Topic 16 Sexual Reproduction

Sexual reproduction benefits

Shuffling gene help survive variable environments, eliminate deleterious mutation/pass beneficial mutation, evolution

Diploid

cell with 2 sets of homologues chromosomes, one set each parent, somatic cells

Homologs

Maternal and Paternal version of chromosomes, contains same genes, different alleles

Alleles

variant version of genes

Haploid

cells with 1 set of chromosomes, gametes(egg/sperm), produced by germ line cells

Gametes

produced by germ line cells, Egg (large and nonmotile) and Sperm (small and motile)

Meiosis

reductive cellular divisions, number chromosomes halved, one DNA replicationa and 2 divisions, 4 gentically unique haploid gametes

Meiosis 1

segaration of homologous chromosomes, maternal and paternal pair and attach, forms Bivalents (2 chromosomes together)

Meiosis 2

separate sister chromatid, no DNA replaction, some have short interphase before, mitotic spindle forms/kinetochores attach

Bivalent / Tetrad

2 chromosome/4 chromatid stuck together, held together by synaptonemal then chiasma

Chromosome pairing

maternal/paternal homologs, attach to one another along length, inprophase

Homologous recombination

homlog exchange genetic information, during Meiosis 1 prophase, between bivalent non sister chromatid

Synaptonemal complex

holds bivalent together, aligns homologs, disassembles at end of prophase

Chiasmata

hold bivalent together, correspond to crossover(made during), link homolog together so they line up during metaphase(until anaphase), 

Oocytes

cell that make egges, 2-3 crossover per bivalent, 10% are aneuploid

Anaphase 1

Cohesin degraded by separase, homolgs pulled apart

Anaphase 2

remaining cohesins degraded by separase, sister chromatid pulled apart

Random assortment

some parental/some maternal, depends how aligns at metaphase (independent of other chromosomes), calculate possible gametes by 2^n where n = haploid number

Nondisjunction

Homolog fail to separate (meiosis 1) or Sister chromatid fail to separate (meiosis 2), lead to aneuploidy gametes

Aneuploidy

gametes having extra/less chromosomes than normal, trisomy 21 causes down

Fertilization

haploid egg + sperm fuses, forms diploid zygote (unicellular)

Fertilization steps

Sperm attracted to egg by its chemical signal, sperm passes through protective layer and tunnels into egg coat (zona pellucida), sperm fuses egg plasma membrane, 2 haploid nuclei trigger Ca2+ release, secretes enzymes harden zona pellucida, trigger egg development, combine chromosomes