Chapter 22 (Meiosis)

Asexual Reproduction

• offspring arise from single organism and inherit the genes of that parent only; doesn’t involve fusion of of gametes, and almost never changes # of chromosomes

• producing clones of 1 thing

• not good bcs if env changes, then the same organism will no be able to survive bcs they have the same makeup

Sexual Reproduction

• production of new living organisms by combining genetic info from 2 individuals of diff sexes

• Humans, animals, some plants do this process

• two parent organisms combine genetic info to make new organisms 

Meiosis

• specialized form of cell to produce gametes

• reduces # of chromosomes in each cell by ½ 

• Chromosomes come in homologous pairs 

• Gametes get one of each pair 

Karyotype

a photo of chromosomes arranged in pairs 

• human somatic cells have 22 pairs of autosomes and 1 pair of sex chromosomes 

• Females have XX; Males have XY 

Homologous pairs + allele

Homologous pairs: one chromosomes from each parent

• allele: version of the gene (‘A’ is an allele and ‘a’ is another allele)

Gametes

Specialized sex cells (egg, sperm)

• produced by meiosis in the gonads (sex organs) 

• Hapolid cells (23 chromosomes)

• Fused gametes (during fertilization) form a diploid zygote

Haploid and Diploid cells

Haploid: cells w one set of 23 chromosomes

Diploid: cells w full 46 chromosomes (mitosis) 

• Men can make sperm til the day they die, women are born w the amount of eggs they will have for the rest of their life and don’t make anymore

• Egg cell has 23 chromosomes (unpaired)

• Sperm cell has 23 chromosomes (unpaired)

• When added together, you get 46 chromosomes which is the normal amount for a humans

Meiosis stages info (two stages) 

DNA is duplicated during interphases

Meiosis takes place in two stages

• Meiosis 1: separating out the homologous pairs into 2 separate cells

• Meiosis 2: separating out the sister chromatids in each cell to produce 4 haploid cells 

Stages (brief)

G1: growth

S-phase: make new DNA (DNA synthesis)

G2: prep for division 

Meiosis 1

Meiosis 

True or False: Meiosis cells are identical to the original cell

false

Stages Meiosis 1

1) end of interphase

2) Prophase 1

• Nucleus disappears

• Crossing over 

  • happens to introduce diversity in the system 

3) Metaphase 1

• Homologous chromosomes align in the middle

• Random Alignment 

4) Anaphase 1

• Homologous chromosomes are separated by shortening of microtubules 

5) Telophase + Cytokinesis 

• 2 daughter cells 

Stages Meiosis 2

6) Prophase 2

• Nucleus disappears 

7) Metaphase 2

• Chromosomes align down the middle of the cell

8) Anaphase 2

• Sister chromatids are separated by shortening of microtubules 

9) Telophase 2 + Cytokinesis 

• 4 haploid daughter cells 

Crossing over

exchange of genetic info betw homologous chromosomes

• occurs during Prophase 1 of Meiosis

• Results in new types of gametes

• Linked genes typically cross over together 

Random alignment

random arrangement and separation of diff pairs of chromosomes during meiosis

• results in genetically distinct gametes 

• Occurs during Metaphase 1 of meiosis