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Karyotypes and Pedigrees

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1 Karyotypes and Pedigrees
HUMAN GENETICS Karyotypes and Pedigrees

2 Inheritance of Traits

3 Karyotypes Definitions Uses
Karyotype – a picture of an individual’s chromosomes. Karyotyping - A technique that uses a picture of an individual’s chromosomes to analyze and detect chromosomal abnormalities. To detect possible fetal abnormalities. Form of genetic screening conducted on potential parents.

4 Methods for Preparing a Karyotype
Individuals Fetus Pre-natal diagnosis Amniocentesis- a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amniotic sac surrounding a developing fetus, and the fetal DNA is examined for genetic abnormalities. (see diagram) 2. Chorionic villi sampling- entails sampling of the placental tissue and testing it for chromosomal abnormalities. Postnatal diagnosis White blood cell test

5 Making the Karyotype

6 Arrangement of a Karyotype
Humans have 23 pairs (46) of chromosomes 22 pairs of autosomes (body cells) 1 pair of sex chromosomes – which determine the sex of the individual Females are XX; males are XY Arranged by size from largest to smallest 1 pair of homologous chromosomes at each site

7 Types of Chromosome Abnormalities
Nondisjunction – failure of homologous pairs of chromosomes to separate during meiosis. Results in trisomy – 3 chromosomes instead of a pair at a given site. Deletion – missing segment of a chromosome. monosomy – missing a whole chromosome Translocation – segment of one chromosome is attached to another chromosome. Crossing over – exchange of parts between two homologous chromosomes. Inversion – genes switch loci (places) on a chromosome. Syndrome – a group of symptoms.

8 Normal Male(46,XY)

9 Normal Female (46,XX)

10 Down’s Syndrome

11 Edward’s Syndrome

12 Patau’s Syndrome


14 Turner Syndrome (45,XO)

15 Cri du chat Syndrome (partial deletion of chromosome 5)

16 Try this one


18 15:21 Translocation

19 Incidence of Chromosomal Abnormalities by Mother’s Age
Incidence per 1000 births 20 1.9 25 2.1 30 2.5 35 4.9 40 13.7 45+ 43.4

20 Incidence of Trisomy 21 by Mother’s Age
Incidence per 1000 births 20 0.6 25 0.8 30 1.1 35 2.7 40 9.2 45+ 30.8

21 Classification of Genetic Disorders
Single Gene Defect Autosomal dominant Autosomal recessive X-linked dominant X-linked recessive Chromosomal Abnormalities Number Structure Multifactorial Defects

22 Pedigree Charts

23 Carriers – individuals that have the gene for a trait but do not have the condition; heterozygous

24 Patterns of Inheritance
Autosomal Dominant Does not skip generations Affects males and females equally Approximately ½ the offspring of a person with the trait will be affected The affected person is usually heterozygous 2. Autosomal Recessive Both parents and grandparents of an affected person are usually normal. ¼ of the siblings of an affected person will also be affected. Affects males and females equally.

25 Patterns of Inheritance
3. X-linked Dominant Affects females more than males Affected males have no normal daughters and no affected sons Affected females who are homozygous transmit the trait to all children Does not skip generations 4. X-linked Recessive Skips generations Affects males more than females Trait is transmitted by “carrier” females An affected male will pass the carrier status to all of his daughters so ½ of their sons will be affected.

26 X-linked Inheritance Genes on the X chromosome have no counterpart on the Y chromosome, therefore, characteristics determined by a gene on the X chromosome are always expressed in males.

27 How many males are affected?
How many females are affected? What is the pattern of inheritance?

28 Pattern of inheritance?



31 Genotypes of certain individuals?

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