Chapter 5 Flashcards
Heterogametic
Sex that produces two different gametes
Homogametic
The sex that produces identical gametes
What are three types of sex determination?
- Chromosomal
- Genic/genetic
- Environmental
What is the proportion of male and female offspring from a chromosomal parental cross?
1) XX-XY: some plants, insects, reptiles, all mammals
2) XX-XO: simple system, females have two XX, males have single X
3) ZZ-ZW: males are homogametic, female is heterogametic
-female produces two different gametes, half with Z chromosomes, other half with W
How is sex determined in drosophila?
X:A ( # of chromosomes/ # of haploid sets of autosomes)
During what phase of meiosis do chromosomes fail to separate resulting in nondisjunction?
Anaphase I
What are some examples of nondisjunction events in humans?
1) Turner’s syndrome: (XO) females do not undergo puberty, inmature female secondary sex characters, low hairline and folds of skin, may have cognitive impairment
2) Klinefelter syndrome: (XXXY, XXXXYY,XXYY) occurs in males, small testes, breast enlargement, reduced facial/pubic hair
3) triplo-X syndrome: (XXX) tall, thin, sometimes normal fertility, normal intelligence
4) XXXX, XXXXX: normal female anatomy, but have cognitive impairment- severity increases with higher # of X chromosomes
What is SRY and what does it do?
SRY is a sex-determining Y region that indicates whether a male is a male or a female is a female.
- found in all males
-absent in all XY females
What is an example of SRY?
Androgen-insensitivity syndrome
-persons have female sexual characteristics, but no reproductive organs
-testes are found in abdominal cavity
How does SRY trigger syndromes such as androgen-insensitivity?
There are no receptors for testosterone, which yields no male characters. The defect is on the X chromosome. Genes for male and female secondary characters on autosomes
What is dosage compensation?
the process by which organisms equalize the expression of genes between members of different biological sexes.
What is a barr body & who discovered it?
A barr body is a darkly staining body in nuclei of cats, which Barr observed in 1949
Who proposed that Barr bodies were a condensed X chromosome?
Oh I in 1956
What is the lyon hypothesis?
Dosage compensation mechanism works in mammals and how it relates to phenotype
What are the basic principles of X-inactivation?
- it occurs randomly (from any parent) in somatic cells during embryogenesis
- miotic daughter cells will maintain the same inactive X
-males and females express X-linked genes at the same level - females that are heterozygous for X-linked genes are mosaic( cell only expresses one of the alleles)
What are the different types of X inactivation?
1) x inactivation: takes place in early development, x remains inactive
2) x inactivation center: expression occurs on inactive X
3) x inactive transcript: long noncoding RNA coats the X creating a change in the chromosome structure to prevent transcription
** every X chromosome over 1 in a cell will be inactivated creating more bar bodies (n-1) **
What is an example of dosage compensation?
In cats, there are only two alleles for an orange coat: X+ (black fur) & X0 (orange). Males either have the genotypes X+Y(black) or X0Y(orange); they cannot create both. Females on the other hand, create three phenotypes: X+X+ (black), X0 X0 (orange), or X+X0 (tortoiseshell)
Who discovered male insects had a strange “body” in nuclei?
Henking in 1891
Mcclung (1901)
Hypothesized that X body was a chromosome; female grasshopper cells had 1 more chromosome than males
Female mealworms have 20 large chromosomes; males have 19 large and one smaller Y, who discovered this?
Stevens in 1905
What is the significance of Wilsons (1906) discovery?
Female butterflies have two X chromosomes; males have one single X
What do pseudoautosomal regions consist of?
-differential region of the x (X-linked genes)
-centromere
-a differential region of the Y (y-linked genes)
-males gene SRY
What does a genomic/genetic sex determining system show?
- no obvious difference in chromosomes
-genes determine the sex of an induvial
found in some protozoans and plants
An environmental sex determining system depends on what?, give an example
Temperature; ex- warms temperatures during development produces males and cool temps produce females, in alligators
