1. Chapter 11.4 Meiosis and Sexual Reproduction
This picture shows
gametes ___________
There are many small
sperm cells competing
to _____________ a
larger egg cell
uniting
fertilize

2. Objectives Summarize the events that occur during meiosis.
Relate crossing-over, independent assortment, and random fertilization to genetic variation.

3. 11.4 Vocabulary
Haploid
Diploid
Somatic cell
Germ cell
Gamete
Meiosis
Homologous chromosome
Crossing over
Independent assortment
Sex chromosomes
Autosome

4. 46 diploid 2n sets mother father Body cells are called somatic cells
All of your somatic cells contain ____ chromosomes, which means they are _________ cells
A diploid cell is mathematically written as ______, which means they have two _______ of chromosomes…
you inherit one set from your _____________ and ____________ 46
diploid 2n
sets
mother
father

5. Sexual Reproduction – Eukaryotic Cells
______ pair of your chromosomes are called your _______ chromosomes, because they are involved with determining your ____________
Your other 22 pairs of chromosomes are called ________________
sex
gender
autosomes

6. X
Your two sex chromosomes are referred to as _____ and _____
You inherit one from each parent
______ = male
______ = female
Females can donate only X’s while males can donate an X or a Y…
Do males or females determine the sex of an offspring? Y XY XX
males

7. sex two gametes egg sperm haploid n one
Your _________ cells reproduce sexually because ______ cells are needed to make another cell
Your sex cells, also called _________________, consist of ________ or _________ cells
Gametes are _____________ cells, which are written mathematically as ______, meaning they have a _____________ set of chromosomes
two
gametes
egg
sperm
haploid n
one

8. 23 unite fertilization zygote
If human somatic cells (2n) have 46 chromosomes…how many chromosomes do gametes (n) have?
When two gametes _____________, they make a diploid body cell in the process of _______________
This fertilized cell is called a ____________ 23
unite
fertilization
zygote

9. mitosis adult into an ___________ organism
` The zygote will then continue to grow and develop through ____________
into an ___________ organism
mitosis
adult

10. homologous shape size content
` In order for sexual reproduction to occur, organisms must inherit ____________ chromosomes, which are similar in ________, ________, and genetic __________
homologous
shape
size
content

11. ` Your 46 chromosomes are actually ____ sets or pairs of homologous chromosomes2

12. Formation of Haploid Cells
Meiosis is a form of cell division that __________ the number of chromosomes when forming specialized reproductive cells, such as __________ or _____________
These specialized cells are _______________
Since the chromosome number is being ______________ by half, this process is often called cell __________________
halves
gametes
spores
haploids
reduced
reduction

13. Quick Check Review! What are the two types of human gametes?
What do gametes do?
Why is it important that they contain half the number of chromosomes as found in a diploid cell?
Sperm and egg cells
They fuse to create a fertilized zygote
So that they create a diploid cell when they fuse

14. Meiosis involves two divisions of the nucleus called…
_________________
Before meiosis begins, the DNA of the original cell must be copied during _______________
This original cell is a _________________ cell
Meiosis I
Meiosis II
interphase
diploid

15. Homologous Chromosomes & Sister Chromatids
When homologous chromosomes copy themselves before cell division, they take on the characteristic X-shaped appearance with each side of the X being called a sister chromatid
Sister chromatids are identical pieces of DNA held together by the centromere

16. Stages of Meiosis Meiosis I includes…. Meiosis II includes I II I II I
Prophase ___
Metaphase ___
Anaphase ___
Telophase ___
Prophase ____
Metaphase ____
Anaphase ____
Telophase ____ I II I II I II

17. Prophase I Nuclear ______________ and _______________ break down
_____________ is arranged
__________________ become visible
How many chromosomes are in the cell?
How many chromatids?
membrane
nucleolus
Spindle
Chromosomes 4 8

18. Prophase I
Meiosis
This stage differs from mitosis because the homologous chromosomes ________ up in a process called ___________
pair
synapsis
Mitosis

19. structure traits mom dad identical tall short
Review...what are homologous chromosomes?
They are a pair of chromosomes that are similar in ________________ and that also contain genes for the same ____________
You inherit one from ______ and one from ______
They are not ________________
For example…dad’s chromosome may have a _________ gene while mom’s has a __________ gene
structure
traits
mom
dad
identical
tall
short

20. Since they are not identical, the homologous chromosomes are ______________ differently
However, the identical copies within each chromosome are colored the same…what are they called?
colored
sister chromatids

21. The homologous structures pair up so ____________ that they form a four part structure called a ________
Within a tetrad, a process
called ________________
may occur
tightly
tetrad
crossing over

22. During crossing over, areas on _______________ chromatids may exchange genetic material
This picture shows
a ___________
cross over
nonsister
single
Letters = genes

23. Before crossing over, how many different gene combinations existed?
After crossing over,
how many different
gene combinations
exist? 2 4

25. Metaphase I
Meiosis
The __________ of homologous chromosomes line up along the _______________
This arrangement is also _____________ to meiosis
pairs
equator
unique
Mitosis

26. Anaphase I
Homologous _______________ are pulled apart by spindle fibers and moved towards ______________ poles of the cell
chromosomes
opposite

27. Telophase I and Cytokinesis
Prophase I
Opposite of ______________
Cytokinesis splits the __________________ and separates the ______ new cells
How many chromosomes are in each new cell?
The chromosome number has been reduced by _______ and the cells are now _____________
cytoplasm 2 2
half
haploid

28. After Meiosis I
After Mitosis
4 chromosomes per cell
2 chromosomes per cell

29. VERY IMPORTANT!!!!!!!!
These two cells do NOT enter ________________ again and do NOT copy their ________ again!
They both proceed with meiosis ____.
interphase
DNA II

30. Prophase II
In each cell, the nuclear membrane and nucleolus ___________
_____________ is arranged
dissolve
Spindle

31. Metaphase II individual
Now, _______________ chromosomes line up along the equator in each cell

32. Anaphase II
Sister _____________ are pulled towards the opposite poles of each cell
After the chromatids separate, what are they called?
chromatids
chromosomes

33. Telophase II and Cytokinesis
In each cell, the nuclear membrane and nucleolus ___________
The spindle ______________
Chromosomes will ____________
Cytokinesis splits the cells into ______ unique haploid cells
reform
dissolves
uncoil 4

34. Meiosis and Genetic Variation
Meiosis is an important process that allows for the rapid generation of new genetic ________________.
Three mechanisms make key contributions to this genetic variation:
_________________________
combinations
Independent Assortment
Random fertilization
Crossing over

35. Independent Assortment
Refers to the _____________ distribution of homologous chromosomes during meoisis I
In metaphase 1 the homologous chromosomes may pair and line up randomly on either side
random

36. segregate
This affects how the chromosomes ________________ and are passed along to the ________________
gametes

37. Since humans have 23 pairs of homologous chromosomes…each pair has ____ ways it may face while lining up
Mathematically, the total number of possible gametes formed is…
2n or = ,388,608 gametes 2

38. Random fertilization fuse offspring variation
Each of the possible gametes (223) must _______ with another one of the possible gametes (223) during fertilization
Mathematically, the total number of possible zygotes is…
x = 70,368,744,000,000 zygotes
So many different ________________ with great _________________ may result
fuse
offspring
variation

39. Crossing over
Since homologous chromosomes may __________ genetic information within a tetrad, the number of possible gametes and zygotes is actually ___________________
exchange
unlimited

40. Importance of Genetic Variation
Meiosis and the joining of gametes are essential to __________________
The pace of evolution is sped up by genetic _______________.
Each offspring contains a combination of genes that is ________________ from each parent
evolution
recombination
different

41. Objective 1 pair tetrads synapsis Crossing haploid chromatids 4
Summarize the events that occur during meiosis.
At the beginning of Meiosis I, homologous chromosomes ________ tightly to form ___________ in a process called _____________. ____________ over may occur. When the homologous chromosomes separate, two ____________ cells are formed
During Meiosis II, the sister ______________ separate, forming _____ different gametes.
pair
tetrads
synapsis
Crossing
haploid
chromatids 4

42. Objective 2
Relate crossing-over, independent assortment, and random fertilization to genetic variation.
Crossing over –
Independent Assortment –
Random fertilization -
Changes gene combinations on
Non-sister chromatids of homologous
chromosomes
The homologous chromosomes line up and segregate randomly during Meiosis I.
The possible gametes fuse randomly