science 300:31 april 2003 chromosome number error (aneuploidy) rose from 1-2% to 40% in mouse eggs!...
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Science 300:31 April 2003
Chromosome number error (aneuploidy) rose from 1-2% to 40% in mouse eggs!
Reason- bisphenol A (BPA), a component of plastic..
….. results in meiosis errors in mouse eggs normal
BPA treated
Meiosis
Environment-induced disruptions in meiosis
Chromosomes andHuman Genetics
Chapter 11
Chromosomes and CancerGenes on chromosomes drive ___________
__________ is uncontrolled cell division
Philadelphia Chromosome
•First abnormal chromosome to be associated with a cancer •Associated with a chronic ________
•Overproduction of white blood cells•Due to _____________________
Genes • Units of information about _______________
• Each has a particular __________
– Location on a _______________
•_______________ are identical in length, size, shape, and gene sequence
A CB
a cb
a cb
A CB
A CBA CB
a cba cb
a cba cb
A CBA CB
•Different __________ forms of a gene•Arise through _____________
Alleles
Fig. 11.4, p. 173
_______________- display of chromosomes
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20 21 22 XX (or XY)
Blood sample
1000X magnification
Sex Chromosomes• Discovered in late ______
• Mammals, fruit flies
– XX is _______, XY is _________
• In other groups XX is male, XY female
XX
XY
XX
XY
X X
Y
X XX
XY
XX
XY
XX
XY
XX
XY
X X
YY
XX
sex chromosome combinations possible in new individual
Y
X
YY
XX
sperm
X
X
X
X
eggs
Female germ cell Male germ cellSex determination
The Y Chromosome
• < ____ genes
• Includes ____ gene- dictates ______
phenotype
• > ______ genes• Most genes - _______ traits• Genes expressed in both males and females
The X Chromosome
Effect of YChromosome
10 weeks
Y present
Y absent
7 weeks
birth approaching
appearance of structuresthat will give rise toexternal genitalia
appearance of “uncommitted” duct system
of embryo at 7 weeks
Y present
Yabsent
testis
ovary
testes ovaries
• Thomas Hunt Morgan - first to associate a specific gene with a specific chromosome in the early 20th century.
• Morgan’s model-Drosophila melanogaster, a fruit fly - have three pairs of __________ and a pair of _____________ chromosomes (XX in females, XY in males).
Normal is called “_________”Red eyes White eyes
Non-normal is called “______”
• Morgan’s experiments-
Red eye X White eye
F1
3:1 Red:white
But- all __________were white, all females red
All Red eye
F2
Morgan concluded that a fly’s eye color was linked to the _ _____________ ___.
= _ _____ _
= _______ _
Know these symbols
Conclude- classic _ ________ _ genetics
Fig. 15.3
Chromosome- 1.5 x 108 base pairs containing about ______ genes
• Genes located on the same chromosome,___ ______ _______, tend to be inherited together because the chromosome is passed along as a unit.
Linked genes tend to be inherited together because they are located on the same chromosome
0.4% of a chromosome, containing 10 genes
15.3
15.215.1
14
13.3
13.11211
11.111.2
12
13.113.213.3
14
15
21
2223.1
23.3
31.131.231.3
3233.133.334
35.135.3
35.2
33.2
23.2
13.2
•Results of crosses with linked genes deviate from those expected according to __ _____________________ __.
Linkage Groups• Genes on one type of chromosome
• Fruit flies
– __ homologous chromosomes
– __ linkage groups
-____________to the distance that separates genes
A B C D
Crossing over will disrupt linkage between
_________ more often than _________
Crossover Frequency
Frequencies can be used to construct a _______________
Incomplete Linkage
Parents:
F1 offspring
Unequal ratios of four types of gametes:
All AaCc
x
meiosis, gamete formation
AC acA
C AC
AC
ac
ac
Ac
aC
ac
Most gametes have parental genotypes
A smaller number have recombinant genotypes
Linkage Mapping in Humans
• Chart that shows _____________ connections among individuals
• Knowledge of probability and Mendelian patterns used to suggest basis of a trait
Called a “________”
I
II
III
IV
V
I
II
III
IV
V
6 7
12
5,5 6,6
5,5 6,6
5,5 6,6
5,5 6,6
5,5 6,6
5,5 6,6
6,6 5,5
6,6 5,5
5,6 6,7
6,6 6,6*Gene not expressed in this carrier.*Gene not expressed in this carrier.
*
malefemale
Pedigree for __________
Unusual number of toes or fingers
Genetic Disorders
Autosomal _________
•_________ conditions that
cause mild to severe medical
problems
Autosomal __________
•Trait typically appears in _______ generation•Most of these ________ from population. WHY?
•Many people are _________•Heterozygous parents-- child will have a _____ chance of being affected
1. Huntington Disorder• Causes involuntary movements, nervous system
deterioration, death
• Symptoms don’t usually show up until person is past age ___
• People often pass allele on before they know they have it
Autosomal dominant diseases
•In homozygous form usually leads to _______• Heterozygotes display a type of _________• Have short arms and legs relative to other body parts
2. Acondroplasia
X-Linked Recessive Inheritance• Males show disorder
_________ females• Son _______ inherit
disorder from his father
1. Color blindness- 2. _________, Blood-clotting disorder; 1/7,000 males 3. ________- Allele has repeated segments of DNA; causes mental retardation4. ____________________ - Appears to be dominant; spontaneous mutation; premature aging effect, early death
Examples
Usually due to ________________
n + 1
n + 1
n - 1
n - 1chromosome alignments at metaphase I
nondisjunction at anaphase I
alignments at metaphase II anaphase II
The wrong number of chromosomes is bad
• Nondisjunction results in too many or to few chromosomes termed ______________ .– some gametes receive two of the same type of
chromosome and another gamete receives no copy.– _______ cells - three copies of a particular chromosome
type and have _______ total chromosomes.– _________ cells - one copy of a particular chromosome
type and have 2n - 1 chromosomes.
• Normally results in embryonic death, but some survive
Organisms with more than two _______ _sets of chromosomes, have undergone _________, e.g. 3n or 4n (rare in ____________)
• Polyploids are more nearly normal in phenotype than ___________.
Other chromosome problems
• An inversion - a chromosomal
fragment ________ to the original chromosome but in the reverse orientation.
• In_ _______, a chromosomal fragment joins a _________ chromosome.
Fig. 15.13c & d
•Some translocations are ___________ others are not.
A ________- a chromosome fragment lacking a ________ is lost during cell division
A ___________- a fragment becomes attached as an extra segment to a sister chromatid
• Homozygous embryos with a large ________ normally die
• A deletion in the X chromosome is _______ in males
• A __ ________________ can alter phenotype because a gene’s expression is influenced by its location.
Results of chromosome errors
Example- Leukemia is due to a growth gene being placed next to an active region resulting in cancer
• Approx. _____ of human embryos are aneuploid and die early in development
Some are viable-• Chromosome 15 trisomy- die at birth• Chromsome 21 trisomy- ________ syndrome
• Down syndrome- trisomy 21.– One in 700 children born in the United States.– result from ___________________ during
gamete production
Fig. 15.14• correlates with the age of the mother.
Karyotype
Phenotype
Extra sex chromosomes are allowed
• _____________________ _an XXY male, occurs once in every 2000 live births.
– Male sex organs, but are_ ________.
– Feminine characteristics; normal intelligence.
• Males with an extra Y chromosome (XYY) tend to somewhat _______ than average.
• Trisomy X (XXX), which occurs once in every 2000 live births, produces _ ________ _ females.
• Monosomy X or _____________ (X0), which occurs once in every 5000 births, produces phenotypic, but
immature females. • XYY and XXYY- males often found in _________.
• In utero testing for genetic screening. 1. _____________ - beginning at the 14th to 16th week of
pregnancy to assess the presence of a specific disease.Fig. 14.17a
•Fetal cells extracted from amniotic fluid are cultured and __________.
• 2. _____________ ________(CVS)- performed as early as the eighth to tenth week of pregnancy.
– Extracts a sample of fetal tissue from the chrionic villi of the placenta are karyotyped.
Fig. 14.17b
• Other techniques- ____________________________
allow fetal health to be assessed visually in utero.– usually reserved for cases in which the risk of
a genetic disorder or other type of birth defect is relatively great.
• If fetal tests reveal a serious disorder, the parents face the difficult choice of terminating the pregnancy or preparing to care for a child with a genetic disorder.