Question

1
Question?

• Does Like really beget Like?
• The offspring will resemble the parents, but
  they may not be exactly like them.

2
Can you pick out the kids for each couple?
3
Chapter 13 - Meiosis and Sexual Life Cycles

• Genetics is the scientific study of the
  transmission of traits from parents to offspring
  (heredity) and the variation (genetic
  differences) between and within generations.

4
An Introduction to Heredity

• Genes are segments of DNA.
• The location of a gene on a chromosome is called
  its locus.

5
An Introduction to Heredity

• Asexual reproduction is a form of reproduction in
  which a single parent is involved in passing on
  all of its genes to its offspring.
• All organisms are similar in appearance. (single
  celled eukaryotes, hydra)

6
An Introduction to Heredity

• Sexual Reproduction is a form of reproduction in
  which two individuals are contributing genes.
• Results in greater genetic variation in the
  offspring.

7
The Role of Meiosis in Sexual Life Cycles

• The life cycle of an organism is the sequence of
  stages in its reproductive history through the
  course of one generation.

8
The Role of Meiosis in Sexual Life Cycles

• Somatic cells are cells other than gametes (egg,
  sperm) they are body cells in humans each
  somatic cell has 46 chromosomes.
• The karyotype of an organism refers to a picture
  of its complete set of chromosomes, arranged in
  pairs of homologous chromosomes from largest to
  smallest size pair.

9
The Role of Meiosis in Sexual Life Cycles

• Homologous chromosomes carry the genes that
  control the same traits.
• They are similar in length, position of
  centromere, and banding pattern when stained.
• One chromosome in each pair is inherited from
  each parent.

10
The Role of Meiosis in Sexual Life Cycles

• Sex chromosomes are not considered a homologous
  pair.
• In humans females have two X chromosomes, and
  males have one X and one Y chromosome.

11
The Role of Meiosis in Sexual Life Cycles

• Non-sex chromosomes are called autosomes and
  occur in homologous pairs.
• 22 autosomes plus one sex chromosome in humans
  means our haploid number is 23.

12
The Role of Meiosis in Sexual Life Cycles

• Gametes (sperm and egg) are haploid (n) cells
• they contain half the number of chromosomes as
  somatic cells.

13
The Role of Meiosis in Sexual Life Cycles

• In fertilization, haploid gametes from the
  parents fuse, and the fertilized egg is called a
  zygote.
• The zygote is diploid (2n) has two haploid sets
  of chromosomes, one from each parent.
• In humans, our diploid number is 46.

14
The Role of Meiosis in Sexual Life Cycles

• Meiosis is the process by which, in the course of
  gamete production, the diploid chromosome number
  is halved so that haploid gametes are formed.
• Fertilization restores the diploid number as the
  gametes are combined

15
The Role of Meiosis in Sexual Life Cycles

• Fertilization and meiosis alternate in the life
  cycles of sexually reproducing organisms.
• There are three types of life cycles.

16
The Role of Meiosis in Sexual Life Cycles

• Humans most animals
• meiosis occurs during gamete production, and the
  diploid zygote divides by mitosis to produce a
  multicellular organism

17
The Role of Meiosis in Sexual Life Cycles

• Fungi, some protists, an algae after gametes
  fuse to form the diploid zygote, meiosis occurs
  to produce haploid cells these then divide by
  mitosis to give a haploid multicellular organism

18
The Role of Meiosis in Sexual Life Cycles

• In plants and some algae, alternation of
  generations occurs.
• The diploid stage is the sporophyte, and meiosis
  in the diploid phase creates haploid spores,
  which divide mitotically to produce the
  gametophyte.
• The gametophyte produce haploid gametes through
  mitosis, fertilization occurs, producing a
  diploid zygote.

19
Meiosis Reduces Chromosome Number from Diploid to
Haploid

• Meiosis and mitosis look similar both are
  preceded by replication of the cells DNA.
• However, meiosis occurs in two stages meiosis I
  and meiosis II.
• The result is four daughter cells with half as
  many chromosomes as the parent cell.
• The stages are describe on the next 7 slides.

20
Meiosis Reduces Chromosome Number from Diploid to
Haploid

• Interphase
• Each of the chromosomes replicate, resulting in
  two sister chromatids attached at their
  centromeres.

21
Meiosis Reduces Chromosome Number from Diploid to
Haploid
http//rds.yahoo.com/S96062883/Kmeiosis/v2/SID
e/TIDI008_74/lIVR/SIG129opmk59/-http3A//www.b
iology.iupui.edu/biocourses/N100/2k4ch9meiosisnote
s.html

• Prophase I
• Chromsomes condense, homologs (2 sister
  chromatids) pair up.
• Synapsis occurs the joining of 2 homologous
  chromosomes along their length, forming tetrads
• Crossing over may occur at the chiasmata
  (overlapping pieces of homologs).
• Centrioles separate, nuclear membrane
  disappears, spindle attaches to kinetochores.

22
Meiosis Reduces Chromosome Number from Diploid to
Haploid

• Metaphase I
• Homologous pairs of chromosomes are lined up at
  middle, microtubules from each pole attach to
  homologous pairs.

23
Meiosis Reduces Chromosome Number from Diploid to
Haploid

• Anaphase I
• Spindle helps to move chromosomes toward
  opposite ends of the cell, sister chromatids stay
  connected and move together.

24
Meiosis Reduces Chromosome Number from Diploid to
Haploid

• Telophase I, Cytokinesis
• Homologous chromosomes reach opposite poles
  each pole contains a haploid set of chromosomes,
  with each chromosome still consisting of 2 sister
  chromatids.
• Cleavage furrow forms in animal cells, cell
  plate in plant cells, two daughter cells are
  formed

25
Meiosis Reduces Chromosome Number from Diploid to
Haploid

• Prophase II
• Spindle forms in each daughter cell.
• Metaphase II
• Chromosomes line up in middle.

http//rds.yahoo.com/S96062883/Kmeiosis/v2/SID
e/TIDI008_74/lIVR/SIG129opmk59/-http3A//www.b
iology.iupui.edu/biocourses/N100/2k4ch9meiosisnote
s.html
26
Meiosis Reduces Chromosome Number from Diploid to
Haploid

• Anaphase II
• Centromeres of sister chromatids break,
  individual chromosomes move to opposite poles
• Telophase II, Cytokinesis
• Chromatids are at opposite pole, nuclear
  membrane reforms, cytokinesis occurs, four
  daughter cells result each with the haploid
  number of chromosomes.

27
Origins of Genetic Variation

• Independent Assortment
• In metaphase I, when homologous chromosomes are
  lined up in the middle, they can pair up in any
  combination, with any of the homologous pairs
  facing either pole.

http//bio.winona.edu/bates/Bio241/images/p13-08.j
pg
28
Origins of Genetic Variation

• Crossing Over
• After Prophase I, homologous chromosomes synapse
  and exchange homologous parts of 2 non-sister
  chromatids. These recombinants are further
  subjected to independent assortment in Metaphase
  I.

http//bio.winona.edu/bates/Bio241/images/p13-09.j
pg
29
Origins of Genetic Variation

• Random Fertilization
• Fertilization is random since each sperm and egg
  is different as a result of independent
  assortment and crossing over, furthermore each
  combination of egg and sperm is unique.

http//nte-serveur.univ-lyon1.fr/nte/EMBRYON/www.u
oguelph.ca/zoology/devobio/miller/meiosis1.gif