzyme. This hypothesis is overly simple.

Question 21

what is neurospora crassa

Answer 21

bread mold studied by Beadle and Tatum to identify nutritional mutants (led to one gene one enzyme hypothesis)

Question 22

Explain lifecycle of N. crassa

Answer 22

Neurospora spends most of its life as a haploid.

Conidia are asexually produced haploid spores of fungi made by a haploid parent. Ascospores are sexually produced haploid spores of fungi made via meiosis from a diploid zygote.

1. Vegetation mycellium (haploid, 1 copy of each chromosome) asexually produces haploid spores called conidia
2. haploid spores grow into vegetative mycelium. The strands develop into a structure called the proto-perithecium which interacts with the conidia from a different mycelium and develops into a perithecium.
3. In a maturing ascus, there are two nuclei one of which comes from the conidium and the other from the proto-perithecium. Each nuclei has only one set of chromosomes (haploid). The two haploid nuclei fuse into a diploid nucleus. The nucleus then divides, separating into two nuclei each with one set of chromosomes. Those nuclei duplicate themselves and then all the nuclei duplicate themselves again. This process yields eight haploid ascospores within a mature ascus.

Question 23

4 reasons one gene-one enzyme hypothesis is incorrect

Answer 23

1.An enzyme may be made of several subunits, with each subunit encoded by a different gene

2.Many genes code for non-enzyme proteins

3.End products of some genes are not polypeptides

4.Some genes can code for multiple protein variants (e.g., due to alternative splicing)

Question 24

bacterial transformation

Answer 24

discovered by Frederick Griffith studying Streptococcus pneumoniae. Bacterial transformation is a process where bacteria take up foreign DNA and integrate it into their chromosomes.

Question 25

how is bacterial recombination utilized in cloning? (simple answer)

Answer 25

This process is a key technique in molecular cloning, where bacteria are used to create multiple copies of a recombinant DNA molecule.

Question 26

explain Griffith experiment (bacterial transformation)

Answer 26

a non-virulent rough strain (no polysac coat) was mixed with a virulent but dead smooth strain (yes polysac coat) and injected into a mouse. Mouse died, found live S strain in mouse, determined R must be transforming into S somehow

Question 27

explain oswald avery experiment (DNA is “transforming” genetic material)

Answer 27

Isolated compounds of virulent smooth (S) bacteria, found only the resulting fibrous strands (DNA) were able to transform R bacteria into S

Question 28

how did Hershey and Chase confirm genetic material was DNA using bacteriophage T2?

Answer 28

radiolabeled protein coats or interiors of bacteriophages (viruses which inject DNA into bacteria), in the treated bacteria they found only the radiolabels from interior where passed on, not labeled from the protein coats

Question 29

Erwin Chargaff discovered what about DNA?

Answer 29

The amounts of bases A/T and G/C are equal

Question 30

What is the mechanism of DNA replication?

Answer 30

semiconservative, meaning after replication each molecule is composed on one old strand and ole new strand

Question 31

explain meselson-stahl experiment (mechanism of DNA replication)

Answer 31

grew e. coli grown in “light” or “heavy” nitrogen, then using density gradient centrifugation spun samples and saw heavy ends up lower in tube than light. If heavy was allowed to grow in light medium one cell cycle then: all DNA is in an intermediate band. After two cell cycles: 50% light 50% intermediate three cell cycles: 75% light 25% intermediate