1. Introduction to Genetics: Mendel and Meiosis
Biology Chapter 11
Introduction to Genetics: Mendel and Meiosis

2. IQ #1
1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?
2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?
3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

3. Section 11-4: Meiosis I. MEIOSIS
A. Meiosis= process of _________________________ in which the number of chromosomes per cell is cut in 1/2
and the homologous chromosomes that exist in a diploid cell are separated. (and produce haploid cells)
B. Purpose=
Reduction Division
Form gametes (egg and sperm)

4. II. DIPLOID AND HAPLOID CHROMOSOME NUMBER
A. During ________________ the genetic material from one parent combines with genetic material from another
Example: A fruit fly has 8 chromosomes
A set of 4 came from the female fly
A set of 4 came from the male fly
fertilization
B. The two sets of chromosomes are said to be
homologous = a female chromosome has a corresponding male chromosome.

5. Sperm (n) = 23 chromosomes
Diploid (2n)
C =contain both sets of homologous chromosomes
D = contain 1 set only
Male gamete
Female gamete
Haploid (n)
Sperm (n) = 23 chromosomes
Egg (n) = 23 chromosomes

6. Meiosis (aka: reduction division) 1 replication; 2 divisions
Question: If we start with a diploid cell, how do we get an organism that produces haploid gametes?
Answer:
Example: what if:
Meiosis (aka: reduction division)
1 replication; 2 divisions 8 46
Human
Fruit fly 16 92 8 46 46
Duplicated
chromosomes 8
Duplicated
chromosomes 4 4 4 4 23 23 23 23

7. PROCESS OF MEIOSIS (DIVIDED INTO 2 STAGES: MEIOSIS I & II INTERPHASE: growth, DNA synthesis, protein production, organelle production
A Meiosis I
    homologous chromosomes pair up (Form tetrads) nucleoli disappear
  nucleus disappears
4. crossing-over occurs: portions of chromatids exchange genetic material
2n (diagram 277)
prophase I

8. exchange of genetic material between homologous chromosomes
Crossing-Over
Crossing Over:
exchange of genetic material between homologous chromosomes
Go to Section:

9. Crossing Over
Go to Section:

10. Crossing Over
Crossing-Over
Go to Section:

11. metaphase I
1. homologous pairs (tetrads) line up at the equator
   2. spindles attach to chromosomes
independent assortment occurs
  anaphase I
1. spindles pull the homologous chromosomes toward opposite ends of the cell
Key point: homologous pairs separate, cell now haploid

12. 1. Nuclear membranes reform
    Telophase I
n n
1. Nuclear membranes reform
2. cell begins to separate into two new haploid cells
    haploid daughter cells

13. Meiosis I Figure 11-15 Meiosis
Section 11-4
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

14. Meiosis I Figure 11-15 Meiosis
Section 11-4
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

15. Meiosis I Figure 11-15 Meiosis
Section 11-4
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

16. Meiosis I Figure 11-15 Meiosis
Section 11-4
Interphase I
Prophase I
Metaphase I
Anaphase I
Cells undergo a round of DNA replication, forming duplicate Chromosomes.
Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.
Spindle fibers attach to the chromosomes.
The fibers pull the homologous chromosomes toward the opposite ends of the cell.
Go to Section:

17. Prophase II Metaphase II Anaphase II Telophase II/ Cytokinesis
B. Meiosis II (similar process as mitosis; no replication)
Prophase II
Metaphase II
Anaphase II
Telophase II/
Cytokinesis n n n n
***RESULT: 4 haploid daughters that are genetically different!!

18. Meiosis II Figure 11-17 Meiosis II Prophase II Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

19. Meiosis II Figure 11-17 Meiosis II
Section 11-4
Prophase II
Metaphase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
Anaphase II
Telophase II
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

20. Meiosis II Figure 11-17 Meiosis II
Prophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Metaphase II
Anaphase II
Telophase II
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

21. Meiosis II Figure 11-17 Meiosis II
Section 11-4
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
Telophase II
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

22. Meiosis II Figure 11-17 Meiosis II
Section 11-4
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Telophase II
Meiosis II results in four haploid (N) daughter cells.
Go to Section:

23. The 4 haploid cells (gametes) = sperm
IV. GAMETE FORMATION (refer to page 278)
A. Males 1.
2. male gametes produced by a process called _________________
B. Females
1. 4 haploid cells are produced but only
1-haploid cell is a
3-produce
2. female gametes produced by a process called _______________
The 4 haploid cells (gametes) = sperm
spermatogenesis
viable egg
polar bodies caused by uneven cytoplasmic division
oogenesis

24. Chapter 18
Sexual Reproduction, Meiosis, and Genetic Recombination
Figure Gamete Formation
(a) In the male, all four haploid products of meiosis are retained and differentiate into sperm. (b) In the female, both meiotic divisions are asymmetric, forming one large egg cell and three (in some cases, only two) small cells called polar bodies that do not give rise to functional gametes. Although not indicated here, the mature egg cell has usually grown much larger than the oocyte from which it arose.
© 1999 by Addison Wesley Longman A division of Pearson Education

25. V. COMPARING MITOSIS AND MEIOSIS
A. Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells.
Mitosis
Meiosis
Number of daughter cells
Type of cells produced
Number of divisions
Number of replications
Purpose of division
2 diploid cells
4 haploid cells
Body cells
gametes 1 2 1 1
Sexual reproduction
Growth, replacement, repair, asexual reproduction

26. Key Ideas: What is the principle of dominance?
Section 11-1
Standards addressed: CA 3.b. Students know the genetic basis for Mendel’s laws of segregation and independent assortment.
National 7 2.c. Students know an inherited trait can be determined by one or more genes. 7.2.d. Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining phenotype while the other is recessive. B1. 2.d. Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization).
Key Ideas: What is the principle of dominance?
What happens during segregation?

27. INTRODUCTION TO GENETICS
I. The work of Gregor Mendel
A : the scientific study of heredity
B. Heredity:
 II. Gregor Mendel's Peas
A. In the 1800's, _____________________________ (an Austrian Monk) conducted the first scientific study of heredity using pea plants.
B. Pea plants contain both
male (pollen:sperm) and female (eggs)
reproductive parts.
Genetics
Passing genes from generation to generation
Gregor Mendel

28. Flowering Plant Structures: Pea Plant
C. _______________ = Joining of male and female reproductive cells
Fertilization

29. D. _________________= a pea plant whose pollen fertilizes the egg cells in the very same flower.
  1. Mendel discovered that some
plants ___________ for certain traits
2. Trait=
Example: seed color, plant height
3.True breeding (a.k.a. pure)=
Example: Short plants that self pollinate for generations always produce offspring that were pure for shortness.
Self-pollination
“Bred True”
Specific Characteristics
Peas that are allowed to self-pollinate produce offspring identical to themselves

30. Cross Pollination
Self pollination

31. Independent Assortment
  E. _______________= male sex cells from one flower pollinate a female sex cell on a different flower.
Cross-pollination
F. Mendel manually cross pollinated pea plants, removing the male parts to ensure no self-pollination would occur. Through a series of experiments, Mendel was able to make discoveries of basic principles of heredity.
1. principle of
2. principle of
3. principle of
Dominance
Segregation
Independent Assortment

32. III. Experiments Mendel performed
A.  Mendel studied __ different traits in pea plants each with 2 contrasting characters. (refer to page 264)
B.  Each trait Mendel studied was controlled by one gene.
C.  Different forms of a gene (trait) =
Example: Gene for plant height has 2 alleles 7
Alleles
Dominant: T = tall Recessive: t = short

33. Mendel’s Seven Crosses on Pea Plants
Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
Section 11-1
Seed Shape
Seed Color
Seed Coat
Color
Pod
Shape
Pod Color
Flower Position
Plant Height
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Go to Section:

34. Mendel Experiment #1:
Parent
Offspring
pure bred tall x pure bred tall
TT X TT
All plants are
pure bred short x pure bred short
tt X tt
Pure bred tall x pure bred short X
TALL
SHORT TT tt
TALL

35. Conclusion: genes did not blend Principle of Dominance
·        individual factors (now known as _________)
·        the factors
 ________________________________= some alleles are dominant (expressed trait;written as a capital letter; ex. T) some are recessive (hidden/masked trait; written as a lower case letter; ex. t)
 From these conclusions, Mendel wanted to continue his experiments to see what happened to the recessive trait
did not blend
Principle of Dominance

36. Principles of Dominance
Section 11-1
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
Go to Section:

37. Principles of Dominance
Section 11-1
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
Go to Section:

38. Principles of Dominance
Section 11-1
P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
3 tall : 1 short
Go to Section:

39. Conclusion:
·        ___________________________: The reappearance of the recessive allele indicated that at some point the allele for shortness separated from the allele for tallness. Mendel suggested that the alleles separated during the formation of the sex cells (gametes)….During meiosis.
Principle of Segregation

40. IV. PROBABILITY AND PUNNETT SQUARES
The likelihood that a particular event will occur
     
    A. Probability =   
     B. Probability=
Example #1: If you flip a coin, what is the probability of landing on heads?
Probability= (side that has a head on it)
( opportunities on a coin; head or tails)
Example #2: If you flip a coin 3 times what is the probability of landing on heads? Probability=
# of times a particular event occurs
# of opportunities for the event to occur (# of trials) 1 2 2
½ x ½ x ½ = 1/8

41. C. The principles of probability can be used to
A. Each flip is
  B.  The
  C. The principles of probability can be used to
independent of the next. Past outcomes do not affect future ones. Similar to alleles that segregate randomly, like a coin flip.
larger the number of trials the closer you get to the expected outcomes
predict the outcomes of genetic crosses.

42. IV.  PUNNETT SQUARES
Use of Punnett squares help determine the probable outcomes of genetic crosses. · 
New vocabulary to help with Punnett squares
 -Homozygous =
 -Heterozygous=
-Genotype=
-Phenotype=
-Hybrids=
Having 2 identical alleles (TT, tt)
Having 2 different alleles (Tt)
Genetic makeup of an organism (TT, tt, Tt)
Physical appearance (tall or short)
The offspring resulting from a cross between parents of contrasting traits

43. homozygous tall( ) x homozygous short( ) TT tt
·        Example of a Punnett square:
Parent (P) cross
homozygous tall( ) x homozygous short( ) TT tt t t T Tt Tt T Tt Tt
F1 offspring
Probability of producing homozygous tall offspring?
Probability of producing hybrid?
0/4
4/4

44. IV. PROBABILITY AND SEGREGATION
For fun, lets cross F1’s to see if Mendel’s assumptions about segregation are correct:
Tt x Tt T t T TT Tt t Tt tt
If the alleles segregate during meiosis, then the probable outcomes will be:
TT= Tall=
Tt= Short=
tt= Ratio tall:short=
1/4 3
2/4 1
3:1
1/4

45. Conclusion:
Mendel was correct in his assumptions about Segregration
IV. PROBABILITY AND INDEPENDENT ASSORTMENT
A. Mendel wondered if one pair of alleles affected the segregation of another pair of alleles.
 B.The two factor cross: Mendel crossed RRYY x rryy (P)(aka:two trait cross)
All offspring are
Do round seeds have to be yellow?
Hybrid (RrYy) (F1)

46. A.   Then he crossed the hybrids (F1):
RrYy x RrYy · 
Punnett square formatting rules for 2 trait crosses
1. Determine the possible gametes produced by the parents. 2 methods:
a.    F- RrYy O- I- L-
irst two
(RY)
utside two
(Ry)
(rY)
nside two
(ry)
ast two

47. a. Use a punnett square. One trait on top and the
a.  Use a punnett square. One trait on top and the
other trait on the side.
Parent 1: RrYy Parent 2: RrYy Y y Y y R RY Ry Ry R RY r r rY ry rY ry
Possible gametes Possible gametes

48. 2. Place one parent’s gametes at the top of a 16-Punnett square and the other parent’s gametes on the side of the 16-Punnett square. RY Ry rY ry
RRYY
RRYy
RrYY
RrYy RY
RRYy
RRyy
RrYy
Rryy Ry rY
RrYY
RrYy
rrYY
rrYy
rryy
Rryy
rrYy ry
RrYy

49. Alleles for seed shape independently assort.
Section 11-3
Probability:
RY (round and yellow)=
Ry (round and green =
rY (wrinkled and yellow)=
ry (wrinkled and green)=
Phenotype Ratio=
  Conclusion=
9/16
3/16
3/16
1/16
9:3:3:1
Alleles for seed shape independently assort.
Go to Section:

50. Independent assortment
Genes for different traits can segregate independently during the formation of gametes
****This is true if the traits you are studying
Just by chance all 7 of Mendel’s traits were on different chromosomes.
are located on different chromosomes

51. **Summary of Mendel’s Principles**
1. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring.
2. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.
3.  In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed.
4. The alleles for different genes usually segregate independently of one another.

52. Summary of Gregor Mendel’s Work
experimented with
concluded that
“Factors”
determine
traits
Alleles are
separated during
gamete formation
Pea
plants
Some alleles
are dominant,
and some alleles
are recessive
which is called the
which is called the
Law of
Dominance
Law of
Segregation

53. Beyond Dominant and Recessive Alleles
Key idea: Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.
 Ex. Four O’clock flowers (see next slide)

54. Incomplete Dominance in Four O’clock Flowers
Incomplete Dominance: One allele is _______________ dominant over another. Therefore the phenotype in the heterozygous is somewhere __________ the two homozygous phenotypes.
not completely
in between

55. Incomplete Dominance in Four O’clock Flowers

56. Codominance: both alleles contribute _________ to the phenotype.
Ex. Cholesterol
  Mutliple Alleles: Genes that have _____________
alleles.
This does not mean an individual can have more than two alleles, but that there are more than two alleles in the _______________ for a given trait.
Ex. Rabbit coat color, blood type
equally
more than two
population

57. Multiple Alleles and Codominance
iA, iB, I
iA and iB are codominant
iA, iB both dominate over i
Blood Type/Phenotype BO BB

58. Polygenic Inheritance: The interaction of many genes controls one trait.
It is usually recognized in traits that show a ____________________ such as skin color, height, and body weight.
range of phenotypes

60. Applying Mendel’s Principles.
 Mendel’s principles do not apply only to plants.
Thomas Hunt Morgan
1. In the early ________, Morgan (a nobel prize winning geneticist) decided to look for a model organism to advance the study of genetics.
2. He studied the _____________, Drosophila melanogaster.
3. This specimen was a good choice because:
·  _______ and can be kept in a small place
·  produce ___________ of offspring
·  has only _________ of chromosomes
·  they can produce a new _______________ every 4 weeks
1900’s
fruit fly
tiny
hundreds
4 pairs
generation

61. Fruit Flies (Drosophila melanogaster)

62. Genetics and the environment
Genes alone ______________________ the characteristics of an organism. The interaction between genes and the ________________are necessary.
Ex. Consider the height of a sunflower. Genes provide a plan for the development of a sunflower but the condition of the soil, climate, and water availability will also influence the height of the sunflower.
do not determine
environment

63. 11-5: Gene Linkage and Gene Maps
Standards addressed: CA B1 3.b students know the genetic basis forMendel’s laws of segregation and independent assortment. *B1 3.d. Students know how to use data on frequency of recombination at meiosis to estimate genetic distances between loci and to interpret genetic maps of chromosomes.
Key concept: What structures actually assort independently?

64. Actually ________________________ do assort independently just as Mendel had suggested but the _______ on the chromosomes can be ____________.
A. Linked genes
1. Genes located on the _________ chromosome
2. Inherited _____________
3. Do not undergo ___________________; they don't follow Mendel's law (Just by chance all the traits Mendel studied were located on separate chromosomes...none were linked.)
the chromosomes
genes
linked together
same
together
independent assortment

65. B. Linkage group= all the genes on a _____________
* If there are ___ pairs of chromosomes then there are ____ linkage groups. Humans have ____ pairs of chromosomes therefore ____ linkage groups
chromosome 4 4 23 23

66. Crossing over produces ___________________
III. Crossing Over
A.     If two genes are found on the same chromosome, does it mean that they are linked forever? NO!
Crossing over produces ___________________
B. Recombinants= individuals with _________________ of genes
  recombinants.
new combinations

67. IV. Gene Mapping
A. Sturtevant stated that:
· crossing over occurs ________________ along the linkage groups.
· the _______________ the genes are from each other the ______________ they will cross over
· using the _______________________ (how often crossing over occurs), a gene _______ can be made for each chromosome
randomly
further
more likely
frequency of recombination
map

68. B. Gene map= the __________________ on a chromosome
Example: gene a and gene b cross over 20%
gene a and gene c cross over 5%
gene b and gene c cross over 75%
positions of genes C A B
chromosome:

69. Figure 11-19 Gene Map of the Fruit Fly Exact location on chromosomes