Heredity, Gene Regulation, and Development I. Mendel's Contributions

Heredity, Gene Regulation, and Development

I. Mendel's ContributionsII. Meiosis and the Chromosomal TheoryIII. Allelic, Genic, and Environmental InteractionsIV. Sex Determination and Sex Linkage



A. Sex Determination1.Environmental Sex Determination

a. Temperature

MT FT




a. Temperature

MT FT




a. Temperature

MT FT


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

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. Sex DeterminationB. Gender

‘Gender’ is a role or behavior that a human society correlates with a sex

Behavior: wear make-up and a skirt

Modern USA Society: Gender = woman

Medieval Scotland, modern Wodaabe: Gender = man

A. Sex DeterminationB. Gender

‘Gender’ is a role or behavior that a human society correlates with a sex

Sexual Behavior: like most behaviors, a given sexual behavior is not necessarily restricted to one sex or another.And sex is used for more than procreation; it is used for communication, conflict resolution, deception, and establishing dominance within and between sexes.

Female Bonobo chimps (Pan paniscus)

‘sneaker’ male

A. Sex DeterminationB. GenderC. Sex Linkage

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


1. For Comparison –heredity for sex (as a trait) and an autosomal dominant trait.

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

MALE

FEMALE

Xg Y

XG XGXg XGY

XG XGXg XGY

MALE

FEMALE

XG Y

Xg XGXg XgY

Xg XGXg XgY


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.

Heredity, Gene Regulation, and Development I. Mendel's Contributions

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