1. GENES AND HEREDITY

2. What we are asked to teach our students
The Standards
What we are asked
to teach our students

3. 7th Grade Life Science Major Concepts/ Skills
Diversity of living
Dichotomous key/classify (6 Kingdoms)
Structure and function of cells
Tissues, organs, and organ systems
Purpose of major human body organ systems
Heredity, genes, and successive generations
Ecosystems
Cycling of matter and energy
Biological evolution
Natural selection and fossil record

4. S7L3. Students will recognize how biological traits are passed on to successive generations.
a. Explain the role of genes and chromosomes in the process of inheriting a specific trait.
b. Compare and contrast that organisms reproduce asexually and sexually (bacteria, protists, fungi, plants & animals).
c. Recognize that selective breeding can produce plants or animals with desired traits.

5. Translating the Standards
What are we trying to help the students understand?

6. Students need to know what genes and chromosomes are
a. Explain the role of genes and chromosomes in the process of inheriting a specific trait
Students need to know what genes and chromosomes are
What is their structure?
How genes code for the proteins that result in interaction with the environment
Students need to know the difference between the genotype and phenotype of an organism
Students need to know the basics of Mendelian genetics and inheritance

7. b. Compare and contrast that organisms reproduce asexually and sexually (bacteria, protists, fungi, plants & animals).
Students need to know that bacteria reproduce asexually by binary fission
Students need to know that mitosis is a type of nuclear and cell division that is used both in growth and asexual reproduction
Students need to know that meiosis is a type of nuclear and cell division that is used to make the sperm and eggs used in sexual reproduction

8. c. Recognize that selective breeding can produce plants or animals with desired traits.
For students to understand selective breeding (artificial selection) they need to recognize that:
Genotype controls phenotype and that a desirable trait is a phenotype
A population of organisms usually has large genetic variation and reflected in a variety of forms of a trait
The only difference between artificial selection and natural selection is the source of the selective pressure

9. Major Topics in Genes and Heredity
The Inheritance of Traits
Mendelian Genetics: When the Role of Genes Is Clear
Quantitative Genetics: When Genes and Environment Interact
Genes, Environment, and the Individual

10. The Inheritance of Traits
Most children are similar to their parents
Children tend to be similar to siblings
Each child is a combination of parental traits
The combination of paternal traits and maternal traits is unique for each individual child

11. The human life cycle
gametes (a male sperm cell + a female egg cell) fuse during fertilization to form a single celled zygote, or embryo
the embryo grows by cell division in mitosis
the embryo grows into a child
the child matures into an adult

12. Figure 6.1 The human life cycle.
A human baby forms from the fusion of an egg cell from its mother and a sperm cell from its father. The single cell that results from this fusion will grow and divide into trillions of cells, each carrying the same information.

13. Figure 6.1 The human life cycle.
A human baby forms from the fusion of an egg cell from its mother and a sperm cell from its father. The single cell that results from this fusion will grow and divide into trillions of cells, each carrying the same information.

14. Genes
Most genes are segments of DNA that carry information about how to make proteins
Structural proteins – for things like hair
Functional proteins – for things like breaking down lactose

15. Genes All cells have the same genes
Only certain genes are active in a single cell
Heart cells and eye cells have genes for the protein rhodopsin, which helps to detect light
This is only produced in eye cells, not heart cells

16. Genes and Chromosomes
DNA is sort of like an instruction manual that shows how to build and maintain a living organism…

17. Figure 6.2 Genes as words in an instruction manual.
Different words from the manual are used in different parts of the body, and even when the same words are used, they are often used in distinctive combinations. In this way, the manual can provide instructions for making and operating the variety of body parts we possess.

18. Genes Are on Chromosomes
The genes are located on the chromosomes
The number of chromosomes depends on the organism
Bacteria – one circular chromosome
Humans – 23 homologous pairs of linear chromosomes

19. Genes Are on Chromosomes
Each of the 23 pairs of chromosomes is a homologous pair that carry the same gene
For each homologous pair, one came from mom and the other from dad

20. Figure 6.3 The formation of different alleles.
(a) Each parent provides a complete set of instructions to each offspring.

21. Gene Variation Is Caused by Mutation
Genes on a homologous pair are the same, but the exact information may not be the same
Sometimes errors or mutations in gene copies can cause somewhat different proteins to be produced
Different gene versions are called alleles

22. Figure 6.3 The formation of different alleles.
(b) The instructions are first copied, and different alleles for a gene may form as a result of copying errors. Some of these misspellings do not change the meaning of the word, but some may result in altered meanings or have no meaning at all.

23. Diversity in Offspring
The combination from the parents creates the individual traits of each child
Environment also plays a role, but differing alleles from parents are the primary reason that non-twin siblings are not identical

24. Diversity in Offspring
Non-twin siblings:
The combination each individual receives depended on the gametes that were part of the fertilization event
Remember that each gamete has 1 copy of each homologous pair

25. Segregation
When a gamete is formed, the homologous pairs are separated and segregated into separate gametes (this is called the law of segregation)
This results in gametes with only 23 chromosomes
1 of each homologous pair

26. Independent Assortment
Due to independent assortment, parents contribute a unique subset of alleles to each of their non-identical twin offspring
Since each gamete is produced independently, the combination of genes is unique

27. Figure 6.4 Each egg and sperm is unique.
This figure uses the instruction manual analogy to show how a single man can produce an enormous diversity of sperm. The same process of independent assortment results in enormous diversity in eggs as well. The cells that are the source of a man’s sperm carry 2 of each chromosome— that is, 2 full copies of the instruction manual—1 set from his mom, the other from his dad. When a sperm cell is produced, it ends up with only 1 copy of each page. Since each sperm is produced independently, the set of pages in each sperm will be a unique combination of the pages that the man inherited from his mom and dad.

28. Diversity in Offspring
That means a unique egg will be fertilized by a unique sperm to produce a unique child
For each gene, there is a 50% chance of having the same allele as a sibling

29. Diversity in Offspring
There are 223 combinations for the way the homologous chromosomes could line up and separate
This is more than 8 million combinations

30. Crossing Over
In addition, crossing over in meiosis can increase diversity
The chromosomes trade information, creating new combinations of information

31. Figure 6.6 Crossing over increases diversity in gametes.
When chromosomes pair at the beginning of meiosis, information may be exchanged via the process of crossing over. (a) In our instruction manual analogy, this means that meiosis can result in the formation of completely new chromosome. (b) A photomicrograph of chromosomes in the process of crossing over during prophase of meiosis I.

32. Random Fertilization
Gametes combine randomly—without regard to the alleles they carry in a process called random fertilization
You are one out of 64 trillion genetically different children that your parents could produce

33. Diversity in Offspring
Mutation, independent assortment, crossing over, and random fertilization result in unique combinations of alleles
These processes produce the diversity of individuals found in humans and all other sexually reproducing biological populations

34. Twins Fraternal (non-identical)
dizygotic: two separate fertilized eggs
not genetically the same

35. Figure 6.7 The formation of twins.
(a) Dizygotic twins form when 2 different eggs combine with 2 different sperm cells, resulting in 2 embryos who are only as similar as siblings.

36. Twins Identical monozygotic: one single fertilized egg that separates
genetically the same

37. Figure 6.7 The formation of twins.
(b) Monozygotic twins form when a newly fertilized embryo splits in half resulting in 2 identical embryos.

38. Mendelian Genetics: When the Role of Genes Is Clear

39. Gregor Mendel Determined how traits were inherited
Used pea plants and analyzed traits of parents and offspring
Figure E6.1a Gregor Mendel

40. Mendelian Genetics
Mendelian genetics – the pattern of inheritance described by Mendel – for single genes with distinct alleles
Sometimes inheritance is not so straightforward

41. Genotype Genotype – combination of alleles
homozygous: two of the same allele
heterozygous: two different alleles

42. Phenotype Phenotype the physical outcome of the genotype
depends on nature of alleles

43. Mendelian Genetics Dominant – can mask a recessive allele
Recessive – can be masked by a dominant allele
Incomplete dominance – alleles produce an intermediate phenotype
Codominance – both alleles are fully expressed

44. Mendelian Genetics Dominant alleles – capital letter
For example: T for tall
Recessive alleles – lower case letter
For example: t for short

45. Figure 6.8 Genotypes and phenotypes.
When 2 alleles for a gene exist in a population, there are 3 possible genotypes and 2 or 3 possible phenotypes for the trait.

46. Genetic Diseases in Humans
Most alleles do not cause diseases in humans
There are some diseases that are genetic:
Recessive, such as cystic fibrosis
Dominant, such as Huntington’s Disease
Codominant, such as sickle-cell anemia

47. Genetic Diseases: Cystic Fibrosis
Affects 1 in 2500 individuals in European populations
Recessive condition: individuals have 2 copies of cystic fibrosis allele
Carriers – have one cystic fibrosis allele but do not have cystic fibrosis; can pass along allele to children

48. Genetic Diseases: Cystic Fibrosis
Produces nonfunctioning proteins
Normal protein transports chloride ion in and out of cells in lungs
Result – thick mucus layer that is difficult from lungs and interferes with absorption of nutrients in intestines

49. Huntington’s Disease Dominant condition Fatal condition
Only one Huntington’s allele needed
Produces abnormal protein that clumps up in cell nuclei – especially nerve cells in the brain

50. Sickle-Cell Anemia Codominant – both alleles are expressed
One allele codes for normal hemoglobin and the other codes for sickle-cell hemoglobin
Figure 6.9 The effect of the sickle-cell allele.
The sickle-cell anemia allele causes red blood cells to look sickled as seen here, on the right. At left, a normal red blood cell appears round and pillow-like.

51. Sickle-Cell Anemia
If you have two normal hemoglobin alleles, you do not have the disease
If you have two sickle-cell hemoglobin alleles, you have sickle-cell disease
If you have one of each, you are a carrier

52. Punnett Squares
Punnett squares are used to predict offspring phenotypes
Uses possible gametes from parents to predict possible offspring

53. Figure 6.10 What are the risks of accepting sperm from a carrier of cystic fibrosis?
This Punnett square helps determine the likelihood that a woman who carries the cystic fibrosis allele would have a child with cystic fibrosis if her sperm donor was also a carrier. With a 25% chance of producing an affected child, most women would consider sperm from a carrier unacceptable, which is why sperm banks do not accept sperm from carrier males.

54. Punnett Squares: Single Gene
A parent who is heterozygous for a trait
Aa can produce two possible gametes
A or a
A parent who is homozygous for a trait
AA can only produce gametes with A

55. Punnett Squares
The possible gametes are listed along the top and side of the square
The predicted offspring genotypes are filled in the center boxes of the square

56. Punnett Squares The offspring can be homozygous or heterozygous
It all depends on the parents and the possible gametes
Punnet squares can be used to predict possibilities of inheriting genetic diseases

57. Figure 6.11 Calculating the likelihood of genetic traits in children.
(a) This Punnett square illustrates the outcome of a cross between a man who carries a single copy of the dominant Huntington’s disease allele and an unaffected woman.

58. Figure 6.11 Calculating the likelihood of genetic traits in children.
(b) The outcome of a cross between two individuals with the sickle-cell trait. The two alleles are codominant—allele S codes for the normal blood protein, and allele s codes for the “sickling” blood protein.

59. Punnett Squares This is a probability for each individual offspring
If there is a 25% chance an offspring will have cystic fibrosis – this means that – for every fertilization event, there is a 25% chance of cystic fibrosis

60. Punnett Squares: Multiple Genes
You can also use Punnett squares to predict the offspring with multiple genes
It is more significantly more difficult as the number of genes being studied increases

61. Figure 6.12 A dihybrid cross.
Punnett squares can be generated to predict the outcome of a cross between individuals when we know their genotypes for more than one gene as long as those genes are on separate chromosomes. This square shows a cross between two pea plants that are heterozygous for both the seedcolor and the seed-shape genes.

62. Quantitative Genetics
The environment plays a role – traits such as height, weight, musical ability, susceptibility to cancer, and intelligence
Quantitative traits show continuous variation; we can see a large range of phenotypes in the population
The amount of variation in a population is called variance

63. Figure 6.13 A quantitative trait.
(a) This graph of the number of men in each category of height is a normal distribution with a center around the mean height of 1.73 m.

64. Figure 6.13 A quantitative trait.
(b) Fourteen-year-old boys and professional jockeys have the same average weight—approximately 114 pounds. However, to be a jockey, you must be within about 4 pounds of this average. Thus the variance among jockeys in weight is much smaller than the variance among 14-year-olds.

65. Why Traits Are Quantitative
Polygenic traits – those traits influence by more than one gene
Eye color is a polygenic trait
There are two genes: pigment and distribution
This produces a range of eye colors

66. Why Traits Are Quantitative
Environment can affect phenotypes
Identical twins with the same genotypes may not have exactly the same appearance…

67. Figure 6.14 The effect of the environment on phenotype.
These identical twins have exactly the same genotype, but they are quite different in appearance due to environmental factors.

68. Why Traits Are Quantitative
Skin color is affected by both genes and environment…

69. Why Traits Are Quantitative
Figure 6.15 Skin color is influenced by genes and environment.
(a) The difference in skin color between these two women is due primarily to variations in several alleles that control skin pigment production.
(b) The difference in color between the sun-protected and sun-exposed portions of the individual in this picture is entirely due to environmental effects.

70. Using Heritability to Analyze Inheritance
Inheritance patterns for these quantitative traits are difficult to understand
Researchers use plants and domestic animals to study heritability – a measure of the relative importance of genes in determining variation in quantitative traits among individuals

71. Using Heritability to Analyze Inheritance
Artificial selection:
controlling the reproduction of organisms to achieve desired offspring

72. Figure 6.16 Artificial selection increases milk production in cows.
Cows that produce exceptional amounts of milk are bred to produce the next generation of dairy cattle. In this example, the female calves of the cow that produces 3.6 gallons of milk daily produce an average of 3.2 gallons of milk per day—23% more than the previous herd.

73. Calculating Heritability in Human Populations
We can’t use artificial selection for humans
So we look at correlations

74. Correlations between Parents and Children
Inject parent and offspring in a bird population
Look for correlation between parents and offspring in ability to produce anti-tetanus proteins

75. Figure 6.17 Using correlation between parents and offspring to calculate heritability.
In this example, the close correlation of immune system response between parents and offspring of a bird species called the blue tit indicates that much of the variation among birds in the strength of their immune response is due to variation in their genes.

76. Correlations between Parents and Children
For human IQ, the correlation between parents and offspring is 0.42
There is also an effect of society and environment on IQ
Nature versus nurture debate – “born that way” or because they were “raised that way”

77. Correlation between Twins
Twin studies allow scientists to test the effects of environment
The DNA is identical in identical twins but the environment may be different
Compare monozygotic (identical) twins to dizygotic (fraternal) twins
Study twins raised together and study identical twins raised apart

78. Table 6.1 To what extent is IQ heritable?
A summary of various estimates of IQ heritability, their shortcomings, and the problems with using them to understand the role of genes in determining an individual’s potential intelligence.

79. Genes, Environment, and the Individual

80. The Use and Misuse of Heritability
Calculated heritability values are unique to a particular environment
Therefore, we must be cautious when using heritability to measure the general importance of genes to the development of a trait

81. The Use and Misuse of Heritability
The environment may cause large differences among individuals, even if a trait has high heritability
Highly heritable traits can respond to environmental change
Traits can be both highly heritable and strongly influenced by the environment

82. The Use and Misuse of Heritability
Knowing the heritability of a trait does not tell us why two individuals differ for that trait
Our current understanding of the relationship between genes and complex traits does not allow us to predict the phenotype of a particular offspring from the phenotype of its parents