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Chromosomes & Human Heredity

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Presentation on theme: "Chromosomes & Human Heredity"— Presentation transcript:

1 Chromosomes & Human Heredity
Chapter 11 p

2 Human Karyotype A karyotype is a pictorial display of human chromosomes Used to determine abnormalities

3 Images of chromosomes stained during metaphase
Section 3 Complex Inheritance and Human Heredity Chromosomes and Human Heredity Karyotype Studies Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size. Images of chromosomes stained during metaphase Chromosomes are arranged in decreasing size to produce a micrograph.

4 Telomeres Telomere caps consist of DNA associated with proteins.
Serves a protective function for the structure of the chromosome

5 • The short arm of chromosome is the “p” arm
• The long arm is the “q” arm • The specific place on a chromosome where a gene /trait is found is called locus (loci) Banning patterns- Staining shows us the different light and dark areas on the chromosomes where genes are located

6 The resulting gametes will not have the correct number of chromosomes
Section 3 Complex Inheritance and Human Heredity Nondisjunction Nondisjunction occurs when either homologues fail to separate during anaphase I of meiosis, or sister chromatids fail to separate during anaphase II. The result is that one gamete has 2 copies of one chromosome and the other has no copy of that chromosome The resulting gametes will not have the correct number of chromosomes It can result in extra copies of a certain chromosome or only one copy of a particular chromosome


8 Having a set of 3 chromosome of one kind is called Trisomy, one extra chromosome (2n+1)
Having only one of a particular type of chromosome is called Monosomy, cell has one missing chromosome (2n-1)

9 The frequency of nondisjunction is quite high in humans, but the results are usually so devastating to the growing zygote that miscarriage occurs very early in the pregnancy. If the individual survives, he or she usually has a set of symptoms - a syndrome - caused by the abnormal dose of each gene product from that chromosome.

10 Human disorders due to chromosome alterations in autosomes (Chromosomes 1-22). There only 3 trisomies that result in a baby that can survive for a time after birth; the others are too devastating and the baby usually dies in utero

11 Down Syndrome Also called trisomy 21
It is the result of an extra chromosome 21 Characteristics are, distinctive facial features, short stature, heart defects, and mental disablitlies. Approximately 1 out of 800 children are born with down syndrome in the United States. It increases with a mothers age

12 Patau syndrome (trisomy 13): serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months.

13 Edward's syndrome (trisomy 18): almost every organ system affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months.

14 Nondisjunction occurs in both autosomes and sex chromosomes
Section 3 Complex Inheritance and Human Heredity Nondisjunction occurs in both autosomes and sex chromosomes

15 Klinefelter syndrome: 47, XXY males
Klinefelter syndrome: 47, XXY males. Male sex organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence.

16 Monosomy X (Turner's syndrome): 1:5000 live births; the only viable monosomy in humans - women with Turner's have only 45 chromosomes!!! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)


18 47, XYY males: Individuals are somewhat taller than average and often have below normal intelligence. Trisomy X: 47, XXX females. 1:1000 live births - healthy and fertile - usually cannot be distinguished from normal female except by karyotype

19 Alterations in chromosome structure
Deletion: a portion of one chromosome is lost during cell division. That chromosome is now missing certain genes. When this chromosome is passed on to offspring the result is usually lethal due to missing genes.

20 Example - Cri du chat (cry of the cat): A specific deletion of a small portion of chromosome 5; these children have severe mental retardation, a small head with unusual facial features, and a cry that sounds like a distressed cat

21 Duplication: if the fragment joins the homologous chromosome, then that region is repeated

22 Example - Fragile X: the most common form of mental retardation
Example - Fragile X: the most common form of mental retardation. The X chromosome of some people is unusually fragile at one tip - seen "hanging by a thread" under a microscope. Most people have 29 "repeats" at this end of their X-chromosome, those with Fragile X have over 700 repeats due to duplications. Affects 1:1500 males, 1:2500 females.

23 Translocation: a fragment of a chromosome is moved ("trans-located") from one chromosome to another - joins a non-homologous chromosome. The balance of genes is still normal (nothing has been gained or lost) but can alter phenotype as it places genes in a new environment. Can also cause difficulties in egg or sperm development and normal development of a zygote. Acute Myelogenous Leukemia is caused by this translocation:

24 Inversion- occurs when a chromosmal fragment reattached to the original chromosome but in the reverse orientation.

25 Fetal Testing Has risk and benefits Test Benefit Risk Amniocentesis
Diagnosis of chromosome abnormalities Diagnosis of other defects Discomfort Slight risk of infection Risk of miscarriage Chronic villus sampling Diagnosis of certain genetic defects Risk of infection Risk of newborn limb defects Fetal blood sampling Checks for blood problems and oxygen levels Medications can be given to the fetus before birth Risk of bleeding from sample site Amniotic fluid might leak Risk of fetal death

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