Sex Linked Traits

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 normal carrier colorblind normal colorblind

3. Are You Color Blind?

4. Hemophilia: X- linked

5. X- linked Traits • 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 • 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 Do women have more of those proteins? 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 • ReciprocationTranslocal • 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. Chrm 1 Chrm 9 This pairing in meiosis I Metaphase plate Leads to...

32. These gametes: Normal Carrier Aneuploid Normal Aneuploid

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

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

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. A B C D E E F Gene Duplications A B C • 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