1. recessive

2. recessive Sickle-Cell Disease
Sickle-cell disease affects one out of 400 African-Americans
The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells
Symptoms include physical weakness, pain, organ damage, and even paralysis
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

4. Distribution of....
Malaria
Sickle Cell Gene

5. Heterozygous phenotype same as that of homo- zygous dominant PP Pp
Fig. 14-UN2
Degree of dominance
Description
Example
Complete dominance
of one allele
Heterozygous phenotype
same as that of homo-
zygous dominant PP Pp
Incomplete dominance
of either allele
Heterozygous phenotype
intermediate between
the two homozygous
phenotypes
CRCR
CRCW
CWCW
Codominance
Heterozygotes: Both
phenotypes expressed
IAIB
Multiple alleles
In the whole population,
some genes have more
than two alleles
ABO blood group alleles
IA , IB , i
Pleiotropy
One gene is able to
affect multiple
phenotypic characters
Sickle-cell disease

6. polydactyly Frequency of Dominant Alleles
Dominant alleles are not necessarily more common in populations than recessive alleles
For example, one baby out of 400 in the United States is born with extra fingers or toes
                              
Photos: eHand.com
(the electronic textbook for hand surgery)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

7. Blood Typing Problem

8. Concept 15.2: Sex-linked genes exhibit unique patterns of inheritance
In humans and some other animals, there is a chromosomal basis of sex determination
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

9. Females are XX, and males are XY
Each ovum contains an X chromosome, while a sperm may contain either an X or a Y chromosome
Other animals have different methods of sex determination
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

10. Inheritance of Sex-Linked Genes
The sex chromosomes have genes for many characters unrelated to sex
A gene located on either sex chromosome is called a sex-linked gene
In humans, sex-linked usually refers to a gene on the larger X chromosome
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

11. Sex-linked genes follow specific patterns of inheritance
For a recessive sex-linked trait to be expressed
A female needs two copies of the allele
A male needs only one copy of the allele
Sex-linked recessive disorders are much more common in males than in females
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

12. Fig. 15-5 X
Figure 15.5 Human sex chromosomes Y

14. Barr body – an inactivated X chromosome in each of a female’s diploid cells.

15. Correlating Behavior of a Gene’s Alleles with Behavior of a Chromosome Pair
In one experiment, Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type)
The F1 generation all had red eyes
The F2 generation showed the 3:1 red:white eye ratio, but only males had white eyes
Morgan determined that the white-eyed mutant allele must be located on the X chromosome
Morgan’s finding supported the chromosome theory of inheritance
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

16. The Chromosomal Basis of Sex
In humans and other mammals, there are two varieties of sex chromosomes: a larger X chromosome and a smaller Y chromosome
Only the ends of the Y chromosome have regions that are homologous with the X chromosome
The SRY gene on the Y chromosome codes for the development of testes
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

17. Fig b
Sex-linked recessive

18. Hemophilia Sex-linked recessive
pingrybiology.pbwiki.com
Hemophilia is a rare, inherited bleeding disorder in which blood doesn’t clot normally. People with hemophilia may bleed for a longer time than others after an injury. Individuals with the disorder may bleed internally, especially in knees, ankles, and elbows. This bleeding can damage organs or tissues and, sometimes, be fatal.

19. Hemophilia & The Royal Family
The European Royal Family
                                                                                                                                                                       
back

20. Photo: www.freewebs.com/georgeromanov/Foto%201913.jpg

21. Color Blindness
some forms are
Sex-linked

22. Fig