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

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

Are You Color Blind?

Hemophilia: X- linked

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

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

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

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

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

Calico Cat Is there a human calico cat?

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

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”

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

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.

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.

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

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)

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

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

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.

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

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.

Chromosome Rearrangements

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

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

Chrm Rearrangements Reciprocation Translocal Inrevsion Deltion Dupliclication

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

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

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

These gametes: Normal Carrier Aneuploid Normal Aneuploid

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

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

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

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)

Gene Duplications Chromosome segment present in multiple copies B 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

Genomic Imprinting