1. Introduction to Genetics
Glencoe Chapters 10-11

3. Mendelian Genetics

6. Mendelian Genetics
Allele-an alternate form of a single gene passed on from generation to generation
Reside at the same locus on homologous chromosomes
One inherited from each parent
If two alleles differ, the one that determines
the organism’s appearance is the
dominant allele
The other allele is recessive
and has no effect on the
organism’s appearance.
Genotype: PP aa Bb
Heterozygous P a b B
Gene loci
Recessive allele
Dominant allele
Homozygous for the dominant allele
Homozygous for the recessive allele

7. Mendelian Genetics
Homozygous-having two of the same alleles for a particular trait
AA or aa
Heterozygous-having two different alleles for a particular trait Aa

8. Mendelian Genetics Genotype: an organism’s allele pairs
Phenotype: observable characteristic or outward expression of an allele pair

9. Mendelian Genetics
Law of segregation-two alleles for each trait separate during meiosis
Law of independent assortment-random distribution of alleles occurs during gamete formation

10. Mendelian Genetics
Monohybrid cross-involves hybrids for a single trait
Dihybrid cross-involves hybrids for two traits

11. Punnett Squares
Monohybrid cross

12. Punnett Squares
Dihybrid cross-four types of alleles from female gamete and four types of alleles from male gamete
The result is a 9:3:3:1 ratio

13. Punnett Squares The rule of multiplication
F1 genotypes
Bb female
Formation of eggs
F2 genotypes
Bb male
Formation of sperm B b 1 2 4
The rule of multiplication
Calculates the probability of two independent events
The rule of addition
Calculates the probability of an event that can occur in alternate ways

14. Gene Linkage and Polyploidy
Genetic recombination-new combination of genes produced by crossing over and independent assortment
Combinations of genes due to independent assortment can be calculated using the formula 2n, where n is the number of chromosome pairs.

15. Gene Linkage and Polyploidy
Genes that are located close together on the same chromosome are linked and usually travel together during gamete formation
Linked genes can separate during crossing over
Chromosome map-drawing showing sequence of genes on a chromosome

16. Gene linkage and Polyploidy
Polyploidy-occurrence of one or more extra sets of all chromosomes in an organism
Triploid organism 3n
Many flowering plants are polyploid

17. Basic Patterns of Human Inheritance
Parents
Offspring
Sperm
Normal Dd 
D d
Eggs D d DD
(carrier) dd
Deaf
Recessive Genetic Disorders
Disorder that occurs when an organism is homozygous recessive
Carrier-an individual who is heterozygous for a recessive disorder
Cystic fibrosis, albinism, Tay-Sachs disease

18. Basic Patterns of Human Inheritance
Dominant Genetic Disorders
Huntington’s disease
Achondroplasia

19. Basic Patterns of Human InheritanceDd
Joshua
Lambert
Abigail
Linnell
D ?
John
Eddy
Hepzibah
Daggett dd
Jonathan
Elizabeth
Dd Dd dd Dd Dd Dd dd
Female Male
Deaf
Hearing
Pedigree-diagram that traces the inheritance of a particular trait through several generations

20. Basic Patterns of Human Inheritance
Solving Pedigrees

21. Complex Patterns of Inheritance
P generation
F1 generation
F2 generation
Red RR
Gametes 
White rr
Sperm
Eggs
Pink Rr R r rR 1 2
Incomplete Dominance- heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes

22. Complex Patterns of Inheritance
Codominance-both alleles are expressed in the heterozygous condition
Sickle cell disease-affects ability to carry oxygen
heterozygous individuals have both sickle shaped and normal shaped cells
High levels of sickle cell in Africa where malaria is prevalent because those who are heterozygous have higher resistance to malaria

23. Complex Patterns of Inheritance
Multiple alleles-inheritance involving more than two forms of an allele
Blood groups in humans- alleles A and B are codominant
O-universal donor
AB-universal recipient

24. Complex Patterns of Inheritance
Epistasis-one allele hides the affect of another allele

25. Complex Patterns of Inheritance
Sex determination-XX or XY
X chromosome carries variety of genetics necessary for development of males and females
Y chromosome mainly has genes related to male development
X-inactivation-one of the X chromosomes in a female cell is inactivated
Completely random in each cell
Barr bodies-inactivated X chromosomes

27. Complex Patterns of Inheritance
Sex-linked traits-traits controlled by genes on X chromosome
Since males only have one X chromosome, they are affected by recessive X-linked traits more than females
Red-green color blindness
Hemophilia

29. Complex Patterns of Inheritance
P generation
F1 generation
F2 generation
Sperm
Eggs
aabbcc
(very light)
AABBCC
(very dark)
AaBbCc  1 8 64 6 15 20
Skin color
Fraction of population
Polygenic traits- phenotypic traits that arise from interaction of multiple pairs of genes

30. Complex Patterns of Inheritance
Environmental influences on phenotype
Sunlight and water
Temperature