1. 6a: Meiosis Describe cells during the cell cycle as
eitherhaploid or diploid Describe the stages of meiosis Identify
male and female gametes Describe the process of crossing over
andindependent assortment as means ofcreating genetic
diversity
2. Some background... You are a multi cellular organism
thatstarted as a single cell... how? How many chromosomes did your
first cellhave? How was that first cell made? How many cells must
those cells have had? What process made those cells?
3. Some background... You are a multi cellular organism that
started as a singlecell... how? Mitosis! How many chromosomes did
your first cell have? 46 How was that first cell made? Sperm
fertilized an egg How many cells must those cells have had? Half of
46 = 23 What process made those cells? Meiosis!
4. Vocabulary Gamete: A sex cell (sperm for male & egg
infemales) Fertilization: The process in which an eggcell fuses
with a sperm cell and male andfemale genetic material combines
Zygote: A fertilized egg. Contains two sets ofchromosomes and will
divide by mitosis todevelop into an embryo
5. Chromosomes A somatic (body) cell contains two sets
ofchromosomes. One from mom and one from dad. These chromosomes
exist in pairs calledhomologous chromosomes. Homologous
Chromosomes: Contain genes forthe same traits in the same
locations, althoughthey may contain different variations of
thosegenes. (eg. Both contain eye colour gene, one for blue and
theother for brown.)
6. Homologous Chromosomes
7. Chromosome Number Diploid: Cell containing two sets of
chromosomes Represented as 2n (in humans 2n = 46) All body cells
are diploid Haploid: Cell has only one set of chromosomes Contains
only 1 chromosome from each homologous pair. eg. Sex chromosomes (1
X or 1 Y) Represented as n (in humans n = 23) Only gametes are
haploid
8. Meiosis Process that produces gametes (egg orsperm) with
half the number ofchromosomes (haploid) In meiosis there is one
round of DNAreplication (during interphase) and two celldivisions
Produces 4 genetically unique haploid cells
9. Life Cycle(mitosis and meiosis)
10. MeiosisA: DNA replicationB: Meiosis IC: Meiosis II
11. Stages of Meiosis Meiosis is divided into two parts each
withprophase, metaphase, anaphase, telophase Meiosis I: Pairs of
homologous chromosomes line up atcenter and separate (different
from mitosis wheresister chromatids separate ) Produces two
daughter cells that are haploid Meiosis II: Sister chromatids are
separated (like mitosis) Produces four daughter cells that are
haploid
12. Meiosis I
13. Meiosis II
14. Result of Meiosis Meiosis produces four genetically
uniquedaughter cells Each cell contains one chromatid
(daughterchromosome) from each homologous pair Cells are haploid
(humans = 23chromosomes)
15. Genetic Variation in Meiosis Every gamete is unique from
all othergametes produced because of twoprocesses that occur during
meiosis I1. Crossing Over2. Independent Assortment
16. Crossing Over Occurs between each homologous pair Pairs of
non-sister homologous chromatidscross over and exchange DNA
Multiple cross overs can occur leading toinfinite
possibilities
17. Independent Assortment Homologous chromosomes line
uprandomly at metaphase I, so the mixture ofchromosomes that end up
in each daughtercell after separation varies
18. Gamete Formation Meiosis is the same in male and females,
aftermeiosis further development occur to specializea cell as
either egg or sperm Male: Meiosis occurs in testes and produces
4sperm cells Produced from puberty on (millions every day) Female:
Meiosis occurs in ovaries and produces1 egg and 3 smaller polar
body cells Produced before birth (about 1-2 million eggspresent at
birth)