I. Allelic, Genic, and Environmental Interactions II. Sex Determination and Sex Linkage

I. Allelic, Genic, and Environmental Interactions II. Sex Determination and Sex Linkage A. Sex Determination Environmental Sex Determination a. Temperature MT FT

I. Allelic, Genic, and Environmental Interactions II. Sex Determination and Sex Linkage A. Sex Determination Environmental Sex Determination a. Temperature MT FT

I. Allelic, Genic, and Environmental Interactions II. Sex Determination and Sex Linkage A. Sex Determination Environmental Sex Determination a. Temperature MT FT

I. Allelic, Genic, and Environmental Interactions II. Sex Determination and Sex Linkage A. Sex Determination Environmental Sex Determination a. Temperature Winter Melon (Benincasa hispida) - flowers begin as perfect in bud - male or female parts aborted as flower develops… monoecious plants with separate male and female flowers - at lower temps, ratio of Abcissic/Indole Acetic Acid declines – influences development = more female flowers (Huang et al. 2012, Grubben 2004)

“Jack-in-the-Pulpit” A. Sex Determination Environmental Sex Determination a. Temperature b. Size/Nutrition Arisaema triphyllum “Jack-in-the-Pulpit” Small plants - male Large plants - female

Benefit of being male – quantity of offspring A. Sex Determination Environmental Sex Determination a. Temperature b. Size/Nutrition Benefit of being male – quantity of offspring Benefit of being female – regulate quality of offspring Cervus elaphus Red deer Starving pregnant females selectively abort male embryos. Small daughters may still mate; small sons will not acquire a harem and will not mate. Selection has favored females who save their energy, abort male embryos when starving, and maybe live to reproduce next year.

Sexually mature female A. Sex Determination Environmental Sex Determination a. Temperature b. Size/Nutrition c. Social Environment Sexually mature female (Inhibits development of males) Sexually mature male Immature males Wouldn’t the species do better if there were more females/group? Yes, but selection favors individual reproductive success.

A. Sex Determination Midas cichlid Brood Environmental Sex Determination a. Temperature b. Size/Nutrition c. Social Environment Midas cichlid Brood

A. Sex Determination Midas cichlid Add Larger juveniles Brood female Environmental Sex Determination a. Temperature b. Size/Nutrition c. Social Environment Midas cichlid Add Larger juveniles Brood female

A. Sex Determination Midas cichlid Add smaller juveniles Brood male Environmental Sex Determination a. Temperature b. Size/Nutrition c. Social Environment Midas cichlid Add smaller juveniles Brood male

ts homozygotes – tassle develops female flowers A. Sex Determination Environmental Sex Determination a. Temperature b. Size/Nutrition c. Social Environment These are still undoubtedly GENETIC effects, likely caused by the activation of different genes under different conditions. MUTATIONS in single genes can influence sex determination. ts homozygotes – tassle develops female flowers At other loci: sk (silkless) ba (barren stalk) No female flowers in silk But these loci that influence sex are not all on the same chromosome.

The presence of 1 or 2 sex chromosomes determines sex A. Sex Determination Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination The presence of 1 or 2 sex chromosomes determines sex Order: Hemiptera “True Bugs” Family Alydidae – Broad-headed bugs

The type of sex chromosomes determines sex A. Sex Determination Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination b. Lygaeus sex determination The type of sex chromosomes determines sex Order: Hemiptera Family: Lygaeidae “Chinch/Seed Bugs”

Which sex is the ‘heterogametic’ sex varies A. Sex Determination Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination b. Lygaeus sex determination Which sex is the ‘heterogametic’ sex varies XX female, XY – male Most mammals, including humans Some insects Some plants ZZ male, ZW female Birds Some fish Some reptiles Some insects (Butterflies/Moths) Some plants

The ratio of X’s to autosomal sets determines sex A. Sex Determination Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination b. Lygaeus sex determination c. Balanced sex determination The ratio of X’s to autosomal sets determines sex Human genotype and sex 2n: 46, XX = female 2n: 46, XY =male 2n+1: 47, XXY = male 2n-1: 45, X = female Have a Y = male No Y = female Drosophila genotype and sex 2n: 8, XX =female 2n: 8, XY = male 2n+1: 9, XXY = female 2n-1: 7, X = male Ratio of autosomal sets:X = 2:1 = male Ratio of autosomal sets:X = 1:1 = female

A. Sex Determination Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination b. Lygaeus sex determination c. Balanced sex determination d. Human sex determination: SRY gene

A. Sex Determination Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination b. Lygaeus sex determination c. Balanced sex determination d. Human sex determination: SRY gene The presence of the Y, regardless of the number of X’s, determines maleness Klinefelter’s Male Turner’s Female

A. Sex Determination Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination b. Lygaeus sex determination c. Balanced sex determination d. Human sex determination: SRY gene SRY gene produces the protein called the testis determining factor, which stimulates the undifferentiated gonadal tissue to become a testis. It is a transcription factor that binds to other genes, stimulating their expression.

A. Sex Determination X X* X*X male Y- XY- female Environmental Sex Determination Chromosomal Sex Determination a. Protenor sex determination b. Lygaeus sex determination c. Balanced sex determination d. Human sex determination: SRY gene X X* X*X male Y- XY- female

A X A Y a X AaXX AaXY a X a Y A X Aa XX Aa XY Sex Determination Sex Linkage: Genes of interest are one of the sex chromosomes (X or Y) 1. For Comparison –heredity for sex (as a trait) and an autosomal dominant trait (A,a). Autosomal genes NECESSARILY assort independently from sex-linked genes RECIPROCAL CROSSES MALE: AAXY FEMALE: aa XX A X A Y a X AaXX AaXY MALE: aa XY FEMALE: AA XX a X a Y A X Aa XX Aa XY All offspring, regardless of sex, express the A trait in both reciprocal crosses

Xg Y XG XGXg XGY XG Y Xg XGXg XgY Sex Determination Sex Linkage 1. For Comparison –heredity for sex (as a trait) and an autosomal dominant trait. 2. Sex Linkage example: red-green coloblindness in humans MALE FEMALE Xg Y XG XGXg XGY MALE FEMALE XG Y Xg XGXg XgY 100% G, for all offspring 50% G daughters, 50% g sons Now, the sex of the parent that expresses the G trait matters; the transmission of this gene correlates with the sex of the offspring, because this trait and ‘sex’ are influenced by the same chromosome.

Queen Victoria of England Her daughter Alice X-linked recessive traits are expressed in males more than females, because females get a second X that may carry the dominant allele.

Sex Determination Sex Linkage Dosage Compensation - Females have two ‘doses’ of X-linked genes, while males have one ‘dose’. Since protein concentration is often important in protein function, how is this imbalance corrected?

Sex Determination Sex Linkage Dosage Compensation - Females have two ‘doses’ of X-linked genes, while males have one ‘dose’. Since protein concentration is often important in protein function, how is this imbalance corrected? In females, one X in each cell condenses. Barr Body

Sex Determination Sex Linkage Dosage Compensation Actually, in all humans and mammals, all but one X condenses, regardless of sex or number of X’s.

Sex Determination Sex Linkage Dosage Compensation Random X-inactivation leads to tortoiseshell heterozygote females

Sex Determination Sex Linkage Dosage Compensation Calico determined by a different autosomal gene that affects rate of melanocyte migration to the skin surface. Melanocytes XBXb, pp No migration of melanocytes to skin White Slow migration Calico XBXb, Pp Inactivation before proliferation Fast migration XBXb,PP Torty Proliferation before inactivation

Sex Determination Sex Linkage Dosage Compensation This happens in humans, too – so that females are really a ‘mosaic’, with some cells in a tissue expressing one X (and it’s X linked traits) and some cells in that tissue expressing the other X. Females heterozygous for red-green colorblindness have patches of retinal cells that can’t distinguish red from green.

Anhidrotic ectodermal dysplasia

- each X has a gene – the Xic (X-inactivation center). Sex Determination Sex Linkage Dosage Compensation How? - each X has a gene – the Xic (X-inactivation center). - this is ‘on’ in inactivated X’s… it produces an RNA (Xist) that binds with the chromosomes, making it inaccessible to transcription enzymes. - this RNA is NOT translated – it is functional as an RNA molecule. - of course, this just pushes the question one step ‘upstream’ – what determines why Xic is only active in one X chromosome? HP1 = “heterochromatic protein 1”

Sex Determination Sex Linkage Dosage Compensation How? - each X has a gene – the Xic (X-inactivation center). - this is ‘on’ in inactivated X’s… it produces an RNA that binds with the X chromosomes, making it inaccessible to transcription enzymes. - this RNA is NOT translated – it is functional as an RNA molecule. - of course, this just pushes the question one step ‘upstream’ – what determines why Xic is only active in one X chromosome? When? - It seems to be an ‘imprinted’ phenomenon, so that daughter cells have the same X inactivated. However, this seems to happen at different points in development for different tissues.