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Meiosis. Types of Human Cells. Sex Cells Gametes (germ cells) Eggs and Sperm Somatic Cells All other cells. Types of Chromosomes. Autosomes – same number in males and females Sex Chromosomes – X or Y Human females: XX Human males: XY

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types of human cells
Types of Human Cells
  • Sex Cells
    • Gametes (germ cells)
    • Eggs and Sperm
  • Somatic Cells
    • All other cells
types of chromosomes
Types of Chromosomes
  • Autosomes – same number in males and females
  • Sex Chromosomes – X or Y
      • Human females: XX
      • Human males: XY
    • Testosterone and other hormones from the Y make a male
humans
Humans
  • 46 chromosomes
  • (23 pairs)
ploidy
Ploidy
  • Describes how many sets of different chromosomes a cell has.
  • n = number of chromosomes in 1 set (haploid number)
  • Haploid Cells: 1n
  • Diploid Cells: 2n
  • In humans, n = 23 (the number of different chromosomes we have)

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Figure 13.5

Haploid gametes (n 23)

Key

Haploid (n)

Egg (n)

Diploid (2n)

Sperm (n)

MEIOSIS

FERTILIZATION

Ovary

Testis

Diploidzygote(2n 46)

Mitosis anddevelopment

Multicellular diploidadults (2n 46)

figure 13 6
Figure 13.6

Key

Haploid (n)

Haploid unicellular ormulticellular organism

Haploid multi-cellular organism(gametophyte)

Diploid (2n)

Gametes

n

n

Mitosis

Mitosis

Mitosis

Mitosis

n

n

n

n

n

n

n

n

Spores

n

MEIOSIS

FERTILIZATION

n

Gametes

n

Gametes

MEIOSIS

FERTILIZATION

FERTILIZATION

MEIOSIS

Zygote

2n

2n

2n

2n

Diploidmulticellularorganism(sporophyte)

Zygote

2n

Diploidmulticellularorganism

Mitosis

Mitosis

Zygote

(a) Animals

(b) Plants and some algae

(c) Most fungi and some protists

Plants and some algae exhibit an alternation of generations.

crossing over
Crossing Over
  • In crossing over, nonsister chromatids exchange DNA segments.
  • Each pair of chromosomes forms a tetrad, a group of four chromatids.
  • Each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred.
figure 13 11 1
Figure 13.11-1

Prophase Iof meiosis

Nonsister chromatidsheld togetherduring synapsis

Pair of homologs

figure 13 11 2
Figure 13.11-2

Prophase Iof meiosis

Nonsister chromatidsheld togetherduring synapsis

Pair of homologs

Chiasma

Centromere

TEM

figure 13 11 3
Figure 13.11-3

Prophase Iof meiosis

Nonsister chromatidsheld togetherduring synapsis

Pair of homologs

Chiasma

Centromere

TEM

Anaphase I

figure 13 11 4
Figure 13.11-4

Prophase Iof meiosis

Nonsister chromatidsheld togetherduring synapsis

Pair of homologs

Chiasma

Centromere

TEM

Anaphase I

Anaphase II

figure 13 11 5
Figure 13.11-5

Prophase Iof meiosis

Nonsister chromatidsheld togetherduring synapsis

Pair of homologs

Chiasma

Centromere

TEM

Anaphase I

Anaphase II

Daughtercells

Recombinant chromosomes