Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-1 Human Genetics Concepts and Applications Seventh Edition Powerpoint Lecture Outline Ricki Lewis Prepared by Mary King Kananen Penn State Altoona

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-2 Chapter 6 Matters of Sex

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-3 Sexual Development In early embryos unspecialized gonads and two sets of reproductive ducts exist until week 6 An embryo develops as a male or female using information from the Y chromosome Figure 6.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-4 Male or Female? Gender is ultimately a genetic phenomenon It also has psychological and sociological components Males have 22 pairs of autosomes and X and Y chromosomes Females have 22 pairs of autosomes and Two X chromosomes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-5 Sex Chromosomes Determine Gender Human males are the heterogametic sex with different sex chromosomes, (XY) Human females are the homogametic sex (XX) In other species sex can be determined in many ways For example, in birds and snakes males are homogametic ZZ female are heterogameticZW

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-6 X and Y Chromosomes X chromosome –contains more than 1,500 genes –Larger than the Y chromosome –Acts as a homolog to Y chromosome in males Y chromosome –95% harbor male specific genes –Many DNA segments are palindromes and may destabilize DNA Figure 6.2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-7 Genes on the Y Chromosome Genes shared with X chromosome define the pseudoautosomal regions (PAR1 and PAR2) Male specific (MSY) including SRY gene SRY gene is important in determining sex Figure 6.3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-8 SRY Gene Encodes for a transcription factor protein Controls the expression of other genes Stimulates male development In response, developing testes secrete anti- Mullerian hormone and destroy female structures Testosterone and DHT are secreted and stimulate male structures

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6-9 Mutations that Disrupt Normal Sexual Development Figure 6.4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Table 6.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Homosexuality Homosexuality has been seen in all cultures for thousands of years Evidence may suggest a genetic component Research in this area is controversial Twin studies Identifying possible markers Altered gene expression in male Drosophila White gene causing decreased serotonin levels and homosexual behavior

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 6.6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Y-linked Traits Genes on the Y chromosome Very rare Transmitted male to male No affected females Currently, identified Y-linked traits involve infertility and are not transmitted

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display X-linked Traits Possible genotypes X + Y Hemizygous wild type male X m Y Hemizygous mutant male X + X + Homozyogus wild female X + X m Heterozygous female carrier X m X m Homozygous mutant female

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display X-linked Recessive Traits Always expressed in hemizygous males Female homozygotes show the trait but female heterozygotes do not Affected males: Inherited from affected or heterozygous mother Affected females : affected fathers and affected or heterozygous mothers

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display X-linked Recessive Inheritance Figure 6.7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 6.8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display X-linked Dominant Inheritance Expressed with one copy Males are often more severely affected Typically associated with miscarriage or lethality in males Passed from father to all his daughters but none of his sons

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display X-linked Dominant Inheritance: Congenital Generalized Hypertrichosis Figure 6.10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Genetics Problems Examples

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display X Inactivation Females have two alleles for every gene on the X chromosome but males have only one In mammals, X inactivation balances this inequality and one X chromosome is randomly inactivated in each cell The XIST gene inactivates the chromosome and encodes for RNA It alters phenotype but not genotype Inactivated X chromosomes form a Barr body

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 6.11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Inactive X Chromosome Is Visible as Barr Body Figure 6.12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Cats Heterozygous for the Coat Color Gene Figure 6.13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sex-limited Traits Traits that affect a structure or function occurring only in one gender May be autosomal or X linked Examples: Beard growth Milk production Pregnancy phenotypes Sperm production levels

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sex-influenced Traits Traits are those in which the phenotype expressed by a heterozygote is influenced by gender. Allele appears dominant in one gender and recessive in the other Example: Pattern baldness is a sex-influenced trait: men women m/m bald bald m/+ bald unaffected +/+ unaffected unaffected

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 6.14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Genomic Imprinting Occurs when the expression of a gene differs when the allele is transmitted maternally versus paternally Function unknown, may play a role in development Genes silenced by an epigenetic event Information not encoded by DNA Imprints maintained in mitotic divisions but lost in meiosis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Genomic Imprinting Figure 6.15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Importance of Genomic Imprinting Experiments suggest that it takes two opposite sex parents to produce a healthy embryo Genes from female parent direct different activities from the genes of the male parent May explain why cloning mammals is so difficult and the offspring are almost always unhealthy Certain assisted reproductive technologies may produce imprinting disorders May explain incomplete penetrance

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Two male pronuclei form a hydatidiform mole Two female pronuclei form a teratoma Figure 6.16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Imprinting and Human Disease Inherited paternally Prader-Willi syndrome Deletion on chromosome 15 reveals imprinting Inherited maternally Angelman syndrome Figure 6.17

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Callipyge (“beautiful buttock”) Sheep Is Caused by Genomic Imprinting Over-muscled hindquarters Autosomal dominant Trait only passed if it came from the father and the female may not carry the trait Seven other genes are overexpessed on chromosome 18

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 6.18