BIO LAB 8

First prepared slides observed (2)

• Onion root tip cells: have rigid cell walls, and a cell plate creates division in the middle, since rigid wall cannot pinch

• Whitefish embryonic cells: cell membrane will be pinching in the middle

Lily slide observed

Shows anaphase 1 and 2 meiosis in lily

• Two large cells on slide, which are megaspore mother cells undergoing meiosis

Insect salivary gland slide

Show what “giant” chromosomes look like (unusually large) and some puffs, which are regions where RNA synthesis is happening (transcription)

Synapsis

Pairing of homologous chromosomes in prophase I of meiosis, also the creation of tetrads

• Is important because it allows for crossing over to occur

Crossing over

Exchange of DNA between homologous chromosomes that occurs during prophase I of meiosis, AFTER synapsis

• Non-sister chromatids exchange genetic material to create new combinations

Assortment

Homologous pairs randomly pairing up during metaphase I

• Crucial for genetic diversity

Segregation

Separation of homologous chromosomes in anaphase I of meiosis, so each gamete receives only one allele for each gene

“Corn” counting exercise

Part of inheritance problems and chi square analysis; had to count and score kernels as per their phenotype (color)

“A” ear in corn exercise

Monohybrid cross where A produces purple seed, a produces yellow seed

“B” ear in corn exercise

Another monohybrid cross, but work backward from progeny to parent

(can take total # of kernels and boil down to simplified proportion of genotype, like 1:1)

“C” ear in corn exercise

Dihybrid cross (Aa, but also B being smooth seed and b being shrunken)

• BOTH parents were heterozygous

“D” ear in corn exercise

Dihybrid cross with same loci as C, but work backwards from progeny to parents again

• Approximates to 1:1:1:1

“E” ear in corn exercise

Represent a dihybrid cross with two unlinked loci

• Observed & expected are very close, so a chi square isn’t very necessary

• Twice as large difference could probably still be by chance, but 10x as large is likely not (but cannot be sure just by looking)

“F” ear in corn exercise

Represent another unlinked loci dihybrid, but with

• Dominant UNLINKED allele I inhibits formation of purple pigment (i does not)

• Yellow seed is the same as first; both parents are doubly heterozygous

• This is called dominant epistasis, since allele I masks expression of other gene regardless of whether D is present

In bead experiment, purpose was to demonstrate

Chromosomes

Centriole representation in model

4 small, short plastic cylinders

Spindle fiber representation in model

Spool of thread

Chromosome representation in model

4 bead strings (2 yellow, 2 red)

In building, each chromosome HAD to have

Either all read OR all yellow (no mixing of colors); 15 beads on each side

Main “message” of mitotic division demonstration

2N parent cell creates 2 identical daughter cells, keeping the # and type of chromosomes constant