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

I. Allelic, Genic, and Environmental InteractionsII. Sex Determination and Sex Linkage


A. Sex Determination1.Environmental Sex Determination

a. Temperature

MT FT

MT FT



a. Temperature

MT FT



a. Temperature

(Huang et al. 2012, Grubben 2004)



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


a. Temperature b. Size/Nutrition

Arisaema triphyllum“Jack-in-the-Pulpit”

Small plants - male

Large plants - female


a. Temperature b. Size/Nutrition

Benefit of being male – quantity of offspring

Benefit of being female – regulate quality of offspring

Cervus elaphusRed 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.


a. Temperature b. Size/Nutrition c. Social Environment

Immature males

Sexually mature male

Sexually mature female

Wouldn’t the species do better if there were more females/group?Yes, but selection favors individual reproductive success.

(Inhibits development of males)



Midas cichlid

Brood



Midas cichlid

BroodAdd Larger juveniles

female



Midas cichlid

BroodAdd smaller juveniles

male



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.

A. Sex Determination1.Environmental Sex Determination2.Chromosomal Sex Determination

a. Protenor sex determination

The presence of 1 or 2 sex chromosomes determines sexOrder: Hemiptera “True Bugs”

Family Alydidae – Broad-headed bugs


a. Protenor sex determinationb. Lygaeus sex determination

The type of sex chromosomes determines sex

Order: Hemiptera Family: Lygaeidae “Chinch/Seed Bugs”


a. Protenor sex determinationb. Lygaeus sex determination

Which sex is the ‘heterogametic’ sex varies

XX female, XY – male

Most mammals, including humansSome insectsSome plants

ZZ male, ZW female

BirdsSome fishSome reptilesSome insects (Butterflies/Moths)Some plants


a. Protenor sex determinationb. Lygaeus sex determinationc. Balanced sex determination

The ratio of X’s to autosomal sets determines sex

Human genotype and sex

2n: 46, XX = female2n: 46, XY =male2n+1: 47, XXY = male2n-1: 45, X = female

Have a Y = maleNo Y = female

Drosophila genotype and sex

2n: 8, XX =female2n: 8, XY = male2n+1: 9, XXY = female2n-1: 7, X = male

Ratio of autosomal sets:X = 2:1 = maleRatio of autosomal sets:X = 1:1 = female


a. Protenor sex determinationb. Lygaeus sex determinationc. Balanced sex determinationd. 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



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.



X X

X* X*X male X*X male

Y- XY- female XY- female

MALE: AAXY

FEMALE: aa XX

A X A Y

a X AaXX AaXY

a X AaXX AaXY

MALE: aa XY

FEMALE:AA XX

a X a Y

A X Aa XX Aa XY

A X Aa XX Aa XY

A. Sex DeterminationB. 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

All offspring, regardless of sex, express the A trait in both reciprocal crosses

RECIPROCAL CROSSES

MALE

FEMALE

Xg Y

XG XGXg XGY

XG XGXg XGY

MALE

FEMALE

XG Y

Xg XGXg XgY

Xg XGXg XgY

A. Sex DeterminationB. 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

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.

A. Sex DeterminationB. Sex LinkageC. 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?


- 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


Actually, in all humans and mammals, all but one X condenses, regardless of sex or number of X’s.


Random X-inactivation leads to tortoiseshell heterozygote females


Calico determined by a different autosomal gene that affects rate of melanocyte migration to the skin surface.

XBXb, Pp

XBXb, pp

XBXb,PP

No migration of melanocytes to skin White

CalicoSlow migration

Inactivation before proliferation

Fast migration

Proliferation before inactivationTorty

Melanocytes


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

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