Meiosis Notes Chromosomes n Chromosomes n Occur in

Meiosis Notes

Chromosomes n Chromosomes: n Occur in _____ n Are made of genes 48 chromosomes 1260 chromosomes n Humans have ____chromosomes, or 23 pairs. n Number of chromosomes does ____ relate to species complexity.

________: Picture of chromosomes

Can’t we just reproduce by Mitosis? ? ? n Mitosis=new cells containing the_______same # and kind of chromosomes as the original cell 46 46 n 46 Why is this a problem? n When fertilization occurs, offspring would have _______ the chromosomes of parents. n How many chromosomes would humans have? ____

Karyotype: Picture of chromosomes Egg(from mom) always has an______chromosome

Diploid and Haploid Cells n Cells can be: ____(2 n)=contain same amount of chromosomes as parents n All cells except egg/sperm are diploid n n _____(n)=contain ½ amount of chromosomes as each parent n n Think half the normal number(hap sounds like half) Only egg/sperm are haploid

Meiosis=Egg and Sperm n n Makes offspring have same # chromosomes as parent 2 separate ______: n n Meiosis I: begins with one diploid(2 n) cell Meiosis II: ends with four haploid(n) cells, or gametes. Produces_____sperm or egg n When sperm fertilizes egg, zygote is diploid(2 n)! Yay! n 23 23 46

So what’s next? n n After the egg and sperm meet(_______), the zygote develops by mitosis. The fusion of haploid gametes is known as SEXUAL REPRODUCTION. 8 weeks 50 days

Homologous Chromosomes n n n Definition: the 2 chromosomes of each pair which have genes for the _______ Occur in a DIPLOID(2 n) cell Class Activity n Draw some examples:

Why are we different from our siblings if we have the same parents? 1. 2. n n Crossing over: change in gene order in ___________ Chromosomes line up at cells equator 2 different ways n Each meiotic cell=23 chromosomes (223) This makes over ______different kinds of egg or sperm. Fertilization 223 x 223 = _______ different zygote possibilities

Nondisjunction n n Definition: the failure of chromosomes to properly ______(Anaphase I or II). Causes gametes to have too few or too many chromosomes. Too few chromosomes usually= _____ Too many usually= developmental problems

Nondisjunction

Too many chromosomes n Trisomy 21(Down syndrome): Zygote has an _____ Chromosomes. 3 instead of 2 on 21 st pair -Total # of chromosomes=47 n Causes mental and physical abnormalities -Chances ____ with age n

Too few chromosomes n Monosomy X: normal gamete fuses with a gamete ______ a chromosome n n n Turner syndrome: Females have only one X chromosome No known cause 98% fetuses miscarried

So, what about twins? Monozygotic(____ egg): -Have nearly the same DNA -Same gender -Can share or have own placenta. Dizygotic(2 diff. eggs): -May be genetic -Only _____ has influence because only she can release eggs -Can be different genders

Polyploidy n n Definition: organisms with _____ than the usual number of chromosome sets Rare in animals(can result in death) n n Turner syndrome, Trisomy 21, etc. Frequently occurs in ______ n n n Can cause plants to grow larger Beneficial for agriculture Understanding of genetics could be beneficial for _______(use chemicals to cause nondisjunction)

Did you know these are polyploids? Tetraploid(4 n) Triploid(3 n) Cavendish (propagation) Hexaploid(6 n) Decaploid(10 n)