Meiosis & Reproduction

Meiosis

special form of cell divison that creates gametes

Gametes

sex cells (ex. eggs, sperm)

Asexual Reproduction

mitosis creates two identical organisms from one individual

Sexual Reproduction

meiosis in diff. individuals in a population creates gametes which combine to make a new organism (egg + sperm = you)

Gene

individual unit of genetic info., a section of DNA that codes for something (one protein) ex. p53, Ras (old def. one gene —> one trait)

Allele

a specific version of a gene

# of genetic material that adult has

half (23 chromosomes in egg + 23 chromosomes in sperm)

Homologous Chromosomes

contain the same genes in the same location (humans have 23 homologous pairs of chromosomes)

Homologous Chromosomes lvl 2

contain same genes, but not identical and may/may not have same alleles

Chromosomes

DNA genes that tell you how to make proteins (analogy: cookbooks: recipes tell you how to make food)

Ploidy

how many distinct copies each chromosome in a cell has, determined by #

Haploid

no homologous chromosomes, only one

Diploid

homologous chromosomes, 2 unique copies per

Chromosome Number (n)

number of unique chromosomes a cell/organism has (humans n=23, haploid=1, diploid = 2n)

Human Life Cycle

egg + sperm cell (haploid gametes) —> FERTILIZATION —> diploid zygote —> MITOSIS —> multicellular diploid adults —> MEIOSIS —> etc.

Human Life Cycle in Chromosome Number (n)

haploid gametes n = 23 —> diploid zygote 2n = 46 —> multicellular diploid adults 2n = 46 —> back

Aneuploidy

irregular ploidy, not having equal amount of chromosomes in each n

Mitosis

parent divides into 2 identical daughters (2 —> 4)

Meiosis

parent divides into 4 haploid gametes (cell divides TWICE —> 4 has ½ of DNA)

Diploid Germline Cell

cell in gonads that form gametes (meiosis starts w/ these then replicates)

Meiosis 1

homologous chromosomes separate into haploid intermediate cells (there’s one X)

Metaphase I

duplicated chromosomes (put into homologous pairs) line up in middle of cell @ centromere

Anaphase I

the homologous chromosomes pulled to opposite ends of the cell, sister chromatids remain attached

Meiosis 2

identical to mitosis; chromosomes line up in middle of the cell, identical sister chromatids from each chromosome are pulled to opposite ends of cell

Meiosis Products

creates 4 daughter cells, all w/ half as many chromosomes as the parent cell

Independent Assortment

each chromosome pairs splits during m eiosis 1 randomly and independently of other pairs

Crossing Over

they have similar DNA sequences, homologous chromosomes exchange part of their DNA during meiosis 1

Crossing Over lvl 2

process serves as a checkpoint to make sure each chromosome is paired up before the chromosomes

When is Homologous Recombination Triggered?

double strand breaks, induced by Spo11 Topoisomerase homoloh

Random Fertilization

one random sperm will encounter one random egg, genetics do no affect fertilization