meiosis paso a paso explicando al final, los dos motivos principales de la variación genética: crossover y distribución independiente Además se explica la no disyunción de cromosomas y sus consecuencias en Anomalías Cromosómicas

1. Miss Sofía Paz

2. Meiosis
Tipo de
division
celular
que resulta en
4 células,
cada una
con la mitad
del numero
de
cormosomas
que la célula
madre

3. Cariotipo
Conjunto
clasificado de los
46 cromosomas
de una persona
Cada cromosoma tiene un cromosoma hermano parecido en
forma y tamaño, uno de la madre y otro del padre
Los lugares específicos de los genes dan puntos de referencia para que
los cromosomas se alinien correctamente antes de la separación durante
la division celular

4.  Llevan la misma secuencia de
genes en las mismas
locaciones
 Controlan las mismas
características hereditarias
 Los genes pueden ser versiones
levemente diferentes
Es un set de un
cromosoma materno y un
cromosoma paterno que
forman un par durante la
meiosis.

5. Cromátides hermanas: dos
mitades idénticas de un
mismo cromosoma replicado
Cromátides hermanas son idénticas, los cromosomas
homólogos son similares entre sí pero no idénticos

6.  2n = 46 (diploide)
 n= 23 (haploide)
 Fertilización
 Fusión del núcleo de un
esperma haploid y un
óvulo haploid para fomrar
un zigoto dipoloide
 Zigoto
 Se desarrolla en un adulto
maduro con trillones de
células (mitosis) capaz de
producir células haploides
fértiles

7. MEIOSIS
Dos divisiones meióticas
• Meiosis I
• Cromosomas
homólogos se
separan.
• Meiosis II
• Cromátides
hermanas se
separan .

9. Meiosis I
Profase I
Los cromosomas
homólogos se
unen gracias a
proteínas
formando una
tétrada
(4 cromátides) y
sucede el
Crossing over
Metafase I
Tétradas se
alinean en el
centro de la
célula
Anafase I
Los cromosomas
homólogos se
separan.
Cromátides
hermanas
quedan juntas
Telofase I and
Citoquinesis
2 Núcleos
haploides ,
dos células
cada una
con un set de
cromosomas

11. Meiosis II
Profase II
Se forma el
huso y se
adhiere a los
centrómeros
Metafase II
Cromosoma
s se alinean
en el centro
de la célula
Anafase II
Cromátides
hermanas se
separan
Telofase II and
Citoquinesis
Chromatides
llegan a los
polos se forman
núcleos y el
citoplasma se
divide

13. • Cromátides no hermanas intercambian
segmentos en la PROFASE ICrossing over
Como la meiosis incrementa la variación genética:
CROSSING OVER y DISTRIBUCIÓN INDEPENDIENTE
Cómo incrementa la variación?:
por recombinación genética, osea,
una nueva combinación de la
información genética

14. El # de
combinaciones
posibles es 2n
Donde n=
número
haploide de
cromosomas
n =2 4 combinations
n =23 8 million
combinations
Como la meiosis incrementa la variación genética:
DISTRIBUCIÓN INDEPENTIENDE
miembros de
un par de
genes están
distribuidos
aleatoriamente
en
los gametos,
independiente
mente de la dis
tribución de
otros pares de
genes.

15. NO disyunción/
nondisjunction
Fallo de las cromátides
hermanas al separarse
durante la meiosis.
Fallo de los cromosomas
homólogas al segregarse o
separarse durante la meiosis

16. Syndrome Karyotype Clinical features
Down Trisomy 21 Short, broad hands with single palmar crease, decreased
muscle tone, mental
retardation, broad head with characteristic features, open
mouth with large tongue,
up-slanting eyes.
Edwards Trisomy 18 Multiple congenital malformations of many organs, low-set
malformed ears, receding
mandible, small eyes, mouth and nose with general elfin
appearance, severe mental
deficiency, congenital heart defects, horseshoe or double
kidney, short sternum,
posterior heel prominence
Patau Trysomy 13 Severe mental deficiency, small eyes, cleft lip and/or
palate, extra fingers and toes,
cardiac anomalies, midline brain anomalies, genitourinary
abnormalities
Klinefelter 47, XXY Male, infertile with small testes, may have some breast
development, tall, mild mental
deficiency, long limbs, at risk for educational problems
Triple X 47, XXX Female with normal genitalia and fertility, at risk for
educational and emotional
problems, early menopause

17. Reviewing Concepts
Multiple Choice
Choose the letter of the best
answer.
1. Which of the following processes occurs in eukaryotic organisms that only reproduce
asexually?
a. mitosis
b. meiosis
c. both mitosis and meiosis
d. fertilization
2. Which of the following is a key event during the S phase of the cell cycle?
a. The genetic material is duplicated.
b. A cell grows in size.
c. The number of organelles increases.
d. The cytoplasm is divided in two.
3. The cytoplasm is divided into two daughter cells during
a. metaphase.
b. prophase.
c. cytokinesis.
d. anaphase.

18. 4. Which of the following steps occurs during prophase in mitosis?
a. Sister chromatids separate.
b. Nuclear envelope disappears.
c. Nuclear envelope reappears.
d. Chromosomes undergo duplication.
5. The spread of cancer cells beyond their original tumor site is called
a. mitosis.
b. fertilization.
c. cytokinesis.
d. metastasis.
6. The products of meiosis from one parent cell are
a. two diploid cells.
b. four chromosome pairs.
c. four haploid cells.
d. two haploid cells.
7. How many possible chromosome combinations are there for the gametes
of an organism with a haploid number equal to 4?
a. 22 = 4
b. 28 = 256
c. 21 = 2
d. 24 = 16

19. Short Answers
8. Give three examples of organisms that reproduce asexually.
9. Describe four events that happen in a typical cell during interphase.
10. Identify the two major events that occur during the mitotic phase of the cell cycle.
11. What is the function of the spindle during mitosis?
12. Explain how cancer tumors spread.
13. Describe the most obvious way the karyotypes of a sister and brother look different.
14. Explain how having a haploid number of chromosomes contributes to the function of gametes in a
life cycle.
15. Describe the structure of a tetrad. When do tetrads form?
16. Describe one similarity between mitosis and meiosis II. Describe one difference.
17. Name two factors that introduce genetic variation during the process of meiosis. Explain how they
introduce variation.

20. Visualizing Concepts
18. The diagram below represents metaphase I of meiosis in a cell that
has two pairs of homologous chromosomes. Using colored pencils or
pens, draw a similar diagram to show how the chromosomes would look
if the cell were in metaphase of mitosis.

21. Applying Concepts
Analyzing Information
19. Analyzing Diagrams Use the diagram below of a
cell undergoing cytokinesis to answer the following
questions.
a. Does the diagram show a plant cell or an animal
cell? Explain.
b. Identify each of the numbered structures in the
diagram.
c. Draw and label a diagram of the final step in this
process.

22. 20. Analyzing Photographs Strawberry plants, such as those shown in the
photograph below, can reproduce by a process in which an existing
plant sends out tiny new plants on long, trailing stems. These new plants
grow roots when they come in contact with soil. If the trailing stems are
severed, the separated plants become completely independent of the
parent plant.
a. Is the process in strawberry plants an example of asexual or sexual
reproduction? Explain your answer.
b. Which process, mitosis or meiosis, is involved in producing the trailing
stems, leaves, and new roots?
c. How do the new strawberry plants compare genetically to the original
plant?

23. Critical Thinking
21. Developing Hypotheses The cells of organisms called plasmodial slime
molds have multiple nuclei. Suggest how a variation on the cell cycle could
give rise to such a situation.
22. Comparing and Contrasting How are the growth of a malignant tumor and
the repair of a cut on your finger similar? How are they different?
23. Making Judgments Suppose you read about a study that relates exposure
to a certain chemical to an increased risk of cancer in rats. What types of
effects at the cellular level do you think the researchers observed? Would you
expect to observe similar effects in humans exposed to the chemical? Why or
why not?
24. What's Wrong With These Statements? Briefly explain why each statement is
inaccurate or misleading.
a. The first stage of mitosis is the duplication of the chromosomes.
b. Every cell of a sexually reproducing organism has the same number of
chromosomes.
c. Cells spend most of their time in the mitotic (M) phase of the cell cycle.

24. http://www.youtube.c
om/watch?v=iCL6d0O
wKt8&feature=player_e
mbedded

25. http://d1geneticswikib.wikispaces.com
/Mitosis,+Meiosis+and+Cell+Cycle