1. To Review: Cells divide to stay small
The process of cell division is called mitosis
Mitosis is a very small part of the cell’s life cycle
Most of the cell’s life is spent in interphase
Interphase is divided into G1, S, and G2
G1 is the period when the cell is doing what it was designed to do
S is DNA replication so there will be 2 copies when it is ready to divide
G2 is the period when the cell is making more organelles and other materials needed for mitosis
Mitosis is divided into prophase, metaphase, anaphase, and telophase
Mitosis is generally followed by cytokinesis
When the cell cycle is out of control, cancer can result

2. To Preview:
Some cells in the reproductive structures of organisms do not divide by mitosis
Some cells in the reproductive structures of organisms divide by meiosis
The reproductive structures in animals are typically called testes in males and ovaries in females
The cells in testes called primary spermatocytes divide by meiosis to become sperm
The cells in ovaries called primary oocytes divide by meiosis to become eggs
The cells in organisms that divide by mitosis are called somatic (soma = body) cells
The cells in organisms that divide by meiosis are called gametes (sex cells; eggs and sperm are gametes)
Both mitosis and meiosis involve chromosomes
Scientists can analyze chromosomes using a karyotype
Sometimes meiosis (or mitosis, actually) doesn’t go perfectly and chromosomal disorders can result
One type of chromosomal disorder that can result from an error in meiosis (or mitosis) is called a nondisjunction disorder, such as Downs syndrome

3. Part 1: Chromosomes

4. Copy, Define, and Illustrate the following terms:
Vocabulary Words
Copy, Define, and Illustrate the following terms:
Gamete
Genes
Haploid
Homologous
Karyotype
Sex Chromosomes
Zygote
Autosome
Centromere
Centrosome
Chromatid
Chromatin
Chromosome
Diploid

5. Differences Among Species
Each organism has a characteristic number of chromosomes
The number is constant with the species
Potatoes, plums, and chimpanzees all have 48 chromosomes

6. Before division, chromatids separate to ensure identical DNA in both
GENE
Units of information
Segment of DNA that codes for a protein or RNA molecule
CHROMOSOME
Composed of DNA and proteins (chromatin)
Consist of 2 identical CHROMATIDS attached by a CENTROMERE when cell is ready to divide (after S of interphase)
Before division, chromatids separate to ensure identical DNA in both

9. Somatic Cells Any cell other than a sperm or egg cell
Have 46 chromosomes in humans
Differ in size, shape, & genes
23 pairs
2 HOMOLOGOUS chromosomes that are similar in size, shape, & genes
One comes from each parent
Diploid (2n)
Contains 2 sets of chromosomes
In humans, 2n=46

10. Gametes Sperm or egg cell Contain 1 set of chromosomes Haploid (n)
23 in humans
Haploid (n)
In humans n=23
Fusion of 2 gametes = FERTILIZATION
Fertilized egg cell is a ZYGOTE
(EGG + SPERM = ZYGOTE)
23 chromosomes + 23 chromosomes = 46 chromosomes
n + n = 2n

11. CHROMOSOMES Autosomes Sex chromosomes
22 of the 23 pairs of chromosomes in somatic cells (44 of 46 chromosomes)
Sex chromosomes
1 of the 23 pairs (2 of the 46 chromosomes)
Contain genes that will help determine the sex of the organism (plus others…)
X and Y chromosomes in many organisms
In most organisms, if there is a Y it is male
XY in humans is male
If there is no Y, it is a female
XX is a normal female in humans
Who determines the sex of the organism?
XO – O refers to no chromosome
birds and butterflies have an XO system
In humans, XO is a genetic disorder called Turner’s

12. This is a photograph of the chromosomes of a cell after DNA replication has occurred. This is typically when scientists try to photograph a squash of the nucleus, which hopefully results in the chromosomes being separated out.
If a karyotype is going to be constructed, a computer can sort the chromosomes, line them up by size, and look for any abnormalities. It can (and used to be) also be done “by hand”: the photograph taken through the microscope would be enlarged and printed, then the chromosomes would be cut apart with scissors and sorted and ordered by hand.

13. Karyotype - photograph of chromosomes grouped in order from largest to smallest in pairs; used to analyze chromosomes
How many autosomes are shown?
How many sex chromosomes?
Is this from a male or a female?
How do you know?
This is a human karyotype.
How many chromosomes are shown?
Was this made from the nucleus of a somatic cell or a gamete?

14. Part 2:
Reproduction

15. Reproduction
Asexual – reproduction resulting from mitosis (or a similar process) that involves only one parent; the offspring are genetically identical to the parent (a clone)
- the only way asexual reproduction can lead to genetic variation is through random mutations.
Sexual – reproduction resulting from an exchange of genetic material; in most organisms this involves the fusion of gametes (formed during meiosis)

16. Ways of Reproducing Asexually
Binary Fission – separation of a parent into 2 or more individuals, ex. bacteria
Single parent passes copies of all its genes to each of its offspring. There is no fusion of haploid cells
Organism that is genetically identical ot its parent.
1. fission, separation of a parent into 2 or more individuals
3.2. frag, body breaks into several pieces - worms
3.3 budding, new individuals split off from existing ones. Bud make break off or remain attached to parent – jellyfish, corals

17. Fragmentation-- body breaks into several pieces, ex. worms

18. Budding-- new individuals split off from existing ones
Budding-- new individuals split off from existing ones. Bud may break off or remain attached to parent, ex. jellyfish, corals, yeast

19. Regeneration– renewal/regrowth of an organism from a part of that organism; ex. starfish, planaria

20. Asexual Reproduction Disadvantages: Benefits/advantages:
DNA varies little between organisms, which may make organisms not be able to adapt to a changing environment
Benefits/advantages:
Produce many offspring in short period of time without using energy to produce gametes or to find a mate
Offspring are perfectly adapted to current environment, therefore often used in stable environments
Produce many offspring in short period of time without using energy to produce gametes or to find a mate.
DNA varies little between organisms, which may make organisms not be able to adapt to a changing environment

21. Sexual Reproduction Disadvantages: Benefits/advantages:
Sexual reproduction uses a lot of metabolic energy in the development and maintenance of gametes, as well as a lot of biochemical resources.
Benefits/advantages:
Sexual reproduction has several advantages over asexual reproduction. One of those advantages is the frequent production of new combinations of genes. This flexibility in the gene pool of a population helps insure the survival of a species, especially if there is rapid or sudden change in the environment. This is important in the process of natural selection. (more later…)
May have begun as a mechanism to repair damaged DNA. (Many modern protists are haploid most of the time, and they reproduce asexually. They form a diploid cell only in response to stress in the environment. Thus the process of meiosis and the pairing of homolgous chromosomes may have allowed early protistan cellls to repair damaged DNA.)
entire span in the life of an organism from one generation to the next. Basic pattern of alteration between the diploid and haploid chromosome numbers.
The zygote is the only diploid cell and it undergoes meiosis after it is formed, creating new haploid cells. Haploid cells give rise to haploid multicellular individuals that produce gametes by mitosis. Through fusion, gametes produce diploid zygote.
When diploid zygote undergoes meiosis it has opportunity to repair damaged DNA through crossing over. Gametes join in fertilization, then divides in mitosis.
Alternates between haploid and diploid

22. Part 3: Meiosis

23. Copy, Define, and Illustrate the following terms:
Vocabulary Words
Copy, Define, and Illustrate the following terms:
meiosis haploid
gamete diploid
genetic variation
crossing over
independent assortment
sexual reproduction
random fertilization
karyotypes

24. Meiosis – the formation of gametes
* source of genetic variation through
* crossing over – during prophase I pieces of homologous chromosomes are exchanged
* independent assortment – during metaphase I and II which chromosomes go to which cell is random
Sexual reproduction – two parents required
* random fertilization – which egg and which sperm are involved is random
Nondisjunction – source of some chromosomal disorders
Karyotypes – picture of all of an organism’s chromosomes

25. What is Meiosis?
Meiosis is a form of cell division that produces sex cells (gametes) used in fertilization.

26. How is Meiosis Different?
There are 2 divisions in meiosis
Meiosis I and meiosis II
The result is 4 cells instead of 2
In meiosis II, the DNA is not replicated again. (No interphase)
The ending number of chromosomes is 23 in humans (egg has 23 and sperm has 23)This is haploid (n).

28. Mitosis Vs. Meiosis Mitosis Meiosis 1 division=2 cells
Daughter cells identical
Diploid cells (2n)=46
Body/Somatic cells
Meiosis
2 divisions = 4 cells
Daughter cells different (crossing over; independent assortment)
Haploid cells (n)=23
Gametes (sex cells—eggs or sperm)

29. Comparing Mitosis and Meiosis
From Pearson Education

30. Things that can occur that lead to genetic variation…
Independent assortment—homologous chromosomes are randomly sorted/distributed during meiosis
Crossing-over—the exchange of genes that can occur between homologous chromosomes during Prophase I
Random-fertilization—the fertilization of an egg and sperm is random

31. Crossing over in Prophase I – results in “new” chromosomes
From Pearson Education

32. Independent Assortment

33. Sexual Reproduction - This is how many new organisms are made!!
Fertilization –syngamy (word parts!)
23 chromosomes +
46 chromosomes (23 pair)
(zygote)

34. Sexual Reproduction Life Cycle for Animals
Baby
YOU!
Growth & Development
From Pearson Education

35. Can you determine which children belong to which couple
Can you determine which children belong to which couple? Genetic variation is important in creating individuals!
From Pearson Education

36. Answer: The first and last picture belong to couple 1
Answer: The first and last picture belong to couple The middle pictures belong to couple 2.

39. Karyotypes, Nondisjunction, & Chromosomal Disorders
Part 4:
Karyotypes, Nondisjunction, & Chromosomal Disorders

40. Copy, Define, and Illustrate the following terms:
Vocabulary Words
Copy, Define, and Illustrate the following terms:
Nondisjunction
Chromosomal disorder
Monosomy
Trisomy

41. A karyotype is a photograph of all of an organism’s chromosomes
KARYOTYPES
A karyotype is a photograph of all of an organism’s chromosomes

42. Humans have 23 pairs of chromosomes.
The last pair (#23) is the sex chromosomes. (XX-female, XY-male)
All others are called autosomes.
A karyotype allows you to study differences in chromosome shape, structure, and size.

43. By looking at a karyotype, you should be able to:
determine the sex/gender of the organism,
determine if the organism is “normal” or has a chromosomal disorder,
identify where the disorder is located and what type of disorder (either monosomy, trisomy, or malformation of a chromosome) and possibly the specific name (like Turner’s, Down, etc.),
determine the number of autosomes and sex chromosomes present.

44. What do you mean, abnormal?
What kind of disorder?
How does this happen?

45. Sometimes during meiosis when gametes are made, the chromosomes fail to separate correctly at anaphase I or anaphase II. This failure to separate is called nondisjunction.
Most nondisjunction disorders are lethal to the developing organism. However, there are a few that do allow the organism to continue developing with varying degrees of effect.
Nondisjunction could result in one of the zygotes (once egg & sperm unite) formed having only one copy of the affected chromosome. This is called monosomy.
Another zygote could have 3 copies of one chromosome. This is called trisomy.

46. Nondisjunction disorders can often be diagnosed with a karyotype.
A karyotype is created from a picture of a cell during mitosis when the chromosomes are condensed and look like little Xs. Then a computer sorts the chromosomes into identical pairs and arranges them from largest to smallest (in length) and puts the 2 sex chromosomes at the end (pair 23).
A doctor or other professional then analyzes the information shown for errors or abnormalities and uses them for an initial diagnosis.

47. Common Nondisjunction Disorders
Klinefelter's Syndrome: Trisomy+ of sex chromosomes (always MALE b/c of Y)
One or more extra sex chromosomes (i.e., XXY or XXXY);
1 out of every 500-1,000 newborn males
Presence of Y chromosome directs development into a male
Underdevelopment of testes; usually infertile; taller than average; less hair than average
Although some lower scores on standardized tests have been reported, this is not necessarily the case.
Can be treatable with hormone therapy

48. Klinefelter’s Karyotype23
Look at Chromosomes #23

49. Common Nondisjunction Disorders
Turner’s Syndrome: Monosomy of the sex chromosomes
One sex chromosome, XO (always FEMALE b/c no Y)
1 in 2500 female births
Absence of Y chromosome  develops into female
Abnormal development of ovaries and secondary sexual characteristics during puberty; often infertile; shorter than normal
“Webbing" of the skin of the neck (extra folds of skin extending from the tops of the shoulders to the sides of the neck)

50. Turner’s Karyotype

51. Common Nondisjunction Disorders
Down Syndrome: Autosomal disorder
Trisomy 21, most common birth “defect”
1 per 800 to 1,000 births (risk goes up as mother’s age goes up)
Mild to moderate learning disabilities (sometimes severe)
Congenital heart defects (50% of individuals) such as atrial & ventricular septal defects
Hypotonia—low muscle tone (all muscles not just skeletal). Eyes that slant upward and small ears that may fold over slightly at the top. Their mouth may be small, making the tongue appear large. Their nose also may be small, with a flattened nasal bridge.

52. Down Syndrome Karyotype
Where did nondisjunction occur? (circle it in the karyotype)
What is the sex of this person? ________

53. Common Nondisjunction Disorders
Patau Syndrome: Autosomal disorder,
Trisomy 13, rarely live past infancy
Extra fingers or toes (polydactyly)
Deformed feet, known as rocker-bottom feet
Neurological problems such as small head (microcephaly), failure of the brain to divide into halves during gestation (holoprosencephaly), severe mental deficiency
Facial defects such as small eyes (microphthalmia), absent or malformed nose, cleft lip and/or cleft palate
Heart defects (80% of individuals)
Kidney defects

54. Patau

55. Common Nondisjunction Disorders
Edward’s Syndrome: Autosomal disorder Trisomy 18, 30% babies die by 1 mo
Moderate to severe learning disabilities
Small head (microcephaly), small and wide-set eyes, small lower jaw
Congenital heart defects (90% of individuals) such as ventricular septal defect and valve defects
Clenched hands with 2nd and 5th fingers on top of the others, and other defects of the hands and feet
Malformations of the digestive tract, the urinary tract, and genitals

56. Edward’s

57. Practice with Karyotypes:

58. Other Chromosomal Mutations
4 Types:
deletion
duplicatiom
inversion
translocation

59. 1. inversion--genes are cut out and reinserted in reverse order
2. deletion--a section of a chromosome (gene) is cut out and lost

60. 3. duplication--a section of a chromosome (gene) is repeated (copied and inserted)
4. translocation (reciprocal in this example)--pieces of nonhomologous chromosomes break off and are swapped; can be nonreciprocal where a portion of a chromosome breaks off from one and attaches to a different chromosome.