Chapter 10.7 Flashcards
Autosomal diseases
are diseases that are controlled by autosomal genes ( affect both sexes equally
eg. Huntington disease, cystic fibrosis
The opposite of AUTOSOMAL DISEASES are
SEX- LINKED genes
SEX -LINKED GENES
produce phenotypes that affect one sex over the other the other. These genes/alleles are found on the sex chromosomes only
XX
female
XY
male
Why does the Y chromosome play a larger part in sex determination
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
the X chromosomes vs. Y and sex linked diseases
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
X linked recessive disorders affect what sex more? Why?
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)
What type of allele causes most X-linked disorders
Recessive alleles cause most X-linked disorders in humans
Why are most diseases in males inherited from their mothers
Because they express all their genes on the X chromosomes including disorders; and they inherited their X chromosome only from their mother
What are probabilities of offsprings ( male and female) of heterozygou mother with x linked recessive disorder
When this mother has children each son has a 50 % chance of being affected, while daughters have 50 % chance of being a carrier
Why is a female with a x- linked recessive disease only a carrier and not affected
She does not exhibit symptoms because her dominant allele encodes for a functional form of that protein
the most common way to transmit any x- linked recessive allele
with a heterozygous carrier mother and a normal male
X - INACTIVATION
where cells balance the inequality relative to male of have duplicate X’s by shutting off one x in each cell
When does INACTIVATION OCCUR
early in embryonic development
Why are x linked dominant disorders less severe in females than in males
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.
What determines a person’s sex?
Sex determination is the factor (genetic or environmental) that decides if an organism is male or female.
What is the role of the SRY gene in sex determination
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.
. Why do males and females express recessive X-linked alleles differently?
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.
Why does X inactivation occur in female mammals?
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.
Whay are x- linked dominant disorders typically less severe in females than in males
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
2 be affected by a x linked gene
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
What determines a person’s sex?
Sex determination is the factor (genetic or environmental) that decides if an organism is male or female.
What is the role of the SRY gene in sex determination?
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.
Why do males and females express recessive X-linked alleles differently
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.
Why does X inactivation occur in female mammals
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.
