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Mader_Essentials_7e_LecturePPT_Ch10_ACCESS.pptxChapter 10
Patterns of Inheritance
Essentials of Biology
SEVENTH EDITION
Sylvia S. Mader Michael Windelspecht
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10.1 Mendel’s Laws
Gregor Mendel
Austrian monk
Worked with garden pea plants in 1860s
When he began his work, most acknowledged that both sexes contributed equally to a new individual.
Unable to account for presence of variations among members of a family over generations
Mendel’s model compatible with evolution
Various combinations of traits are tested by the environment.
Combinations that lead to reproductive success are the ones that are passed on.
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Mendel’s Experimental Procedure
Mendel’s experimental procedure:
Used garden pea, Pisum sativa
Easy to cultivate, short generation time
Normally self-pollinates but can be cross-pollinated by hand
Chose true-breeding varieties—offspring were like the parent plants and each other
Kept careful records of large number of experiments
His understanding of mathematical laws of probability helped interpret results.
Particulate theory of inheritance—based on the existence of minute particles (genes)
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Figure 10.1 Mendel Working in His Garden
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Figure 10.2a Garden Pea Anatomy and Traits
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Figure 10.2b Garden Pea Anatomy and Traits
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One-Trait Inheritance
One-trait inheritance:
Original parents called P generation
First-generation offspring F₁ generation
Second-generation offspring F₂ generation
Crossed green pod plants with yellow pod plants
All F₁ are green pods.
Had yellow pods disappeared?
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Figure 10.3 One-Trait Cross
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Punnett Square
Punnett square:
Shows all possible combinations of egg and sperm offspring may inherit
When F₁ allowed to self-pollinate, F₂ were 3/4 green and 1/4 yellow.
F₁ had passed on yellow pods.
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Mendel’s Interpretation
Mendel reasoned
ratio only possible if:
F₁ parents contained two separate copies of each heritable factor
(one dominant and one recessive)
Factors separated when gametes were formed and each gamete carried only one copy of each factor.
Random fusion of all possible gametes occurred at fertilization.
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Mendel’s First Law
Mendel’s first law of inheritance—law of segregation
Cornerstone of his particulate theory of inheritance
The law of segregation states the following:
Each individual has two factors for each trait.
The factors segregate (separate) during the formation of the gametes.
Each gamete contains only one factor from each pair of factors.
Fertilization gives each new individual two factors for each trait.
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One-Trait Testcross 1
One-trait testcross:
To see if the F₁ carries a recessive factor, Mendel crossed his F₁ generation green pod plants with true-breeding, yellow pod plants.
He reasoned that half the offspring would be green and half would be yellow.
His hypothesis that factors segregate when gametes are formed was supported.
Testcross
Used to determine whether or not an individual with the dominant trait has two dominant factors for a particular trait
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One-Trait Testcross 2
One-trait testcross, continued
If a parent with the dominant phenotype has only one dominant factor, the results among the offspring are
If a parent with the dominant phenotype has two dominant factors, all offspring have the dominant phenotype.
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Figure 10.4 One-Trait Testcross
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The Modern Interpretation of Mendel’s Work
Modern Interpretation of Mendel’s Work
Scientists note parallel between Mendel’s particulate factors and chromosomes
Chromosomal theory of inheritance
Chromosomes are carriers of genetic information.
Traits are controlled by discrete genes that occur on homologous pairs of chromosomes at a gene locus.
Each homologue holds one copy of each gene pair.
Meiosis explains Mendel’s law of segregation and why only one gene for each trait is in a gamete.
When fertilization occurs, the resulting offspring again have two genes for each trait, one from each parent.
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Alleles
Alleles—alternative forms of a gene
Dominant allele masks the expression of the recessive allele.
For the most part, an individual’s traits are determined by the alleles inherited.
Alleles occur on homologous chromosomes at a particular location called the gene locus.
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Figure 10.5 Alleles on Homologous Chromosomes
a. Various alleles are located at specific loci.
b. Duplicated chromosomes show that sister chromatids have identical alleles.
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Genotype Versus Phenotype
Genotype versus phenotype:
Genotype—alleles the individual receives at fertilization
Homozygous—two identical alleles
Homozygous dominant
Homozygous recessive
Heterozygous—two different alleles
Phenotype—physical appearance of the individual
Mostly determined by genotype
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Table 10.1 Genotype Versus Phenotype
| Allele Combination | Genotype | Phenotype |
| A A | Homozygous dominant | Normal pigmentation |
| A a | Heterozygous | Normal pigmentation |
| a a | Homozygous recessive | Albinism |
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Two-Trait Inheritance
Two-trait inheritance:
Mendel crossed tall plants with green pods (TTGG) with short plants with yellow pods (ttgg).
F₁ plants showed both dominant characteristics—tall and green pods.
Two possible results for F₂
If the dominant factors always go into gametes together, F₂ will have only two phenotypes.
Tall plants with green pods
Short plants with yellow pods
If four factors segregate into gametes independently, four phenotypes would result.
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Figure 10.6 Two-Trait Cross by Mendel 1
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Figure 10.6 Two-Trait Cross by Mendel 2
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Mendel’s Second Law—Independent Assortment
Based on the results, Mendel formulated his second law of heredity.
Law of independent assortment
Each pair of factors segregates (assorts) independently of the other pairs.
All possible combinations of factors can occur in the gametes.
When all possible sperm have an opportunity to fertilize all possible eggs, the expected phenotypic results of a two-trait cross are always
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Two-Trait Testcross
Two-trait testcross in fruit fly
Fruit fly Drosophila melanogaster
Used in genetics research
Wild-type fly has long wings and gray body
Some mutants have vestigial wings and ebony bodies.
L= long, l = short, G = gray, g = black
Can’t determine genotype of long-winged gray-bodied fly (L Blank G Blank)
Cross with short-winged black-bodied fly (lowercase llgg)
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Figure 10.7 Two-Trait Testcross
In this example,
ratio
of offspring indicates L blank G Blank fly was L lowercase l G lowercase g (dihybrid).
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Mendel’s Laws and Probability
Mendel’s laws and probability:
Punnett square assumes:
Each gamete contains one allele for each trait
Law of segregation
Collectively the gametes have all possible combinations of alleles
Law of independent assortment
Male and female gametes combine at random.
Use rules of probability to calculate expected phenotype ratios
Rule of multiplication—chance of two (or more) independent events occurring together is the product of their chances of occurring separately
Coin flips—odd of getting tails is ½, odds of getting tails when you flip 2 coins ½ × ½ = ¼
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Figure 10.8 Mendel's Laws and Meiosis
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10.2 Mendel’s Laws Apply to Humans
Pedigree
Chart of a family’s history in regard to a particular genetic trait
Males are squares.
Females are circles.
Shading represents individuals expressing disorder.
Horizontal line between circle and square is a union.
Vertical line down represents children of that union.
Counselor may already know pattern of inheritance and then can predict chance that a child born to a couple would have the abnormal phenotype.
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Pedigrees for Autosomal Disorders
Pedigrees for autosomal disorders
Autosomal recessive disorder
Child can be affected when neither parent is affected.
Heterozygous parents are carriers.
Parents can be tested before having children.
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Figure 10.9 Autosomal Recessive Pedigree
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Autosomal Dominant Disorder
Autosomal dominant disorder:
Child can be unaffected even when parents are heterozygous and therefore affected.
When both parents are unaffected, none of their children will have the condition.
No dominant gene to pass on
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Figure 10.10 Autosomal Dominant Pedigree
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Figure 10.11 Methemoglobinemia
Genetic disorders of interest
Autosomal disorders
Methemoglobinemia—lack enzyme to convert methemoglobin back to hemoglobin
Relatively harmless, bluish-purplish skin
Division of Medical Toxicology, University of Virginia
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Figure 10.12 Cystic Fibrosis
Cystic fibrosis—autosomal recessive disorder
Most common lethal genetic disorder among Caucasians in the United States
Chloride ion channel defect causes abnormally thick mucus.
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Figure 10.13 Alkaptonuria
Alkaptonuria—autosomal recessive disorder
Lack functional homogentisate oxygenase gene
Accumulation of homogentisic acid turns urine black when exposed to air
Biophoto Associates/Science Source
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Figure 10.14 Sickle-Cell Disease
Sickle-cell disease—autosomal recessive disorder
Single base change in globin gene changes one amino acid in hemoglobin
Makes red blood cells sickle-shaped
Leads to poor circulation, anemia, low resistance to infection
Eye of Science/Science Source
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Figure 10.15 Huntington Disease
Huntington disease—autosomal dominant disorder
Progressive degeneration of neurons in brain
Mutation for huntingtin protein
Patients appear normal until middle-aged—usually after having children.
Test for presence of gene
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10.3 Beyond Mendel’s Laws
Incomplete dominance
Heterozygote has intermediate phenotype.
The best examples are in plants. In a cross between a true-breeding, red-flowered plant strain and a white-flowered strain, the offspring have pink flowers. Crossing the pink plants, the offspring’s phenotypic ratio is 1 red-flowered : 2 pink-flowered : 1 white-flowered.
Familial hypercholesterolemia is an example in humans. Persons with one mutated allele have an abnormally high level of cholesterol in the blood, and those with two mutated alleles have a higher level still.
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Figure 10.16 Incomplete Dominance in Plants
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Figure 10.17 Incomplete Dominance in Humans
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Multiple-Allele Traits
Multiple-allele traits:
ABO blood group inheritance has three alleles
antigen on red blood cells
antigen on red blood cells
i = neither A nor B antigen on red blood cells
Each individual has only two of the three alleles
Both
are dominant to i
are codominant—both will
be expressed equally in the heterozygote.
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Figure 10.18 Inheritance of ABO Blood Type
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Polygenic Inheritance
Polygenic inheritance:
Trait is governed by two or more sets of alleles
Each dominant allele has a quantitative effect on phenotype and effects are additive.
Result in continuous variation—bell-shaped curve
Multifactorial traits—polygenic traits subject to environmental effects
Cleft lip, diabetes, schizophrenia, allergies, and cancer
Due to combined action of many genes plus environmental influences
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Figure 10.19 Height in Humans, a Polygenic Trait
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Environmental Influences
Environmental influences:
In response to UV radiation, melanin is produced.
Human production of melanin in skin increases closer to the equator to protect skin from radiation.
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Figure 10.21 Gene Interactions and Eye Color
Multiple pigments are involved in determining eye color.
(red eye): Mediscan/Alamy Stock Photo; (brown eye): stylephotographs/123RF; (blue eye): lightpoet/123RF
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Pleiotropy
Pleiotropy:
Single genes have more than one effect.
Marfan syndrome is due to production of abnormal connective tissue.
Other examples include sickle-cell anemia and porphyria.
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Figure 10.22 Marfan Syndrome, Multiple Effects of a Single Human Gene
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Linkage
Two traits on same chromosome—gene linkage
Two traits on same chromosome do NOT segregate independently
Recombination between linked genes
Linked alleles stay together—heterozygote forms only two types of gametes, produces offspring only with two phenotypes.
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Figure 10.23 A Selection of Traits Located on Human Chromosome 19
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10.4 Sex-Linked Inheritance
Females are XX
All eggs contain an X
Males are XY
Sperm contain either an X or a Y
Y carries SRY gene—determines maleness
X is much larger and carries more genes.
X-linked—gene on X chromosome
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Sex-Linked Alleles
Sex-linked alleles:
Fruit flies have same sex chromosome pattern as humans.
When red-eyed female mated with mutant white-eyed male, all offspring were red-eyed.
In the F₂, the
ratio was found but underline all of the white-eyed
flies were males
Y chromosome does not carry alleles for X-linked traits.
Males always receive X from female parent, Y from male parent.
Carrier—female who carries an X-linked trait but does not express it.
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Figure 10.24 X-Linked Inheritance
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Pedigree for Sex-Linked Disorder
Pedigree for sex-linked disorder
X-linked recessive disorder
Male offspring inherit trait from the female parent—son’s X comes from the female parent
More males than females have disorder—allele on X is always expressed in males
Females who have the condition inherited the mutant allele from both their female parent and their male parent
Conditions appear to pass from male grandparents to male grandsons
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Figure 10.25 X-Linked Recessive Pedigree
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X- and Y-Linked Disorders
X-linked dominant
Only a few traits
Daughters of affected males have the condition.
Affected females can pass condition to female offspring and male offspring
Depends on which X inherited from a carrier female parent if male parent is normal
Y chromosome
Only a few disorders
Present only in males and are passed to all male offspring but not female offspring
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X-Linked Recessive Disorders
X-linked recessive disorders:
Color blindness
About 8% of white males have red-green color blindness.
Duchenne muscular dystrophy
Absence of protein dystrophin causes wasting away of muscles.
Therapy—immature muscle cells injected into muscles
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Figure 10.26 Muscular Dystrophy
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(left, right): Courtesy of Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory, University of Rochester Medical Center; (center): ©Muscular Dystrophy Association
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Figure 10.1 Mendel Working in His Garden - Text Alternative
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The chart shows the data as follows:
Trait 1. Stem length. Recessive: short; Dominant: tall. Trait 2. Pod shape. Recessive: Constricted. Dominant: Inflated. Trait 3. Seed shape. Recessive: Wrinkled. Dominant: Round. Trait 4. Seed color. Recessive: Green. Dominant: Yellow. Trait 5. Flower position. Recessive: Terminal. Dominant: Axial. Trait 6. Flower color. Recessive: White. Dominant: Purple. Trait 7. Pod Color. Recessive: Yellow. Dominant: Green.
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Figure 10.2a Garden Pea Anatomy and Traits - Text Alternative
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A. Flower structure. Pollen grains containing sperm are produced in the anther. When pollen grains are brushed onto the stigma, sperm fertilizes eggs in the ovary. Fertilized eggs are located in ovules, which develop into seeds.
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Figure 10.2b Garden Pea Anatomy and Traits - Text Alternative
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B. Cross-pollination. 1. Cut away anthers. 2. Brush on pollen from another plant. 3. The result of a cross from a parent that produces round, yellow seeds and a parent that produces wrinkled yellow seeds.
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Figure 10.3 One-Trait Cross - Text Alternative
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In the P generation, the green pod and yellow pod with gametes (uppercase g and lowercase g) are crossed. In F1 generation, all plants are green (uppercase g lowercase g). In F2 generation, the uppercase g lowercase g eggs and uppercase g lowercase g sperms are crossed. The offspring produced are uppercase g lowercase g, lowercase g lowercase g, uppercase g uppercase g, and uppercase g lowercase g. Except lowercase g lowercase g which is yellow the rest are green. F2 generation phenotypic ratio is 3 green: 1 yellow. The key is uppercase G equals green pod and lowercase g equals yellow pod.
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Figure 10.4 One-Trait Testcross - Text Alternative
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First the uppercase g lowercase g green pod and lowercase g lowercase g yellow pod are crossed. The possible genotypes produced are uppercase g lowercase g green pod and lowercase g lowercase g yellow pod. Phenotypic ratio: 1 green: 1 yellow. Next, the uppercase g uppercase g green pod and lowercase g lowercase g yellow pod are crossed. The possible genotypes produced are uppercase g lowercase g green pod. Phenotype: all green pods.
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Figure 10.6 Two-Trait Cross by Mendel 1 - Text Alternative
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P generation has green pod T T G G (all uppercase), and yellow pod t t g g (all lowercase). P gametes are T G (both uppercase) and t g (both lowercase). In F1 generation, all plants are tall with green pods uppercase T lowercase t uppercase G lowercase g.
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Figure 10.6 Two-Trait Cross by Mendel 2 - Text Alternative
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In Punnett square, the F1 gametes are TG, Tg, tG and tg. The vertical axis is marked sperm, the horizontal top axis is marked as eggs and the horizontal bottom axis as offspring. The F2 generation has gametes TTGG, TTGg, TtGG, TtGg, TTGg, TTgg, TtGg, Ttgg, TtGG, TtGg, ttGG, ttGg, TtGg, Ttgg, ttGg, ttgg. F2 phenotypic ratio is given as 9 tall plant, green pod (green highlight) : 3 tall plant, yellow pod (yellow) : 3 short plant, green pod (orange) : 1 short plant, yellow pod (blue). Key: T equals tall plant, t equals short plant, G equals green pod, g equals yellow pod.
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Figure 10.5 Alleles on Homologous Chromosomes - Text Alternative
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A homologous pair has the alleles (uppercase g lowercase g, uppercase r lowercase r, uppercase s lowercase s and lowercase t uppercase t) placed at a gene locus. The duplicated chromosomes show that sister chromatids have identical alleles.
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Figure 10.7 Two-Trait Testcross - Text Alternative
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Two-trait test cross has P generation genotypes LlGg (long wings and gray body) crosses with llgg (short wings and black body). In Punnett square, the F1 generation has gametes LG, Lg, IG and ig on the vertical axis marked sperms, ig eggs on horizontal top axis and offspring is marked on horizontal bottom axis. The offsprings formed are LiGg, Llgg, llGg and llgg. The F1 phenotypic ratio are 1 long wings, gray body (green highlighted) : 1 long wings, black body (yellow) : 1 short wings, gray body (orange) : 1 short wings, black body (blue). Key: L equals long wings, l equals short wings, G equals gray body, g equals black body. The F1 generation is 1:1:1:1.
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Figure 10.8 Mendel's Laws and Meiosis - Text Alternative
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The parent cell has two pairs of homologous chromosomes (uppercase a lowercase a, uppercase b lowercase b). In meiosis 1: Homologues can align either way during metaphase. At the end of meiosis 2, all possible combinations of chromosomes and alleles result: Uppercase a uppercase b, lowercase a lowercase b, uppercase a lowercase b, lowercase a uppercase b.
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Figure 10.9 Autosomal Recessive Pedigree - Text Alternative
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The pedigree shows that the parents are carriers for an autosomal recessive disorder. An affected parent (aa) on cross with an unaffected A_ (one allele unknown) on step 1 to form A_, Aa, Aa and A_ in step 2. The alleles in step 3 are Aa, Aa, A_, and A_. Alleles in the final step 4 are aa, aa and A_. Key: aa equals affected, Aa equals carrier (unaffected), AA equals unaffected and A_ equals unaffected (one allele unknown).
The text underneath reads:
Unaffected parents can produce children who are affected.
Heterozygotes (Aa) are unaffected.
Both males and females may be affected with equal frequency.
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Figure 10.10 Autosomal Dominant Pedigree - Text Alternative
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The pedigree shows that the parents are carriers for an autosomal dominant disorder. Two affected parents (Aa) on crossing in step 1 forms aa, Aa, A_, aa, aa and aa alleles in step 2. The alleles in step 3 are Aa, Aa, aa, aa, aa and aa. Key: AA equals affected, Aa equals affected, A_ equals affected and aa equals unaffected.
The text underneath reads:
Children who are affected will have at least one parent who is affected.
Heterozygotes (Aa) are affected.
Both males and females may be affected with equal frequency.
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Figure 10.12 Cystic Fibrosis - Text Alternative
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The cytoplasm contains the chloride ions (Cl minus in green) and water (H2O in blue), are trapped inside the cell. The defective chloride ion channel does not allow chloride ions to pass through them. The lumen of respiratory tract are filled with thick and sticky mucus.
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Figure 10.15 Huntington Disease - Text Alternative
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The micrograph at the left has, many neurons in normal brain and the micrograph at the right shows the loss of neurons in a brain with Huntington’s disease which is a neurological disorder.
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Figure 10.16 Incomplete Dominance in Plants - Text Alternative
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The crossing of two pink flowers as parents (R1R2 cross R1R2), gives the offspring which are given in Punnett square. The vertical axis is marked sperm, the horizontal top axis is marked eggs and the horizontal bottom axis is marked as offspring. The offspring are as follows: R1R1, a red flower; R1R2, a pink flower; R1R2, a pink flower; R2R2, a white flower. Key: 1 R1R1 equals red flower: 2 R1R2 equals pink flower: 1 R2R2 equals white flower. Phenotypic ratio is 1:2:1. The reappearance of the three phenotypes in this generation shows that they are still dealing with a single pair of alleles.
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Figure 10.17 Incomplete Dominance in Humans - Text Alternative
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The vertical axis ranges from 0 through 1000 in the intervals of 100. The approximate data are as follows: Normal: 160 through 260, heterozygote: 290 through 550, and homozygote: 600 through 1,020. The photo of a human hand on the side has bulges, marked as cholesterol deposits.
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Figure 10.18 Inheritance of ABO Blood Type - Text Alternative
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The parent alleles taken for mating are uppercase I superscript B lowercase i and uppercase I superscript A lowercase i in which allele is recessive and the uppercase I superscript A and uppercase I superscript B are dominant parent genotypes. On mating, the resulting offspring are given in Punnett squares. The vertical axis is marked sperm, the horizontal top axis is marked eggs and the horizontal bottom axis is marked offspring. The offspring obtained are uppercase I superscript A uppercase I superscript B (purple highlighted), uppercase I superscript B lowercase i (red highlighted), uppercase I superscript A lowercase I (blue highlighted), and lowercase i lowercase I (colorless). Phenotype ratio as 1:1:1:1. Key: Blood type A (blue highlighted), Blood type B (red highlighted), Blood type AB (violet color) and Blood type O (colorless).
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Figure 10.19 Height in Humans, a Polygenic Trait - Text Alternative
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In the graph at the bottom, the horizontal axis from short to tall, ranges from 62 through 74 in increments of 2. A bell curve starts at the origin, reaches a peak at height equals 68 inches and slopes down to the horizontal axis. The region under the curve between height equals 65 inches and 71 inches is shaded and labeled most are this height, and the areas on either side are labeled few. The graph at the top with the horizontal axis labeled height in inches, ranging from 60 through 75 in increments of 5, shows a photo of people standing in the shape of the bell-shaped curve. Please note the data are approximate.
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Environmental Influences - Text Alternative
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The vertical axis shows the frequency. The horizontal axis shows the number of dominant alleles ranging from 0 through 6 in the intervals of 1 units. The graph shows a bell-shaped curve indicating many phenotypes which are categorized from 0 through 6. The majority have dark skin in middle ranges (1.5 through 4.5) and only few have extreme range of skin. The data is as follows:
0: a a b b c c (all lowercase.
1: uppercase A a b b c c, a a uppercase B lowercase b c c, a a b b uppercase C c.
2: uppercase A a uppercase B b c c, uppercase A a b b uppercase C c, a a uppercase B b uppercase C c, uppercase A uppercase A b b c c, a a uppercase B uppercase B c c , a a b b uppercase C uppercase C.
3: uppercase A a uppercase B b uppercase C c, a a uppercase B b uppercase C uppercase C, uppercase A uppercase A b b uppercase C c, uppercase A a b b uppercase C uppercase C, uppercase A uppercase A uppercase B b c c, a a uppercase B uppercase B uppercase C c, uppercase A a uppercase B uppercase B c c.
4: a a uppercase B uppercase B uppercase C uppercase C, uppercase A uppercase A b b uppercase C uppercase
