Chapter 10.7 Flashcards

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1
Q

Autosomal diseases

A

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

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2
Q

The opposite of AUTOSOMAL DISEASES are

A

SEX- LINKED genes

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3
Q

SEX -LINKED GENES

A

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

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4
Q

XX

A

female

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5
Q

XY

A

male

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6
Q

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

A

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

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7
Q

the X chromosomes vs. Y and sex linked diseases

A

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

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8
Q

X linked recessive disorders affect what sex more? Why?

A

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)

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9
Q

What type of allele causes most X-linked disorders

A

Recessive alleles cause most X-linked disorders in humans

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10
Q

Why are most diseases in males inherited from their mothers

A

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

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11
Q

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

A

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

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12
Q

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

A

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

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13
Q

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

A

with a heterozygous carrier mother and a normal male

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14
Q

X - INACTIVATION

A

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

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15
Q

When does INACTIVATION OCCUR

A

early in embryonic development

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16
Q

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

A

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.

17
Q

What determines a person’s sex?

A

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

18
Q

What is the role of the SRY gene in sex determination

A

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.

19
Q

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

A

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.

20
Q

Why does X inactivation occur in female mammals?

A

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.

21
Q

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

A

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

22
Q

2 be affected by a x linked gene

A

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

23
Q

What determines a person’s sex?

A

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

24
Q

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

A

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.

25
Q

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

A

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.

26
Q

Why does X inactivation occur in female mammals

A

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.