1. Human Genetics and Pedigrees Honors Biology Ms. Day
Lecture #31
Human Genetics and
Pedigrees
Honors Biology
Ms. Day

2. Many human traits follow Mendelian patterns of inheritance
Humans are not convenient subjects for genetic research
However, the study of human genetics continues to advance
We use pedigrees!

3. Pedigree Analysis A pedigree
family tree  describes relationships & inheritance btw parents & children across generations
Can also be used to make predictions about future offspring

4. Inheritance patterns of particular traits can be traced and described using pedigreesWw ww WW or
First generation
(grandparents)
Second generation
(parents plus aunts
and uncles)
Third
generation
(two sisters) Ff ff
FF or Ff FF
Widow’s peak
No Widow’s peak
Attached earlobe
Free earlobe
(a) Dominant trait (widow’s peak)
(b) Recessive trait (attached earlobe)
Figure A, B

8. Recessively Inherited Disorders
Many genetic disorders are inherited in recessive manner
Show up only in individuals homozygous for the alleles
Carriers (only for RECESSIVE TRAITS)
Are heterozygous individuals, who carry recessive allele but are show “normal” phenotype

9. Cystic Fibrosis Example of recessive autosomal disorder
Affect mostly Caucasian people of (European descent)
Deletion of codon  mutated NaCl channel protein in membrane
Symptoms
Mucus buildup in internal organs (lungs)
Abnormal absorption of nutrients in small intestine

10. Sickle-Cell Disease Another recessive autosomal disorder
Affects mostly African-Americans
caused by point mutation in hemoglobin gene  protein in red blood cells
Symptoms
Physical weakness, pain, organ damage and even paralysis

11. Achondroplasia Autosomal dominant disorder
Form of dwarfism lethal when homozygous for the dominant allele
AA= die
Aa= dwarf
aa= normal height

12. Another Autosomal Dominant Disorder
Huntington’s disease (HD)
degenerative disease of nervous system (brain tissue breaks down)
No obvious phenotypic effects until about 35 to 40 years of age HD
Normal

13. Nondisjunction of sister chromatids in meiosis II
Figure 15.12a, b
Meiosis I
Nondisjunction
Meiosis II
Gametes
n + 1
n  1
n – 1
n –1 n
Number of chromosomes
Nondisjunction of homologous
chromosomes in meiosis I
Nondisjunction of sister
chromatids in meiosis II
(a)
(b)

14. Disorders from Nondisjunction
Down syndrome
Results with an extra chromosome 21
trisomy 21
Other disorders:
Klinefelter’s XXY
Turner’s XO
Edward’s 18th
Patau Syndrome 13th

15. Genetic Testing and Counseling
Genetic counselors
provide information to prospective parents concerned about a family history for a specific disease

16. Tests for Identifying Carriers
For many diseases
Tests are available that identify carriers and help define the odds (probabilities) more accurately
Examples
Tay Sachs, HD & CF

17. Can make karyotypes, too!
Fetal Testing
In amniocentesis
The liquid that bathes fetus is removed & tested
In chorionic villus sampling (CVS)
A sample of the placenta is removed and tested
Can make karyotypes, too!

18. Newborn Screening Some genetic disorders can be detected at birth
Simple tests are now routinely performed in most hospitals in the United States
Example- PKU test