Genetics exam 1

Key terms and concepts

Transmission genetics

mendelian genetics- how genes move from parent to offspring

population genetics

variation in a group

blending inheritance

the incorrect theory that parental traits blend together like paint and are passed down like that; if this was true we would see genetic variations disappear

pangenesis

Darwins wrong hypothesis that all body parts produce particles which are passed to offspring

preformationism

belief that a fully formed mini organism exists and grows larger

germ plasm theory

Weismanns theory that hereditary info is transmitted only from germ cells

inheritance of acquired characteristics

Lamarcks idea that traits acquired in a lifetime can be passed on - false

Prokaryotes

Eubacteria and archaea; don’t have membrane bound organelles, have cell walls, no nucleus, have circular chromosomes, unicellular typically, and can undergo binary fission

Eukaryotes

have a nucleus, have membrane bound organelles, include animals, plants, fungi, protists; have linear chromosomes, and have histones

• have more similar structural traits to archaea and they have a common ancestor

Histones

Has DNA wrapped around it to create chromatin; that chromatin condenses and packs the DNA to chromosomes; only in Euk

Viruses

non living; have a protein coat and dsDNA, ssDNA, or ssRNA

prokaryotic cell reproduction

1 origin of rep, high rate of rep, simple process in a circular chromosome

Eukaryotic cell rep

complex, homologous pairs, with multiple points of origin in a linear chromosome

• Haploid: 1 set of chromosome

• Diploid: 2 sets of genetic info (chromosomes in pairs)

Chromosomes

Have a centromere which holds together the 2 sister chromatids; telomeres: the tips of the linear chromosome, kinetochore: where the spindle fibers connect and moves the chromatids in the M phase

• Homolog pairs: contain the same genes from different parents

• Sister chromatids: independent copies of a single chromosome joined together after DNA rep

The cell cycle

Interphase: period between cells divisions, DNA synthesis, Chromosome replication

M phase: mitotic phase or meiosis phase

G1, G1S, S, G2, G2M, Mitosis, Cytokenesis

• G1 : growth phase; proteins that enable growth —> sometimes leads to G0 where cell is resting or non dividing

• G1S: a check point that signals cell can move on to S phase

• S: synthesis phase; DNA replication

• G2: Preparation for division'

• G2M: Check point, DNA must be fully replicated and undamaged

Mitosis

2 cells identical to each other and the parent; contains a full set of chromosomes, contains half the cytoplasm and organelles content of the parent

PPMAT

• Prophase: spindle fibers form; chromosomes condense

• Prometaphase: nuclear envelope disappears, kinetochores form, spindle fibers attach

• Metaphase: Chromosomes line up in the middle

• Anaphase: sister chromatids are separated to opposite sides

• Telophase: nuclear envelope reforms, chromosomes uncoil, spindles disappear

• Cytokenesis: technically separate, cytoplasm of a single parental cell divides into two daughter cells

Meiosis

results in 4 unique haploid daughter cells with genetic variation; has two phases

M1: separation of homologous pairs, reduction of chromosome by half, 2n —> n, in prophase 1 synapsis occurs where homologous chromosomes pair and overlap creating a tetrad; this allows crossing over in which segments of sister chromatids swap

M2: separation of sister chromatids also known as equational division 2 haploid cells —> 4 haploid cells; does not have a reduction in chromosome number, crossing over does not occur again, individual chromosomes line up rather than homologs

Cohesion

protein that holds chromatids together; forms cohesion rings that break down during anaphase

• in meiosis: shugoshin protects cohesion at the centromere in meiosis 1 so all the chromatids do not separate just the chromosomes

reproduction in animals

Spermatogenesis and oogenesis

• Oogonium (2n) —> primary oocyte (2n) —> secondary oocyte (1n) and polar body —> secondary oocyte gets fertilized —> zygote (2n)

reproduction in plants

Microsporogenesis, megasporogensis

• Alternation of generations: sporophyte (2n) —> spores (1n) —> gametophytes —> 1n gametes —> fusion of gametes —> 2n zygote —> diploid sporophyte

condensin

a large, multi-subunit protein complex that packs long, tangled DNA strands into compact, orderly chromosomes during cell division

bivalent

A bivalent is a pair of connected homologous chromosomes that form during the first stage of meiosis; different from a tetrad as they are two joined chromosomes

• consist of 1 maternal and 1 paternal that associate during prophase 1

polyploid

a cell that has more than two complete sets of chromosomes

Mendelian genetics

used pea plants because of their short generation time and their ability to produce many offspring; self fertilization and controlled cross pollination

Characteristic vs Trait

Characteristic: feature possessed by an organism —> overarching group —> eye color

Trait: appearance or manifestation of characteristic —> variant —> blue eye color

Monohybrid cross

between two parents that differ by 1 characteristic

4 conclusions Darwin drew from monohybrid crosses

1. one character is encoded by 2 genetic factors

2. 2 genetic factors (alleles) separate when gametes are formed

3. the concept of dominant and recessive traits

4. 2 alleles separate with equal probability into the gametes

Reveals the principle of segregation and dominance

principle of segregation

each individual diploid organism possesses 2 alleles for any particular characteristics; these 2 alleles segregate in anaphase 1 when gametes are formed and 1 allele goes to each.

• if no crossing over occurs segregation only happens in anaphase 1 but if crossing over occurs it also happens in anaphase 2

concept of dominance

when 2 alleles are present in a genotype only the trait encoded by one of them is observed as a phenotype —> the dominant allele is observed

Independent assortment

alleles on different loci separate independently; occurs in metaphase 1

probability

likelihood of the occurrence of a particular event

• addition rule= probability of rolling two numbers on a die

• multiplication rule= probability of rolling the same number twice

Test cross

between individuals with an unknown genotype and one with a homozygous recessive genotype —> (A_ x aa)

Dihybrid crosses

examine 2 traits at the same time

—> proves independent assortment

often 9:3:3:1 ratio but not always

• can preform a cross or use the branch method

Chi sq goodness of fit

indicates the probability that the difference between the observed and expected values is due to chance

• when using the table of crit values look at the degree of freedom and the value received from the equation

• if P<0.05 - the difference is statistically significant, not due to chance and we reject the null hypothesis

• if P>0.05 - the difference is not significant and due to random chance, we fail to reject the mendelian ratio (normal situation)

locus

a specific place on a chromosome occupied by an allele

recipricol cross

a pair of crosses where the sexes of the parents are reversed to see if the trait's inheritance depends on the parent's sex

back cross

a genetic crossing of a hybrid offspring with one of its parents or an individual that is genetically similar to the parent

pedigree

a pictorial representation of family history

• view autosomal recessive traits as they seem to skip generation

• view autosomal dominant traits as they don’t skip generations and seen to appear with equal frequency in both sexes

proband

The person from whom the pedigree is initiated (the first affected person)

consanginuity

the condition of being related to another person by blood through a common biological ancestor

Sex determination

sexual reproduction alt between haploid and diploid states; female and male gametes differ in size

• also relies on environmental and gene interactions

pseudoautosomal regions

PAR - regions that allow for X and Y chromosomes to pair and undergo recombination in meiosis; this is the only location where they are similar/homologous - the rest of the composition is completely different

• it is located in between the telomeres and the X or Y specific genetic DNA

• consists of the primary and secondary PAR: 1 PAR is is bigger than 2 PAR and it has more DNA

Genic sex determination system

some have no sex chromosomes and only have alleles which are located at different loci for sex determination

Environmental factors in sex determination

temperature is an examples of env factors affecting determination.

sex det in drosophilia

based on a ratio of X:A

• The number of X chromosomes to the number of haploid sets of autosomes

• A= 1 haploid set of 3 autosomes, AA= 6 autosomes/ 2 sets, AAA= 9 autosomes

when dividing X/A; if it is 1.0= female, 0.5= male, 1< = meta female, 0.67 = intersex, 0.5> = metal male

The Y chromosome is only beneficial for sperm production and determines fertility

O = male but infertile

SRY gene and sex det in humans

determines maleness on the y chromosome

• Turners: XO

• Poly X

• Klinefelters: XXY, XXXY, XXXXY, XXYY

X linked characteristics

some characteristics are linked to sex chromosomes. Example is color blindness; most of the time if the mother is affected then the son will also be affected

• genotypes written like: X⁺X⁺, X⁺X^W, X^WY, etc.

Dosage compensation

mechanism that balances the expression of X linked genes between sexes

Lyon Hypothesis

explains mammalian dosage compensation by nondominant X chromosome inactivation females

Y linked

only present in males, all male offspring express the trait

• y chromosomal dna lost over time

Barr bodies

random inactivation of an X chromosome later on if it has multiple X’s; the X chromosome becomes condensed and forms a barr body

• random x inactivation leads to the formation of calico cats coats

• not all genes are silenced as some x linked traits escape inactivation

locus

location of a chromosomes where a particular gene is found

incomplete dominance

the phenotype of a heterozygote is intermediate between the phenotype of 2 homozygotes; a red flower and a white flower makes a pink flower

codominance

the phenotype of the heterozygote includes the phenotypes of both homozygotes; roan cow has red and white fur

Cystic fibrosis

the levels of phenotypes may effect dominance

• CFTR: mutates in cystic fibrosis and reduces or eliminates CFTR chloride channel function —> in heterozygotes enough functional CFTR is made that they do not experience cystic fibrosis

Penetrance

the percentage of individuals having a particular genotype that expresses the expected phenotype

expressivity

the degree to which a trait is expressed; how strongly does an individual show the trait?

• penetrance and expressivity are shaped by environment and developmental processes not only by the genotype

• individuals do not always express the expected phenotype (ex. having extra digits)

Compound heterozygote

an individual with 2 different mutant alleles of the same gene; one on each homologous chromosome

lethal alleles

an allele that causes death at an early stage of development; some genotypes may not occur amongst the progeny as they cause ratios to shift

multiple alleles

for a given locus, more than two alleles are present within a group of individuals

• ABO blood type