Upload
whitney-norman
View
223
Download
0
Tags:
Embed Size (px)
Citation preview
Fig. 15-6a
(a) The X-Y system
46 XY
46 XXParents
46 XY
46 XX
23 X
23 X
23 Y
or
or
Sperm Egg
+
Zygotes (offspring)
HELP! I need genes!
Meiosis & Fertilization
Fig. 13-8
Prophase I Metaphase I Anaphase I Telophase I andCytokinesis
Prophase II Metaphase II Anaphase II Telophase II andCytokinesis
Centrosome(with centriole pair)
Sisterchromatids Chiasmata
Spindle
Homologouschromosomes
Fragmentsof nuclearenvelope
Centromere(with kinetochore)
Metaphaseplate
Microtubuleattached tokinetochore
Sister chromatidsremain attached
Homologouschromosomesseparate
Cleavagefurrow
Sister chromatidsseparate Haploid daughter cells
forming
Phases of Meiosis
Fig. 13-UN1
Prophase I: Each homologous pair undergoessynapsis and crossing over between nonsisterchromatids.
Metaphase I: Chromosomes line up as homolo-gous pairs on the metaphase plate.
Anaphase I: Homologs separate from each other;sister chromatids remain joined at the centromere.
Fig. 13-UN2
F
H
The point of Meiosis I
is to separatehomologous pairs
Fig. 13-UN4
Meiosis Video
Changes of chromosome number or structure cause some genetic disorders
• Large-scale chromosomal alterations often lead to Spontaneous abortions (miscarriages) or cause a variety of developmental disorders
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Abnormal Chromosome Number
• In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosis
• As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 15-13-1
Meiosis I
(a) Nondisjunction of homologous chromosomes in meiosis I
(b) Nondisjunction of sister chromatids in meiosis II
Nondisjunction
Fig. 15-13-2
Meiosis I
Nondisjunction
(a) Nondisjunction of homologous chromosomes in meiosis I
(b) Nondisjunction of sister chromatids in meiosis II
Meiosis II
Nondisjunction
Fig. 15-13-3
Meiosis I
Nondisjunction
(a) Nondisjunction of homologous chromosomes in meiosis I
(b) Nondisjunction of sister chromatids in meiosis II
Meiosis II
Nondisjunction
Gametes
Number of chromosomes
n + 1 n + 1 n + 1n – 1 n – 1 n – 1 n n
• Aneuploidy results from the fertilization of gametes in which nondisjunction occurred
• Offspring with this condition have an abnormal number of a particular chromosome
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• A monosomic zygote has only one copy of a particular chromosome
• A trisomic zygote has three copies of a particular chromosome
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Patau Syndrome (Trisomy 13)
Patau Syndrome (Trisomy 13)• cleft palate• fetuses with this condition rarely to go to term• so it occurs in only 1 in 6000 live births • It is rare for babies to survive for very long if
liveborn because of the multitude of anomalies • atrial septal defect • inguinal hernia• polydactyly of hands and feet• Sometimes cyclopia or absence of eyes
Edward Syndrome (Trisomy 18)• Sometimes due to translocation• Survival rate of Edwards Syndrome is very low • Approximately 95% die in utero. • Of liveborn infants, only 50% live to 2 months, and only 5–10% will survive
their first year of life. • The median life span is five to fifteen days• One percent of children born with this syndrome live to age ten, typically in
cases of the less severe Edwards syndrome.• heart defects at birth • intestines protruding outside the body• Feeding and breathing difficulties• Microcephaly• Clenched fists
• Polyploidy is a condition in which an organism has more than two complete sets of chromosomes– Triploidy (3n) is three sets of chromosomes– Tetraploidy (4n) is four sets of chromosomes
• Polyploidy is common in plants, but not animals• Polyploids are more normal in appearance than
aneuploids
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
polyploidy
Fig. 15-14
Alterations of Chromosome Structure
• Breakage of a chromosome can lead to four types of changes in chromosome structure:– Deletion removes a chromosomal segment– Duplication repeats a segment– Inversion reverses a segment within a chromosome– Translocation moves a segment from one
chromosome to another
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 15-15
DeletionA B C D E F G H A B C E F G H(a)
(b)
(c)
(d)
Duplication
Inversion
Reciprocaltranslocation
A B C D E F G H
A B C D E F G H
A B C D E F G H
A B C B C D E F G H
A D C B E F G H
M N O C D E F G H
M N O P Q R A B P Q R
Fig. 15-17
Normal chromosome 9
Normal chromosome 22
Reciprocaltranslocation Translocated chromosome 9
Translocated chromosome 22(Philadelphia chromosome)
Disorders Caused by Structurally Altered Chromosomes
• The syndrome cri du chat (“cry of the cat”), results from a specific deletion in chromosome 5
• A child born with this syndrome is mentally retarded and has a catlike cry; individuals usually die in infancy or early childhood
• Certain cancers, including chronic myelogenous leukemia (CML), are caused by translocations of chromosomes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Human Disorders Due to Chromosomal Alterations
• Alterations of chromosome number and structure are associated with some serious disorders
• Some types of aneuploidy appear to upset the genetic balance less than others, resulting in individuals surviving to birth and beyond
• These surviving individuals have a set of symptoms, or syndrome, characteristic of the type of aneuploidy
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Down Syndrome (Trisomy 21)
• Down syndrome is an aneuploid condition that results from three copies of chromosome 21
• It affects about one out of every 700 children born in the United States
• The frequency of Down syndrome increases with the age of the mother, a correlation that has not been explained
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 15-16a
Fig. 15-16b
Autosomes arePairs 1-22
Sex chromosomes-XX
Click on photo:
Click on microscope
click on diagram
Aneuploidy of Sex Chromosomes
• Nondisjunction of sex chromosomes produces a variety of aneuploid (or abnormal # of chromosomes) conditions
• Klinefelter syndrome is the result of an extra chromosome in a male, producing XXY individuals
• Monosomy X, called Turner syndrome, produces X0 females, who are sterile; it is the only known viable monosomy in humans
• TOTAL # of chromosomes ????
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
•1 out of every 2,000-2,500 female live births •Almost all (95%) have
•Short stature •Loss of ovarian function
•Caused by the absence of a set of genes from the short arm of one X chromosome •Single X chromosome
•75-80% single X is contributed by mother •X-O = Female (Turner Syndrome) •X-X-Y=Male (Klinefelter Syndrome)
•Hearing loss due to otosclerosis is common in adults
•Appearance •Short stature
•Absent adolescent growth spurt •Average adult height is 4 feet 8 inches •Loss of SHOX gene necessary for growth of long bones
•Short fingers (4th metacarpal)
Turner’s Syndrome
Click on photo→