Post on 05-Jan-2016
What is different about a reproductive cell compared to the rest of the cells in your body?
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The division of one cell into twoidentical cells, each with the samenumber of chromosomes that youstarted with in the original cell.• In humans, normally 46 chromosomes
• During mitosis, doubles to 92, so 46 can go to each new “daughter cell”
Recall the four steps of mitosis:ProphaseMetaphaseAnaphaseTelophase
This process includes chromosomesduplicating, and resulting in 2 identicalcells.
46 Chromosomes• Of the chromosomes in humans, you have two of each chromosome, one from each parent. (DIPLOID, 2N)• really 23 PAIR of chromosomes
• You have 2 full sets of information- youpass on ONE of those to your offspring.
Takes 46-chromosome cells• randomly selects one of each chromosome into new cell• Makes HAPLOID (one of each chromosome, N) cell• ** Sex cells have 23 chromosomes!
• 2 haploid cells, one from each parent,combine to make your diploid genetic code.
• Begin with 1 cell • Cell essentially goes through mitosis first• Next, cell splits again, but does NOT replicate its DNA, so only 23 chromosomes go to each cell.
• Leaves you with 4 DIFFERENT cells.
Crossing Over• Chromosomes get tangled during meiosis and switch spots
Genes close to each other onchromosomes tend to be foundtogether.
Example- Red hair and freckles areclose on chromosomes, so they usually travel together.
When chromosomes do not separateduring meiosis, causing zygote to havetoo many or too few chromosomes.
Down Syndrome- Nondisjunction ofchromosome 21.
• Asexual reproduction-• Only makes identical cells, so little genetic variation in speciesSexual Reproduction-
• All sex cells are different.• leads to variation within species
• Allows species to survive changes better
• Traits can ONLY be passed on if the trait is carried in the sex genes• If you get a mutation leading to cancer, it can only be passed on if it is carried in sperm/egg cells also.
Why do you look different fromyour siblings if you both havemom and dad’s genes?