Genetics Exam 2 (Final Draft)

NOTE: CRISPR will not be on the exam

innate immunity vs adaptive immunity

innate immunity is non specific defences that act the same way against all foreign agents.

Adaptive immunity is a specific response for each individual pathogen.

Bacteriophage

a virus that infects bacteria

CRISPR purpose

bacteria's adaptive immunity defense system against bacteriophages

CRISPR gene region consists of

repeats & spacers

CRISPR repeats

Repeated sequences of nucleotides that are distributed throughout a CRISPR region - genetic signature

CRISPR spacers

in between repeated sequences, unique DNA sequences that are derived from past encounters with viruses or other foreign genetic elements

CRISPR adaptation phase

occurs when bacteria are exposed to bacteriophage virus for the first time, cas1 and cas 2 genes are expressed as a cas1cas2 complex and break up bacteriophage DNA strand, some pieces of it are then inserted into CRISPR system

nucleases

degrade nucleic acids (DNA & RNA)

nucleases in CRISPR response

Cas1 and Cas2 expressed genes together

what is transcribed in CRISPR expression phase

transcription of entire CRISPR gene (Repeats and spacers)

What occurs during CRISPR expression phase?

precrRNA and tracrRNA are transcribed and bind together due to complimentary base pairing. Cas9 proteins are also expressed, and these bind to the complex just formed.

CRNA guides cas protein to bind to complimentary pairs of DNA or RNA of foreign material, then they break up and degrade these foreign sequences.

The chromosomal theory of inheritance states that

chromosomes are carriers of genetic information

sytenic genes

genes located on the same chromosome

Bateson and Punnett dihybrid cross results

Crossed purple/red and long/round pollen genes true breeding for each, and allowed F1 generation to self fertilize. Found that parental phenotypes were most numerous.

Why did Bateson and Punnett still see differing phenotypes from the parents despite linked assortment occurring?

Crossing over events could have occurred between the parental chromosomes that were dominant or recessive linked.

What did Bateson and Punnett results tell us?

Crossing over can occur, but it is more likely that it does not occur in the offspring production

synaptonemal complex

a zipper-like structure composed of proteins, which connects two homologous chromosomes tightly along their lengths in prophase 1

Chiasma

The microscopically visible site where crossing over has occurred between chromatids of homologous chromosomes during prophase I of meiosis.

recombinant chromosomes

A chromosome created when crossing over combines the DNA from two parents into a single chromosome.

More space between genes on a chromosome means

more space for crossing over to occur - higher chance of a random cross over event to happen

More recombinants in a cross is due to

more distance between two genes on homologs

test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

Distance of genes formula

= (total # recombinants/total# of all offspring ) * 100

units used to describe distance

map units (m.u.) or CentiMorgans

1 map unit = __% recombination in a test cross

1%

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape in an organized manner.

Autosomes

non-sex chromosomes (1-22)

sex chromosomes

XY, determine sex of an individual

metaphase spread

Analysis of chromosomes arrested during metaphase. The chromosomes are highly condensed at this stage of cell division and are visible under a light microscope.

Classification of chromosomes for a karyotype

size (first is largest), location of centromere, G-banding

metaphase chromosome centromere locations

metacentric, submetacentric, Afrocentric, telocentric

metacentric

centromere approximately in middle of chromosome

submetacentric

centromere slightly off center

acrocentric

centromere close to end

telocentric

centromere at end

G-banding of chromosomes

Giemsa stain binds to naked DNA. Stains phosphate groups, darker in regions rich of A-T base pairs. Allows for identification of chromosomes in karyotype

p chromosome

short arm of chromosome

q chromosome

long arm of chromosome

does a metacentric chromosome still have a long arm and short arm?

Yes

types of changes in chromosomal structure

deletion, duplication, inversion, simple translocation, reciprocal translocation

chromosomal structure deletion

region of chromosome is deleted

chromosomal structure duplication

region of chromosome is duplicated

chromosomal structure inversion

region of chromosome is inverted (flipped)

simple translocation chromosomal structure

one region moves and attaches to another region

reciprocal translocation chromosomal structure

one region from each chromosome switch places

types of chromosomal deletions

terminal deletion & interstitial deletion

terminal deletion

deletion at end of chromosome

interstitial deletion

chromosome breaks at two locations, the central fragment is lost, and the outer pieces rejoin

clastogens

any substances that can break the backbone of DNA

Non-allelic homologous recombination (NAHR)

a form of homologous recombination that occurs between two lengths of DNA that have high sequence similarity, but are not alleles (not at the same spot on each chromosomes - misaligned)

two ways you can get deletions

clastogens or NAHR

Cri du chat syndrome

A deletion of the short arm of chromosome 5, many issues caused by a small deletion

when is deletion most important?

when a part or an essential gene is deleted

essential gene

a gene that is essential for survival

replication slippage

occurs during DNA replication, DNA polymerase can be unstable and fall off replicating strand, and return at a spot it has already replicated because the region looks similar, thus, some of the region after replication has been duplicated

Processitivity

how stable enzyme is on DNA backbone

Homologues

chromosomes that are given the same number, but are of opposite parental origin

How do homologues form

gene duplication occurs, over generations, the two genes can become very different due to gradual accumulation of DNA mutations

Paralogs

homologous genes in the same species

pericentric inversion

inversion that includes the centromere

peracentric inversion

inversion that does not include the centromere

Most inversions

do not result in an abnormality

Detrimental inversion cases

position effect, chromosomal break happens in middle of an essential gene

position effect

change in expression of a gene associated with a change in the gene's location within the genome

Euchromatin

loosely packed chromatin

Heterochromatin

tightly packed chromatin

tightly packed chromatin usually results in gene...

silencing

facultative heterochromatin

Regions that can interconvert between euchromatin and heterochromatin

facultative heterochromatin is useful because

it helps control gene expression with its versatility

Chromatin

Clusters of DNA, RNA, and proteins in the nucleus of a cell

constitutive heterochromatin

Regions that are always heterochromatic, telomeres & centromeres

variegation in drosophila example

position effect, genes on euchromatin are inverted and are then closer to centromere (heterochromatin region), and now the gene is less likely to be expressed

hemophilia example

essential gene is disrupted by chromosomal break, sequence is inverted, and gene is unable to be finished because exons are out of order

The middle gene of a three gene mapping experiment can be determined by examining the genotypes of which of the following?

Offspring that exhibit double crossover events.

A crossover in meiosis is an exchange of genetic material between __________.

non-sister chromatids of homologous chromosomes

define the principle of linkage?

Both two or more genes that are physically connected on a chromosome and genes that are transmitted to the next generation as a group

The production of gene families, such as the globin genes is the result of ________.

gene duplications

When does crossing over occur?

Prophase 1

Gene duplications may be caused by __________.

crossing over of misaligned chromosomes

A tall (T) tomato plant with mottled (m) leaves is crossed with a short (t) plant with normal (M) leaves. You get all tall, normal leafed F1 plants.You cross the F1 plants with a short, mottled leafed plant. What would be the expected values from this hypothesis?

Tall mottled 250, Short normal leaves 250, Tall normal leaves 250, Short mottled leaves 250 - explain: TtMm x ttmm gives TtMm, ttMm, Ttmm, and ttmm possibilities. 4 options mean divide total pop. /4 = 1000/4 = 250 expected for each phenotype

two mechanisms that result in translocation events

non homologous crossover/recombination, chromosomal breakage incorrectly repaired

incorrect chromosomal repair from environmental breakage - how does it happen?

environmental agent causes 2 chromosomes to break, DNA repair recognize reactive ends and incorrectly correct them, causing reciprocal translocation.

Homologous Recombination vs nonhomologous recombination vs non allelic homologous recombination

homologous: crossing over between homologous chromosomes (we want this to happen, exact same spot). nonhomologous: crossover between non homologous chromosomes that results in reciprocal translocation. Non-allelic: occurs between high similar sequences that are not alleles, not at the exact same place (misaligned)

non homologous recombination

cross over between nonohomologous chromosomes results in reciprocal translocation

balanced translocation

a translocation, such as a reciprocal translocation, in which the total amount of genetic material is normal or nearly normal

Why translocation is usually detrimental

position effect, if break occurs in middle of important gene

Philadelphia chromosome & CML

chromosomal break between chromosome 9 and 22, ABL on chromosome 9 encourage cell cycle division, common break BCR region on chromosome 22, both sites break, and the ABL and BCR genes come together on chromosome 22 (changed Philadelphia chromosome), this new chromosome cannot be silenced - continuous cell division, results in CML type of cancer.

Familial Down Syndrome

Robertsonian translocation between chromosomes 14 and 21

Robertsonian translocation - how does it happen (criteria for it)

two ACROCENTRIC chromosomes, fusion of both long arms

How does robertsonian translocation lead to familial Down syndrome?

A parent who has undergone robertsonion translocation in reproduction makes some gametes with only one chromosome copy, when a normal sperm interacts with a long arm mutant chromosome, the long arm counts as a trisomy and leads to familial Down syndrome

Euploidy

total number of chromosomes divides into perfect sets

Types of Euploidy

diploid (2n), triploid (3n), tetraploid (4n)

Aneuploidy

total # of chromosomes do not divide into perfect sets

types of aneuploidy

trisomy (2n+1), monosomy (2n-1)

imbalance of gene products in trisomy and monosomy

normal individuals make 100% expression, trisomy makes the one 3 chromosome set have 150%, monosomy has the one one chromosome set have 50%

Trisomy where an organism can still live

13, 18, 21 (note: these are generally smaller chromosomes, fewer genes changed in expression means lesser drastic effects)

why don't trisomies happen in chromosome 1?

it is so detrimental that a spontaneous abortion would happen before the mother even knew

Nondisjunction can occur when

anaphase of meiosis 1 and 2