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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
1. Environmental Sex Determination
a. Temperature
MT
FT
I. Allelic, Genic, and Environmental Interactions
II. Sex Determination and Sex Linkage
A. Sex Determination
1. Environmental Sex Determination
a. Temperature
MT
FT
I. Allelic, Genic, and Environmental Interactions
II. Sex Determination and Sex Linkage
A. Sex Determination
1. Environmental Sex Determination
a. Temperature
MT
FT
I. Allelic, Genic, and Environmental Interactions
II. Sex Determination and Sex Linkage
A. Sex Determination
1. 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)
A. Sex Determination
1. Environmental Sex Determination
a. Temperature
b. Size/Nutrition
Arisaema triphyllum
“Jack-in-the-Pulpit”
Small plants - male
Large plants - female
A. Sex Determination
1. 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.
A. Sex Determination
1. 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
1. Environmental Sex Determination
a. Temperature
b. Size/Nutrition
c. Social Environment
Midas cichlid
Brood
A. Sex Determination
1. Environmental Sex Determination
a. Temperature
b. Size/Nutrition
c. Social Environment
Midas cichlid
Add Larger juveniles
Brood
female
A. Sex Determination
1. Environmental Sex Determination
a. Temperature
b. Size/Nutrition
c. Social Environment
Midas cichlid
Add smaller juveniles
Brood
male
A. Sex Determination
1. 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.
A. Sex Determination
1. Environmental Sex Determination
2. 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
A. Sex Determination
1. Environmental Sex Determination
2. 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”
A. Sex Determination
1. Environmental Sex Determination
2. Chromosomal Sex Determination
a. Protenor sex determination
b. Lygaeus sex determination
Which sex is the ‘heterogametic’ sex varies
XX female, XY – male
ZZ male, ZW female
Most mammals, including humans
Some insects
Some plants
Birds
Some fish
Some reptiles
Some insects (Butterflies/Moths)
Some plants
A. Sex Determination
1. Environmental Sex Determination
2. 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
Drosophila genotype and sex
2n: 46, XX = female
2n: 46, XY =male
2n+1: 47, XXY = male
2n-1: 45, X
= female
2n:
2n:
2n+1:
2n-1:
Have a Y = male
No Y = female
Ratio of autosomal sets:X = 2:1 = male
Ratio of autosomal sets:X = 1:1 = female
8, XX =female
8, XY = male
9, XXY = female
7, X = male
A. Sex Determination
1. Environmental Sex Determination
2. Chromosomal Sex Determination
a. Protenor sex determination
b. Lygaeus sex determination
c. Balanced sex determination
d. Human sex determination: SRY gene
A. Sex Determination
1. Environmental Sex Determination
2. 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
1. Environmental Sex Determination
2. 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
1. Environmental Sex Determination
2. 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*X male
X*X male
Y-
XY- female
XY- female
A. Sex Determination
B. 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
AX
FEMALE:
aa XX
MALE: aa XY
AY
aX
AaXX AaXY
aX
AaXX AaXY
aX
FEMALE:
AA XX
aY
AX
Aa XX Aa XY
AX
Aa XX Aa XY
All offspring, regardless of sex, express the A trait in both reciprocal crosses
A. Sex Determination
B. 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
XG
XGXg
XGY
100% G, for all offspring
MALE
FEMALE
XG
Y
Xg
XGXg
XgY
Xg
XGXg
XgY
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 Determination
B. Sex Linkage
C. 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?
A. Sex Determination
B. Sex Linkage
C. 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
A. Sex Determination
B. Sex Linkage
C. Dosage Compensation
Actually, in all humans and
mammals, all but one X
condenses, regardless of
sex or number of X’s.
A. Sex Determination
B. Sex Linkage
C. Dosage Compensation
Random X-inactivation leads to
tortoiseshell heterozygote
females
A. Sex Determination
B. Sex Linkage
C. Dosage Compensation
Calico determined by a different autosomal
gene that affects rate of melanocyte
migration to the skin surface.
Melanocytes
XBXb, pp
XBXb,
No migration of melanocytes to skin
Slow migration
Pp
White
Calico
Inactivation before proliferation
XBXb,PP
Fast migration
Torty
Proliferation before inactivation
A. Sex Determination
B. Sex Linkage
C. 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 redgreen colorblindness have patches of retinal cells that can’t distinguish red
from green.
Anhidrotic ectodermal
dysplasia