1. AP BIOLOGY Chapter 12 Chromosomal Basis of Inheritance
Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to life processes.

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4. Essential knowledge 3.A.3: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring.
a. Rules of probability can be applied to analyze passage of single gene traits from parent to offspring.
AaBbCcDD
Probability of aBcD
½ x ½ x ½ x 1 =1/8
GENOTYPE
TT = 25%
Tt = 50 % tt = 25%
PHENOTYPE % dominant trait % recessive trait
Punnett by Riedell

5. Essential knowledge 3. A. 3. b
Essential knowledge 3.A b. Segregation and independent assortment of chromosomes result in genetic variation.
Evidence of student learning is a demonstrated understanding of each of the following: Segregation and independent assortment can be applied to genes that are on different chromosomes.
~ The behavior of chromosomes during meiosis accounts for Mendel’s laws of segregation and independent assortment

6. Essential knowledge 3. A. 3. b
Essential knowledge 3.A b. Segregation and independent assortment of chromosomes result in genetic variation.
Evidence of student learning is a demonstrated understanding of the following: Segregation and independent assortment can be applied to genes that are on different chromosomes.

7. Essential knowledge 3.A.4: The inheritance patterns of many traits cannot be explained by simple Mendelian genetics b. Some traits are determined by genes on sex chromosomes.
To foster student understanding of this concept, instructors can choose an illustrative example such as: • Sex-linked genes reside on sex chromosomes (X in humans) • In mammals and flies, the Y chromosome is very small and carries few genes • In mammals and flies, females are XX and males are XY; as such, X-linked recessive traits are more common in males.

8. Inheritance of Sex-Linked Genes
The sex chromosomes have genes for many characters unrelated to sex
A gene located on either sex chromosome is called a sex-linked gene
In humans, sex-linked usually refers to a gene on the larger X chromosome
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

9. Sex-linked genes follow specific patterns of inheritance
For a recessive sex-linked trait to be expressed
A female needs two copies of the allele
A male needs only one copy of the allele
Sex-linked recessive disorders are much more common in males than in females
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

10. Y chromosome-small & carries only a few genes
Y linked traits show up ONLY in MALES EX: hairy pinna
SRY gene Master control gene turns on other genes Creates a cascade of activation to make developing embryo into a MALE

11. X-Linked Genes Recessive genes carried on the X chromosome
Red-green colorblindness Mutation in protein receptors in eye that distinguish colors
Hemophilia
Inability to make blood clotting factors
Duchenne Muscular Dystrophy
Change in muscle proteins; results early death

12. (a) (b) (c) Sperm Sperm Sperm Eggs Eggs Eggs XNXN  XnY XNXn  XNY
Fig. 15-7
XNXN 
XnY
XNXn 
XNY
XNXn 
XnY
Sperm Xn Y
Sperm XN Y
Sperm Xn Y
Eggs XN
XNXn
XNY
Eggs XN
XNXN
XNY
Eggs XN
XNXn
XNY XN
XNXn
XNY Xn
XnXN
XnY Xn
XnXn
XnY
Figure 15.7 The transmission of sex-linked recessive traits
(a)
(b)
(c)

13. X-chromosome Inactivation
In female cells ONE X chromosome is randomly switched off
It condenses and forms a dense region in the nucleus called a
BARR BODY

14. CAT COLOR In cats the gene that
controls color is carried on the X chromosome Tortoiseshell cats express different alleles in different cells
FEMALE CATS: Female cat can have BOTH
black and orange spots
See a video

15. CAT COLOR MALE cats have only one X chromosome, so they can only have
MALE cats have only
one X chromosome, so they can only have
ONE COLOR of spots!
THINK ABOUT IT?
How many colors of spots could a male cat with
Klinefelter syndrome have?

16. Essential knowledge 3. A. 3. b
Essential knowledge 3.A b. Segregation and independent assortment of chromosomes result in genetic variation.
Evidence of student learning is a demonstrated understanding of each of the following:
2. Genes that are adjacent and close to each other on the same chromosome tend to move as a unit; the probability that genes will segregate as a unit is a function of the distance between them.
The farther apart genes
are on a chromosome
the more likely they are
to be separated
during crossing over

17. ~ Genes that assort independently are either:
Many fruit fly genes were mapped initially using recombination frequencies
T.H. Morgan did experiments with fruit flies to see how linkage affects the inheritance of two different characters
~ Linked genes that are close together on the same chromosome do not assort independently
~ Genes that assort independently are either:
- on separate chromosomes OR are far apart on the same chromosome
Mutant phenotypes
Short
aristae
Black
body
Cinnabar
eyes
Vestigial
wings
Brown
Long aristae
(appendages
on head)
Gray
Red
Normal
Wild-type phenotypes II Y I X IV
III
48.5
57.5
67.0
104.5
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

18. Linkage Mapping: Using Recombination Data
Cross true breeding parents of different phenotypes
Cross heterozygous F organisms with pure-breeding recessives (like a TEST CROSS)
Count recombinants (ones that look different from parental phenotype)

19. Determine the sequence of genes along a chromosome based on the following recombination frequencies
A-D 10%
B-C 15%
B-D 5%

20. Determine the sequence of genes along a chromosome based on the following recombination frequencies
A-D 30%
B-C 24%
B-D 16%

21. Determine the sequence of genes along a chromosome based on the following recombination frequencies
A-B 8%
A-C 28%
A-D 25%
B-C 20%
B-D 33%

22. A Wild type fruit fly (heterozygous for gray body and normal wings) is mated with a black fly with vestigial wings.
OFFSPRING: wild type 785- black-vestigial 158- black- normal wings 162- gray body-vestigial wings
What is the recombination frequency between these genes? How many map units apart are
the genes?

23. A Wild type fruit fly (heterozygous for red eyes and normal wings) is mated with a HOMOZYGOUS RECESSIVE dumpy winged fly with purple eyes .
OFFSPRING: wild type (red eyes, normal wings) 841- dumpy wings-purple eyes 147- purple eyes- normal wings 152- red eyes-dumpy wings
What is the recombination frequency between these genes? How many map units apart are
the genes?

24. A Wild type fruit fly (heterozygous for gray body and red eyes) is mated with a black fly with purple eyes.
OFFSPRING: gray body/red eyes black body/purple eyes 49- gray body/purple eyes 45- black body/red-eyes
What is the recombination frequency between these genes? How many map units apart are
the genes?

25. Alterations of Chromosome Structure
A deletion occurs when a chromosome fragment lacking a centromere is lost during cell division.
This chromosome will be missing certain genes.
A duplication occurs when a fragment becomes attached as an extra segment to a sister chromatid.
Images from: Biology; Campbell and Reese; Pearson Education, Inc., publishing as Benjamin Cummings
Slide from: Slide show by Dr. Chuck Downing

26. Alterations of Chromosome Structure
Chromosomal translocations between nonhomologous chromosome are also associated with human disorders.
Chromosomal translocations have been implicated in certain cancers, including chronic myelogenous leukemia (CML).
CML occurs when a fragment of chromosome 22 switches places with a small fragment from the tip of chromosome 9.
Normal chromosome 9
Reciprocal
translocation
Translocated chromosome 9
Philadelphia
chromosome
Normal chromosome 22
Translocated chromosome 22

27. Alterations of Chromosome Structure
An inversion occurs when a chromosomal fragment reattaches to the original chromosome but in the reverse orientation.
In translocation, a chromosomal fragment joins a nonhomologous chromosome.
See a Video
See a Video
Slide from: Slide show by Dr. Chuck Downing
Images from: Biology; Campbell and Reese; Pearson Education, Inc., publishing as Benjamin Cummings

28. Duplications and translocations are typically harmful
Cri du chat
Is a disorder caused by
a deletion in chromosome #5
Mental retardation
Small head
Unusual facial features
“cat cry”

29. Nondisjunction Normal Meiosis
Enduring understanding 3.C: The processing of genetic information is imperfect and is a source of genetic variation.
Essential knowledge 3.C.1: Changes in genotype can result in changes in phenotype c. Errors in mitosis or meiosis can result in changes in phenotype.
Evidence of student learning is a demonstrated understanding of each of the following: Changes in chromosome number often result in human disorders with developmental limitations, including Trisomy 21 (Down syndrome) and
XO (Turner syndrome). [See also 3.A.2, 3.A.3]
Nondisjunction
Normal Meiosis

30. Nondisjunction –
Failure of homologous chromosomes OR chromatids to separate at anaphase

31. Nondisjunction
Results in ANEUPLOIDY = one or more chromosomes have extra or missing copies
AFTER FERTILIZATION: Cell with only 1 copy of a chromosome instead of 2
= MONOSOMY
Cell with 3 copies of a
chromosome instead of 2
= TRISOMY

32. Down syndrome (Trisomy 21)
Most common chromosomal abnormality (1 in 800 births)
Similar facial features Slanted eyes / Protruding tongue Mild to severe mental retardation
50% have heart defects that need surgery to repair
Both older (35+ years) and younger (under 16 years) mothers are more at risk.

33. Some individuals with Down syndrome have the normal number of chromosomes but have all or part of a third chromosome 21 attached to another chromosome by translocation.

34. Turner syndrome (X0) 1 in 5000 births
1 in 5000 births
Females have only one X chromosome
Small size
Broad chest
Slightly decreased intelligence
35% have heart abnormalities
Hearing loss common
Reproductive organs don’t develop at puberty

35. Klinefelter syndrome 1 in 2000 births live births
Klinefelter syndrome
1 in 2000 births live births
Males have extra X chromosomes
(Can be XXy, XXXy, or XXXXy)
Taller than average
Normal intelligence have male sex organs, but are sterile. may be feminine characteristics,
Often not discovered until puberty when don’t mature like peers
Presence of BARR BODIES

36. Karyotype can show: Sex of baby Missing or extra chromosomes
Major deletions or translocations
Can’t see individual gene changes

37. Polyploidy -common among plants
Ex: Strawberries = octaploid wheat = hexaploid
Much less common in animals LETHAL in humans
Polyploids are more nearly normal in phenotype than aneuploids.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

38. POLYPLOIDY Organisms with more than two complete sets of chromosomes
Can occur when a normal gamete fertilizes another gamete in which there has been nondisjunction of all its chromosomes.
Results in triploid (3n) zygote
OR if 2n zygote fails to divide after replicating its chromosomes Results in a tetraploid (4n) embryo
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

39. PRADER-WILLI Syndrome
Victor Age Victor Age 2
Born floppy and pale At first refuse to nurse, but later eat until they become obese
Tiny hands and feet Underdeveloped sex organs
Mildly retarded
Spectacular temper tantrums especially if refused food
Exceptional proficiency with Jig-saw puzzles
Missing piece of chromosome #15

40. ANGELMAN’S SYNDROME Taut, not floppy Thin Hyperactive Insomniac
Small head
Move jerkily like puppets
Happy disposition
Severely mentally retarded
Rarer than Prader-Willi
Missing SAME piece of Chromosome #15
Colin Farrell’s son has
Angelman’s syndrome

41. WHAT’S THE DIFFERENCE?
In Prader-Willi missing piece of #15 was from father
In Angelman’s, missing piece of #15 was from the mother
How does a gene “remember” where it came from?
GENOMIC IMPRINTING

42. GENOMIC IMPRINTING
Involves the silencing of certain genes that are “stamped” with an imprint during gamete production so same allele (maternal or paternal) is expressed in all body cells
Involves methylation (-CH3) (turns genes OFF)
or demethylation (turns genes on)
of cytosine nucleotides
Several hundred mammalian
genes, many critical for
development, may be subject
to imprinting.

43. EPIGENETICS “above genetics” Molecules sit on top of the genome
Control which genes are ON or OFF

44. Imprinting is critical for normal development.
In the new generation, both maternal and paternal imprints are apparently “erased” in gamete-producing cells.
Then, all chromosomes are reimprinted according to the sex of the individual in which they reside.
Imprinting is critical for normal development.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

45. Addition or removal or “methyl tags” may be influenced by environment
Twins start with same methyl tags but become more different with age
Agouti rats – changing diet of pregnant mom can change expression of genes
VIDEO

46. Addition or removal or “methyl tags” may be influenced by environment
DIET
STRESS
EXERCISE
CHEMICALS

47. GENOMIC IMPRINTING Tags Maternal/Paternal chromosomes
Differentiation of cell types (blood, skin, etc)
Embryonic development
Changes in puberty, pregnancy, aging
X chromosome inactivation (Barr bodies)
differences can lead to diseases (cancer)
and genetic disorders

48. LINKS TO CANCER http://www.landesbioscience.com/journals/epigenetics/
BRCA =
tumor suppressor gene
If it’s turned OFF
cancer cells are NOT
repaired and can grow
into a tumor

49. Fragile X syndrome, which leads to various degrees of mental retardation, also appears to be subject to genomic imprinting.
This disorder is named for an abnormal X chromosome in which the tip hangs on by a thin thread of DNA.
This disorder affects one in every 1,500 males and one in every 2,500 females.
Inheritance of fragile X is complex, but the syndrome is more common when the abnormal chromosome is inherited from the mother.
This is consistent with the higher frequency in males.
Imprinting by the mother somehow causes it.
Image from:
Slide Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

50. It’s not just a MOM thing Epigenetic therapy in future ????
SO WHAT?
It’s not just a MOM thing
Epigenetic therapy in future ????
How does what you do affect your kids’ and grandkids’ epigenome?
We are just beginning to understand . . .

51. c. Some traits result from nonnuclear inheritance
c. Some traits result from nonnuclear inheritance. Evidence of student learning is a demonstrated understanding of each of the following: Chloroplasts and mitochondria are randomly assorted to gametes and daughter cells; thus, traits determined by chloroplast and mitochondrial DNA do not follow simple Mendelian rules.
2. In animals, mitochondrial DNA is transmitted by the egg and not by sperm; as such, mitochondrial-determined traits are maternally inherited.

52. EXTRANUCLEAR GENES
The inheritance of traits controlled by genes present in the chloroplasts or mitochondria
Depends solely on the maternal parent because the zygote’s cytoplasm comes from the egg
EX: Variegated leaves result from mutations in pigment genes located in plastids inherited from mother
Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2005

53. EXTRANUCLEAR GENES
Some diseases affecting the muscular and nervous systems are caused by defects in mitochondrial genes that prevent cells from making enough ATP

54. MITOCHONDRIAL DISEASES are RARE
Accumulation of mitochondrial mutations may play role in aging process, diabetes, heart disease, Alzheimer’s
EX: mitochondrial myopathy-
weakness,
intolerance of exercise
muscle deterioration

55. Essential knowledge 3.A.3:
d. Many ethical, social and medical issues surround human genetic disorders. To foster student understanding of this concept, instructors can choose an illustrative example such as: • Reproduction issues • Civic issues such as ownership of genetic information, privacy, historical contexts, etc.