meiosis and karyotypes. somatic cells v. gametes 0 somatic – body cells 0 ex. skin, liver,...
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Meiosis and Karyotypes
Somatic Cells v. Gametes
0Somatic – body cells0 Ex. Skin, liver, eyeballs
0Gametes – sex cells0 Ex. Egg or sperm (DNA
here gets passed on to your kids!)
0 We have 46 total. 0 We get 23 from mom, 23 from dad – so we have two pairs of
23. Get it?0 Each pair in the set is genetically identical, unless a
mutation occurs.0 Homologous chromosomes – two chromosomes (one
from ma, one from pop) that look the same, are the same length and HAVE THE SAME GENES.
Autosome v. Sex Chromosome
0Autosomes – Contain genes not directly related to your sex.
0Humans have 44 (Chromosome pairs 1-22)
0Sex chromosomes – directly control development of sexual characteristics
0Pair #230Humans have two
options: X, Y0 XX = female0 XY = male
Sexual Reproduction v. Asexual Reproduction
0 Remember we called mitosis a form of asexual reproduction. The cells are identical. We use it for growth and repair all the time!!
0 Sexual reproduction involves fusing two gametes to make a genetic MIXTURE of both parents.0 When human gametes fuse we call it fertilization.0 The nucleus of the egg (23 chromosomes) fuses with the
nucleus of the sperm (23 chromosomes) to make a new nucleus for a new individual (23+23 = ??)
Diploid v. Haploid
0Diploid – cell has two copies of the chromosomes
0Also known as 2N0 In humans, 2N or diploid
= 460Somatic cells are diploid0Mitosis
0Haploid – cell has ONE copy of the chromosome
0Also known as 1N0 In humans, 1N or
haploid = 230Gametes are haploid0Meiosis
Meiosis!
0Two cell divisions0Dividing the nucleus to make four HAPLOID cells that
are all genetically different0 Involved in sexual reproduction0During Prophase 1 of meiosis crossing over (the
exchange of genetic material between homologous chromosomes) occurs.
0Crossing over helps ensure genetic diversity
Homologous chromosomes v. sister chromatids
0Homologous chromosomes – get one from mom and one from dad
0Similar length, carry same genes
0NOT copies of each other
0Divided in Meiosis 1
0Sister chromatid – chromatids attached by a centromere
0Divided in Meiosis 2
Karyotype
0Picture of all the chromosomes in a cell, used to study chromosomes, help determine where genes are on chromosomes
0Show changes in chromosomes – like too many or too few
0Sometimes chromosomes don’t separate properly, this is called nondisjunction0 Down Syndrome – extra copy of chromosome #210 Can have extra chromosomes on any pair, even sex
chromosomes