Biol 350 Spring Exam 1

Principle of independent assortment

segregation of each pair of alleles is independent

Principle of independent assortment only applies when genes

are on different chromosomes or are far apart on the same chromosome

9:7 epistasis

observed when homozygous recessive mutation in either or both of 2 different genes gives same mutant phenotype

9:4:3 epistasis

when homozygosity for recessive allele at one gene masks expression of the genotype of a different gene

Noncomplementation

combination of two recessive mutations results in mutant phenotype; mutations are alleles of same gene

Complementation

results in wildtype phenotype; mutations are alleles of different genes

Mutations block enzyme production if

if both copies of gene are defective

Histones

pack DNA in chromatin

Dense chromatin

heterochromatin (very few genes); regions at centromere & telomeres of most chromosomes

Less dense chromatin

euchromatin (gene rich)

Non-dividing nuclei

DNA wraps around histone proteins, DNA-protein chain coils into fibers, & fibers loosely organized into loops

Dividing nuclei

during nuclear division chromatin highly compact to facilitate chromosome movement

Cell cycle

G1, S, G2, M

G1

pre-DNA replication

S

DNA replication

G2

post-DNA replication

Mitosis Prophase

Chromosomes condensate, individual chromosomes become visible, & nuclear envelope disintegrates

Mitosis Metaphase

Mitotic spindle forms, spindle fibers organize & attach to chromosomes, & chromosomes line up in center

Mitosis Anaphase

Centromeres divide, sister chromatids separate, & one member of each pair pull to either pole of the cell

Mitosis Telophase

two daughter nuclei organize, chromosomes reverse condensation, & after cytokinesis, daughter cells are diploid

Meiosis I: Prophase I

Genetic recombination, homologous chromosomes pair (synapsis), physical exchange of genetic material between homologous chromosomes, Chiasmata link chromosomes, & chromosome condensation begins

Meiosis I: Metaphase I

Independent assortment of genes on different chromosomes & nonhomologous chromosomes align at random on metaphase plate

Meiosis I: Anaphase I

Independent segregation (physical separation of homologous chromosomes)

Meiosis II: Prophase II

may or may not involve recondensation of chromosomes; no chromosome replication between Meiosis I & II

Chi squared equation

(o-e)^2/e

p > 0.05

fail to reject the null hypothesis

Law of segregation occurs in

anaphase I & II

Independent assortment occurs in

metaphase I