Chapter 10.7

Question 1

Autosomal diseases

Answer 1

are diseases that are controlled by autosomal genes ( affect both sexes equally
eg. Huntington disease, cystic fibrosis

Question 2

The opposite of AUTOSOMAL DISEASES are

Answer 2

SEX- LINKED genes

Question 3

SEX -LINKED GENES

Answer 3

produce phenotypes that affect one sex over the other the other. These genes/alleles are found on the sex chromosomes only

Question 4

XX

Answer 4

female

Question 5

XY

Answer 5

male

Question 6

Why does the Y chromosome play a larger part in sex determination

Answer 6

All human embryos start with rudimentary female structures. An embryo having a working copy of a Y- chromosome gene called SRY developed into male.

SRY encodes a protein that switches other genes that direct the underdeveloped testes to secrete testosterone; and also turn on other genes that encode protein that dismantle embryonic female structures

Question 7

the X chromosomes vs. Y and sex linked diseases

Answer 7

y carries 100 genes
X carries 1000 genes

y determines the sex of the offspring
x genes have nothing to do with sex determination

y-linked disease are rare ( usually sperm defect)
X -most sex linked diseases are controlled by genes found on the X chromosome

Question 8

X linked recessive disorders affect what sex more? Why?

Answer 8

males
Males express all disorders found on the X ( whether dominant or recessive) chromosome because they do not have a backup X chromosome to compensate or mask/ or a dominant allele to code for a functional protein. In contrast a x linked disorder in a female is only expressed as a carrier because it has a extra X chromosome to compensate/mask/ be dominant.

A female must have a recessive allele on both x chromosomes for her to express the disease ( one from each parent)

Question 9

What type of allele causes most X-linked disorders

Answer 9

Recessive alleles cause most X-linked disorders in humans

Question 10

Why are most diseases in males inherited from their mothers

Answer 10

Because they express all their genes on the X chromosomes including disorders; and they inherited their X chromosome only from their mother

Question 11

What are probabilities of offsprings ( male and female) of heterozygou mother with x linked recessive disorder

Answer 11

When this mother has children each son has a 50 % chance of being affected, while daughters have 50 % chance of being a carrier

Question 12

Why is a female with a x- linked recessive disease only a carrier and not affected

Answer 12

She does not exhibit symptoms because her dominant allele encodes for a functional form of that protein

Question 13

the most common way to transmit any x- linked recessive allele

Answer 13

with a heterozygous carrier mother and a normal male

Question 14

X - INACTIVATION

Answer 14

where cells balance the inequality relative to male of have duplicate X’s by shutting off one x in each cell

Question 15

When does INACTIVATION OCCUR

Answer 15

early in embryonic development

Question 16

Why are x linked dominant disorders less severe in females than in males

Answer 16

Because of x-chromosome inactivation a heterozygous female will only express the decease in some of her cells, unlike males she express the disease in every cell.

Question 17

What determines a person’s sex?

Answer 17

Sex determination is the factor (genetic or environmental) that decides if an organism is male or female.

Question 18

What is the role of the SRY gene in sex determination

Answer 18

In human sex determination, the Y chromosome’s SRY gene encodes a protein that acts as a master switch. The SRY protein turns on other genes, which direct the undeveloped testes to secrete the male sex hormone testosterone. SRY also turns on a gene encoding a protein that causes embryonic female structures to disassemble. If a functional SRY gene is not present, an embryo will develop as a female.

Question 19

. Why do males and females express recessive X-linked alleles differently?

Answer 19

Each female has a pair of X chromosomes, whereas a male has only one X chromosome. Any trait a male has on its X chromosome will be expressed. Recessive alleles on an X chromosome of a female may be masked by dominant alleles on its homologous X chromosome.

Question 20

Why does X inactivation occur in female mammals?

Answer 20

X inactivation happens to one of the two copies of a gene on the homologous X chromosomes. Only females have two copies of the X chromosome.

Question 21

Whay are x- linked dominant disorders typically less severe in females than in males

Answer 21

Thanks to X chromosome inactivation, a female who is heterozygous for san X-linked gene will only express the disease in only some of her genes. While an affected male will express the dominant allele in every cell

Question 22

2 be affected by a x linked gene

Answer 22

a female must be heterozygous dominant for the gene and carries homozygous recessive for for both alleels her genes
And male can either be dominate or recessive

Question 23

What determines a person’s sex?

Answer 23

Sex determination is the factor (genetic or environmental) that decides if an organism is male or female.

Question 24

What is the role of the SRY gene in sex determination?

Answer 24

In human sex determination, the Y chromosome’s SRY gene encodes a protein that acts as a master switch. The SRY protein turns on other genes, which direct the undeveloped testes to secrete the male sex hormone testosterone. SRY also turns on a gene encoding a protein that causes embryonic female structures to disassemble. If a functional SRY gene is not present, an embryo will develop as a female.

Question 25

Why do males and females express recessive X-linked alleles differently

Answer 25

Each female has a pair of X chromosomes, whereas a male has only one X chromosome. Any trait a male has on its X chromosome will be expressed. Recessive alleles on an X chromosome of a female may be masked by dominant alleles on its homologous X chromosome.

Question 26

Why does X inactivation occur in female mammals

Answer 26

X inactivation happens to one of the two copies of a gene on the homologous X chromosomes. Only females have two copies of the X chromosome.