2 Types of Cellso “Body cells” (somatic) vs. reproductive cells (gametes).o Examples of somatic cells: skin cell, liver cell, brain cell, red blood cell…o Human somatic cells - 46 chromosomes.o Examples of gametes: egg cell or sperm cello Human gametes - 23 chromosomes.
How much DNA is in our cells?o DNAchromosomeso How many chromosomes in a human somatic cell?o 46 chromosomes or 23 homologous pairso What is the origin of these pairs?o Homologous pair- chromosomes that carry the same geneso These cells are diploid.o The diploid number in humans is 46.
How much DNA is in our cells?o How many chromosomes are in a gamete (reproductive cell)?o 23 chromosomeso Mom and dad pass on one chromosome from each homologous pair.o These cells are haploid.o The haploid number in humans is 23.
How are reproductive cells formed?o Meiosis is nuclear division that produces haploid gametes.o Chromosomes - no longer in pairs.o Each parent passes on one chromosome from each homologous pair in the gamete.o Reproductive cells contain half the number of chromosomes that a somatic cell contains.o 4623
How is Mitosis different from Meiosis?MITOSIS MEIOSISChromosome # Chromosome #stays same reduced half2 new cells produced 4 new cells producedSomatic cells GametesIdentical Variation
What are reproductive cells?o In males reproductive cells originate from cells called spermatogonium.o In females reproductive cells (egg cells) originate from cells called oogonium.
Meiosis Errorso Errors during meiosis cause gametes to be defective.o Most common error is called nondisjunction.o When nondisjunction occurs, chromosomes fail to separate correctly.o Creates gametes (egg/sperm cells) with too many (trisomy) or too few chromosomes (monosomy).