Genetics Test 1

Genetics

the study of heredity and the expression of inherited traits

agriculture, medicine, biotechnology, and evolution

What has genetics greatly influenced in our daily lives?

Genome

the complete set of genetic instructions for any organism—> all are encoded in nucleic acids (RNA or DNA)

transmission, population and molecular genetics 

What are the 3 major subdisciplines of the study of genetics?

Transmission genetics

Encompasses the basic principles of heredity and how traits are passed from one generation to the next

• addresses the relation between chromosomes and heredity, the arrangement of genes and chromosomes, and gene mapping

• focuses on the individual organism

Molecular genetics 

Concerns the chemical nature of the gene itself: how genetic information is encoded , replicated, and expressed

• includes the cellular processes of replication, transcription, translation and gene regulation 

• focus is on the gene and its structure, organization and function

Population genetics

Explores the genetic composition of populations and how that composition changes geographically and with the passage of time—fundamentally the study of evolution because evolution is genetic change

• focus is on the group of genes found in a population

Model genetic organisms 

extensively studied, simple organisms used to model genetic interactions in more complex organisms

short generation time, numerous progeny, ability to carry out controlled genetic crosses, can be reared in labs, genetic variants, knowledge of genetic systems

Common characteristics of model organisms

germ-plasm theory

the concept all cells contain a complete set genetic information

cell theory

all life is composed of cells and cells arise only from cells

mendelian inheritance

traits are inherited in accord with defined principles   

viruses

• Not cellular organisms

• They are neither prokaryotic nor eukaryotic

• They are simple structures composed of an outer protein coat surrounding a nucleic acid

• not considered alive

• they can only reproduce within host cells

Requirements for successful reproduction of any cell

1. genetic information must be copied

2. the genetic copies must be separated from each other

3. the cell must divide

Prokaryotic cell replication by binary fission 

Involves the replication of the circular chromosome—replication usually begins at a specific place on the circular chromosome, called the origin of replication

• under optimal conditions, this process can occur every 2 minutes 

ploidy

indicates how many sets of genetic information it possesses

size, membrane-bound organelles, genomes

Major differences between eukaryotic and prokaryotic cells 

eukaryotes have a lot more chromosomes to copy 

Why is eukaryotic cell reproduction more complex than in prokaryotes? 

centromere, telomeres, and origin of replication

What are the 3 essential elements of a functional chromosome?

centromere

a constricted region of the chromosome where the kinetochores and spindle microtubules form

telomeres

the specific DNA sequences and associated proteins located at the tips of whole linear chromosomes; they protect and stabilize the chromosome ends 

origins of replication

the sites where DNA replication begins

• chromosome structure changes during the cell cycle and varies between each chromosome—> there are 4 major shapes

submetacentric

a chromosome shape where the centromere is located off-center, resulting in one arm being significantly longer than the other. The shorter arm is designated the 'p' arm, and the longer arm is the 'q' arm. This off-center position gives the chromosome an L-shape when the sister chromatids separate during anaphase

metacentric 

A chromosome shape where the centromere is in the middle of the 2 sister chromatids, making an “X” shape 

telocentric

chromosome shape that has its centromere positioned at the very end, resulting in only one visible chromosome arm at the microscopic level

acrocentric

chromosome shape where the centromere is located very close to one end, resulting in one very long arm and one very short arm

the cell cycle

the series of stages through which a cell passes from one division to the next

checkpoints

they allow or prohibit a cell’s progression to the next stage during the cell cycle

• regulate the cell cycle; also called oncogenes

interphase and mitotic phase 

What are the 2 major phases of the cell cycle? 

interphase

extended period of growth and development between cell divisions; the cell spends most of it’s time here, the nuclear membrane is present and the chromosomes are relaxed

G1, S, G2, and sometimes G0

What are the stages of interphase?

G1 phase

First growth phase in interphase; checkpoint ensures that the cell is good to go for DNA replication 

S phase

Phase of interphase where DNA is copied; chromosomes are relaxed in order to replicate 

G2 phase

The second growth phase in interphase; checkpoint ensures that DNA was copied correctly before dividing

G0 phase

stable, nondividing period of variable length if cell isn’t ready for S phase

mitotic phase

Period of active cell division during the cell cycle; includes mitosis (PPMAT) and cytokinesis

prophase/prophase II

chromosomes condense and each chromosome has 2 sister chromatids; mitotic spindle forms

prometaphase/prometaphase II

The nuclear envelope completely disintegrates and spindle microtubules anchor to kinetochores

metaphase/metaphase II

Chromosomes align on the metaphase plate and the spindle-assembly checkpoint occurs

anaphase/anaphase II

sister chromatids separate, becoming individual chromosomes, and migrate towards opposite spindle poles

Telophase/telophase II

Chromosomes arrive at spindle poles, the nuclear envelope reforms and the condensed chromosomes relax

cytokinesis

The cytoplasm divides, which yields 2 identical daughter cells

• In plant cells this is when the cell wall forms

meiosis

process of cell division that allows sexual reproduction, which produces genetic variation via genetically unique haploid gametes

reduction division and equational division

Meiosis occurs in 2 stages: Meiosis I (_________) and Meiosis II (_____________)

crossing over

exchange of genetic material between homologous but non-sister chromatids

prophase I

When does crossing over/genetic recombination occur?

leptotene, zygotene, pachytene, diplotene, and diakinesis 

What are the five stages of prophase I? 

Prophase I

chromosomes condense, homologous chromosomes synapse, crossing over occurs, the nuclear envelope breaks down, and the mitotic spindle forms

synapsis

the process in meiosis where homologous chromosomes pair up and form a stable association, facilitated by the formation of the synaptonemal complex (SC).

• is a crucial step for crossing over (genetic recombination) to occur, which shuffles genetic material and creates new allele combinations, ultimately increasing genetic diversity in the offspring

tetrad/bivalent

a structure formed during prophase I of meiosis, consisting of a pair of homologous chromosomes, with each chromosome consisting of two sister chromatids, for a total of four chromatids bundled together

chiasmata

a point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.

Metaphase I

Homologous pairs of chromosomes line up along the metaphase plate 

anaphase I

Homologs separate and move towards opposite poles 

telophase I

chromosomes arrive at spindle poles and cleavage furrow is visible

Cytokinesis I

cytoplasm divides to produce 2 genetically unique diploid cells

Interkinesis

the period between meiosis I and II where the nuclear membrane re-forms, the spindle breaks down and the chromosomes relax

Cytokinesis II

the cytoplasm divides to produce 4 genetically unique haploid cells

cohesin forms a ring structure around each chromatid pair and holds them together  

How do sister chromatids stay together?

cohesin

a protein that becomes established in S phase and persists through G2 and early mitosis—is broken down by seperase during anaphase all along the length of the chromosome so the sister chromatids can separate 

shugoshin

protects the cohesin located at the centromere of each chromosome during anaphase I, but degrades by the end of metaphase II—allows just sister homologs to separate in meiosis I

because they were easy to grow, grew rapidly, produced many offspring, and there were many decipherable varieties available

Why was Mendel so successful with peas?

gene

an inherited factor (encoded in DNA) that helps determine a characteristic 

allele

one or two alternative forms of a gene

locus

specific place on a chromosome occupied by an allele

genotype 

set of alleles possessed by an individual organism

homozygote

an individual organism possessing 2 of the same alleles at a locus

heterozygote

an individual organism possessing 2 different alleles at a locus

characteristic/character

an attribute or feature possessed by an organism 

Phenotype/trait

the appearance or manifestation of a characteristic

monohybrid cross

a genetic cross that only looks for 1 trait

Mendel’s law of segregation

Observations:

1. Each individual organism possess 2 alleles encoding a trait

2. Alleles separate when gametes are formed

3. Alleles separate in equal proportions

Mendel’s law of independent assortment

Alleles at different loci separate independently

chromosomal theory of heredity

the idea that genes are located on chromosomes

concept of dominance

states that when 2 different alleles are present in a genotype, only the trait encoded by one of them is observed in the phenotype 

backcross

a cross between the F1 genotype and either P genotype

probability

the chance an event will occur in the future; (# of individuals with a given phenotype)/(total # of individuals)

multiplication rule

the probability that 2 or more independent events will occur is equal to the product of the individual probabilities 

• Keywords “and” and “birth order”

addition rule

the probability that one of two or more mutually exclusive events will occur is equal to the sum of the individual probabilities of events

• keyword: “or”

binomial expansion

used when events are neither mutually exclusive nor in a specific sequence; used for an unordered combination of events

testcross

dominant individual with unknown genotype is crossed with a homozygous recessive individual

dihybrid cross

genetic cross between 2 individuals that involves 2 genes

• there are always 4 possible gamete combinations and this can be used to determine if genes are on the same chromosome 

when observed ratios are not what were expected

When is the chi squared goodness-of-fit test used?

chi squared test

statistically determines if observed data fits a theoretical expectation

null hypothesis 

when there is no difference between the observed and expected values 

P value

the probability that deviations between observed and expected values are up to chance

• when less than .05, a significant difference between observed and expected values exists

inverses, chi square value

P value and chi square are _________ of each other; the bigger the ____________, the more likely there will be a statistical difference in variation

chromosomally, genically, and environmentally 

What are the three ways sex can be determined?

chromosomal sex determination

sex chromosomes differ morphologically or in number between males and females

• Males and females don’t possess the same number of alleles at sex-linked loci

Genic sex determination

Where a species has no sex chromosomes; genotypes at one or more loci determine sex

• allows for sequential hermaphrodism

ex: yeasts, organisms with mating types, etc.

environmental sex determination

environmental factors (ex: temperature) determine sex

y chromosome

An acrocentric sex chromosome that is much smaller than it’s counterpart; contains the SRY gene that determines maleness

XX-XO and XX-XY sex determination

females are homogametic and males are heterogametic

pseudoautosomal regions at the tips allow for crossing over to occur

How are X and Y chromosomes able to pair in meiosis?

ZZ-ZW sex determination

males are homogametic and females are heterogametic 

haplodiploidy

Where a species has no sex chromosomes; the females are diploid and the males are haploid

Turner Syndrome XO

• Biologically female

• short, may have underdeveloped secondary sex characteristics

• normal intelligence 

• sometimes sterile

• 1 in 3000 female births 

Klinefelter syndrome XXY or XXYY

• Biologically male

• produce less testosterone, so secondary sex characteristics are sometimes impacted

• normal intelligence

• often sterile

• 1 in 1000 male births

Poly-X syndrome XXX-XXXXX

• Biologically female

• tall, thin

• usually fertile

• XXX normal intelligence

• >3X’s results in intellectual disability

• 1 in 1000 female births 

nondisjunction

the failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis, resulting in gametes (egg or sperm) or daughter cells with an incorrect number of chromosomes

Androgen Insensitivity Syndrome 

• Have SRY region on Y chromosomes

• Female external sexual characteristics

• Testes inside body still produce testosterone

• Defective androgen receptors—body can’t respond to testosterone signals