1. Chapter 10 Patterns of Inheritance

2. Genetics
Genetics is the branch of science that studies how the characteristics of living organisms are inherited.
In classic or Mendelian genetics, the central question is how are characteristic seen in parent distributed among offspring.

3. Alleles An allele is a specific version of a gene.
Examples: eye color, hair color, earlobe type
The two different alleles are on the same part of a chromosome

4. Fundamentals of Genetics
The interaction of alleles determines the appearance of the organism.
The genotype of an organism is the combination of alleles that are present in an organism’s cells
Ex. BB, Bb, bb
Homozygous – two identical alleles
Heterozygous – two different alleles
The phenotype of an organism is how it appears outwardly and is a result of an organism’s genotype
Blue eyes, brown eyes

5. Fundamentals of Genetics
A dominant allele masks the recessive allele in the phenotype of an organism
Dominant allele is usually shown by a capital letter
Recessive alleles are usually shown by a lower-case letter.
B – brown-eyes, b – blue-eyes BB Bb bb

6. Fundamentals of Genetics
Genetic cross is a planned mating between two organisms
Punnett square shows the possible offspring of a particular genetic cross
Aa x Aa

7. Punnett Square Earlobes: E=free, e=attached EE x ee Ee x Ee EE x Ee
EE: EE: EE:
Ee: Ee: Ee:
ee: ee: ee:

8. The Father of Genetics Gregor Mendel (1822-1884)
Mendel was an Augustian monk in the Czech Republic.
He studied physics and botany at the University of Vienna.
He worked for 12 years on his genetic experiments and published them in the local natural history journal in 1866.
Mendel’s results were forgotten until the early 20th century.

9. Pea Plants
Mendel performed experiments concerning the inheritance of seven certain characteristics of pea plants.

10. Pea Plants
Mendel had one pure breeding purple and one pure breeding white flower plant and crossed them. This generation, is known as the Parental, or P.
CC x cc

11. Pea Plants
As seen in the previous slide, all the offspring of the P generation resulted in a purple color, with a genotype of Cc. This generation is known as the F1 generation. Mendel allowed the F1 generation to self-fertilize.
This results in the F2 generation.

12. Mendel Mendel recognized four genetic principles
Organisms have two pieces of genetic information for each trait (later called alleles)
Law of Dominance states that some alleles interact with each other in a dominant and recessive manner, where the dominant allele masks the recessive trait
Gametes fertilize randomly
Law of Segregation says when a diploid organisms forms gametes, the two alleles for a characteristic separate from one another.

13. Single-Factor Cross Let’s try a single-factor cross of our own now
Two heterozygous for pod color; Green is dominant and yellow is recessive

14. Double-Factor Cross
Genes on non-homologous chromosomes are inherited independently.
Step 1) One parent has yellow, round seeds (YYRR) and the other has green, rough seeds (yyrr).
Seed color - green (y)
Seed shape - rough (r)
Seed color - yellow (Y)
Seed shape - round (R)

15. Double-Factor Cross
To predict the number of different gametes, use 2n where n = # of heterozygous genes on non-homologous chromosomes.
In this case, 22 = 4 different gametes.
Gamete Possibilities:
Seed color - green
Seed color - yellow
Seed shape - rough
Seed shape - round

16. Double-Factor Cross
Time for the Punnett Square for F1

17. Double-Factor Cross
Now lets do an F2 generation of heterozygous (YyRr)
Possible gametes:

18. Double-Factor Cross
Time for the Punnett Square for F1

19. Double-Factor Cross

20. Human Traits – Dominant or Recessive
Cleft in chin - No cleft dominant, cleft recessive
Widow peak dominant, straight hairline recessive
Free lobe dominant, attached recessive
Freckles dominant, no freckles recessive
Roller dominant, nonroller recessive

21. Autosomal Dominant Traits: Polydactyly
Polydactyly is the appearance of more than the normal number of digits on the hand or the foot.
While the overall frequency is 1 in 500 births, it is more common in some populations (e.g., Amish in U.S.).
Polydacytly is the result of an autosomal dominant genetic trait.

22. Autosomal Dominant Traits: Polydactyly
What will the children look like if one parent is a heterozygous polydactylous parent and other is a “normal” pentadactylous parent?
6 5 5
The chance that any child will be polydactylous (65) is 50:50.
The chance that any child will be pentadactylous (55) is 50:50.

23. Autosomal Recessive Traits: Phenylketonuria
Phenylketonuria (PKU) is caused by a mutation on chromosome 12 which prevents the synthesis of an enzyme which degrades phenyalanine, an amino acid.
Fig. 10.4, pg. 200

24. Autosomal Recessive Traits: Phenylketonuria
Phenylketonuria appears in 1 in every 17,000 births.
Phenylketonuria is an autosomal recessive trait.
Only individuals who are homozygous recessive (2 copies of the phenylketonuria allele) will have this disorder.
Because heterozygotes have one normal copy of the gene which makes the key enzyme, they will not show the disorder
Heterozygous individuals are called carriers.

25. Autosomal Recessive Traits: Phenylketonuria
What will the children look like if two parents are both carriers of the phenyketonuria?
The chance that any child will be totally free of the disorder (NN) is 25%.
The chance that any child will be a carrier (Nn) is 50%.
The chance that any child will have phenyketonuria (nn) is 25%.

26. Complete Dominance
In the genes that Mendel examined, one allele demonstrated complete dominance.
In heterozygotes, the dominant allele was expressed in the phenotype and the alternative allele (recessive) was repressed.
An individual with a dominant phenotype could have either a homozygous dominant genotype (PP) or a heterozygous genotype (Pp).

27. Incomplete Dominance
In other genes, a heterozygous individual has a phenotype that is intermediate.
A heterozygous snapdragon CRCW is pink.
F2 offspring of P1 homozygous cross will show three phenotypes and genotypes in a 1:2:1 ratio.

28. Incomplete Dominance
Let’s do a Punnett Square for Incomplete Dominance. FRFW x FWFW
Genotype
Phenotype
FWFW
White Flower
FWFR
Red Flower
FRFW
Pink Flower

29. Codominance
In codominance the effects of both alleles are visible as distinct effects on the phenotype.
Like incomplete dominance, the F2 offspring of a monohybrid cross of two codominant alleles will lead to 3 types of offspring with 3 genotypes in a 1:2:1 ratio.
A good example of codominance is expression of the A and B blood type alleles in humans.

30. Codominance
Multiple Alleles refers to situations in which there are more than 2 possible alleles that control a particular trait
For blood type there are three different alleles
IA – blood has type A antigen on rbc surface
IB – Blood has type B antigen on rbc surface
i – Blood type O has neither type A nor type B antigens on rbc surface

31. Interactions Among Alleles
Type A blood has anti-B antibodies.
Type B blood has anti-A antibodies
Type O blood has no antibodies for A or B

32. Codominance
Another Punnett Square for a child who has a parent with type A blood and type O blood.

33. Codominance
Type O individuals (ii) are universal donors and type AB are universal recipients

34. Polygenic Inheritance
The final phenotype may depend on the additive effects of several genes.

35. Pleiotropy
Pleiotropy occurs when the alleles from a single gene have multiple phenotypic effects.

36. Linkage Groups
A linkage group is a set of genes located on the same chromosome.
They will be inherited together
Crossing-over may occur in prophase I of Meiosis I, which may split up these linkage group
A child can have gene combinations not found in either parent alone
The closer together two genes are to each other, the less likely crossing over would occur

37. Autosomal and Sex Linkage
Autosomes are chromosomes not directly involved in sex detrmination
Sex Linkage occurs when genes are located on the chromosomes that determine the sex of an individual
The Y chromosome is shorter than the X chromosome and has few genes for traits found on the X chromosome
So, the X chromosome has many genes for which there is no matching gene on the Y chromosome

38. Sex Linkage
Males have both a Y chromosome with a few genes on it and the X chromosome has many of the recessive characteristics present on the X chromosome appear more frequently in males than females.
X-linked genes are only found on the X chromosome
Y-linked genes are only found on the Y chromosome

39. Sex Linkage
Color-Blindness

40. Sex Linked Color Blindness Females (XBXB or XBXb) Males (XBY)
Allele Symbols
Possible Genotypes
Phenotypes
XB = normal color vision
Xb =color-deficient vision
Y= no gene for color vision
Females (XBXB or XBXb)
Males (XBY)
Female with normal color vision
Male with normal color vision
Females(XbXb)
Males (XbY)
Female with color-defective vision
Male with color-defective vision

41. Sex Linkage
One last Punnett Square for a mother who is homozygous for normal color vision, and a father who is color-defective vision

42. Sex Linkage