Incomplete Vs. Co-dominance• Codominance - A form of inheritance in which

both alleles are equally shown. • Incomplete dominance - A form of

inheritance in which the heterozygous alleles are both expressed, resulting in a combined phenotype. – Most commonly found in plants.

• A red and a white allele gives pink. If it were codominance, you would see the red and white colors.

Test Cross• Used to determine an organisms genotype.

– Either Bb or BB

• Always a dominant unknown mated with pure recessive

– B? X bb

Human Genetics: Karyotypes

46 TOTAL

23 homologous

pairs

46 TOTALChromosomes

23 homologous

pairs

What is the difference between an Autosome and a Sex-chromosome?

• Autosomes are the first 22 homologous pairs of human chromosomes that do not influence the sex of an individual.

• Sex Chromosomes are the 23rd pair of chromosomes that determine the sex of an individual.

Autosomal Traits• Genes located on Autosomes control

Autosomal traits and disorders.

2 Types of Traits:• Autosomal Dominant• Autosomal Recessive

Autosomal Recessive Traits• In order to express the trait, two recessive alleles

must be present.

• What would be the genotype of an individual with an autosomal recessive trait? (A = dominant)– aa

• What would be the genotype of an individual without the autosomal recessive trait?– AA or Aa – Aa – called a Carrier because they carry the

recessive allele and can pass it on to offspring, but they do not express the trait.

Albinism

Defect of melanin production that results in little or no color in the skin, hair, and eyes

Albinism

Albinism

How does it

happen?

Affected Genotype:

aa

Cystic FibrosisDisease that causes the body to produce unusually thick, sticky mucus that:

•Clogs the lungs and leads to lung infections • Obstructs the pancreas

• Stops natural enzymes from helping the body break down and absorb food

How does it

happen?

Affected Genotype:

cc

Sickle Cell Anemia

Caused by an abnormal hemoglobin shape which causes the red blood cells to have a crescent shape.

Red blood cells carry oxygen.

How does it

happen?

Affected Genotype:

ss

Tay–Sachs disease

• Symptoms:– a build up of lipids in the brain– Seizures– blindness

• Mainly occurs in Jewish people

Tay-Sachs Disease

PKU (phenylketournia)

• symptoms;– cannot break down the specific amino acid

(phenylalanine found in foods like milk)– results in brain damage

• Mainly occurs in people of European descent

Autosomal Dominant Traits

• If dominant allele is present on the autosome, then the individual will express the trait.

• What would be the genotype of an individual with an autosomal dominant trait?– AA and Aa (Heterozygotes are affected)

• What would be the genotype of an individual without the autosomal dominant trait?– aa

Huntington’s Disease

Causes the break down of brain cells, (neurons) in certain areas of the brain.

Causes uncontrolled movements, loss of intellectual faculties, and emotional disturbance.

How does it

happen?

Affected Genotype: HH or Hh

Progeria• Drastic premature aging, rare, die by age 13.

Symptoms include limited growth, alopecia, small face and jaw, wrinkled skin, atherosclerosis, and cardiovascular problems but mental development not affected.

Sex-Linked Traits• Sex-linked traits are produced by genes only on the X

chromosome. – They can be Dominant or Recessive.

• What would be the genotypes of a male and female that have a Sex-linked Dominant trait and do not express the trait?

• Expresses Trait: Male - XA Y Female - XA XA or XA Xa

• No Expression: Male - Xa Y Female - Xa Xa

• What would be the genotypes of a male and female that have a Sex-linked Recessive trait and do not express the trait?

• Expresses Trait: Male - Xa Y Female - Xa Xa

• No Expression: Male - XA Y Female - XA XA or XA Xa (Carrier)

• Most Sex-linked traits are Recessive!

Color Blindness

Inability to see colors in the normal way

How does it happen?

Affected Genotypes:

XbXb

XbY

HemophiliaInability of the blood to clot properly

How does it happen?

Affected Genotypes:

XhXh

XhY

Pedigree Analysis

• A pedigree shows the relationship between parents and children over the generations and how a trait is passed down from one generation to the next.

How to Construct a Pedigree?• A Pedigree is a visual showing the pattern of

inheritance for a trait. (Family tree)

• Symbols and Rules:• Male = Female = • Affected = Unaffected = Carrier =• Link parents together with a line and then

make a vertical line to connect to offspring.

Autosomal Dominant Pedigree• Draw a Pedigree showing a cross between

Heterozygous parents that have 2 boys and 2 girls. (Show all possibilities)

Genotypes of Affected and Unaffected:• AA and Aa = Affected aa = Unaffected

Aa Aa

Aa Aa AAaa

Autosomal Recessive Pedigree• Draw a Pedigree showing a cross between

Heterozygous parents that have 2 boys and 2 girls. (Show all possibilities)

Genotypes of Affected and Unaffected:• AA=Unaffected Aa=Carrier, Unaffected

aa=AffectedAa Aa

Aa Aa AAaa

Sex-Linked Recessive Pedigree

• Draw a Pedigree showing a cross between a normal male and a Carrier Female.

• Genotypes of Parents:• Male = Xh Y Female = XH Xh

XRY

XRY XrY XRXR XRXr

XRXr

Characteristics of Autosomal Dominant, Autosomal Recessive, and Sex-linked Recessive Traits

• In groups, analyze your notes on each type of disorder and examine the pedigrees.

• Come up with rules/characteristics for each type of Trait.

Types of Pedigrees: Recessive

Affected Genotypes: bb

Unaffected Genotypes: BB or Bb

HINT: Recessive Disorders skip generations

Is the Pedigree below showing Recessive Inheritance?

Recessive Inheritance?

Recessive Inheritance?

Types of Pedigrees: Sex-linked

Affected Genotypes: XbXb or XbY

Unaffected Genotypes: XBXB or XBXb and XBY

HINT: Mainly males are affected

Is the Pedigree below showing Sex-Linked Inheritance?

Sex-linked Inheritance?

Sex-linked Inheritance?

Types of Pedigrees: Dominant

Affected Genotypes: BB or Bb

Unaffected Genotypes: bb

Is the Pedigree below showing Dominant Inheritance?

Dominant Inheritance?

Dominant Inheritance?

How many generations?What is genotype of Individual I-1?What type of Inheritance?

How many generations?What is genotype of Individual I-1?What type of Inheritance?

Pedigrees and Genetic Disorders

Mutations

Gene Mutations 1. Caused by a change in the amino acid sequence of a

protein2. Impacts of mutations: lethal, neutral, or beneficial3. Gene mutation are caused by a change to one or more

bases in nucleotide sequence of DNAA. mutations are rare because cells have proofreading and

correction enzymesB. these chance events (mutations) are caused by mutagens

Ex. viruses, UV light, chemicals like mustard gas

Mutations

Chromosomal Mutations1. Caused by a change in structure or number of

chromosomes2. Detected by KARYOTYPING which matches

homologous chromosomes in a diploid (2N) cell by:

1. Size of chromosome 2. Length of chromatid arms 3. Centromere location

Karyotype

1 2 3 4 5

6 7 8 9 10

16 17 18 19 20

Karyotype of a normal female

21 22 23

11 12 13 14 15

1 2 3 4 5

6 7 8 9 10

16 17 18 19 20

Karyotype of a normal male

21 22 23

11 12 13 14 15

Chromosomal Mutations

Structure a. Deletion - loss of part of a chromosome AC DEFb. Duplication - segment is repeated ABBC DEFc. Inversion - orientation is reverse of normal AED CBF

(twisting)d. Translocation - parts are broken off and added to another

chromosome Ex. ABC DEF and GH IJK is changed to ABC JK and GH IDEF

A B C D E F

Theoretically Normal Chromosome Structure

G H I J Kand

note : each letter or segment on a chromosome represents a gene in proper locus

Chromosomal MutationsNondisjunction deals with whole chromosomes or sets

of chromosomes "not coming apart.”During meiosis a cell gets both copies of a chromosome

and the other cell is missing one chromosome because sister chromatids didn’t separate

I. Monosomy is the condition of having only 1 chromosome of a homologous pair

Turner Syndrome= monosomy of 23rd pairII. Trisomy is the condition of having 3 chromosomes of a

homologous pairDown syndrome (21st pair), Klinefelter Syndrome (23rd pair), XYY syndrome (23rd pair)

Down Syndrome

Cystic fibrosis

• Caused by a recessive allele; ff• Symptoms:

– organs produce a thick mucus causing congestion in the lungs

– digestive tract problems– pneumonia like symptoms

• Mainly occurs in Caucasians

Albinism

• Caused by a recessive allele; aa• Symptoms:

– no melanin in the skin• resulting in an albino:

– white skin– pink to red eyes

Huntington disease

• Caused by a dominant allele; HH or Hh

• Symptoms:– breaks down the nervous system, fatal

Sickle Cell Anemia• Caused by a co-dominant allele (A’) which codes for

abnormal hemoglobin – hemoglobin is found on the red blood cells and carries

oxygen• Symptoms:

– sickle shape red blood cells, clotting, extensive pain, can be fatal

• Genotypes:– AA = normal– AA’ = normal but a carrier– A’A’ = diseased

• Mainly African people

Color blindness

• Sex-linked disorder caused by a recessive allele only found on the X sex chromosome:– XC XC = normal female; XC Xc= normal, but a carrier– Xc Xc= color blind female– XC Y = normal male; XcY = color blind male

• Symptoms:– cannot distinguish red from green

Color Blindness

Hemophilia

• Sex-linked disorder caused a recessive allele only found on the X sex chromosome– normal female = XH XH= normal, but a carrier XH Xh

– hemophiliac female = XhXh

– normal male = XHY; XhY = hemophiliac male

• Symptoms:– excessive bleeding from a minor injury, fatal

Down syndrome (trisomy)

• Cause by nondisjunction– too many chromosomes: 3 chromosomes for the

21st pair of homologous chromosomes; resulting in 47 total chromosomes

• Symptoms:– Almond shape eyes– Enlarged tongues– Some can be mentally and physically challenged

Down syndrome (trisomy)

Klinefelter syndrome

• Cause by nondisjunction– too many chromosomes: 3 sex chromosomes =

XXY; the sex is male; resulting in 47 total chromosomes

• Symptoms:– Underdeveloped male sex organs– Sterility– May have feminine body parts

Turner Syndrome

• Cause by nondisjunction– not enough chromosomes; 1 sex chromosome =

XO the sex is female; resulting in 45 total chromosomes

• Symptoms:– Females are usually short– Sex organs may not develop– Sterility

Turner Syndrome

• In a pedigree chart, certain shapes indicate gender and colors signify whether or not they carry the trait or show the trait

• A circle represents a female.

• A square represents a male.

• A horizontal line between 2 people indicates marriage.

• A vertical line extending from a marriage line indicates the offspring from the couple.

• A solid shaded shape represents a person who shows the trait in their phenotype.

• A half shaded shape represents a person who is a carrier of the trait but does not show the trait. NOTE: some pedigrees don’t indicate carriers

Pedigree Analysis

Pedigree Analysis

Pedigree AnalysisGenerations are indicated with Roman numerals (I, II, III) and individuals within generations are marked with arabic numbers (1, 2, 3, 4).

Pedigree Questions: this pedigree doesn’t indicate carriers1. What sex is individual I-2? 2. How many children are in the 2nd generation

from the union of I-1 and I-2? 3. What are their sexes? 4. Which individual was married in generation 2?5. How many daughters are in generation 3?6. How many sons are in generation 4?7. List the 3 individuals who were afflicted with

sickle cell anemia?8. Were individuals I-1 and I-2 carriers of sickle cell?9. How do you know? (Explain your answer to #8)10. List another carrier of sickle cell anemia.

= sickle cell anemia

Karyotype Practice

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23

Down Syndrome Male

Karyotype Practice

Klinefelter Male

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23

Karyotype Practice

Turner Syndrome Female

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23

Karyotype Practice

XYY Syndrome Male

1 2 3 4 5

6 7 8 9 10

11 12 13 14 15

16 17 18 19 20

21 22 23

Unit 9, Part 4 NotesPedigrees and Genetic Disorders

• Definition: a graphic representation of genetic inheritance used by geneticists to map genetic traits

What is a pedigree?What does a pedigree

look like?• Generations in separate

rows indicated by Roman numerals (I, II, III…)

• Individuals within one generation indicated by Arabic numerals (1, 2, 3…)

• Parents connected by horizontal lines

• Offspring connected by vertical lines

Affected

Dead

• Occurs in people of Jewish descent

• Enzyme that breaks down lipids in the brain is defective. Lipid buildup kills brain cells.

• Always results in death, usually by age 5

• Caused by a recessive allele

Let’s look at an example…

Tay Sachs disease

Pedigree for Tay Sachs disease

CarrierCarrier

• Caused by a rare dominant allele

• Doesn’t show up till age 30-50

• Breaks down areas of the brain, loss of control of all body functions

• No treatment

Huntington’s Disease

Pedigree for Huntington’s Disease

carriernormal

What if the trait is sex-linked? How can you tell?

Answer: Most affected individuals are males

Let’s try one…Is this sex-linked or not?

Answer: Yes

• Interactive pedigree activity

• Pedigree quiz• Punnett Square and Pedigr

ee problemsMore practice

with pedigrees…

Sex Chromosomes

• 2 sex chromosomes• Typical Female = XX• Typical Male = XY

Autosomes

Autosomes: Any

chromosome that’s not a sex chromosome

•44 Autosomes•22 pairs of Autosomes

Autosomal Recessive Traits• Heterozygotes are Carriers with a normal phenotype.• Most affected children have normal parents. (Aa x Aa)• Two affected parents will always produce an affected child.

(aa x aa)• Two unaffected parents will not produce affected children

unless both are Carriers. (AA x AA, AA x Aa)• Affected individuals with homozygous unaffected mates will

have unaffected children. (aa x AA)• Close relatives who reproduce are more likely to have

affected children.• Both males and females are affected with equal frequency.• Pedigrees show both male and female carriers.

Examples of Autosomal Recessive Disorders

• Congenital Deafness• Diabetes Mellitus• Sickle Cell anemia• Albinism• Phenylketoneuria (PKU) – Inability to break down

the amino acid phenylalanine. Requires elimination of this amino acid from the diet or results in serious mental retardation.

• Galactosemia – enlarged liver, kidney failure, brain and eye damage because can’t digest milk sugar

• Cystic Fibrosis – affects mucus and sweat glands, thick mucus in lungs and digestive tract that interferes with gas exchange, lethal.

• Tay Sachs Disease – Nervous system destruction due to lack of enzyme needed to break down lipids necessary for normal brain function. Early onset and common in Ashkenazi Jews; results in blindness, seizures, paralysis, and early death.

Autosomal Dominant Traits

• Heterozygotes are affected• Affected children usually have affected parents.• Two affected parents can produce an unaffected

child. (Aa x Aa)• Two unaffected parents will not produce affected

children. (aa x aa)• Both males and females are affected with equal

frequency.• Pedigrees show no Carriers.

Examples of Autosomal Dominant Disorders• Dwarfism• Polydactyly and Syndactyly• Hypertension• Hereditary Edema

• Chronic Simple Glaucoma – Drainage system for fluid in the eye does not work and pressure builds up, leading to damage of the optic nerve which can result in blindness.

• Huntington’s Disease – Nervous system degeneration resulting in certain and early death. Onset in middle age.

• Neurofibromatosis – Benign tumors in skin or deeper• Familial Hypercholesterolemia – High blood cholesterol and propensity for heart disease• Progeria – Drastic premature aging, rare, die by age 13. Symptoms include limited growth,

alopecia, small face and jaw, wrinkled skin, atherosclerosis, and cardiovascular problems but mental development not affected.

Examples of Sex-Linked Recessive Disorders

• Red/Green Colorblindness – Difficulty perceiving differences between colors (red or green, blue or yellow).

• Hemophilia – Absence of one or more proteins necessary for normal blood clotting.

• Deafness• Cataracts – opacity in the lens that can lead to blindness• Night blindness – (Nyctalopia) rods do not work so that can not see in the

dark• Glaucoma – pressure in the eye that can lead to optic nerve damage and

blindness• Duchenne Muscular Dystrophy – progressive weakness and degeneration

of skeletal muscles that control movement due to absence of dystrophin (protein that maintains muscle integrity). Mainly in boys, onset 3-5 yrs, by 12 years can’t walk, and later needs respirator.

Sex-Linked Disorder

Linked to sex chromosomes

Recessive Disorders – caused by recessive alleles

Sex-Linked Recessive Traits• More males than females are affected.• An affected son can have parents who have the

normal phenotype. (XAY x XAXa)• For a daughter to have the trait, her father must also

have it. Her mother must have it or be a carrier. (XaY, XaXa, XAXa)

• The trait often skips a generation from the grandfather to the grandson.

• If a woman has the trait (XaXa), all of her sons will be affected.

• Pedigrees show only female carriers but no male carriers.

Genetic Counselor Activity• Imagine that you are a Genetic

Counselor assigned to family to discuss with them the possibility of their child inheriting a genetic disorder.

• You are given the family history and whether or not the disorder is Autosomal Dominant or Autosomal Recessive.

• Draw Punnett Squares to determine odds of children inheriting the disease and answer the questions on the worksheet.

What is a Pedigree???

Diagram showing a family tree and patterns of inheritance.