Top3-Ch4-P78-97EndReverse

Question 1

sex is determined by a balance between genes on the autosomes and genes on the X chromosome.

Answer 1

What is genic balance system?

Question 2

The system is called the genic balance system. Scientific name is drosophila melanogaster.

Sex is determined between genes on X chromosome and balance of genes on autosomes. Despite having XX (females) and XY (males) the Y chromosome does not determine maleness. Instead maleness comes from the autosomes A. To determine fruit fly sex must calculate X:A ratio with 1.0 being female and 0.5 being male.

Examples, XX:AA = 1.0 female, XY:AA=0.5 male, XXX:AA= 1.5 metafemale, XO:AAA0.33 metamale, XXXY:AA= 1.5 metafemale

Answer 2

Explain sex determination of fruit fly and what the system is called? Also give scientific name for fruit fly.

Question 3

SRY for Sex determining region Y which was discovered in 1990. The gene is found in XX males or XY females. This happens because the gene can move off the Y chromosome onto another chromosome to still create maleness.

See diagram below of where SRY gene is located.

Answer 3

What is the name of the gene on the Y chromosome that determines maleness?

Question 4

Only has a single X chromosome referred to as XO. Affects females, seen in 1 in 3000 females, frequently short, relatively broad chested, folds of skin on neck. Intelligence usually normal, usually sterile women from this.

No known cases in which a person misses both X chromosomes indicating that at least one X chromosome is necessary for human development.

Answer 4

Explain Turner Syndrome

Question 5

• Individuals have multiple X chromosomes and one or more Y chromosomes (usually XXY), but can be XXXY, XXXXY or XXYY.
• Phenotype is male
• Reduced facial hair
• Sterile
• Occurs 1 in 1000 male births.

Answer 5

Explain Klinefelter syndrome

Question 6

• Has three X chromosomes which is called triplo-X-Syndrome
• Have normal female phenotype and slightly greater chance on sterility and mental retardation
• Mental retardation occurs when more than three X-chromosomes and severity increases with each added X chromosome.

Answer 6

Explain Poly-X females

Question 7

1. X-chromosome is essential, at least one copy has to be active
2. male determining gene is on the Y chromosome
3. absence of Y chromosome means female phenotype
4. genes affecting fertility on both X and Y chromosomes
5. additional copies of the X chromosome may affect normal development

Answer 7

Explain roles of sex chromosomes (5 points)

Question 8

Contain XY, but appear externally as female and have male testes inside. Reason, is SRY creates gonads that produce testosterone to have affect testosterone must bind to an androgen receptor. But the receptor is defective in females with androgen-insensitivity syndrome so their cells are insensitive to testosterone and female characteristics develop.

Answer 8

Androgen-insensitivity syndrome

Question 9

Determined by genes located on the sex chromosomes, X-linked characteristics and Y-linked characteristics

Answer 9

Sex-Linked Characteristics are?

Question 10

Thomas Hunt Morgan and he showed that eye colour was an X-linked trait in Drosophila

Answer 10

Who was the first biologist to explain sex-linked inheritance? And what did he show?

Question 11

No.

Answer 11

Are there homologous alleles on the Y chromosome?

Question 12

eye colour alleles are only on X chromosome. Y chromosome does not have homologous alleles. So females can be homozygous or heterozygous for eye colour alleles. But for males with just one X chromosome can only carry a single eye color allele on the Y. Males are then said to be hemizygous for X-linked loci.

Answer 12

Explain how eye colour for fruit fly work on X and Y chromosomes.

Question 13

Answer 13

Look on P82 for Thomas Hunt Morgan’s fruitfly experiment. See attached diagram in answers

Question 14

when homologous chromosomes fail to separate during meiosis

Answer 14

non-disjunction is?

Question 15

Answer 15

When Thomas Hunt Morgan crossed his original white eyed males with homozygous red-eyed females all 1237 of the progeny had red eyes except for 3 white eyed males. His student Calvin Bridges did experiments to show what happened. See diagram on next page.

Question 16

X^c is allele for red-green colour blindness which is recessive. Allele for blue pigment vision is on chromosome 7. X⁺ is allele for normal colour vision.

Answer 16

See diagram for x-linked colour blindness in humans.

Question 17

autosomes

Answer 17

Sex chromosomes have evolved from

Question 18

No. Because of this the Y chromosome reduces in size and becomes more and more mutated

Answer 18

Is there crossing over between X- and Y chromosomes in males?

Question 19

For Y chromosome it does not cross over with X except for tiny part. This lack of interchromosomal recombination leads to an accummulation of deleterious mutations on the Y chromosome and the loss of genetic material. Evidence suggests the two arms of the Y chromosome recombine with each other. Also palindromic sequences within the Y chromosome can also undergo internal recombination.

Answer 19

Talk about interchromosomal recombination and palindromic sequences for Y chromosome.

Question 20

people

Answer 20

Y chromosomes have mutations that occur which don’t do anything but stay on the chromosome. These mutations vary among individuals. You can use these mutations as Y-linked genetic markers to trace the relationships of present day _______

Question 21

mother

Answer 21

A male always inherits his X chromosome from his ______?

Question 22

dosage compensation.

Answer 22

Females have twice the X chromosomes of males and this would produce twice the gene product (proteins) which would be highly detrimental as protein is important in development. Animals overcome this potential problem through _________, which equalises the amount of protein produced by X linked genes in two sexes.

Question 23

that there is a random inactivation of one of the X chromosomes in each cell during 32-64 cell stage of development. The descendant cells follow the same X is inactive. This explains mosaic patterns as the inactive X can vary throughout the body.

Answer 23

What is the Lyon Hypothesis?

Question 24

it is an inactivated X chromosome.

See below the dark Barr body on the left cell but not on the right cell.

Answer 24

What is a Barr body

Question 25

males, male, degenerating

Answer 25

Y-linked characteristics are present only in _____ and are inherited by their ______ offspring.
Y chromosome is _________.

Question 26

1. increasing productivity of single X in males
2. halving activity of both Xs in females
3. Inactivation of one X.chromosome (placental mammals)

Answer 26

Name three ways how dosage compensation is achieved?