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Unit 8 – Part 1 Notes Meiosis and Mutations. How does sexual reproduction lead to the production of genetically different cells?. Vocabulary. genes Sex Chromosome Autosome Homologous chromosome Karyotype Diploid Haploid synapsis tetrad. gametes zygote Crossing-over meiosis

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unit 8 part 1 notes meiosis and mutations

Unit 8 – Part 1 Notes Meiosis and Mutations

How does sexual reproduction lead to the production of genetically different cells?

Unit 8 notes - part 1 - meiosis

vocabulary
Vocabulary
  • genes
  • Sex Chromosome
  • Autosome
  • Homologous chromosome
  • Karyotype
  • Diploid
  • Haploid
  • synapsis
  • tetrad
  • gametes
  • zygote
  • Crossing-over
  • meiosis
  • Genetic recombination
  • Independent assortment
  • Spermatogenesis
  • Oogenesis
  • Polar body
  • Sexual reproduction

Unit 8 notes - part 1 - meiosis

review
Review
  • Chromosomes are rod-shaped structure made of DNA and proteins.
  • Genes are segments of DNA that control traits
  • DNA replicates (S phase of cell cycle) before cell division takes place
  • Replicated chromosomes are made up of two identical chromatids (sister) joined by a centromere.
  • DNA in its less tightly coiled form is called chromatin.

Unit 8 notes - part 1 - meiosis

chromosome numbers
Chromosome Numbers

XY - male

  • Chromosomes are categorized as either sex chromosomes or autosomes.
    • Sex chromosomes are the chromosomes that have genes that determine the sex of an organism. (23rd chromosome)
    • Autosomes are chromosomes with genes that determine traits other than sex. (1-22)

XX - female

Unit 8 notes - part 1 - meiosis

slide5

eye color

locus

eye color

locus

hair color

locus

hair color

locus

  • Every cell in an organisms produced by sexual reproduction has two copies of chromosomes – one from each parent.
  • Two copies of each chromosome from a parent are called homologous chromosomes.
  • Homologous chromosomes or homologues are the same size and shape and carry genes for the same traits.

Unit 8 notes - part 1 - meiosis

slide6

A karyotype is a photomicrograph of the chromosomes in a normal dividing cell.

  • Humans have 46 chromosomes – 22 pairs of autosomes and 1 pair of sex chromosomes
    • Males are XY
    • Females are XX

Unit 8 notes - part 1 - meiosis

karyotype
Karyotype

Unit 8 notes - part 1 - meiosis

Female - XX

karyotype1
Karyotype

Down Syndrome – Trisomy 21

Unit 8 notes - part 1 - meiosis

Female - XX

diploid and haploid
Diploid and Haploid
  • Cells having two sets of chromosomes are diploid. Called 2n (n is haploid chromosome)
  • All body (somatic)cells are diploid.
  • Cells with one set of chromosomes are haploid or n.
  • Haploid cells have ½ the number of chromosomes present in diploid cells.
    • Diploid 46
    • Haploid 23

Unit 8 notes - part 1 - meiosis

fertilization

sperm

n=23

n=23

egg

2n=46

zygote

Fertilization
  • The fusion of a sperm and egg to form a zygote.
  • A zygote is a FERTILIZED EGG

Unit 8 notes - part 1 - meiosis

meiosis
Meiosis
  • The form of cell divisionby which GAMETES (sex cells), with HALF the number of CHROMOSOMES, are produced.
  • DIPLOID (2n)  HAPLOID (n)
  • Meiosis is SEXUALreproduction (combining of sex cells with different characteristics of parents).
  • TWO divisions (MEIOSIS Iand MEIOSIS II).

Unit 8 notes - part 1 - meiosis

meiosis1
Meiosis
  • Sex cells divide to produce GAMETES(sperm or egg).
  • Gametes have HALF the normal number of chromosomes.
  • Occurs only in GONADS (testes or ovaries).
  • Male: SPERMATOGENESIS-production of sperm cells
  • Female: OOGENESIS - production of egg or ova

Unit 8 notes - part 1 - meiosis

spermatogenesis

n=23

human

sex cell

sperm

n=23

n=23

2n=46

n=23

n=23

diploid (2n)

haploid (n)

n=23

Meiosis I

Meiosis II

Spermatogenesis

Unit 8 notes - part 1 - meiosis

oogenesis

Haploid (1n)

n=23

human

sex cell

egg

n=23

2n=46

n=23

diploid (2n)

Meiosis I

Meiosis II

Oogenesis

Polar Bodies (die)

Unit 8 notes - part 1 - meiosis

meiosis animation
Meiosis Animation

Unit 8 notes - part 1 - meiosis

interphase i
Interphase I
  • Similar to mitosis interphase.
  • CHROMOSOMES(DNA)replicate in the S phase
  • Each duplicated chromosome consist of twoidenticalSISTER CHROMATIDS attached at their CENTROMERES.
  • CENTRIOLE pairs also replicate.

Unit 8 notes - part 1 - meiosis

interphase i1
Interphase I
  • Nucleus and nucleolus visible.

Nucleus

chromatin

cell membrane

nucleolus

Unit 8 notes - part 1 - meiosis

meiosis i four phases
Meiosis I (four phases)
  • Cell division that reduces the chromosome number by one-half.
  • Four phases:

a. Prophase I

b. Metaphase I

c. Anaphase I

d. Telophase I

Prophase I

Unit 8 notes - part 1 - meiosis

prophase i
Prophase I
  • Longest and most complex phase (90%).
  • Chromosomes condense.
  • Synapsis occurs - Homologous chromosomescome togetherto form a tetrad.
  • Tetrad is two chromosomesor four chromatids (sister and non-sister chromatids).

Unit 8 notes - part 1 - meiosis

non sister chromatids homologs
Non-Sister Chromatids-HOMOLOGS
  • Homologs contain DNA that codes for the same genes , but different versions of those genes
  • Genes occur at the same loci

Unit 8 notes - part 1 - meiosis

prophase i synapsis

Homologous chromosomes

sister chromatids

sister chromatids

Tetrad

Prophase I - Synapsis

Unit 8 notes - part 1 - meiosis

homologous chromosomes
Homologous Chromosomes
  • Pair of chromosomes (maternal and paternal) that are similar in shape and size.
  • Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits.
  • Each locus(position of a gene) is in the same position on homologues.
  • Humans have 23 pairs of homologous chromosomes:

a. First 22 pairs of autosomes

b. Last pair of sex chromosomes

LOCI

Unit 8 notes - part 1 - meiosis

homologous chromosomes1

eye color

locus

eye color

locus

hair color

locus

hair color

locus

Paternal

Maternal

Homologous Chromosomes

Unit 8 notes - part 1 - meiosis

crossing over
Crossing Over
  • Crossing over may occur between non-sister chromatids at sites called chiasmata.
  • Crossing over: segments of nonsister chromatids break and reattach to the other chromatid.
  • Chiasmata (chiasma) are where chromosomes touch each other and exchange genes (crossing over.)
  • Causes Genetic Recombination – new mixture of genetic material

Unit 8 notes - part 1 - meiosis

genetic recombination

Tetrad

nonsister chromatids

chiasmata: site of crossing over

Genetic Recombination

Unit 8 notes - part 1 - meiosis

variation

prophase i1

spindle fiber

centrioles

aster

fibers

Prophase I
  • Nucleus & Nucleolus disappear
  • Spindle forms
  • Chromosomes coil & Synapsis (pairing of homologues) occurs
  • Tetrads form & Crossing over Occurs

Unit 8 notes - part 1 - meiosis

TETRAD

metaphase i
Metaphase I
  • Shortest phase
  • Tetrads align on the equator.
  • Independent assortment occurs – chromosomes separate randomly causing GENETIC RECOMBINATION

Unit 8 notes - part 1 - meiosis

metaphase i1

OR

Homologs line up at equator or metaphase plate

Metaphase I

Unit 8 notes - part 1 - meiosis

anaphase i
Anaphase I
  • Homologous chromosomes separate and move towards the poles.
  • Sister chromatids remain attached at their centromeres.

Unit 8 notes - part 1 - meiosis

telophase i
Telophase I
  • Each pole now has haploid (1n) set of chromosomes.
  • Cytokinesis occurs and two haploid daughter cells are formed.

Unit 8 notes - part 1 - meiosis

telophase i1
Telophase I

cytokinesis

Unit 8 notes - part 1 - meiosis

meiosis ii
Meiosis II
  • No Interphase II or very short
  • No DNA Replication
  • Remember: Meiosis II is similar to mitosis

Unit 8 notes - part 1 - meiosis

prophase ii
Prophase II
  • Same as Prophase in mitosis
      • Nucleus & nucleolus disappear
      • Chromosomes condense
      • Spindle forms

Unit 8 notes - part 1 - meiosis

metaphase ii

Chromosomes (not homologs) line up at equator

Metaphase II
  • Same as Metaphase in mitosis

Unit 8 notes - part 1 - meiosis

anaphase ii
Anaphase II
  • Same as Anaphase in mitosis
  • SISTER CHROMATIDS separate

Unit 8 notes - part 1 - meiosis

telophase ii
Telophase II
  • Same as Telophase in mitosis.
  • Nuclei and Nucleoli reform, spindle disappears
  • CYTOKINESIS occurs.
  • Remember: FOUR HAPLOID DAUGHTER cells are produced.
  • Called GAMETES (eggs and sperm)

1n Sperm cell fertilizes 1n egg to form 2n zygote

Unit 8 notes - part 1 - meiosis

telophase ii1
Telophase II

Unit 8 notes - part 1 - meiosis

variation
Variation
  • Also known as GENETIC RECOMBINATION
  • Important to population as the raw material for NATURAL SELECTION.
  • All organisms are NOT alike
  • Strongest “most fit” survive to reproduce & pass on traits

Unit 8 notes - part 1 - meiosis