Human Genetics chapter 7

Question 0

Gametes

Answer 0

Unfertilized germ cells

Question 1

Zygote

Answer 1

Fertilized egg that develops into a new individual

Question 2

Gonads

Answer 2

Organs where gametes are produced, testes and ovaries

Question 3

Testes

Answer 3

Male gonads that produce spermatozoa and sex hormones

Question 4

Ovaries

Answer 4

Female gonads that produce oocytes and female sex hormones

Question 5

Three steps in sex determination

Answer 5

1. First, Chromosomal sex (xx, XY) happens at fertilization, but is necessarily male or female until week 7 or 8
2. Second, gonadal sex. Y-linked expression either promotes or degenerates undifferentiated internal gonads
3. Third, sexual phenotype. Testosterone and DHT signal formation of external genitals or absence of the hormones prevents external genitalia to develop

Question 6

What kinds of mutations uncouple chromosomal sex and Phenotypical sex?

Answer 6

1. Chromosomal events may exchange segments of X and Y chromosomes
2. Mutations may affect ability of cells to respond to Y linked gene products
3. Autosomal genes may control events on the X and Y chromosomes (epistasis)

Question 7

What sex will you be (45, X)?

Answer 7

Female

Question 8

What sex will you be (47, XXY)?

Answer 8

Male (anyone with a Y-chromosome is almost always a male, no matter how many X’s)

Question 9

SRY

Answer 9

A gene, called the sex determining region on the Y, located near the end of the of the short arm of the Y chromosome that plays a major role in causing the undifferentiated gonad to develop into a testis.

Question 10

Testosterone

Answer 10

1. A steroid hormone produced by the testis, the male sex hormone
2. Stimulates the wolffian system

Question 11

Anti-Mullerian hormone

Answer 11

A hormone produced by the developing testis that causes the breakdown of the Müllerian ducts in the embryo

Question 12

DHT

Answer 12

In males, testosterone is converted into dihydrotestosterone, which directs the formation of the external genitalia and influences brain development and organ size

Question 13

Complete androgen insensitivity

Answer 13

1. An X linked genetic trait that causes XY individuals to develop into phenotypic females
2. Caused by a mutation in a hormone receptor (AR, androgen receptor), and no receptors for male hormones are produced.
3. Testosterone and DHT is present but cannot respond to their presence, so development proceeds toward default female.
4. Chromosomal males with female external genitalia (usually sterile)

Question 14

Pseudhermaphroditism

Answer 14

1. Chromosomally male, but identified and raised as females
2. Both male and female structures at different times in their lives
3. Failure to produce enough testosterone and DHT result in genitalia that are essentially female
4. At puberty testosterone is increased and females turn into males

Question 15

Barr body

Answer 15

1. A densely staining mass in the somatic nuclei of mammalian females, an inactivated X chromosome
2. Under the microscope, small dense spot on the inside of the nuclear envelope

Question 16

Dosage compensation

Answer 16

1. A mechanism that regulates the expression of sex linked genes
2. Males and females have the same amount of X linked gene products
3. Only one X chromosome is active in females, the second is inactivated and forms a Barr body
4. The Inactivated X chromosome can come from either parent
5. Inactivation takes place early in development
6. Inactivation is random and permanent (the descendant of a cell will have the same X chromosome inactivated)
7. DC allows certain x-linked recessive disorders to be expressed in heterozygous females (like color blindness, the same X chromosomes are not always inactivated in retinal cells)

Question 17

Mary Lyon thesis

Answer 17

1. Hypothesis generated from studying in mice coat color
2. Lyon realized in heterozygous females both alleles were active but not in the same cells (like codominance)
3. One X chromosome is active in females while the other coils to form a Barr body
4. The Inactivated X chromosome can come from either parent
5. Inactivation takes place early in development
6. Inactivation is random and permanent (the descendant of a cell will have the same X chromosome inactivated)

Question 18

Female mosaics

Answer 18

1. Female mammals are constructed of two different cell types, some cells express genes from the mothers X chromosome and some from the fathers X chromosome. (Mosaics for x linked genes)
2. Human female example, x linked gene that controls formation of sweat glands (anhidrotic ectodermal dysphasia). Patches of skin with and without sweat glands
3. EX. Blaschko lines

Question 19

Calico cat coat color

Answer 19

1. Is usually female
2. Is heterozygous (O/o, orange, black)
3. Has to be an x linked trait

Question 20

X inactivation center (xic)

Answer 20

A region on the X chromosome where inactivation begins

Question 21

Sex influenced traits

Answer 21

1. Traits controlled by autosomal genes that are usually dominant in one sex but recessive in the other.
2. EX. Pattern baldness (expressed more often in males than in females)
3. Dominant in males, recessive in females
4. Testosterone is higher in males and this environment interacts to determine phenotypic expression

Question 22

Sex limited genes

Answer 22

1. Loci that produce a phenotype in only one sex
2. Inherited by both males and females but normally expressed only in one sex
3. EX. Autosomal trait that control precocious puberty. Only in heterozygous males not heterozygous females.
4. EX. Duchenne muscular dystrophy is a X linked recessive disorder

Question 23

Imprinting

Answer 23

A phenomenon in which gene expression depends on whether paternally or maternally inherited