1

The Final Exam: (150 points)

• Lab 9 -ReproductiveSystems/Development

• Lab 10 –Abortion

• Lab 11 – Mankind and Biodiversity

• Lab 12 – Patterns of Genetic Inheritance (Ch. 20 in the text)

•DON’T FORGET – Lab Notebook check. (40 points)

2

Chapter 20

Patterns of Genetic Inheritance

Why do they share their distinctive traits?

It’s all in the genes.

3

Review

• Genotype and Phenotype• One- and Two-Trait Inheritance• Beyond Simple Inheritance Patterns• Sex-Linked Inheritance

4

Introduction• Genetics?

• the study of heredity. . . .

• the study of how traits are passed from one generation to the next.

• Mendelian Genetics is our focus today.

• Gregor Mendel (1859) – pea plants – Principles (Laws) of Inheritance. . . .

• 1. Law of dominant and recessive

• 2. Law of unit characteristics (now called ‘genes’)

5

• 3. Law of segregation

• 4. Law of independent assortment

• Before we examine these concepts, let us examine some of the genetic terms in Lab #12:

• Chromosomes, genes, and alleles.

• The other terms (definitions) found in the lab will be addressed as we examine this chapter (Ch. 20) in the text.

• You definitely want to know all of these terms for the exam.

6

Genotype and Phenotype

• Genotype refers to an individual’s genes (genetic traits, represented by letters).– Alleles are alternate forms of a gene.

Dominant alleles are assigned uppercase letters, while recessive alleles are assigned lowercase letters.

Homozygous Dominant = EE. Homozygous Recessive = ee. Heterozygous = Ee.

• Phenotype refers to an individual’s physical appearance (physical traits or characteristics)

7

Genetic Inheritance

8

One- and Two-Trait Inheritance• Two types of cell division:• Mitosis – normal cell division (‘duplication

division’).• Meiosis – reduction division (producing sex

cells).• Forming the Gametes.

– Reduction of chromosome number occurs when pairs of chromosomes separate as meiosis occurs.

– Spermatogenesis, oogenesis.

9

Gametogenesis

10

One-Trait Cosses

• Punnett square ?• A square with 4 squares within it.• Is used to determine the phenotypic /genotypic

ratios (the physical and genetic traits and their occurrence in the next generation) among the offspring when all possible sperm are given an equal chance to fertilize all possible eggs.

– If both parents are heterozygous, each child has a 25% chance of exhibiting the recessive phenotype.

11

Heterozygous-Heterozygous Cross

•What phenotypes do you see?

•What genotypes?

•What is the genotypic ratio?

• How would we know an individual’s genotype as to whether they were heterozygous or homozygous?

• Do a test cross.

12

13

• This was called a monohybrid cross.

• They involved a single trait.

• What would it be called if we were following 2 traits?

• Dihybrid cross.

• There would be 16 boxes, not 4!

• Three traits?

• Trihybrid cross.

• What are some examples of complete dominance?

14

15

16

17

18

19

20

21

22

• because a gene is either dominant or recessive.

• Let us go back to the lab and do some genetics problems involving complete dominance in Sections I and II.

• Now let us return to the text (Ch. 20) and look at the topic of “Family Pedigrees for Genetic Disorders”.

23

Family Pedigrees for Genetic Disorders

• A pedigree chart (Family tree) shows the pattern of inheritance for a particular disorder.– Males are designated by squares.– Females are designated by circles.– Shaded circles or squares are affected

individuals.– Vertical line down represents a child,

while an attached horizontal line across represents more children (siblings).

24

Genetic Genetic Disorders Disorders of of InterestInterest

25

Autosomal Recessive Disorders

• In this pattern, the child is affected but neither parent is affected.

• Therefore, since the parents are heterozygous, they can be called carriers.

• Recessive disorders can by passed on by parents who are unaffected (ie. Albinism).

– Tay-Sachs Disease. Allele located on chromosome 15. Jewish of central, eastern European descent. Lysosome buildup in brain, leads to

progressive neurological / psychomotor deterioration.

26

Autosomal Recessive Pedigree Chart

P1

F1/P2

F2/P3

F3/P4

27

• Phenylketonuria (PKU).• Allele located on chromosome 12.• Unable to metabolize phenylalanine causing severe mental retardation.• Treatment: diet low in until brain develops, around age 7.

• Sickle-Cell Disease• Description …..

• Origin…..• HbA vs. HbS• Heterozygotes protected from malaria.

• Prognosis……

28

• Cystic Fibrosis.• Allele located on chromosome 7.• Most common lethal genetic disorder among U.S. Caucasians.

• Epecially thick mucus in the lungs and pancreas.Epecially thick mucus in the lungs and pancreas.• Treatment……Treatment……

29

30

Autosomal Dominant Disorders

• In this pattern, the child and at least one parent are affected, due to a dominant allele on an autosomal chromosome.

• Dominant disorders are passed on by a parent who has, or will develop, the disorder (ie. Achondroplasia, brachydactyly, hyercholesterolemia, Marfan syndrome).

– Neurofibromatosis (NF) Also known as von Recklinghausen disease. Allele located on chromosome 17.

– Huntington Disease (HD). Allele located on chromosome 4.

31

Autosomal Dominant Pedigree Chart

32

HEALTH FOCUS

Preimplantation Genetic Diagnosis !!!!!!

33

Beyond Simple Inheritance Patterns• Unfortunately, life is not so simple as simple

dominance problems would imply.• There are complicating factors, other patterns

of inheritance. . . . • Polygenic (Multifactorial) Inheritance.

– Polygenic - one trait is governed by two or more sets of alleles.

Continuous variation of phenotypes. Skin Color, height, weight, metabolic

rate, behavior, intelligence.– Multifactorial - a polygenic trait that is

particularly influenced by the environment.

34

Polygenic (Multifactorial) Inheritance

35

Environmental Influences• The environment can influence the phenotype.• Human disorders include: cleft lip/palate, club-foot,

hypertension, diabetes, schizophrenia ……• For example: Siamese cats, Himalayan rabbits are

darker in color at the ears, nose, paws, and tail.• Why?• Homozygous for allele involved in melanin

production (ch) via produced enzyme that is active only at lower temperature………

• Therefore, black fur occurs at the extremities where body heat is lost to the environment!

• Polygenic traits seem to be particularly influenced by the environment.

36

Beyond Simple Inheritance Patterns

• Incomplete Dominance and Codominance.– Codominance occurs when alleles are equally

expressed in a heterozygote.– Example: human blood type AB.– Incomplete Dominance is exhibited when the

heterozygote has an intermediate phenotype between that of either homozygote.

Familial hyper/cholesterol/emia (FH) Sickle Cell Disease.

HbA vs. HbS

Heterozygotes protected from malaria.

37

Incomplete Dominance

• Note the characteristics:

• Two different letters are used for the alleles.

• Usually, both letters are lower case.

• The heterozygote represents an “in between” trait.

38

• Now let us return to the lab and examine some problems involving incomplete dominance in section III and IV.

• However, there are yet other patterns influencing inheritance which complicate the process. . . .

• Let us return to the text (Ch. 20) and examine these.

39

Beyond Simple Inheritance

• Multiple Allele Inheritance.– Gene exists in several allelic forms,

although an individual usually only has two of the possible alleles.

ABO Blood Types. A - A antigen on red blood cells. B - B antigen on red blood cells. O - Neither A or B antigen on red

blood cells.

40

Inheritance of Blood Type

41

• Let us now return to the lab problems and do section V.

• Note: there are 4 pages of practice problems which should be completed to get full credit for the lab in your notebook check.

• However, again there are yet other patterns of inheritance. . . . .

• These involve not the autosomes (the 22 pair of non-sex chromosomes) but the sex chromosomes.

• Let us return to the text (Ch. 20) and take a look at . . . .

42

Sex-Linked Inheritance• Traits controlled by alleles on the sex chromosomes

are said to be sex-linked.– On X chromosome = X-linked.– On Y chromosome = Y-linked.

• Most sex-linked alleles are on the X chromosome and are recessive.

• Therefore, males demonstrate if get, females don’t unless homozygous for it.

• Examples of X-linked recessive disorders:– Muscular Dystrophy (Duchenne MD).– Red-Green Color Blindness.– Hemophilia

43

Color-Blindness Cross

44

Pedigree for X-Linked Disorders

45

X-Linked Recessive Disorders• More males than females are affected.• Examples:

– Red-green color blindness.– Muscular Dystrophy

Duchenne Muscular Dystrophy which is a muscle wasting disease.

Symptoms include waddling gait, toe walking, frequent falls, difficulty rising.

Become wheel chair bound, usually die by age 20.

Allele located on chromosome 17.

46

• Hemophilia.• Allele located on chromosome 4.• Two types…….• Hemophilia A – absence of factor VIII.• Hemophilia B – absence of factor IX.• What are other names associated with this

disease ?• Bleeder’s disease, King’s disease, “free bleeders”.• Why was Queen Victoria of the British Commonwealth of significance concerning this disease?

47

Royal Hemophilia Pedigree

48

BIOETHICAL FOCUSGenetic Profiling

1.1. Should people be encouraged, or even required, to have Should people be encouraged, or even required, to have their DNA analyzed so that they can develop programs their DNA analyzed so that they can develop programs to possibly prevent future illness?to possibly prevent future illness?

2.2. Should employers be encouraged, or required, to Should employers be encouraged, or required, to provide an environment suitable to a person’s genetic provide an environment suitable to a person’s genetic profile? Or, should the individual avoid a work profile? Or, should the individual avoid a work environment that could bring on an illness?environment that could bring on an illness?

3.3. How can we balance individual rights with the public How can we balance individual rights with the public health benefit of matching genetic profiles to health benefit of matching genetic profiles to detrimental environments?detrimental environments?

49

Sex-Influenced Traits

• Some traits carried on autosomes can be influenced by gender – through one’s hormones.

• Examples?

• Male-pattern baldness where the male hormone (testosterone) is the culprit.

• Acts as dominant trait in males, recessive in females.

• Length of index finger (longer than ring finger)

50

51