Sex Determination and Sex-Linked Characteristics

Flashcards based on lecture notes about sex determination mechanisms, chromosomal systems, and sex-linked traits.

What two states does sexual reproduction alternate between?

Haploid and diploid.

What are the two sexual phenotypes that most organisms possess?

Male and female.

What process produces haploid gametes?

Meiosis.

Does the fertilization process produce, in terms of ploidy a haploid or diploid zygote?

A diploid zygote.

Define hermaphroditism.

Both sexes are present in the same organism.

Define monoecious.

Both male and female reproductive structures are in the same organism.

Define dioecious.

Either male or female reproductive structures are in one organism.

What are the sex chromosomes in grasshoppers

XX is female, XO is male

What are the sex chromosomes in mammals?

XX is female, XY is male

What are pseudoautosomal regions important for?

X-Y chromosome pairing in meiosis in males.

What organisms use a genic sex-determining system?

Some plants, fungi, protozoans, and fish.

What is environmental sex determination?

Sex determination influenced by environmental factors like limpet's position or temperature in turtles.

What is the genic balance system?

Sex determination in Drosophila based on the X:A ratio (X chromosomes to haploid sets of autosomes).

What determines sex in Drosophila?

Genes on x chromosome

What happens if the critical developmental phase is shortened in Drosophila?

Intersex, not enough time to accumulate X chromosome gene products.

What is the sexual phenotype of a fruit fly with XXYYY sex chromosomes and two sets of autosomes?

Female (X:A ratio is 1.0).

What gene on the Y chromosome determines maleness in humans?

SRY gene.

What syndrome is associated with XO chromosome complement?

Turner syndrome.

What syndrome is associated with XXY, XXXY, XXXXY, XXYY, chromosome complement?

Klinefelter syndrome.

What are the characteristics of poly-X females?

Tall and thin, slightly lower intellectual ability, many are fertile.

Define nondisjunction.

The failure of chromosomes to separate properly during cell division.

What is the result of fertilization involving gametes from nondisjunction?

Trisomic (2n+1) or monosomic (2n-1) zygotes.

What did Bridges propose in relation to white-eyed Drosophila females?

That white eyed female has two X chromosomes and a Y chromosome (XwXwY)- X:A ratio of 1 so female

Why are a few white-eyed females and red-eyed males produced from a cross between a white-eyed female and a red-eyed male?

Nondisjunction in an XXY female.

What is the role of the X chromosome?

Contains genetic information essential for both sexes; at least one copy is required.

What is the role of the Y chromosome?

The male-determining gene is located here; a single Y produces a male phenotype.

What is the result of absence of Y chromosome?

Female phenotype.

What does the SRY gene encode?

A transcription factor that regulates genes that promote differentiation of the testes.

Color-blindness in humans

X-Linked characteristics

What is the conclusion of reciprocal crosses made in the experiment about white eyes in fruit flies?

The results of reciprocal crosses are consistent with X-linked inheritance as opposed to autosomal recessive traits.

What does Bridges work in the experiment about white eyes in fruit flies proves and confirmed?

Proved that sex genes on X and confirmed chromosomal theory of inheritance

What characteristic makes more males affected by X-linked recessive traits?

X-linked recessive traits alternate between the sexes: Appearing in females in one generation and in males in the next generation -Affected female to sons not to daughter but affected father to grandsons

What is important for sex determination in SRY?

Important for sex determination in SRY Y chromosome lost DNA over time

What leads to degeneration of the chromosomes?

Lack of crossing over between the X and the Y chromosomes leads to degeneration of the Y.

How to prevent total degeneration of Y chromosome?

Palindromic sequence can allow recombination -offsetting lack of X and Y crossing over 5’ TGGGAG…..CTCCCA 3’ 3’ ACCCTC….. GAGGGT 5’

What is dosage compensation?

The amount of protein produced by X-linked genes and randomly inactivated in two sexes

What is Lyon hypothesis?

Dosage compensation: the amount of protein produced by X-linked genes and randomly inactivated in two sexes

What is Barr body?

Barr body is an inactivated X chromosome

What is the result caused by Females mosaics for X-linked genes?

Heterozygous at X linked locus: 50% of cell will express one allele; 50% 0f cells will express the other allele

What is the result of XY female, XO (broken Y with two centromeres)?

Gene rearrangement causing gene loss due to Palindromic sequence.

What is Androgen-insensitivity syndrome?

Female XY, caused by the defective androgen receptor: Testosterone can’t bind.

Where is the SRY gene located?

On the Y chromosome.

What is the key difference between XX-XO and XX-XY systems?

The presence of a Y chromosome in the XX-XY system, which is absent in the XX-XO.

In what organisms is the ZZ-ZW system found?

Birds, fishes, butterflies.

Are autosomal genes play any role in sex determination in Drosophila?

No

Does crossing over occur in Y-linked characteristics?

No crossing over- no male genes in females

Which X-linked characteristics are in human?

X-linked color blindness in humans

Which Y-linked characteristics are found in male?

Y chromosome determination in SRY

What type of system is found some invertebrates, turtles, alligators?

Environmental sex determination

What is the sexual phenotype for XXXY with XX-XY system?

Male

What is the sexual phenotype for XXX with XX-XY system?

Female

What is the sexual phenotype for XO with XX-XY system?

Female

What is the sexual phenotype for XYY with XX-XY system?

Male

What is X inactivation?

Dosage compensation where the amount of protein produced by X-linked genes is equalized.

What happened to the Y chromosome over the generation?

Y chromosome accumulates mutations and lose genes.

Wasps are in which system?

Haplodiploidy system

Snakes are in which system?

ZZ-ZW system

Mammals are in which system?

XX-XY system

Grasshoppers are in which system?

XX-XO system

What did Engineered SRY in XX mice do?

Developed into male.

In tortoiseshell: which patches are black or orange?

In orange patch: black allele is inactivated, In Black patch: orange allele is inactivated

How can Y chromosome repair gene mutation?

Crossing over can repair gene mutation

Does Y-linked characteristics alternate sexes?

No.

What does monoecious refer to?

An organism having both male and female reproductive structures.

What does dioecious refer to?

Organisms having only one type of reproductive structure: male or female.

What does a ratio of 0.33 mean?

Metamale in Drosophila.

What does a ratio of 0.67 mean?

Intersex in Drosophila

What does a ratio of 1.0 mean?

Female in Drosophila.

What does a ratio of 1.5 mean?

Metafemale in Drosophila

What does a ratio of 0.5 mean?

Metafemale in Drosophila

What is the full form of SRY?

Sex-determining region Y

What does X:A represents

X chromosomes; A, number of haploid sets of autosomes

What are the three environmental determination

Limpet's position in the stack, temperature in turtles, and some invertebrates

Where does the Androgen-insensitivity syndrome gene inherit from?

X-chromosome localized- inherit from mother

In males and females both, what are females mosaics for?

Females are mosaics for X-linked genes

How much percentage of X-linked gene ESCAPE inactivation?

15%

How much percentage of X-linked gene are inactivated in some females but not others?

10%

What is suppression keep for gene for male?

Suppression of crossing over keeps genes for male traits linked to male-determining gene

Where did sex chromosomes evolve from?

Sex chromosome evolved from autosomes.

Describe one difference between the XO, XXY, and XYY genotype?

XO is Turner, XXY is Klinefelter.

What can cause a gene causing during gene fragmentation?

But can cause gene rearrangement causing gene loss: like XY female, XO (broken Y with two centromeres

Give one example on a experiment of Drosophila

Are white eyes in fruit flies inherited as an autosomal recessive trait?

How to explain anomaly on cross for Experiment?

Failure of two X chromosomes in female fail to separate (10% of the time)

What is the probability that the child will be color blind? If But her mother was color blind/Betty has normal vision/Bill Is color blind.

Probability that the child will be color blind is 50%

Mutations at other genes affect what?

Affect male characteristics

How does a single X linked gene determine color?

X+ black and X0 –orange

What are males hemizygous:

Black (X+Y)or orange (X0Y)- never black AND orange

What are Females color can express on gene?

Females can be black (X+X+); orange (X0X0) or tortoiseshell (X+X0)

Sex Determination

The mechanism by which sex is established

Sex Chromosomes

Chromosomes that differ in males and females

Autosomes

Non-sex chromosomes that are the same for both males and females

Monoecious

Organisms that bear both male and female reproductive structures

Dioecious

Organisms that bear either male or female reproductive systems

Haplodiploidy

Sex-determination system with haploid males and diploid females

Genic Balance System

Sex is determined by the ratio of sex chromosomes to autosomes

SRY gene

The sex-determining region Y gene

Dosage Compensation

Mechanism to equalize the amount of protein produced by X-linked genes in the two sexes

X-Inactivation

When mammals equalize the dose of X-linked genes, one X chromosome is randomly inactivated in each female cell

Are X & Y chromosomes homologous

No

XX

female mammal