Gen 2.0

Male/ female determination is based on

specific chromosomes

Primary sexual differentiation

involves only gonads where gametes are produced

Secondary sexual differeniation

involves the overall appearance of the organisim

Plants and animals that contain only male or female reproductive organs are ____

unisexual (dioecious or gonochoric)

Plants and animals that contain both male and female reproductive organs and produce both male and female gametes are ____

bisexual (monoecious or hermaphroditic)

In maize (Zea mays), the diploid sporophyte stage predominates, and both male and female structures are present on the adult plant. What does this indicate?

that sex determination must occur differently in different tissues of the same plant

In some organisms, sexual determination is genetically determination is ______

determined and regulated

Mutant genes can cause what?

sex reversal

When homozygous, all mutations are classified as tassel seed (ts) interfere with tassel production and then ______

induce production of female structures instead

The recessive mutations silkless (sk) and barren stalk (ba) interfere with the development of the pistil, resulting ______

in plants with only male-functioning reproductive organs

XY system is

mammals and some insects

X O system is

some insects

ZZ/ZW system is

reptiles, birds, some amphibians and insects

No special sex chromosomes include

plants and fungi

Female gametes all have an_____

X chromosome

Male gametes have either an ______

X or a Y chromosome

Zygotes with two X chromosomes resulting in female offspring is called

homogametous

Zygotes with one x and one Y chromosome resulting in male offspring is called

heterogametous

The XX/XO Protenor (butterfly) mode of sex determination depends _______

random distribution of the X chromosome into half of the male gametes

Males are always heterogametic sex

False

In some organisms, females are the heterogametic sex

True

In chickens, what is the sex determination of a female chicken?

ZW (heterogametic)

In chickens, what is the sex determination of a male chicken?

ZZ (homogametic)

With respect to primary sex determination, male gametes containing one of each autosome plus a Y chromosome result in _______

male offpsrings because they lack an X chromosome

Genetic Balance theory

threshold of maleness is reached when the X: A ratio is 1:2 (X:2A), but the presence of additional X (XX:2A) alters the balance and results in female differentiation

C. elegans, a model species, has two sexual phenotypes. Males consist of what?

one testes have only one X chromosome, no Y

C. elegans, a model species, has two sexual phenotypes. Hermaphrodites (bixsexual) consist of?

having two X chromosomes, no Y

eggs are fertilized by stored sperm— self fertilization

Majority of offspring are hermaphrodites but

less that 1% are males

Temperature-dependent sex determination (TSD)

the enviroment, specifically temperture, has a profound influence on sex determination

Example of TSD

For all crocodiles, most turtles, and some lizards, sex determination is determined by the incubation temperature of eggs during a critical period of embryonic development.

Three different patterns of temperature sex determination in reptiles. What does Case I say?

Low temperature yield 100% females, and high tempereture yield 100% males

Three different patterns of temperature sex determination in reptiles. What does Case II say?

The exact opposite happens coming from Case I

Three different patterns of temperature sex determination in reptiles. What does Case III say?

Low and high temperatures yield 100 percent females, and intermediate temperatures yield various proportions of males.

Mechanisms underlying TSD. This temperature different is believed to involve ______

steroids (mainly estrogen) and the enzymes involved in their synthesis

Aromates does what?

converts androgens (testosterone) to estrogen (estradiol)

The presence of the Y chromosome alone does NOT mean it determines maleness

True

What is the function of SRY?

sex-determining region Y

What is the function of MSY?

Male-specific region of Y

How many genes do Y chromosomes have?

75 genes

How many genes do X chromosomes have?

900-1400 genes

Pseudautosomal regions (PARs) characterisctics

They are present on both ends of the Y chromosome

Share homology with regions on the X chromosome

Synapse and recombine with X during meiosis

What is crucial to the segregation of the X and Y chromosomes during male gametogenesis?

the presence of such a pairing region

Where is the SRY located?

adjacent to the PAR of the short arm of the Y chromosome

Some portions of MSY share homology with the X chromosome, others do not

True

Euchromatic

functional genes

Heterochromatic

nonfunctional genes

The nonrecombining region of the Y chromosme is called

MSY

Testis-determining factor (TDF) is what?

a protein encoded by a gene in the SRY that triggers testes formation

Where is the testis- determining factor located

within the SRY

SRY/TDF expressed result in

gonads develop into testis

SRY/TDF NOT expressed result in

gonads develop into overaies

XX males have a translocation from

Y to the X

XY females have a

deletion of part of the Y

Klinefelter syndrome (males with extra Xs)

XXY, 47XXY, 48XXXY, 49 XXXXY

Tall stature, with long arms and legs

Undeveloped testes and prostate gland- no facial hair

Phenotypically male, infertile,slight breast enlargerment and hips often rounded

Turner syndrome (XO)

45, XO karotype

Female external genitalia and internal ducts but the ovaries are rudimentary

Short stature, skin flaps on back of the neck, flat undeveloped breast, broad shield-like chest

XXX Syndrome (triple-x)

Abnormal presence of three X chromosomes along with a normal set of autosomes, resulting in female differentiation

Normal and unaware of the condition

Other cases: undeveloped secondary sex characteriscs, sterility, and mental retardation

Dosage compensation prevents ______

excessive expression of X-linked genes in humans and other mammals

X-inactivation in human females

Lyon hypothesis

Where does the Lyon hypothesis occur

somatic cells and then passed on to progeny cells by mitosis

Example of Lyon Hypothesis

Heterozygote female mice with mottled coat color for color genes on the X chromosome

Calico cats black and yellow-orange patches of fur color

Barr body- the inactivated X

Inactive X chromosomes are highly condensed and can be observed in stained interphase cells.

The arise from the random inactivation of either the maternal or. paternal chromosome

True

N-1 rule

Regardless of how many X chromosomes a somatic cell possesses, all but one of them are inactivated. N= # of chromosomes

Mechanism of inactivation

chemically modified DNA that gets inactivated, silencing most genes, creates a memory that keeps the same homolog inactivated following chromosome replications and cell division—- imprinting

Androgen Insenstivity— Testicular Ferminization XY karotype

mutation in a gene on the X that codes for the testosterone receptor

What is the phenotype of Androgen insenstivity?

Normal female but sparse or absent body hair

How is it internally in Androgen insensitivity?

blind vagina, no uterus, tetstis, present abdominal cavity

What are some aspects of chromosomal mutations?

A change in the total # of chromosomes

Deletion or duplication of genes or segments of a chromosome

Rearrangements of the genetic material within or among chromosomes

Euploidy

complete haploid sets of chromosomes are present

Aneuploidy

gain or loss one or more chromosomes and has other than an exact mulitple of the haploid set

Polyploidy

occurs when more than two sets of chromosomes are present

Nondisjuction (refresher)

Chromosomes or chromatids fail to dijoin and move to opposite poles during meiosis I or II, leading to a variety of conditions in humans and other organisms

Monosomy is

one copy of a chromosome

Trisomy is

three copies of one chromosome

(2n+1)

XXY condition

Nonjunction— Meiosis II in the Y-bearing cell, you would get a sperm with two Ys (from two sister chromatids) and a sperm without any sex chromosomes

XYY or XO

What happens if nondisjunction occurs in meiosis I (XYY condition)?

results in sperm with both an X and a Y chromosome or no sex chromosome.

XXY XO

Haploinsufficiency

one normal copy of a gene is not enough to produce a normal phenotype

Down syndrome: Trisomy 21

• Prominent epicanthic fold in each eye

• Flat face, round head, short stature with protruding tongue

• Short broad hands with characteristic palm and fingerprint. pattern

• Mental retardation

How does Down syndrome occur?

critical region of chromosome 21 contains the genes that are dosage sensitive in this trisomy and are responsible

Does Down syndrome occur in meiosis II or I

Meiosis I

An extra chromosome 21 can come from maternal and paternal gametes, but the incidence increases with maternal age

True

Down syndrome is cause by ________

random error disjunction of chromosome 21, thus the disorder is not expected to ne inherited

Familiail Down syndrome

Chromosome 21 is attached to another chromosome (#14)

The cause is because of translocation, and it CAN BE inherited

Patau syndrome

Caused by trisomy 13 (three copies of chromosome 13)

Causes severe developmental problems and birth defects

Deafness

Edward syndrome

Caused by trisomy 18 (3 copies of chromosome 18)

Severe developmental and growth problems

Triploid has

3n chromsome

Tetraploid has

4n chromsome

Pentaplod has

5n chromosome

Autopolyploidy

The addition or one more sets or chromosomes identical to the haploid complement of the same species

Allotetraploid/ amphidiploid

Combination of chromosome sets from different speices as a consequence of interspecific matings

What are the results of an allotetraploid/ amhidiploid?

hybridization of two closely related species

Sterile hybrids can undergo a natural or induced chromosomal doubling, producing fertile amphidiploids

True

Polyploid contain

four haploid genomes derived from separate species

tetraploids arise when _____

chromosome have replicated and the parent cell fails to divide and instead enters interphase: the chromosome number will have duplicated

How can scientist can artificially create polyploid organisms

experimentally done by applying heat or cold shock to diploid cells undergoing meiosis or by appyling colchicine to somatic cells undergoing mitosis

Examples of autopolyploid flowers and fruits

• Potatoes

• Winesapp apples

• Seedless bananas

• seedless watermelon

Two genes that encodes G1 cyclins are ______

repressed when ploidy increases

The polyploid cell stays in G1 phase longer and _______

grows to a larger size

Change in total amount of genetic information include

• Deletions

• Insertion

• Duplications