1. AP BIOLOGY Chapter 15 Chromosomal Basis of Inheritance
Big Idea 3: Living systems store, retrieve, transmit and respond to information essential to life processes.

2. 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

3. 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

4. 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.

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:
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

6. ~ 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

7. 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)

8. Essential knowledge 3.A.3.b Evidence of student learning is a demonstrated understanding of each of the following: 3. The pattern of inheritance (monohybrid, dihybrid, sex-linked, and genes linked on the same homologous chromosome) can often be predicted from data that gives the parent genotype/ phenotype and/or the offspring phenotypes/genotypes.
female flies with red eyes (wild type)
male flies with white eyes
The F1 generation all had red eyes
F2 generation showed the 3:1 red:white eye ratio,
but only males had white eyes
T.H. Morgan proposed that the white eye mutation
was carried on X chromosome

9. Essential knowledge 3.A.4: The inheritance patterns of many traits cannot be explained by simple Mendelian genetics. a. Many traits are the product of multiple genes and/or physiological processes.
Evidence of student learning is a demonstrated understanding of the following: Patterns of inheritance of many traits do not follow ratios predicted by Mendel’s Laws and can be identified by quantitative analysis, where observed phenotypic ratios statistically differ from the predicted ratios.

10. (d) The haplo-diploid system
Different systems of sex determination
are found in other organisms
22 + XX X
76 + ZZ ZW 16
(Haploid)
(Diploid)
(b) The X–0 system
(c) The Z–W system
(d) The haplo-diploid system
Temperature determination- some reptiles

11. 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 always expressed in males.

12. 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

13. 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

14. X-linked traits show up more frequently in males
The X chromosome in males . . .
flies WITHOUT a copilot!

15. What’s the pattern:
X-LINKED RECESSIVE traits ~ Show up more frequently in males
because they have no back up X
~ Females need two recessive alleles to show the trait.
~ Females can be carriers for X linked traits
~ Male can never be carriers of X linked recessive traits
AUTOSOMAL RECESSIVE traits
~ Both males and females can be carriers for autosomal recessive traits.

16. MALES BB or Bb = bald bb= not bald
Essential knowledge 3.A.4. The inheritance patterns of many traits cannot be explained by simple Mendelian genetics • Some traits are sex limited • Expression depends on the sex of the individual Ex: milk production in female mammals pattern baldness in males.
MALE PATTERN BALDNESS SEX LIMITED (SEX INFLUENCED) AUTOSOMAL- NOT ON A SEX CHROMOSOME BUT SHOWS DIFFERENT PATTERN IN MALES & FEMALES
Almost like B is dominant in males and b is dominant in females
MALES BB or Bb = bald bb= not bald
FEMALES BB = bald Bb or bb= not bald

17. 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.
c. Certain human genetic disorders can be attributed to the inheritance of single gene traits or specific chromosomal changes, such as nondisjunction To foster student understanding of this concept, instructors can choose an illustrative example such as: • Sickle cell anemia • Tay-Sachs disease • Huntington's disease • X-linked color blindness • Trisomy 21/Down syndrome • Klinefelter syndrome

18. AUTOSOMAL RECESSIVE
Phenylketonuria-PKU Enzyme to break down phenylalanine is missing Build up in brain causes mental retardation Need diet low in proteins
TAY SACHS Lysosomal storage disorder Fats aren’t broken down; build up in brain Cause blindness, retardation; early death More common in Jewish populations
CYSTIC FIBROSIS Mutation in gene for Cl- ion transport Build up of mucous in body organs Digestive/respiratory problems
More common in Caucasian populations

19. AUTOSOMAL DOMINANT (Homozygous Dominant = LETHAL)
ACHONDROPLASIA “Dwarfism” Growth plates in long bones fuse too early
HUNTINGTON’S Multiple CAG repeats result in neurological degeneration in middle age
Hear song

20. AUTOSOMAL CODOMINANT
SICKLE CELL ANEMIA Mutation in hemoglobin gene Causes red blood cells to change shape in low oxygen conditions More common in African Americans
HETEROZYGOTE ADVANTAGE: 1 sickle cell allele/1 normal allele provides protection against MALARIA
Watch a video about
sickle cell and malaria

21. CLOSER LOOK AT RELATIONSHIP
BETWEEN DOMINANCE AND PHENOTYPE REVEALS AN INTRIGUING FACT:
DOMINANCE ? CODOMINANCE? INCOMPLETE DOMINANCE ? Depends on how you look at it!

22. TAY-SACHS DISEASE Human genetic disorder in which brain cells are
Image from:
TAY-SACHS DISEASE
Human genetic disorder in which brain cells are
unable to metabolize certain lipids because
a crucial enzyme does not work properly.
As these lipids build up in brain infant suffers seizures, blindness, loss of motor & mental function > > > leads to early death.
At ORGANISMAL LEVEL acts as a recessive trait. Child with two copies of Tay-Sachs allele (tt-homozygous) has the disorder. Child with Tt or TT does not (COMPLETE DOMINANCE)
At BIOCHEMICAL LEVEL- Tt individual has enzyme activity level in between the TT and tt person (INCOMPLETE DOMINANCE ?)
At the MOLECULAR LEVEL – Tt individual makes equal number of normal and dysfunctional enzyme molecules (CODOMINANT ?)

23. 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

24. 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

25. 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

26. 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”

27. 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

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

29. 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

30. 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.

31. 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.

32. 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

33. 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

34. Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006

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

36. Polyploidy -common among plants
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 new phenotypes, including sterility caused by triploidy and increased vigor of other polyploids [See also 3.A.2]
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

37. 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

38. If having extra chromosomes causes genetic problems,
how come having two X chromosomes in females and
one X in males is not a problem?

39. 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

40. 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

41. 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?

42. “La Monstrua Vestida” “La Monstrua Desnuda”
Images from:
“La Monstrua Vestida” “La Monstrua Desnuda”
Paintings in Prado Museum in Madrid by Juan Carrneño Miranda
of a 5 year old girl named Eugenia Marinez Vallejo

43. 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

44. 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

45. 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

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

47. 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.

48. 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

49. 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

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

51. 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

52. 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

53. 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

54. 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 . . .

55. 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.

56. 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

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

58. 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

59. 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.