Meiosis & Genetics Sexual Cell Reproduction Ch. 10.2

Genetics The Study of Inherited Characteristics

Chromosome DNA Code for traits

Genes on chromosomes : Segments of DNA on a chromosome Code for a trait Hair Color Eye Color

Gene Segment For Hair color

Trait Characteristic Feature Variations in a population

Chromosome Number Different # for different species Full set = 2N=Diploid N= # pairs 1 pair from mother 1 pair from father Humans= 23 pairs or 46 total Homologous Chromosomes are the sets of each pair

Autosomes & Sex Chromosomes Autosomes = # for all traits except sex Sex chromosomes= Pair # 23 XX(female) or XY(male)

Why do cells divide by Meiosis? To reduce chromosome number In sex cells Or in single celled organisms: Under changing conditions for Chromosome Variety Sperm N egg N 2N baby

Gonads make gametes! Testes make sperm

Gonads make gametes! Ovaries make eggs

Gamete develoment Imature egg or sperm cell = full set of chromosome (2N) Undergoes meiosis with 2 cell divisions Develops into a mature egg or sperm (1N) 2N 1N

Meiosis in the Gonads Sperm Meiotic cell division Egg

Stages in Meiosis: Interphase Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Final Telophase Full set of chromosomes (2N) DNA has doubled (4N) 1st cell division (2N) DNA does not double 2nd division Sperm & Egg (1N) 2nd division (1N)

Meiotic Cells…….. Divide twice to 1/2 Chromosome number “Haploid” Sperm or eggs 2N 1N 4N Immature Egg or sperm

Genetic Recombination Variety in chromosomes from Crossing over = Exchange of parts Of Homologous chromosomes A A B B

Nondysjunction = chromosomes fail to “dis-join” or separate: Trisomy=gamete with 3 of one type Monosomy=gamete with 1 of one type Tripoidy= zygote with three of one type 2N empty1N 2 nd division 2N egg 1N sperm + = 3N Eggs forming

Down Syndrome= 3 of #21

Klinefelter’s = XXY

Turner’s Syndrome XO sex chromosome Instead of XX female Or XY for male: X Empty sperm = XO +