chapter 6 - matters of sex Flashcards
biological maleness or femaleness is determined at _____
conception
SRY gene
in mice, sex-determining region of Y chromosome
TDF gene
testis determining factor in humans, essential for male development
Wnt4 gene
essential for development / maturation as a biological female
mutations in Wnt4 cause
- XX females develop high levels of male sex hormones
- lack of development of vaginal canal and uterus
- ovaries do not develop properly
beta-catenin
induces ovary producing genes and blocks SRY (TDF)
heterogametic sex
males; have different sex chromosomes (XY)
homogametic sex
females; have the same sex chromosomes (XX)
how many genes in X chromosome
more than 1500 genes
the X chromosome is _______ than the Y chromosome
larger
X chromosome acts as a _____ to Y in males
homolog
how many genes are in the Y chromosome
more than 230 genes
Y chromosome does not _____ _____ along all of its length
cross over
the Y chromosome has many DNA segments that are _______ and may destabilize ___ ________
palindromes; DNA replication
Y chromosome anatomy
1 short arm, 1 long arm
pseudoautosomal regions of Y chromosome
PAR1 & PAR2
5% of the Y chromosome….
contains 63 genes shared with X chromosome that contribute to bone growth, cell division, etc
MSY
male specific region, most of the chromosome
MSY 3 classes of DNA sequences
1 - sequence almost identical to X chromosome. 2 - somewhat identical to X chromosome. 3 - palindromes
how many genes are in the MSY
22 genes
AZF gene
encodes a protein essential for producing sperm
AZF gene mutations cause
infertility
hermaphroditism
older/more general term for individual with male and female sexual structures
intersex
individuals whose internal structures are inconsistent with external structures or whose genitalia are ambiguous
pseudohermaphroditism
refers to the presence of both female/male structures but at different life stages
pseudohermaphroditism includes
- androgen insensitivity syndrome, 5-alpha reductase deficiency, congenital adrenal hyperplasia
androgen insensitivity syndrome
mutation on the X - chromosome blocks formation of androgen receptors
5-alpha reductase deficiency
unable to convert testosterone to DHT, child has inside male anatomy but looks like a girl on the exterior
congenital adrenal hyperplasia
enzyme block causes androgens to accumulate, and can cause precocious puberty in males or male secondary sex characteristics to develop in females
in normal male prenatal development, activation of a set of genes beginning with SRY sends signals that destroy _____ _____, while activating the biochemical pathway that produces ______ and ________ ,which promotes the development of male structures
female rudiments; testosterone; dihydrotestosterone
congenital adrenal hyperplasia results in excess ____ and ____
testosterone and dihydrotestosterone
androgen insensitivity syndrome and 5-alpha reductase deficiency lower levels of _____ _____
male hormones
same-sex attraction
person’s phenotype and genotype are consistent, but physical attraction is towards members of the same sex
sex ratio
calculated by number of males / number of females, multipled by 1000
primary sex ratio
at conception is 1000; equal
secondary sex ratio
at birth is 1050; Y bearing sperm weight lighter than X bearing sperm, so it could enter the oocyte faster
tertiary sex ratio
at maturity, doesn’t say what it is though
Y-linked traits
-genes on Y chromosome
-very rare
-transmitted from male to male
X-linked traits in females
passed like autosomal traits
X-linked traits in males
a single copy of an X-linked allele causes expression of the trait or illness
human male is considered _______ for X-linked traits
hemizygous
X-linked recessive trait is always expressed in _____
male
X-linked recessive trait is expressed in female _____ and very rarely in a female ______
homozygote; heterozygote
X-linked recessive traits - affected female inherits from…
affected father and affected or heterozygote mother
X-linked dominant trait is expressed in _____ in one copy
females
X-linked dominant traits have more severe effects in _____
males
X-linked dominant traits cause high rates of ______ due to early lethality in males
miscarriage
X-linked dominant traits are passed from male to all ______ but not to ___
daughters; sons
X-linked recessive trait is expressed in females if the allele is _____ _____ ___ ____
present in 2 copies
examples of X-linked recessive traits
ichthyosis, colorblindness, hemophilia
ichthyosis
enzyme deficiency blocks removal of cholesterol from skin cells
colorblindness
about 8% of males of european ancestry have the condition
hemophilia
disorder of blood-clotting
hemophilia B is an X-linked _____ disease that usually passes from a _____ woman to ______ daughters or ______ sons.
recessive; heterozygous; heterozygous; hemizygous
why are males that inherits x-linked dominant traits usually more severely affected?
he has no other allele to mask its effect
most cases of x-linked dominant traits are a result of ____ _______, rather than ____ ____ __ _____
new mutations; transmission from a parent
examples of x-linked dominant traits
rett syndrome, incontinentia pigment
sex-limited traits
traits that affect a structure or function that is present in only 1 sex
- could be autosomal or x-linked
sex-limited traits examples
- beard growth
- milk production
- preeclampsia in pregnancy
sex-influenced traits
allele is dominant in 1 sex but recessive in the other
- could be autosomal or x-linked
- difference in expression can be caused by hormonal differences between sexes
sex-influenced traits examples
pattern baldness in humans - heterozygous male is bald heterozygous female is not, response to treatment for glioblastoma - female patients live longer than male patients after surgery, radiation and use of a drug, temozolomide
X inactivation
balances the inequality of expression of genes on the X chromosome
XIST gene
encodes an RNA that binds to and inactivates the X chromosome
X inactivation occurs early in _____ _______
prenatal development
X inactivation alters the _____ and not the ____.
phenotype; genotype
barr body
inactive X chromosome
manifesting heterozygote
female that expresses the phenotype corresponding to an X-linked gene
X inactivation can be used to identify carriers of some X-linked disorders, such as
hunter syndrome, lesch-nyhan syndrome, affects the severity of rett syndrome
unequal x inactivation pattern can occur if…
the 2 X chromosomes have different alleles for a gene that controls cell division, giving certain cells a survival advantage
mechanisms of parent-of-origin effects
genomic imprinting
genomic imprinting
parental effect on gene expression is seen as diseases inherited from a parent
function of genomic imprinting
not super well understood, but may be a way to regulate abundance of key proteins in the embryo
imprinted genes are in ____ along a chromosome, controlled by ______ _____
clusters; imprinting centers
male genome controls _____ development, female genome controls ______ development
placenta; embryo
humans have ____ imprinted genes. at least ____ of them affect health if they are abnormally expressed
150+; 60
chromosome 15 deletion syndromes
prader-willi syndrome - inherited from father; angelman syndrome - inherited from mother
abnormal imprinting is associated with:
diabetes mellitus, autism, alzheimers, schizophrenia, male-male attraction
