Genetics Chapter 4: Sex Determination and Sex-Linked Traits

the formation of offspring that are genetically distinct from their parents

what is sexual reproduction?

haploid gametes

what does meiosis produce?

diploid zygotes

what does fertilization produce?

sexual phenotype

what does sex refer to?

small, large

males produce ___ gametes, while females produce relatively ___ gametes

the mechanism by which biological sex is established

what is sex determination?

a category assigned by the individual or others based on behavior and cultural practices, need not coincide with one's biological sex

what is gender?

a condition in which both sexes are present in the same organism

what is hermaphroditism?

the organism bears both male and female reproductive structures

what does it mean to be monoecious?

the organism has either male or female reproductive structures

what does it mean to be dioecious?

chromosomally, genetically, or environmentally

how is sex determined in dioecious species?

discovery that sex chromosomes in insects determined their sex

how was the chromosome theory of heredity proven?

the nonsex chromosomes, same for males and females

what are autosomes?

individual genes on the sex chromosomes (not the sex chromosomes themselves)

what determines sex?

females have 2 X chromosomes (XX), males have a single X chromosome (XO) (seen in grasshoppers)

what is the XX-XO sex determination system?

males

what is the heterogametic sex in the XX-XO sex determination system?

females

what is the homogametic sex in the XX-XO sex determination system?

which type of male gamete fertilizes the egg

what is the sex of an individual determined by in XX-XO sex determination?

acrocentric (not y-shaped)

what is the shape of the Y chromosome?

the male

what is the heterogametic sex in the XX-XY sex determination system?

the female

what is the homogametic sex in the XX-XY sex determination system?

not generally

are X and Y chromosomes homologous?

they are homologous in small regions called the pseudoautosomal regions

how do X and Y chromosomes pair and segregate during meiosis?

at both tips

where are the pseudoautosomal regions in human X and Y chromosomes?

patches of genes on different chromosomes that are the same and allow them to pair up

what are pseudoautosomal regions?

females are ZW and males are ZZ

what is the ZZ-ZW sex determination system?

females

which sex is heterogametic in the ZZ-ZW sex determination system?

males

which sex is homogametic in the ZZ-ZW sex determination system?

when genotypes at one or more loci determine the sex of an individual

what is genic sex determination?

no, chromosomal sex determination is

is genic sex determination present in humans?

the SRY gene, located on the Y chromosome

what controls sex determination in humans?

when sex is determined fully or in part by environmental factors

what is environmental sex determination?

they stack on top of each other, females form first, which secretes factor that induces male to form, sequential hermaphroditism

how is slipper limpet sex determined?

the X chromosome: autosome ratio,

how is sex determined in drosophila melanogaster (fruit fly)?

failure of the Y chromosome to segregate properly, resulting in a XO genotype and developmental defects

what is Turner Syndrome?

a defect in which cell's have one or more Y chromosomes and multiple X chromosomes (normally XXY, sometimes XXXY, XXYY, etc.) normally tall and sterile

what is Klinefelter syndrome?

cells possess three X chromosomes, no distinctive features other than being tall and thin

what is triple-X syndrome?

males have no distinctive physical characteristics except being a little taller than normal

what results from XYY?

contains genetic information essential for both sexes, required for human development

what is significant about the X chromosome?

the male determining gene is located here, a single copy usually produces a male phenotype, absence usually results in a female phenotype

what is significant about the Y chromosome?

on both the X and Y chromosome, female usually needs at least 2 copies of X chromosome to be fertile

where are genes for fertility located?

upset normal development in both males and females

what may additional X chromosome copies do?

sex-determining region Y gene, male-determining gene in humans

what is the SRY gene?

it induces the gonad to become testes

what happens when the SRY gene becomes active?

the gonad becomes ovaries and female features develop

what happens in the absence of the SRY gene?

transcription factor

the SRY gene encodes a ___ ___, which binds and stimulates transcription of specific genes

they are XY with female external sexual characteristics, have testes that secrete testosterone, but no functional androgen (testosterone) receptor

describe what happens in people with androgen-insensitivity syndrome

by genes on the X chromosome

how are X-linked characteristics determined?

by genes on the Y chromosome

how are Y-linked characteristics determined?

Thomas Hunt Morgan

who was the first to discover sex-linked characteristics?

white eyes in fruit flies, X-linked

what sex-linked trait did Morgan research?

X-linked

is color blindness X- or Y-linked?

female carriers and normal vision males

what does the mating of a colorblind male and normal vision female produce?

female carriers and colorblind males

what does the mating of a colorblind female with a normal color vision male produce?

when a pair of homologous chromosomes fail to separate in anaphase I of meiosis

what is non-disjunction?

they evolved from a pair of autosomes

how is it theorized that the X and Y chromosome first came to be?

a suppression of crossing over

what keeps maleness genes Y-linked?

mechanisms to regulate/equalize the amounts of protein produced by the single X and by two autosomes in the heterogamic sex

what is dosage compensation?

increased expression of dosage-sensitive genes on the X chromosome (in males and females) and inactivation of one of the X chromosomes in females

what does dosage compensation involve in placental mammals?

the second X chromosome in a female that is inactivated by condensation

what is a Barr body?

the number of Barr bodies present in cells = n-1 (n = # of X chromosomes)

what is the Lyon hypothesis?

using mouse genetics

how did Mary Lyon demonstrate that Barr body is the mechanism for dosage compensation?

when one or the other X chromosome is inactivated randomly during early development, and the X that was inactivated in a cell will continue to inactivate the same X in clonal progeny

what is random X inactivation?

tortoiseshell cats

what is a good example of Random X Inactivation?