1. Sex Linked Traits Sex chromsomes: 1 pair female = XX male = XY
X chromosome: Y chromosome:
larger, more genes male traits
female traits distribution of body fat
Color vision height genes
Blood-clotting hair on ears
Hair on head

2. Color Blindness: X- linked
Genotypes
Phenotypes
XN XN
XN Xn
Xn Xn
XN Y
Xn Y
normal
carrier
colorblind
normal
colorblind

3. Are You Color Blind?

4. Hemophilia: X- linked

5. X- linked Traits XN Xn Xn Y XN Xn XN Y Xn Y
Males need only 1 bad allele, females need 2 bad alleles
to be expressed
Males have a greater chance of expressing X-linked traits
XN Xn
Xn Y
XN Xn
XN Y
Xn Y

6. Sex-Chromosomes Switched:
some organisms have
female = XY male = XX
birds, moths, butterflies, some reptiles, some fish
Some may use different letters besides X and Y
Chickens: female = WZ male = WW

7. Other sex-linked disorders
Duchenne’s muscular dystrophy
Some forms of baldness
Retinitis pigmentosa

8. Predict the phenotype (sex) of the following genotypes:XX XY
XXX
XYY
XXY XO YO
(O = no other sex chrm present)

9. The X chrm encodes proteins we all need
Do women have more of those proteins?
In females, one of the two X’s is randomly inactivated in all somatic cells
Females are genetic mosaics for X-linked genes
Barr body = inactive X chromosome
–> Dosage Compensation
Why?-because too much of that good stuff would be bad

10. Calico Cat
Is there a human calico cat?

11. X-linked conditions that show a partial phenotype in females
Calico cat
Hemizygous males: brown or orange or white
Het females: alternating patches of color
Absence of sweat glands
hemizygous males : with few sweat glands
het females : alternating patches

12. Human somatic cells are diploid:
46 chromosomes
22 pairs of autosomes (1, 2, … 22)
1 pair of sex chromosomes (XX or XY).
Human gametes are haploid:
23 chromosomes
1 each of the 22 autosomes
X or Y
= “haploid set” or “monoploid set”

13. Euploid, aneuploid
A cell that contains a multiple of the haploid set of chromosomes is called euploid.
Cells that do not contain a multiple of the haploid set are called aneuploid.
Aneuploid cells contain missing or additional chromosomes

14. Common types of aneuploidy
Monosomy - only 1 copy of a given chrm in an otherwise diploid cell.
Trisomy - 3 copies
The most frequent cause of aneuploidy
… is chromosomal nondisjunction.

15. Meiosis Error: Nondisjunction
Chrms or chromatids fail to “disjoin” during meiosis
Fertilization produces a zygote with monsomy or trisomy.
Risk of nondisjunction increases dramatically with maternal age.

17. Polyploidy Has entire extra sets of chromosomes (3n, 4n, etc.)
35% of flowering plants are polyploid, as well as several of agricultural value.
Triploid plants often infertile
pairing and segregation is disrupted in meiosis
commercially beneficial (e.g. seedless fruit)
In humans, polyploidy is lethal before or shortly after birth

18. Sex Chromosome Aneuploidies
trisomy-X = 47, XXX (female)
0.1% female births
double-Y = 47, XYY (male) 0.1% male births
Klinefelter Syndrome = 47, XXY (male, sterile) 0.1% male births
Turner Syndrome = 45, X (female, sterile) 0.5% female births
(45, Y = embryonic lethal)

19. Klinefelter Syndrome = 47, XXY (male, sterile)
0.1% male births

21. Turner Syndrome = 45, X
(female, sterile,do not develop
Secondary sex characteristics)0.5% female births

22. Trisomy of chromosome 21 = most common autosomal (non-sex chrm) aneuploidy (1/800 live births).
Approx. 75% of trisomy 21 conceptions are spontaneously aborted (miscarriages).
Down Syndrome = genetic disorder due to trisomy 21.

23. Down syndrome Mental retardation Gastrointestinal tract obstruction
Congenital heart defects
Respiratory infections
15-20 X higher risk of leukemia
Characteristic appearance
Research - determine the critical genes on chrm 21 responsible

24. Other Aneuploidies Trisomy 13 - Edward Syndrome
(1/10,000 live births)
Trisomy 18 - Patau Syndrome (1/6,000 live births)
95% affected fetuses spontaneously aborted.
90% mortality during first year of life.
All other trisomies and monosomies are embyronic lethals, resulting in spontaneously aborted fetuses.

25. Chromosome Rearrangements

26. Chrm Abnormalities and Pregnancy Loss
About 1/3 of human pregnancies are lost spontaneously after implantation
Chrm abnormalities are the leading known cause of pregnancy loss
A minimum 10-15% of conceptions have a chrm abnormality
At least 95% of these conceptions spontaneously abort

27. Birth Defects Most common cause of infant death in U.S.
2-3% of babies are born with a recognizable birth defect
Can be caused by genetic defects
Chrm abnormality
Mutation in gene involved in development
Can be caused by environment
Fetal alcohol syndrome - Rubella
Thalidomide - Low folic acid

28. Chrm Rearrangements
Reciprocation Translocal
Inrevsion
Deltion
Dupliclication

29. Chrm Rearrangement: Translocation
Interchange of genetic info between non-homologous chrms
Present in at least 1/500 people
Probably result from a mistake by the recombination machinery

30. Reciprocal Translocation
between p arms of 1 and 9
telomere { p
arm
centromere { q
arm
telomere
Chrm 9
Chrm 1

31. This pairing in meiosis I
Metaphase
plate
Chrm 1
Chrm 9
Leads to...

32. These gametes:
Normal
Carrier
Aneuploid
Normal
Aneuploid

33. Chrm Rearrangement: Inversion
genetic rearrangement in which the order of genes is reversed in a chromosome segment A B C D E F G H A B C D G F E H

34. Chromosome Inversions
As with translocations, genetic information unchanged (except at/near breakpoints)
At synapsis (= homologous pairing), inversion loops form
If a crossover (recombination) occurs in the loop, then two abnormal chrms result

36. Chromosome Deletions A B C A B C D E F D G G H H
Deletions = missing chrm segment
Large deletions often lethal (even in heterozygote) A B C D E F G H A B C D G H

37. Some Deletion Syndromes
Cri-du-chat (del 5p)
Wolf-Hirschhorn (del 4p)
Prader-Willi/Angelmann (del 15q11-13)
Langer-Giedion (del 8q24)
Miller-Dieker (del 17p13.3)
DiGeorge Anamoly (del 22q11)
Smith-Magenis (del 17p11.2)
Williams (del 7q1)
Wilms Tumor/Aniridia (del 11p13)

38. Gene Duplications Chromosome segment present in multiple copiesB C A B C D E F
Chromosome segment present
in multiple copies
Provide material for evolution
Tandem duplications
repeated segments are adjacent
often result from unequal crossing-over D E F

39. Genomic Imprinting