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Klinefelter Syndrome
- 47, XXY
- genetalia and internal ducts male
- testes underdeveloped; no sperm.
- feminine sexual development is not entirely suppressed resulting in slight breast enlargement
- 2/1000 male births
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Turner Syndrome
- 45, X
- female external genetalia and internal ducts
- rudimentary ovaries
- short (<5 ft tall)
- webbed neck
- broad, shield-like chest
- 1/3000 female births
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47, XXX Syndrome
- frequency 1/1200 female births
- highly variable in expression; some individuals are normal while others exhibit underdeveloped secondary sexual characters, sterility, and mental retardation.
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Why does it matter if there are extra X chromosomes?
- disrupts the balance of genetic info
- too much gene product
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Jacob Syndrome
- 47, XYY
- studied by Patricia Jacobs in 1935
- studied Scottish inmates in max security prison
- "criminal phenotype"
- in 1974, Walzer and Gerald wanted to follow XYY individual through lives but pressured to drop study
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5th week of gestation
gonadal primordial tissue arises as a pair of ridges associated with each embryonic kidney
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1. Wolffian
2. Mullerian ducts
- 1. undifferentiated male ducts
- 2. undifferentiated female ducts
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7th week of gestation
- if the cells of the genital ridge have the XY constitution, development of the medullary region into testis is initiated
- if no Y-chromosome, the cortex forms ovarian tissue
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12th week of gestation for females
the oogonia within the ovaries begin meiosis and primary ooccytes can be detected
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25th week of gestation (females)
all oocytes become arrested in meiosis and remain dormant until puberty
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Primary spermatocytes produced
when males reach puberty
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Hermaphrodites
- true ones are rare
- less extreme cases occur up to 2% of the time
- about 30 genetic and hormonal conditions can result in this
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PAR
- Pseudoautosomal regions on Y-Chromosome
- shares homology with the x-chromosome
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NRY
- Nonrecombining Region on y-chromosome
- 20 genes
- 12 genes fall into two groups: 5 have homologs and are expressed in a wide range of tissues, 7 lack x-homologs and are expressed only in testis.
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SRY
- Sex determining region of the Y-chromosome
- this area encodes Testis Determining Factor
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TDF
- Testis Determining Factor
- genes responsible for triggering undifferentiated gonadal tissue of the embryo to form testis
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Sex Ratio
the actual proportion of male to female offspring
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Primary Sex Ratio
reflects the proportion of males to females conceived in the population
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Secondary Sex Ratio
reflects the proportion of males to females born in a popultion
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In US, fetal mortality was higher in which sex according to a 1948 study?
males
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What is the general sex ration in US Caucasians according to recent studies?
1.2-1.6
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Barr and Bertram
worked with interphase nerve cells of cats and found dark staining body against nuclear envelope in females but not males
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Barr Body
- inactivated X-chromosome
- provided a mechanism for dosage compensation of X-linked genes
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Lyon and Russell
- studied X-chromosome deactivation
- found it randomly inactivated different X-chromosomes
- found that it occurs early in embryonic development
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Lyon Hypothesis
Mammalian females are mosaics for all heterozygous x-linked traits
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Red-green color blindness
- support of Lyon hypothesis
- Hemizygous males fully color blind
- heterozygous females display mosaic retinas
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Anhidrotic ectodermal dysplasia
- supports Lyon hypothesis
- hemizygous males show absences of teeth, sparse hair growth, and lack of sweat glands.
- Heterozygous females reveal patches of tissues without sweat glands.
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Calico cats
supports Lyon hypothesis
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Mechanism of X-inactivation
- XIST (X-Inactive Specific Transcript) gene withing the XIC (X-inactivation Center)
- expressed only on chromosomes to be inactivated.
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Sex-determination in Drosophila
- Y-chromosome doesn't have male determining factors, but does contain info important to male fertility.
- some female determining factors are located on the X-chromosome.
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Genetic Balance Theory
- a threshold for maleness is reached when X:A is 1:2
- additional X alters this balance and results in femaleness
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Sxl: Sex-lethal
Master switch for activation of a least 4 regulatory genes in Drosophila
activated when X:A and results in female development - Mutations in Sxl mill female embryos but not males
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Dosage Compensation in Drosophila
- no x-chromosome inactivation
- Male X-linked genes are transcribed at twice the level compared to X-linked genes in females.
- Dosage compensation is regulated by at least 4 autosomal male specific lethal genes, controlled by Sxl.
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Euploid
complete haploid sets of chromosomes are present
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Aneuploid
organism gains of losses one or more chromosomes but not a complete haploid set
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Polyploid
3 or more complete haploid sets of chromosomes (Triploid - 3n, tetraploid = 4n, pentaploid = 5n, etc)
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Monosomy
- loss of a single chromosome
- reveals lethal recessive alleles
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Cri-du-chat
- 46, -5p
- partial monosomy in humans
- only a part of a chromosome is lost: SEGMENTAL DELETION
- loss of 1/2 short arm chromosome 5
- anatomical malformations (cardiac, gastrointestinal, abnormal development of glottis and larynx)
- size of deletion influences severity
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Down Syndrome
- trisomy 21
- 47, 21+
- usually due to nondisjunction during ovum formation
- shortened life expectansy (into their 50s)
- prone to respiratory disease, heart malformations, leukemia, and Alzheimer's disease.
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Patau Syndrome
- 47, 13+
- trisomy 13
- not mentally alert, cleft palage, polydactyly
- average life span 3 months
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Edward Syndrome
- trisomy 18
- 47, 18+
- small newborn
- elongated skulls
- webbed neck, congenital dislocation of hips, receding chim
- average survival time is 4 months with death usually caused by pneumonia or heart failure.
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Autopolyploid
each additional set of chromosomes is identical to parent species.
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Producing autopolyplods
- heat/cold shock during meiosis
- apply colchicine to somatic cells undergoing mitosis.
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Upland Cotton
- 26 pairs of chromosomes
- allotetraploid AADD
- hybrid between American and Asian coton
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Endopolyploidy
cells in normal diploid organism becomes polyploid through ENDOMITOSIS
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