Sex Determination Lecture Slides PDF

Benjamin A. Pierce Genetic s A Conceptual Approach SEVENTH EDITION Lecture Slides CHAPTER 4 Sex Determination and Sex-Linked Characteristics Copyright © 2020, W.H. Freeman and Company Sex Determination and Sex-Li...

Benjamin A. Pierce Genetic s A Conceptual Approach SEVENTH EDITION Lecture Slides CHAPTER 4 Sex Determination and Sex-Linked Characteristics Copyright © 2020, W.H. Freeman and Company Sex Determination and Sex-Linked Characteristics (1 of 3)  Sex Determination and Sex-Linked Characteristics (2 of 3) There are several different mechanisms of sex determination. The X and Y chromosomes pair during meiosis, even though they are not homologous (the genes located on each are different). Sex Determination and Sex-Linked Characteristics (3 of 3)  Sex Determination (1 of 3) Sexual reproduction alternates between haploid and diploid states (Fig. 4.3). Most organisms have two sexual phenotypes, male and female. Male and female gametes differ in size (Fig. 4.4). Sex Determination (2 of 3) Sex Determination (3 of 3)  Concept Check 1 (1 of 2) What process causes the genetic variation seen in offspring produced by sexual reproduction?  Concept Check 1 (2 of 2) What process causes the genetic variation seen in offspring produced by sexual reproduction? Meiosis  Sex Determination Mechanisms Hermaphroditism: both sexes in the same organism – Monoecious: both male and female reproductive structures in the same organism – Dioecious: either male or female reproductive structures in one organism  Chromosomal Sex-Determination Systems: Sex Chromosomes and Non-Sex Chromosomes (Autosomes) (1 of 3) XX-XO system: – XX – female – XO – male – Grasshoppers XX-XY system: – XX – female – XY – male – Mammals Chromosomal Sex-Determination Systems: Sex Chromosomes and Non-Sex Chromosomes (Autosomes) (2 of 3) Chromosomal Sex-Determination Systems: Sex Chromosomes and Non-Sex Chromosomes (Autosomes) (3 of 3)  Chromosomal Sex-Determining Systems ZZ-ZW system: – ZZ – male – ZW – female – Birds, snakes, butterflies, some amphibians, and fishes Haplodiploidy system: – Haploid set – male – Diploid set – female – Bees, wasps, and ants  Concept Check 2 (1 of 2) How does the heterogametic sex differ from the homogametic sex? a. The heterogametic sex is male; the homogametic sex is female. b. Gametes of the heterogametic sex have different sex chromosomes; gametes of homogametic sex have the same sex chromosome. c. Gametes of the heterogametic sex all contain a Y chromosome. d. Gametes of the homogametic sex all contain an X chromosome.  Concept Check 2 (2 of 2) How does the heterogametic sex differ from the homogametic sex? a. The heterogametic sex is male; the homogametic sex is female. b. Gametes of the heterogametic sex have different sex chromosomes; gametes of homogametic sex have the same sex chromosome. c. Gametes of the heterogametic sex all contain a Y chromosome. d. Gametes of the homogametic sex all contain an X chromosome.  Genic Sex-Determining System No sex chromosomes, only the sex-determining genes Found in some plants, fungi, protozoans, and fish  Environmental Sex Determination (1 of 2) Environmental factors – Limpet’s position in the stack – Temperature in turtles Environmental Sex Determination (2 of 2)  TABLE 4.1 Some common sex- determining systems System Mechanism Heterogametic Sex Organisms XX-XO Females XX Males X Male Some grasshoppers and other insects XX-XY Females XX Males XY Male Many insects, fishes, amphibians, reptiles; mammals, including humans ZZ-ZW Females ZW Males ZZ Female Butterflies, birds; some reptiles and amphibians Genic sex No distinct sex Varies Some plants, fungi, determination chromosomes Sex protozoans, and fishes determined by genes on undifferentiated chromosomes Environmental Sex determined by None Some invertebrates, sex determination environmental factors turtles, alligators  Concept Check 3 (1 of 2) How do chromosomal, genic, and environmental sex-determining systems differ?  Concept Check 3 (2 of 2) How do chromosomal, genic, and environmental sex-determining systems differ? In chromosomal sex determination – Males and females have chromosomes that are distinguishable. In genic sex determination – Sex is determined by genes, but the chromosomes of males and females are indistinguishable. In environmental sex determination – Sex is determined fully or in part by environmental effects.  Sex Determination in Drosophila melanogaster Genic balance system X:A ratio (X, number of X chromosomes; A, number of haploid sets of autosomes) TABLE 4.2 Chromosome complements and sexual phenotypes in Drosophila Sex-Chromosome Haploid Sets of Autosomes X : A Ratio Sexual Complement Phenotype XX AA 1.0 Female XY AA 0.5 Male XO AA 0.5 Male XXY AA 1.0 Female XXX AA 1.5 Metafemale XXXY AA 1.5 Metafemale XX AAA 0.67 Intersex XO AAA 0.33 Metamale XXXX AAA 1.3 Metamale Sex Determination in Humans XX-XY (1 of 3) SRY gene on Y chromosome determines maleness Turner syndrome: XO; 1/3000 female births Klinefelter syndrome: XXY, or XXXY, or XXXXY, or XXYY; 1/1000 male births Poly-X females: 1/1000 female births Sex Determination in Humans XX-XY (2 of 3) Sex Determination in Humans XX-XY (3 of 3)  The Role of Sex Chromosomes The X chromosome contains genetic information essential for both sexes; at least one copy of an X is required. The male-determining gene is located on the Y chromosome. A single Y, even in the presence of several Xs, still produces a male phenotype. The absence of Y results in a female phenotype.  The Male-Determining Gene in Humans (1 of 2) Sex-determining region Y (SRY) gene Androgen-insensitivity syndrome – Caused by the defective androgen receptor The Male-Determining Gene in Humans (2 of 2)  Concept Check 4 (1 of 2) What is the phenotype of a person who has XXXY sex chromosomes? a. Klinefelter syndrome b. Turner syndrome c. poly-X male  Concept Check 4 (2 of 2) What is the phenotype of a person who has XXXY sex chromosomes? a. Klinefelter syndrome (correct) b. Turner syndrome c. poly-X male Sex-Linked Characteristics Are Determined by Genes on the Sex Chromosomes (1 of 3) X-linked characteristics – X-linked white eyes in Drosophila  Figures 4.12 and 4.13 – X-linked color blindness in humans  Figure 4.14 Sex-Linked Characteristics Are Determined by Genes on the Sex Chromosomes (2 of 3) Sex-Linked Characteristics Are Determined by Genes on the Sex Chromosomes (3 of 3)  Concept Check 5 (1 of 3) What was the genotype of the few live F1 red-eyed males obtained by Bridges when he crossed a white eyed female with a red-eyed male? a. X+ b. XwX+Y c. X+Y d. X+X+Y  Concept Check 5 (2 of 3) What was the genotype of the few live F1 red-eyed males obtained by Bridges when he crossed a white eyed female with a red-eyed male? a. X+ b. XwX+Y c. X+Y (correct) d. X+X+Y Concept Check 5 (3 of 3)  Concept Check 6 (1 of 2) Hemophilia (reduced blood clotting) is an X-linked recessive disease in humans. A woman with hemophilia mates with a man who exhibits normal blood clotting. What is the probability that their child will have hemophilia?  Concept Check 6 (2 of 2) Hemophilia (reduced blood clotting) is an X-linked recessive disease in humans. A woman with hemophilia mates with a man who exhibits normal blood clotting. What is the probability that their child will have hemophilia? 1/2 Z-Linked Characteristics  Y-Linked Characteristics (1 of 2) Only present in males All male offspring exhibit the trait Y chromosome lost DNA over time Important for sex determination in SRY Y-Linked Characteristics (2 of 2)  Concept Check 7 (1 of 2) What unusual feature of the Y chromosome allows some recombination among the genes found on it?  Concept Check 7 (2 of 2) What unusual feature of the Y chromosome allows some recombination among the genes found on it? Eight large palindromes allow crossing over within the Y chromosome.  X-Linked Characteristics (1 of 2) Dosage compensation: the amount of protein produced by X-linked genes and randomly inactivated in two sexes – Figure 4.17 Lyon hypothesis X-Linked Characteristics (2 of 2)  Number of Barr Bodies in Human Cells with Different Complements of Sex Chromosomes Sex Chromosomes Syndrome Number of Barr Bodies XX None 1 XY None 0 XO Turner 0 XXY Klinefelter 1 XXYY Klinefelter 1 XXXY Klinefelter 2 XXXXY Klinefelter 3 XXX Triple-X 2 XXXX Poly-X female 3 XXXXX Poly-X female 4 Random X Inactivation  Concept Check 8 (1 of 2) How many Barr bodies does a male with XXXYY chromosomes have in each of his cells?  Concept Check 8 (2 of 2) How many Barr bodies does a male with XXXYY chromosomes have in each of his cells? Two Barr bodies