1. Inquiry into Life Twelfth Edition
Lecture PowerPoint to accompany
Inquiry into Life Twelfth Edition
Sylvia S. Mader
Chapter 23
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 23.1 Mendel’s Laws Gregor Mendel
Investigated inheritance at the organism level (1860’s)
Concluded that plants transmit distinct factors to offspring
Based on his studies, he formulated the law of segregation

3. 23.1 Mendel’s Laws The Law of Segregation
Each individual has two factors for each trait
The factors segregate (separate) during the formation of gametes
Each gamete contains only one factor from each pair of factors
Fertilization gives each new individual two factors for each trait

4. 23.1 Mendel’s Laws
Today we know genes determine characteristics of an organism, genes are found on chromosomes
Chromosomes that are homologous are members of a pair and carry genes for the same traits in the same order
Alleles are alternate forms of a gene for the same trait
Alleles are always at the same locus (location) on each chromosome of a homologous pair

5. Homologous Chromosomes

6. 23.1 Mendel’s Laws The Inheritance of a Single Trait
Phenotype: physical appearance of the individual with regard to a trait
Genotype: Alleles responsible for a given trait
Two alleles for a trait
A capital letter symbolizes a dominant allele (W)
A lower-case letter symbolizes a recessive allele (w)
Dominant refers to the allele that will mask the expression
of the alternate (recessive) allele

7. 23.1 Mendel’s Laws

8. 23.1 Mendel’s Laws Gamete Formation
During meiosis, homologous chromosomes separate so there is only 1 member of each pair in a gamete
There is one allele for each trait, such as hairline, in each gamete
No two letters in a gamete can be the same letter of the alphabet
If genotype is Ww, then gametes from this individual will contain either a W or a w

9. 23.1 Mendel’s Laws One-Trait Cross
A homozygous man with a widow’s peak
(X)
A woman with a straight hairline

10. 23.1 Mendel’s Laws One-Trait Cross Two individuals who are both Ww
A Punnett Square is useful to solve this problem

11. 23.1 Mendel’s Laws One-Trait Crosses and Probability
The chance of 2 or more independent events occurring together is the product of their chance of occurring separately
In the cross Ww X Ww, what is the chance of obtaining either a W or a w from a parent?
Chance of W = ½ and the chance of w = ½
Therefore the probability of having these genotypes is as follows
Chance of WW= ½ X ½ = ¼
Chance of Ww = ½ X ½ = ¼
Chance of wW= ½ X ½ = ¼
Chance of ww = ½ X ½ = ¼

12. 23.1 Mendel’s Laws The One-Trait Test Cross
Breeders of plants and animals may do a test cross to determine the likely genotype of an individual with the dominant phenotype
Cross with a recessive individual-has a known genotype
If there are any offspring produced with the recessive phenotype, then the dominant parent must be heterozygous

13. One-Trait Testcross

14. 23.1 Mendel’s Laws Practice Problems
Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles?

15. 23.1 Mendel’s Laws Practice Problems
Both you and your sibling have attached ear lobes, but your parents have unattached lobes. Unattached earlobes (E) are dominant over attached (e). What are the genotypes of your parents?

16. 23.1 Mendel’s Laws Practice Problems
A father has dimples, the mother of his children does not, and all 5 of their children have dimples. Dimples (D) are dominant over no dimples (d). Give the probable genotypes of all persons concerned.

17. 23.1 Mendel’s Laws The Inheritance of Two Traits
The Law of Independent Assortment:
Each pair of factors assorts independently (without regard to how the others separate)
All possible combinations of factors can occur in the gametes

18. The Inheritance of Two Traits

19. Two-Trait Crosses (Dihybrid Cross)

20. 23.1 Mendel’s Laws Two-Trait Crosses (Dihybrid Cross) WwSs (X) WwSs
Phenotypic Ratio:
9 widow’s peak, short fingers
3 widow’s peak, long fingers
3 straight hairline, short fingers
1 straight hairline, long fingers

21. 23.1 Mendel’s Laws Two-Trait Crosses and Probability Probability Laws
Probability of widow’s peak = ¾
Probability of short fingers= ¾
Probability of straight hairline= ¼
Probability of long fingers= ¼
Using the Product Rule
Probability of widow’s peak and short fingers = ¾ X ¾ = 9/16
Probability of widow’s peak and long fingers = ¾ X ¼ = 3/16
Probability of straight hairline and short fingers = ¼ X ¾ = 3/16
Probability of straight hairline and long fingers = ¼ X ¼ = 1/16

22. 23.1 Mendel’s Laws Practice Problems
Attached earlobes are recessive, What genotype do children have if one parent is homozygous recessive for earlobes and homozygous dominant for hairline, and the other is homozygous dominant for unattached earlobes and homozygous recessive for hairline?

23. 23.1 Mendel’s Laws Practice Problems
If an individual from this cross reproduces with another of the same genotype, what are the chances that they will have a child with a straight hairline and attached earlobes?

24. 23.1 Mendel’s Laws Practice Problems
A child who does not have dimples or freckles is born to a man who has dimples and freckles (both dominant) and a woman who does not. What are the genotypes of all persons concerned?

25. 23.1 Mendel’s Laws Pedigrees
A chart of family’s history with regard to a particular genetic trait
Males =
Females =
Affected individuals (for a given trait) are shaded

26. A Human Pedigree

27. 23.2 Beyond Simple Inheritance Patterns
Incomplete Dominance
Occurs when the heterozygote is intermediate between the two homozygotes
Codominance
Occurs when alleles are equally expressed in a heterozygote
Blood type AB is an example
Red blood cells have both Type A and Type B surface antigens

28. Incomplete Dominance

29. 23.2 Beyond Simple Inheritance Patterns
Multiple Allele Inheritance
A trait is controlled by multiple alleles, the gene exists in several allelic forms.
Each person has only two of the possible alleles.

30. 23.2 Beyond Simple Inheritance Patterns
Multiple Allele Inheritance
ABO Blood Types
IA = A antigens on red blood cells
IB = B antigens on red blood cells
i = has neither A nor B antigens on red blood cells
Both IA and IB are dominant over i, IA and IB are codominant
Phenotype Genotype
A IAIA or IAi
B IBIB or IBi
AB IAIB
O ii

31. 23.2 Beyond Simple Inheritance Patterns
Multiple Allele Inheritance
ABO Blood Types
Both IA and IB are dominant over i, IA and IB are codominant
The Rh factor is inherited separately from ABO blood types.

32. Inheritance of Blood Types

33. 23.2 Beyond Simple Inheritance Patterns
Practice Problems
If a person with straight hair marries someone with wavy hair, can they have a child with curly hair?

34. 23.2 Beyond Simple Inheritance Patterns
Practice Problems
A child with type O blood is born to a mother with type A blood. What is the genotype of the child? The mother? What are the possible genotypes of the father?

35. 23.2 Beyond Simple Inheritance Patterns
Practice Problems
From the following blood types determine which baby belongs to which parents:
Baby 1 type O Mrs. Doe type A Mrs. Jones type A
Baby 2 type B Mr. Doe type A Mr. Jones type AB

36. 23.2 Beyond Simple Inheritance Patterns
Sex-Linked Inheritance
In Humans:
22 pairs of autosomes, 1 pair of sex chromosomes
X and Y
In females, the sex chromosomes are XX
In males, the sex chromosomes are XY
Note that in males the sex chromosomes are not homologous
Traits controlled by genes in the sex chromosomes are called sex-linked traits
X chromosome has many genes, the Y chromosome does not

37. 23.2 Beyond Simple Inheritance Patterns
Sex-Linked Alleles
Red-green colorblindness is X-linked
The X chromosome has genes for normal color vision
XB = normal vision
Xb – colorblindness
Genotypes Phenotypes
XBXB female with normal color vision
XBXb carrier female with normal color vision
XbXb colorblind female
XBY male with normal color vision
XbY colorblind male

38. Cross involving an X-linked Allele

39. 23.2 Beyond Simple Inheritance Patterns
Practice Problems
Both the mother and the father of a colorblind male appear to be normal. From whom did the son inherit the allele for colorblindness? What are the genotypes of the mother, father, and the son?

40. 23.2 Beyond Simple Inheritance Patterns
Practice Problems
A woman is colorblind. What are the chances that her son will be colorblind? If she is married to a man with normal vision, what are the chances that her daughters will be colorblind? Will be carriers?

41. 23.2 Beyond Simple Inheritance Patterns
Practice Problems
A husband and the wife both have normal vision. The wife gives birth to a colorblind daughter. Is it more likely the father had normal vision or was colorblind? What does this lead you to deduce about the girl’s parentage?

42. 23.2 Beyond Simple Inheritance Patterns
Polygenic Inheritance
Occurs when a trait is governed by two or more sets of alleles.
Each dominant allele codes for a product
The effects of the dominant alleles are additive.
The result is continuous variation.
Examples of traits include size or height, shape, weight, and skin color.

43. Polygenic Inheritance

44. 23.2 Beyond Simple Inheritance Patterns
Practice Problems
A certain polygenic trait is controlled by three pairs of alleles: A vs a, B vs b, and C vs c.
What are the extreme genotypes for this trait?

45. 23.3 Environmental Influences
Environmental factors can influence the expression of genetic traits.
Examples:
Primrose flowers are white at warmer temperatures and red at cooler temperatures
Siamese cats and Himalayan rabbits are darker in color where body heat is lost to the environment.

46. Coat Color in Himalayan Rabbits

47. 23.4 Inheritance of Linked Genes
All the alleles on one chromosome form a linkage group.
Recall that during meiosis crossing over sometimes occurs
If crossing over occurs between two alleles of interest, then four types of gametes are formed instead of two

48. Linkage Groups

49. 23.4 Inheritance of Linked Genes
The occurrence of crossing-over can help determine the sequence of genes on a chromosome
Crossing-over occurs more often between distant genes than genes that are close together
In the example below, it is expected that recombinant gametes would include G and z more often than R and s.

50. 23.4 Inheritance of Linked Genes
Practice Problems
When AaBb individuals reproduce, the phenotypic ratio is about 3:1. What ratio was expected? What may have caused the observed ratio?

51. 23.4 Inheritance of Linked Genes
Practice Problems
The genes for ABO blood type and for fingernails are on the same homologous pair of chromosomes. In an actual family, 45% of offspring have type B blood and no fingernails, and 45% have type O blood and fingernails; 5% have type B blood and fingernails, and 5% have type O blood and no fingernails. What process accounts for the recombinant phenotypes?