Chromosomes, Mapping, and Meiosis-Inheritance Connection PDF

Chromosomes, Mapping and the Meiosis-Inheritance Connection Chapter 13  X-Linked Genes Drosophila melanogaster T. H. Morgan crossed the mutant male to a normal red-eyed female...

Chromosomes, Mapping and the Meiosis-Inheritance Connection Chapter 13  X-Linked Genes Drosophila melanogaster T. H. Morgan crossed the mutant male to a normal red-eyed female - all F1 progeny red eyed = dominant trait (R) Morgan crossed F1 females x F1 males F2 generation contained red and white- eyed flies - but all white-eyed flies were male  X-Linked Genes Loading… Testcross of a F1 female with a white-eyed male showed the viability of white-eyed females Morgan concluded that the eye color gene resides on the X chromosome  What Determines the Sex of an Organism? flies Sex determination in ↑ Drosophila is based on the - = - = number of X chromosomes – 2 X chromosomes = female; 1 X and 1 Y chromosomes = male Sex determination in humans is based on the presence of a Y = - chromosome - – 2 X chromosomes = female; having a Y chromosome (XY) = male  What is “Male” on the Y chromosome? Loading… In humans, the Y chromosome has the sex determining region Y = (SRY) gene * - encodes the testis determining factor (TDF) protein - Swyer syndrome – not functional SRY gene Y chromosome is affected, X chromosome is normal · - => male genotype (XY), female phenotype (no testes, female external genitalia, uterus, but no ovaries)  What is “Male” on the X chromosome? In humans, males must produce androgens (e.g., testosterone) and respond to them The X chromosome of males has a gene that encodes androgen receptor - Androgen insensitivity syndrome – androgen receptor is mutated X chromosome is affected, Y chromosome is normal ---- male genotype (XY), female phenotype (no testes)  Sex-Linked Disorders Associated with sex chromosomes (X or Y) - X-linked disorders show up in both genders but more often in males because they only have one X chromosome hemophilia (blood-clotting disorder) is caused by an X-linked recessive allele H= normal h= hemophilia XHX XH h Y XHX XH h Y XHX XH h Y Xh Y  Hemophilia in humans is an X-linked recessive trait. What will be the results of mating between a normal (non-carrier) female and a hemophiliac male? A.half of daughters are normal H H and half of sons are hemophilic n Hh +h O B. all daughters are carriers and all sons are normal n Ah Hh C. half of sons are normal and half are hemophiliac; all daughters are carriers B.all daughters are normal and all sons are carriers In a cross between a homozygous, red-eyed female fruit fly and a white-eyed male, what percent of the male offspring will have white eyes? White eyes are X-linked recessive. O A.100% r r B.50% y ru ru C.75% wrw ru D.0 % E.25%  Do Women Really Need Two X Chromosomes? Maternal Paternal X chromosome X chromosome In females, cells don’t use both X chromosomes Dosage compensation = 1X chromosome is inactivated In each female cell, 1X chromosome is inactivated and is highly condensed into a Barr body, while the other X chromosome is decondensed  Calico cats are females with a patchy distribution of dark, orange, and white fur They are heterozygous for alleles of the fur color gene on the X Loading…chromosome The patchy distribution and white color is due to the second gene that is epistatic to the fur color gene  Do we Always Inherit One Maternal Chromosome and One Paternal Chromosome? Nuclear DNA Mitochondrial DNA Both men and women inherit mitochondrial DNA only from their mothers  Problems with the X & Y Chromosomes Nondisjunction is a failure of homologous chromosomes n = 23 chromosomes or sister chromatids to separate properly during meiosis I or II n1 + n - 1 Aneuploid gametes have one less or one extra n +1 chromosome 24 = n - 1 = 22n - 1 n 1 + - monosomy = one chromosome is absent - trisomy = extra ↑ N chromosome is present  Nondisjunction of Sex Chromosomes xroBarrbody chromosomes Trisomy XX + Y = XXY – male (Klinefelter syndrome) with breast enlargement and undeveloped testes (sterile) nothing no Barriedor a monosomy O + X = XO – female (Turner syndrome) with no breast growth and infertile O + Y + YO – nonviable zygote extra - chromosomes Trisomy & YY + X = XYY – male (Jacob syndrome) normal trisonic /nromosomes extra 2 barr development > - bodies XX + X = XXX – female (Triple X syndrome) Nondisjunction of Sex Chromosomes cabareane getriple a ninvora Problems with Autosomal Chromosomes chromosome pairs 1-22 Edwards syndrome = trisomy 18 - die within a few - months - Down syndrome = trisomy 21 - can survive to adulthood O O - mother’s age 2n + 1 = 46 + 1 = 4) influences risk  How are Genetic Disorders Tested? ① many cause miscarriage Amniocentesis collects fetal cells from the amniotic fluid (fluid that surrounds the fetus) for examination - performed between 14-20 weeks of pregnancy Amniotic fluid Fetus analyze gene products : other or enzymes 1/ proteins 2 - 3  How are Genetic Disorders Tested? (CVS) may still cause miscarriage Chorionic villus sampling is another procedure that obtains fetal cells from chorionic villi (finger-shaped growths found in the placenta) for karyotyping - performed between 8-12 weeks of pregnancy - c flexible tube If Two Alleles are on the Same Chromosome, They can be Inherited Together Maternal Paternal chromosome #10 chromosome #10 plocus Gene X determines hair color G 3 A = dominant allele Linked genes a = recessive allele Located on the 88 Gene Y determines eye color same chromosome B = dominant allele b = recessive allele All gametes are parental with parental combination of alleles  …But Not Always Between and genes If crossing over occurs, not only parental but also recombinant > - gametes would be produced - recombinant gametes have a new combination of alleles 80  Using Recombination to Measure Distance Between Genes… mutant linked E Gene X for body color onormal genes -Short Gene Y for wing size Homozygous homozygous recessive dominant heterozygous  Using Recombination to Measure Distance Between Genes… in ant