Download LECTURE OUTLINE (Chapter 11) I. An Introduction to Mendel and

LECTURE OUTLINE (CHAPTER 11)
I. An Introduction to Mendel and His Peas
A. Research in Brno, Czech Republic (Section 11.1).
1. Mendel worked in the period from 1856 to 1863, observing generations of pea plants
and applying mathematics to create a set of principles to govern inheritance.
2. Without ever knowing what genes were, he figured out how they worked.
3. Basic ideas:
a. Basic units of genetics are material elements that come in pairs.
b. Elements do not change, even over many generations.
c. Pairs separate during the formation of gametes.
B. The benefits of Mendel’s experimental model: Pisum sativum (Section 11.2).
1. Anatomy: Figure 11.2
2. Life cycle allows for rapid generations and cross- and self-pollination: Figure 11.3.
3. Wide range of described characters, each of which had two varieties—such as white
and purple flower color—called traits: Table 11.1.
C. Phenotype and genotype—Phenotype is the physical function, bodily characteristic, or
action. Genotype is the underlying genes that determine the phenotype.
II. Monohybrid Crosses and the Segregation of Alleles (Sections 11.3 and 11.4)
A. Setting up crosses.
1. Mendel began with true-breeding stocks (gave only similar offspring), such as yellow
seeds versus green seeds.
2. Starting generation of test is called P for parental generation; took pollen from one
variety and placed it on the stigma of the other variety.
3. Offspring are called F1 for first filial; could have been mix of traits, but they were all
yellow (dominant). To determine where green went, Mendel self-pollinated these F1
plants.
4. Next generation of offspring is called F2 for second filial (6,022 yellow and 2,001
green). Green came back, but only as a specific proportion—3:1; Table 11.2.
B. Interpreting the results.
1. Unlike his predecessors, Mendel carefully counted and interpreted the numbers.
2. Found that varieties did not blend—one is dominant (shows up), and the other
recessive (is masked by the dominant). These varieties are called alleles.
3. The F3 generation—of the yellow F2, two-thirds gave mixtures of green and yellow (not
pure yellow parents), and one-third were all yellow in the F3 (pure yellow). Of the
green, all were true-breeding.
4. Give the alleles names, Y and y, and review the parental cross as separation of
chromosomes during meiosis: Figure 11.5a.
5. Homozygous versus heterozygous.
6. Review how to use a Punnett square to keep track of alleles: Figure 11.5b.
7. Essay: Proportions and Their Causes: The Rules of Multiplication and Addition—
Punnett square shows all possible combinations in their given proportions; same can be
done for flipped coins.
a. Likelihood of getting both alleles yy is same as getting two heads in a row in a coin
toss, 1/2  1/2 = 1/4. Rule of multiplication: the probability of two events happening
is the product of their respective probabilities.
b. Probability of getting Yy when either can be yY or Yy is the sum of probabilities. Like
getting a head and a tail, or a tail and a head: 1/2 + 1/2 = 1.
C. Mendel’s first law is the segregation of alleles.
1. Pea cells contain two copies of each gene (alleles).
2. Alleles do not blend (one copy, dominant, can mask the expression of the recessive
copy).
3. Alleles must separate during meiosis (Mendel had no knowledge of chromosomes or
meiosis): Figure 11.8.
4. Continue to show the cross of the F1 and F2 and F3: Figure 11.6.
5. Show genotypic and phenotypic ratios: Figure 11.7.
III. Dihybrid Crosses and Independent Assortment of Alleles (Section 11.5 & Section 11.6)
A. An example is: Yellow (Y)/green (y) and smooth (S)/wrinkled (s): Figure 11.9a.
1. F1 all yellow and smooth, self-pollinated.
2. F2 ratio—9 yellow and smooth: 3 yellow and wrinkled: 3 green and smooth: and 1
green and wrinkled. Punnett square: Figure 11.9b.
B. Law of Independent Assortment—during gamete formation, gene pairs assort
independently.
1. Due to random nature of how tetrads line up during prophase I of meiosis.
2. Figure 10.2c.
C. Reception of Mendel’s ideas was nonexistent. Essay: Why So Unrecognized?
IV. Variations on Mendel
A. Incomplete dominance (Section 11.7): Figure 11.10.
1. Red  white = pink in F1
2. Not blending of alleles, because in F2 you get 1 red: 2 pink: 1 white.
3. Genes make proteins—red gene makes red pigment; with only one allele, you get only
half the pigment.
B. ABO blood types and codominance (Section 11.8).
1. Codominance of a single gene on chromosome 9.
2. Multiple alleles; phenotypes and genotypes of all possible combinations of A, B, and
O: Figure 11.11.
C. Polygenic inheritance—one trait that is determined by many genes (Section 11.9).
1. Most traits in humans are influenced in this way. Height: Figure 11.13. Probabilities
and complex traits, such as cancer susceptibility.
D. Genes and the environment (Section 11.10): Figure 11.14.
1. Identical cuttings of Hydrangea macrophylla can be blue or red, depending on the soil.
2. Take three identical timberline plants; plant them at different altitudes, and they will
grow to different heights. Same genes, but different environment.
E. Pleiotropy: One gene with multiple effects; fragile-X syndrome (Section 11.11).
KEY TERMS
allele
bell curve
codominance
cross-pollinate
dihybrid cross
dominant
first filial generation (F1)
genotype
heterozygous
homozygous
incomplete dominance
Law of Independent
Assortment
Law of Segregation
monohybrid cross
multiple alleles
parental generation (P)
phenotype
pleiotropy
polygenic inheritance
recessive
rule of addition
rule of multiplication
LECTURE OUTLINE (CHAPTER 12)
I. An Introduction to Human Genetics
A. Why should you be interested in genetics? The dichotomy of these questions:
1. How can sickle cells be both deleterious and protective (malaria)?
2. Why should a woman’s chromosomal makeup give her protection against color
blindness?
3. How can a healthy parent give their offspring an extra copy of a chromosome, as in
Down syndrome?
B. It’s estimated that we all have between 5 and 10 genes with mutant alleles that cause
disease. Why are genetic disorders relatively rare, then? What are they?
II. X-Linked Inheritance (Section 12.1)
A. Essay: Thomas Hunt Morgan: Using Fruit Flies to Look More Deeply into Genetics
1. Morgan was first to find a gene transmitted differently in males and females, because it
was linked (located) on the X chromosome: essay figures 1 and 2.
2. Frequency of recombination and distance separating two genes (breaking a stick).
B. Examples of X-linked genes in humans: Table 12.1.
1. Hemophilia is caused by a mutation in a gene that codes for a blood-clotting protein
(Factor VIII).
2. Duchenne muscular dystrophy is caused by a mutation in the gene that codes for a
protein called dystrophin, found in the sarcolemma of muscle fibers that help regulate
Ca+ ions.
3. Red-green color blindness:
a. Genes code for the proteins that make pigments in the eye necessary for absorbing
the different-colored wavelengths in light.
b. Red and green pigments are made by proteins on the X chromosome.
c. Mutations in the genes for these pigments result in inability to see those colors.
d. These mutations are recessive because one good copy of the gene is sufficient for
color vision: Figure 12.2.
C. Affect men much more frequently than women.
1. Because women have two X chromosomes, they can be heterozygous (have one mutant
allele) but still have normal color vision (0.5 percent of women are color-blind).
2. Men have only one X chromosome, so if they have one mutant allele, they will be color
blind (8 percent are color-blind).
III. Autosomal Genetic Disorders (Section 12.2)
A. A recessive dysfunction related to an autosome is an autosmal recessive disorder.
1. Examples: Table 12.1.
a. Sickle-cell anemia:
i. Prevalent in populations in or from Africa.
ii. Red blood cells become distorted into sickle shape in low oxygen: Figure 12.3.
iii. Mutation is in the gene for the -chain protein of hemoglobin.
iv. Hemoglobin S has a substitution of one amino acid, causing the chain to coalesce
into crystals that distort the red blood cells.
v. Persons with one S allele and one normal A allele do not have the condition but
are called carriers because they can pass the gene on to their offspring (8 percent
of African Americans are carriers).
b. Cystic fibrosis—most common genetic disorder in Caucasian Americans; 1 in 25 is a
carrier.
c. Tay-Sachs—most common in Jewish Americans of central European descent; 1 in
30 is a carrier.
2. The pattern of inheritance.
a. Both parents must have the allele to have a child born with the condition:
Figure 12.4a.
b. Even if both parents are carriers, they have only a one-in-four chance of having an
offspring with the condition.
3. Why are these recessive conditions in which a “faulty” protein is made so prevalent?
a. Confers some advantage.
b. In the case of sickle-cell anemia, which occurs more frequently in populations from
malaria-ravaged sections of Africa, heterozygotes are more resistant to malarial
infection.
c. Malaria is caused by a protozoan parasite transmitted by the Anopheles mosquito.
Some of the life cycle of the parasite must be spent in human red blood cells.
B. Autosomal dominant disorders.
1. Examples: Table 12.1.
a. Huntington disease is a degenerative neural disorder.
b. ALS—Lou Gehrig disease—is also a degenerative neural disorder.
2. Patterns of inheritance (single “faulty” allele of a gene causes damage, even with a
“good” allele present): Figure 12.4b.
C. Pedigrees (Section 12.3)—confronted with medical condition running in a family,
geneticists like to create family tree diagrams or pedigrees, which can be used to
determine whether the disorder is dominant or recessive, and the probability of future
inheritance.
1. Examples: albinism: Figure 12.5.
2. Symbols.
3. Deduction to determine carriers.
IV. Chromosome Aberrations
A. Polyploidy (Section 12.4)—aberrations in the number of chromosome sets.
1. Animals and many plants are diploid (have two of each chromosome).
2. Sometimes organisms are formed with more than this diploid set and are called
polyploid.
3. Although lethal for humans (only 1 percent survive even to birth), polyploid plants may
be more robust (many crop species are polyploid, such as wheat).
B. Aneuploidy (Section 12.5)—incorrect chromosome number.
1. Members of the same species almost always have the same number of chromosomes.
2. Exceptions with fewer or more than the normal number commonly occur (5 percent of
human pregnancies) but are usually lethal.
3. Aneuploidy is caused by nondisjunction—failure of homologous chromosomes or
sister chromatids to separate during meiosis, creating sperm or eggs with more or fewer
than the normal 23 chromosomes: Figure 12.7.
4. Down syndrome—most common form of aneuploidy in human births (0.1 percent of
all live births).
a. Ninety-five percent are caused by trisomy 21.
b. Phenotype—small, oval head; lower-than-normal IQ; short stature; reduced life
span; and infertility in males: Figure 12.8a.
c. Most trisomy 21 is result of nondisjunction during egg formation; only 10 percent
during sperm formation. Detected by karyotype analysis.
d. Frequency of nondisjunction (and Down syndrome) increases with age of the
mother: Figure 12.8b.
5. Abnormal numbers of sex chromosomes.
a. Examples: Table 12.1, Turner syndrome (sterile females with XO) and Klinefelter
syndrome (sterile males with XXY).
b. Usually have a lower-than-normal IQ and other phenotypes.
C. Essay: PGD: Screening for a Healthy Child
1. Using in vitro fertilization technology to screen embryos, so that only those without
genetic mutation are implanted (called preimplantation genetic diagnosis, or PGD).
2. Ethical issues, such as the conditions screened for. Should you screen for height or hair
color?
3. Description of process of IVF (in vitro fertilization): essay figures 1a and 1b.
D. Structural anomalies (Section 12.6): aberrations that occur within a given chromosome.
1. Caused when pieces of chromosomes break off (deletions) and are lost. Example—cridu-chat syndrome, which involves deletion on short arm of chromosome 5: Figure
12.10.
2. May also result when the broken pieces rejoin the same chromosome in the opposite
orientation (inversions, Figure 12.11) or a different chromosome (translocations).
3. May also result when errors occur during recombination, resulting in unequal exchange
(duplications).
KEY TERMS
aneuploidy
autosomal dominant disorder
autosomal recessive disorder
carrier
deletion
pedigree
dominant disorder
Down syndrome
inversion
nondisjunction
polyploidy
recessive disorder
translocation