1. Lecture # 6 Date _________
Chapter 14~ Mendel & The Gene Idea

2. Mendelian genetics Character (heritable feature, i.e., fur color)
Trait (variant for a character, i.e., brown)
True-bred (all offspring of same variety)
Hybridization (crossing of 2 different true-breds)
P generation (parents)
F1 generation (first filial generation)

3. Leading to the Law of Segregation
Alternative versions of genes (alleles) account for variations in inherited characteristics
For each character, an organism inherits 2 alleles, one from each parent
If the two alleles differ, then one, the dominant allele, is fully expressed in the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance
The alleles for each character segregate (separate) during gamete production (meiosis).
Mendel’s Law of Segregation

4. Genetic vocabulary…….
Punnett square: predicts the results of a genetic cross between individuals of known genotype
Homozygous: pair of identical alleles for a character
Heterozygous: two different alleles for a gene
Phenotype: an organism’s traits
Genotype: an organism’s genetic makeup
Testcross: breeding of a recessive homozygote X dominate phenotype (but unknown genotype)

5. The Law of Independent Assortment
Law of Segregation involves 1 character. What about 2 (or more) characters?
Monohybrid cross vs. dihybrid cross
The two pairs of alleles segregate independently of each other.
Mendel’s Law of Independent Assortment

6. Non-single gene genetics, I
Incomplete dominance: appearance between the phenotypes of the 2 parents. Ex: snapdragons
Codominance: two alleles affect the phenotype in separate, distinguishable ways Ex: Tay-Sachs disease
Multiple alleles: more than 2 possible alleles for a gene Ex: human blood types

7. What is the difference between incomplete and codominance?
Incomplete-heterozygous phenotype that “appears” to be a blend of both homozygotes. (pink flowers)
Codominance-heterozygote that equally expresses the traits from both alleles. (flowers with some red and white)

9. P Generation Red White CRCR CWCW Gametes CR CW Pink F1 Generation CRCW
Fig
P Generation
Red
White
CRCR
CWCW
Gametes CR CW
Pink
F1 Generation
CRCW
Gametes
1/2 CR
1/2 CW
Sperm
1/2 CR
1/2 CW
F2 Generation
1/2 CR
CRCR
CRCW
Eggs
1/2 CW
CRCW
CWCW

10. Human Blood Types Human blood types come from 3 different alleles.
Codominance and multiple alleles
Ia, Ib, I
Ia and Ib are codominant and produce an antigen (protein)
i-no antigen
Genotype-Ia,i=A blood type
Genotype Ib, i=B blood type
Genotype ii=O blood type
Book pg 205

12. Red blood cell appearance Phenotype (blood group)
Fig
Allele
Carbohydrate IA A IB B i
none
(a) The three alleles for the ABO blood groups
and their associated carbohydrates
Red blood cell
appearance
Phenotype
(blood group)
Genotype
IAIA or IA i A
IBIB or IB i B
IAIB AB ii O
(b) Blood group genotypes and phenotypes

13. Human Blood Types Genotype-Ia,i=A blood type
Genotype Ib, i=B blood type
Genotype ii=O blood type
Genotype Ia,Ib=AB blood type
Book pg 205
Donors-

14. Non-single gene genetics, II
Pleiotropy: genes with multiple phenotypic effect. Ex: sickle-cell anemia
Epistasis: a gene at one locus (chromosomal location) affects the phenotypic expression of a gene at a second locus. Ex: mice coat color
Polygenic Inheritance: an additive effect of two or more genes on a single phenotypic character Ex: human skin pigmentation and height

15. Pleiotropy Genes have multiple phenotypic effects.
Pea plants-the gene that effects flower color also affects the color of the seed coating.

16. Polygenic Traits
Human skin color result of four genes that interact to produce a color range.
Eye color-blue, green, brown-still do not know all genes used in eye color.

17. Epistasis
Expression of one gene can interfere with the expression of other genes.
Fur color in mammals-2 genes give general color, 2 genes give shading
5th gene-interfers with the expression of other genes (albinism)

18. Human disorders The family pedigree
Recessive disorders: •Cystic fibrosis •Tay-Sachs •Sickle-cell
Dominant disorders: •Huntington’s
Achondroplasia
Testing: •amniocentesis •chorionic villus sampling (CVS)

19. (b) Is an attached earlobe a dominant or recessive trait?
Fig c
1st generation
(grandparents) Ff Ff ff Ff
2nd generation
(parents, aunts,
and uncles) FF or Ff ff ff Ff Ff ff
3rd generation
(two sisters) ff FF or Ff
Attached earlobe
Free earlobe
(b) Is an attached earlobe a dominant or recessive trait?

20. Parents Normal Normal Aa Sperm A a Eggs Aa AA A Normal (carrier)
Fig
Parents
Normal
Normal Aa  Aa
Sperm A a
Eggs Aa AA A
Normal
(carrier)
Normal
Figure Albinism: a recessive trait Aa aa a
Normal
(carrier)
Albino

21. Parents Dwarf Normal Sperm Eggs Dwarf Normal Dwarf Normal Dd dd D d Dd
Fig
Parents
Dwarf
Normal Dd  dd
Sperm D d
Eggs Dd dd d
Figure Achondroplasia: a dominant trait
Dwarf
Normal Dd dd d
Dwarf
Normal

22. Fetal Screening