10.2 meiosis
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10.2 MEIOSIS. Martin 2022. GENES, CHROMOSOMES, AND NUMBERS. A. Dipolid and Haploid Cells: Diploid Cells: cell that have two of each kind of chromosome 2n Found in all “body” cells Haploid Cells: only have 1 of each kind of chromosome n Found ONLY IN SEX CELLS (sperm and egg) - PowerPoint PPT PresentationTRANSCRIPT
10.2 MEIOSISMartin 2022
GENES, CHROMOSOMES, AND NUMBERS•A. Dipolid and Haploid Cells:
▫Diploid Cells: cell that have two of each kind of chromosome 2n Found in all “body” cells
▫Haploid Cells: only have 1 of each kind of chromosome n Found ONLY IN SEX CELLS (sperm and egg)
Sex cells also known as gametes
GENES, CHROMOSOMES, AND NUMBERS•B. Homologous Chromosomes:
▫Two chromosomes in each pair of a diploid cell
▫Each pair has genes for the same trait Genes arranged in the same order, but may be different in their alleles (dominant or recessive)
GENES, CHROMOSOMES, AND NUMBERS•Why Meiosis?:
▫Meiosis: a type of cell division that allows gametes (sex cells) to form, so that after fertilization, offspring have the same number of chromosomes as their parents Sperm: male gametes Egg: female gametes
GENES, CHROMOSOMES, AND NUMBERS•Meiosis is used to create cells for sexual reproduction:▫Male gamete (23) fertilizes female
gamete (23) and produces a zygote (offspring with 46 chromosomes)
•Remember, this is different from mitosis▫Mitosis = 2n 2n▫Meiosis = 2n n
THE PHASES OF MEIOSIS
•PMAT I, then PMAT II ▫Has 2 cell divisions that lead to 4 haploid
cells•During PROPHASE I
▫2 homologous chromosomes pair so tightly that crossing over can occur Where non-sister chromatids can break off and
exchange genetic information Can occur at ANY LOCATION on a
chromosome, at several locations, and at the same time
Crossing Over
THE PHASES OF MEIOSIS
•METAPHASE I▫Homologous chromosomes line up along
the midline/equator as a pair (tetrads)• ANAPHASE I
▫Homologous chromosomes separate•METAPHASE II
▫Chromosomes line up independently/randomly along equator
•ANAPHASE II▫Sister chromatids are separated
MEIOSIS PROVIDES FOR GENETIC VARIATION•This variation can be because of crossing
over during metaphase I•Can also be due to genetic
recombination▫the reassortment of chromosomes and the
genetic information they carry by crossing over or independent segregation of homologous chromsomes
NONDISJUNCTION
•Sometimes there’s an error in meiosis•Nondisjunction:
▫The failure of homologous chromsomes to separate during meiosis
▫Leaves 1 gamete with an extra chromosome, and 1 gamete with 1 missing chromosome (22, 24)
▫Trisomy 21 = Down Syndrome