1. UNIT VI - MENDELIAN GENETICS
Baby Campbell – 11,12
Big Campbell – Ch 14, 15

2. I. MENDEL Mendel Mendel’s Principles
Alternative versions of genes known as ______________ account for variations in inherited characters.
Organisms inherit _____ alleles for each trait
If alleles at a locus differ; that is; if the genotype is _______________, the allele that shows is known as the ________________ allele.
Law of Independent Assortment
Law of Segregation

3. II. ANALYZING PROBABILITIES
Test Cross
Punnett Square
Multiplication Rule
States the probability of 2 or more independent events occurring together can calculated by multiplying individual probabilities
For example,
Determine the probability of a homozygous recessive short plant produced from F1 X F1
Cross =
Probability of tt offspring =

4. II. ANALYZING PROBABILITIES, cont
Addition Rule
States that the probability of 2 or more mutually exclusive events occurring can be calculated by adding together their individual probabilities
For example,
Determine the probability of a heterozygous plant produced from F1 X F1

5. II. ANALYZING PROBABILITIES, cont
Crosses Involving Multiple Characters
Determine the genotype ratio of the offspring for the cross
BbCCDD X BBccDd

6. II. ANALYZING PROBABILITIES, cont
Determine the expected phenotypes of the offspring for the cross
YyRrSS X yyRrss

7. II. ANALYZING PROBABILITIES, cont
In the cross, PpYyRr X Ppyyrr, what is the probability of offspring that are purple, green, & round?
P= purple, p = white
Y = yellow, y = green
R = round, r = wrinkled

8. III. VARIATIONS IN INHERITANCE
Co-Dominance
Both alleles affect phenotype in separate & distinguishable ways
Incomplete Dominance
Neither allele is dominant; heterozygotes show a blend of two homozygous phenotypes

9. III. VARIATIONS IN INHERITANCE, cont
Epistasis
Gene at one locus alters
phenotypic expression of a
gene at a second locus
For example,
A dominant allele, P causes the production of purple pigment; pp individuals are white. A dominant allele C is also required for color production; cc individuals are white. What proportion of offspring will be purple from a ppCc x PpCc cross?

10. III. VARIATIONS IN INHERITANCE, cont
Phenotype
Genotype A B AB O
Multiple Alleles
Many genes have more than 2 alleles
Example, ABO blood groups in humans
Three alleles
Rh Factor
A woman with O positive blood has a child with Type A negative blood. The man she claims is the father has AB positive blood. Is it possible that he is the father of this child?

11. III. VARIATIONS IN INHERITANCE, cont
Polygenic Inheritance
For example, AABBCC = very dark skin; aabbcc = very light skin.
Intensity based on units; in other words, AaBbCc and AABbcc individuals would have the same pigmentation

12. III. VARIATIONS IN INHERITANCE, cont
Pleiotropy

13. III. VARIATIONS IN INHERITANCE, cont
Environmental Impact on Phenotypes

14. IV. SEX-LINKED INHERITANCE
First recognized by Thomas Hunt Morgan
Drosophila melanogaster
Fruit flies
Excellent organism for genetic studies
Prolific breeding habits
Simple genetic make-up; 4 pairs of chromosomes → 3 pairs of autosomes, 1 pair of sex chromosomes
Crossed true-breeding wild-type females with true-breeding mutant males
Mutant trait showed up in ½ male F2 offspring ; was not seen in F2 females
Determined mutant allele was on X-chromosome; thus inherited differently in males versus females
In females,
In males,

15. IV. SEX-LINKED INHERITANCE, cont
The gene for amber body color in Drosophila is X-linked recessive. The dominant allele produces wild type body color. The gene for black eyes is autosomal recessive; the wild type red eyes are dominant. If males with amber bodies, heterozygous for eye color are crossed with females heterozygous for eye color and body color, calculate the expected phenotype ratios in the offspring.

16. IV. SEX-LINKED INHERITANCE, cont
X Inactivation in Females
During embryonic development, one X chromosome in female cells is inactivated due to addition of methyl group to its DNA
Dosage compensation
Inactive X chromosome condenses; known as Barr body

17. IV. SEX-LINKED IN INHERITANCE, cont
Occurs randomly
Females will have some cells where “Dad’s copy” of X is inactivated, some where “Mom’s copy” is inactive
Therefore, females are a mosaic of cells
Preserved in mitosis
In ovaries, Barr body chromosome is reactivated for meiosis and oogenesis

18. V. PEDIGREE ANALYSIS

19. V. PEDIGREE ANALYSIS, cont

20. VI. CHROMOSOMAL BASIS OF INHERITANCE
Chromosomal Theory of Inheritance
States genes occupy specific loci on chromosomes
During meiosis, chromosomes undergo segregation & independent assortment
Linked Genes
During Thomas Morgan’s work with Drosophila, he recognized
Two genes located on same chromosome were linked; that is, inherited together
However, offspring phenotypes showed this wasn’t always true

21. VI. CHROMOSOMAL BASIS OF INHERITANCE, cont
Linked Genes, cont
In fruit flies, normal wild-type phenotype is gray body, normal wings – both genes are located on same chromosome
G = wild-type (gray) body; g = black body
W = wild-type wings; w = mutant wings
True-breeding wild type flies X true-breeding mutants
F1 showed all
F1 X test cross
Counted 2300 offspring
Should have counted

22. VI. CHROMOSOMAL BASIS OF INHERITANCE, cont
Linked Genes, cont
Instead Morgan counted
965 GWgw 944 gwgw 206 Gwgw 185 gWgw
Morgan realized variation in probabilities due to
Linkage Maps
In crossing over, the further apart two genes are …

23. VI. CHROMOSOMAL BASIS OF INHERITANCE, cont
Linkage Maps, cont
Recombination Frequency =
# recombinants_
total # offspring
One map unit = 1% recombination
Morgan’s Data …
F1 X test cross
GW/gw X gw/gw
Counted 2300 offspring
Should have counted
965 GWgw 944 gwgw 206 Gwgw 185 gWgw

24. VI. CHROMOSOMAL BASIS OF INHERITANCE, cont
In a genetics experiment with fruit flies, P generation true-breeding flies are crossed. The female parent is brown and wingless while the male parent is black with normal wings. All of the F1 flies are brown with normal wings.
In the next cross, F1 females are test-crossed with black, wingless males. The following offspring are counted:
85 brown winged flies
728 black winged flies
712 brown wingless flies
75 black wingless flies
How many map units apart are the two genes?

25. VI. CHROMOSOMAL BASIS OF INHERITANCE, cont
The genes for vestigial wings, black body color, and cinnabar eyes are linked genes.
In controlled crosses …
The gene for vestigial wings (vg) and body color (b) have a 17% crossover rate.
The gene for eye color (cn) and vestigial wings have a 9% crossover rate.
The gene for eye color and body color have an 8% crossover rate.
Draw the chromosome.

26. VII. MUTATIONS Change in the nucleotide sequence of DNA
May be spontaneous mistakes that occur during replication, repair, or recombination
May be caused by mutagens; for example, x-rays, UV light, carcinogens
Classification
Gene
Chromosomal

27. VIII. INHERITED GENETIC DISORDERS
Most often due to gene mutations
Classified according to type of chromosome on which affected gene is located
Autosomal Disorders
X-linked Disorders
Grouped according to path of inheritance

28. VIII. INHERITED GENETIC DISORDERS
Autosomal Recessive Disorders
Albinism
Cystic Fibrosis
PKU
Tay Sachs

29. VIII. INHERITED GENETIC DISORDERS, cont
Autosomal Co-Dominant Disorders
Sickle Cell Anemia
Autosomal Dominant Disorders
Huntington’s Disease
Marfan Syndrome
Achondroplasia
Hypercholesteremia

30. VIII. INHERITED GENETIC DISORDERS, cont
X-Linked Disorders
Hemophilia
Colorblindness
Duchenne Muscular Dystrophy

31. IX. CHROMOSOMAL MUTATIONS
Abnormal Chromosome Structure
Often due to mistakes in

32. IX. CHROMOSOMAL MUTATIONS, cont
Abnormal Number of Chromosomes
Most commonly due to nondisjunction
Results in aneuploid gametes
Detected with ________________________

33. IX. CHROMOSOMAL MUTATIONS, cont
Chromosomal Number Disorders
Examples
Down Syndrome

34. IX. CHROMOSOMAL MUTATIONS, cont
Turner Syndrome

35. IX. CHROMOSOMAL MUTATIONS, cont
Klinefelter Syndrome

36. X. GENETIC TESTING Identification of Carriers/Genetic Counseling
Gene testing is available for Tay-Sachs, sickle cell, cystic fibrosis, Huntington’s, PKU, & many others
Fetal Testing
Gene Testing
Amniocentesis
Chorionic Villus Sampling (CVS)
Karyotype
Newborn Screening
PKU
PGD
Pre-Implantation Genetic Diagnosis