Bio 1A- Information Flow, last midterm was shit

gametes

sperm and egg cells

centromere

“waist” where chromatids meet in the middle

chromatid

one of the two identical halves of a chromosome after DNA replication

progeny cells

daughter cells- after separation into these cells, chromatids are called chromosomes again

Phases of cell cycle

Interphase —> mitotic phase

Phases of interphase

G1 —> S —> G2

(G phases grow the cell, S phase = DNA synthesis)

Phases of mitotic (M) phase

mitosis —> Cytokinesis

(mitosis distributes chromosomes into two identical nuclei, Cytokinesis divides cytoplasm)

Stages of Mitosis

prophase, metaphase, anaphase, telophase

cell cycle checkpoints

G1, G2, M

-G1 is most important, and rerouts unready cells to Go

-M: cell receives stop if any chromosomes aren’t attached to spindle fibers in prometaphase

Somatic cells

cells in the body that are diploid

diploid

contains two complete sets of chromosomes, one from each parent (2n = 46 total chromosomes arranged in 23 pairs)

haploid

having a single set of unpaired chromosomes (23, or n); ex- gametes (sex cells)

Meiosis

-5 stages including interphase

-occurs in somatic cells

-purpose is sexual reproduction

-produces 2 diploid daughter cells

Meiosis I

separates homologous chromosomes, PMAT I

Meiosis II

separates replicated chromatids, PMAT II

chiasmata

the X shaped points where homologous chromosomes physically exchange genetic material during meiosis (crossing over)

kinetochore

protein which is the attachment point for spindle microtubules during cell division

(ensures sister chromatids are accurately separated)

cohesion proteins

protein which acts as a glue, holding sister chromatids together from the end of replication until the anaphase of cell division

how do the progeny cells of Mitosis differ from those of meiosis?

mitosis: 2× 2n progeny cells

meiosis: 4× 1n progeny cells

4 laws of meiosis

• law of segregation

• law of independent assortment

• crossing over

• slot machine

law of segregation

maternal and paternal copies of a given chromosome SEPARATE during meiosis and end up in different gametes at random (with = probability)

• when an organism makes gametes, each gamete receives just one copy of each chromosome, which occurs randomly

• probability of receiving the mat/pat version of a chromosome is completely random

law of independent assortment

maternal and paternal chromosomes of any homologous pair segregate into gametes INDEPENDENTLY of all other homologous pairs of chromosomes

• the pairs of homologous chromosomes get segregated into gametes independently of one another

• the version of chromosome 1 selected has no effect on which version (mat/pat) of the other chromosomes will be selected

crossing over

maternal and paternal chromosomes exchange genetic information during prophase I

slot machine/meiosis comparison

meiosis is like a slot machine that produces 4 genetically distinct HAPLOID cells

synapsis

process in prophase I of meiosis where homologous chromosomes pair up tighly to form a structure called a tetrad, held together by the synaptonemal complex

• allows for crossing over to occur at chiasmata

combinations possible when chromosomes assort independently into gametes

2^n, where n = haploid number

for humans, n=23

random fertilization

any sperm can fuse with any unfertilized egg, adds to genetic variation

particulate hypothesis of heredity

traits are passed down through discrete, indivisible units called genes, rather than blending together (previously held idea)

two laws that Mendel described

law of segregation and law of independent assortment

characteristics that make pea plants good genetic models

• true breeding- specific traits are passed to all subsequent generations

• short generation time

• lots of progeny

• mating can be controlled; self pollinate/cross pollination

allele

alternative versions of genes- each progeny inherits one allele from each parent

law of segregation applies to alleles

two alleles separate from eachother during gamete formation and end up in gametes

• an egg or sperm gets only one of the two alleles present in the parent

• this is explained by the behavior of chromosomes in MEIOSIS

phenotype vs genotype

phenotype is the result while genotype is the gene ratio from parents

• can be determined from a test cross with a recessive phenotype (pp) 

dihybrid cross

YYRR x yyrr

• result: phenotypic ratio of 9YR: 3Yr: 3yR: 1yr  

Mendel’s law of independent assortment

• each pair of alleles segregates independently of any other pair of alleles during gamete formation

• MEIOSIS: each pair of homologous chromosomes follows the law of segregation without influence of other chromosomes

• applies only to genes on different nonhomologous chromosomes, or those taht are far apart on the same chromosome

multiplication rule

probability that 2+ independent events will occur together (this AND that) is the product of their individual probabilities

addition rule

the probability of any one of 2+ mutually exclusive events will occur (this OR that) is the sum of their individual probabilities

homozygous

identical alleles of a particular gene

heterozygous

different alleles of particular gene

incomplete dominance

neither allele is completely dominant

codominance

two dominant alleles affect the phenotype in separate, distinguishable ways

epistasis

phenotypic expressiion of one gene affects that of another

polygenic inheritance

additive effect of 2+ genes on a single phenotypic character

• quantitative variation (varies in a population along a continuum) indicates polygenic inheritance 

sex linked traits

characteristics caused by genes located on sex chromosomes (X or Y) instead of autosomes

gene mapping

various techniques, including genetic linkage mapping to determine relative positions based on recombination frequencies, fluorescent in situ hybridization (FISH) to visualize specific DNA sequences, and genome sequencing to identify the precise DNA sequence and gene locations

Chromosome theory of inheritance

genes are located on chromosomes; chromosomes are carriers of genetic information and responsible for mendelian inheritance

wild type (wt) or (w+)

natural, non mutated form of a gene or organism most commonly found in a natural population 

Morgan’s discovery

white eyes correlates to the sex of flies because it’s located on the X and Y sex chromosomes; helped develop the theory of inheritance

sex linked genes

genes on sex chromosomes that exhibit unique patterns of inheritance

X linked genes in humans

some disorders are caused by recessive alleles on the X chromosome in humans; female needs to be homozygous and a male needs only one copy of the allele (hemizygous) to be expressed

X inactivation in female mammals

one of the 2 chromosomes in each cell randomly inactivates during embryonic development

• the inactive X condenses into a Barr Body

• shown as genetic mosaic

Barr body (aka X- chromatin)

tightly coiled DNA of inactivated X chromosome; appears as small, dark staining, condensed structure attached to nuclear envelope

• most genes on barr bodies becomes inactive

Are mitochondrial genes randomly inherited

No- not mendelian

• mitochondria have different genomes than chromosomes or nucleus: not segregated during meiosis

• passed through cytoplasm of egg = maternally inherited

linked genes

genes that tend to be inherited together

• often near eachother on the same autosome

• observed by Morgan in his fruit fly experiment

dihybrid testcross

crossing an unknown genotypic individual for two traits with a double recessive individual

• determines genotype of unknown

• demonstrates independent assortment (if 1:1:1:1)

recombination frequency

percent likelyhood that recombination between 2 genes happens

• <50% means genes are linked

• the percent  of recombination frequency = physical distance in map units (cM) on the chromosome

• the closer two genes are, the LOWER the recombination frequency

recombinant offspring

• know parental genotypes and phenotypes

• determine the four possible offspring phenotypes

  • recombinant genome is mixed dominant/recessive from heterozygous parent

  • any combination of phenotypes NOT IN PARENTS is recombinant

• recombination occurs due to crossing over between homologous chromosomes during meiosis in the heterozygous parent

linkage map

expresses distances between genes on a chromosome to determine recombination freuency

• 1 map unit = 1% recombination frequency

aneuploidy

when there is an abnormal number of a particular chromosome (leads to developmental disorders/miscarriages)

polyploidy

having multiple complete sets of chromosomes (many plants are polyploidy)

nondisjunction

pairs of homologous chromosomes don’t separate normally during meiosis (I or II)

• one gamete receives 2 of the same type of chromosome, another receives no copy

deletion

removal of a chromosomal segment

Inversion

reversal of a segment within a chromosome

duplication

repeating of a segment in a chromosome

translocation

movement of a segment from one chromosome to a nonhomologous chromosome

differences between recombination in linked and unlinked genes

linked- occurs bc of crossing over during meiosis

unlinked- bc of independent assortment of chromosomes during meiosis