Unit 11: Inheritance Patterns of Human Traits

Simple Autosomal Recessive

• TT-normal
• Tt-carrier
• tt-affected
• Albinism
• a defect of the gene that results in the absence of the pigments such as melanin
• pale skin, eye conditions, sensitive to the sun

• Cystic Fibrosis
• thick mucus in the lungs and digestive track
• one of the most common genetic disease in white Americans
• can be treated with physical therapy, special diets, drug therapies, and gene therapy

• Phenlyketonuria (PKU)
• caused by a missing enzyme that is needed to break down fats 
• can cause severe mental retardation but all babies in U.S. are tested soon after birth
•  Children that have this disease must have a special diet that does not have phenylalanine in it until they reach around 5 or 6
• Hereditary Deafness (Otosclerosis)
• Hitchhiker's Thumb

• Tay-Sachs
• Common in Jewish people
• this disease is caused by a missing enzyme that breaks down a lipid produced and stored in the tissues of the central nervous system
• The child dies by the age of 2 or 3
• no cure

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Simple Autosomal Dominant

• TT, Tt-affected
• tt-normal
• No carriers
• Tongue Rolling

• Huntington's Disease
• the tissue in the middle of the brain begins to die
• symptoms begin between ages of 30-50
• these people lose control of their muscles.
• Cataracts
• the clouding of the lens of the eye
• Polydactyly (extra fingers or toes)
• Common - 1 in every 800 births
• See http://www.examiner.com/article/here-comes-honey-boo-boo-niece-s-duplicate-thumb-likely-caused-by-mutant-gene

• Achondroplasia (dwarfism)

Autosomal Dominant and Autosomal recessive Diseases:

• Some diseases are carried by dominant alleles (B), some are carried by recessive alleles (b).
• If the disease is carried by a dominant alleles, then the offspring need only inherit one allele to express the disease (BB or Bb).
• If the disease is carried by a recessive allele, then the offspring needs two recessive alleles to express the disease (bb).
• If a person has just one defective gene (Bb), then the person is known as a carrier. They will not express the disease but can pass it to their offspring. Only recessive alleles can be carried.

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Codominant Autosomal Recessive

• Sickle-Cell Anemia
• red blood cells are abnormal (have a crescent shape) blocking small blood vessels causing pain and anemia (low red blood cell count)
• pain, lethargy, anemia, organ failure, stroke
• common in African Americans
• TT-normal
• Tt-shows both normal and sickle cells - has few symptoms, however
• tt-all sickle cells

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Sex-Linked Recessive (Carried on the X Chromosome)

• XcXc, XcY-affected
• XCXc-carrier, not affected
• XCXC, XCY-normal
• Colorblindness
• total or partial loss of ability to distinguish colors
• Hemophilia
• a disorder in which the blood does not clot properly
• Muscular Dystrophy
• the muscles atrophy (become smaller and no longer function properly)
• causes muscle weakness and loss of muscle tissue, which get worse over time

• Icyhyosis Simplex (dry, scaly skin)

Polygenic (Controlled by more than one gene)

• Skin, Hair, Eye color
• Foot size
• Nose length
• Height

Multiple Alleles (More than two alleles available in the gene pool)

• ABO Blood Groups
• Rh Blood Factor

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Chromosome Problems

Nondisjunction

Down Syndrome (Trisomy 21; Mongolism)

• An extra chromosome of the 21st pair
• Caused by nondisjunction
• Mentally retarded
• Slanted Eyes
• Large, thick tongue
• Poor muscle tone
• Abnormal palm and foot prints
• Usually overweight

Kleinfelter Syndrome

• An extra X chromosome (XXY)
• Male
• Tall and thin
• Mentally retarded
• Abnormal breast tissue
• Caused by nondisjunction
• May appear normal
• Sterile

Turner's Syndrome

• Monosomy - missing X chromosome (X_)
• Caused by nondisjunction
• Immature sexual characteristics
• Mentally Retarded
• Sterile

• Linda Hunt of NCIS Los Angeles

Super Female; Triple X (XXX)

• Caused by nondisjunction
• Female
• An extra X chromosome (XXX)
• Good Athelete
• Mentally retarded to a certain extent

• Ewa Klobukowska, a 1964 Olympic sprint bronze medalist who was the first woman to fail the sex chromosome test during the 1967 European Cup. “One chromosome too many to be declared a woman for the purposes of athletic competition” was the statement, and she was obliged to return all her medals. She gave birth to a baby the following year. 
• Also see a 2006 case: http://espn.go.com/olympics/story/_/id/8192977/failed-gender-test-forces-olympian-redefine-athletic-career-espn-magazine

Jacob's Syndrome (XYY)

• Caused by nondisjunction
• Male over six feet tall
• Persistent acne
• Speech problems
• Delayed maturity
• Extremely aggressive*
• High percentage are criminally insane

XXXY

• Caused by nondisjunction)
• Male
• Infertile
• Extremely agressive* behavior problems
• High Voice

XXYY

• Male
• 48 Chromosomes
• See: http://xxyysyndrome.org/main/

Fragile X Syndrome

• caused by a gene mutation on the X chromosome (the expansion or lengthening of the FMR1 gene)
• When the gene lengthens it switches off production of a protein that is involved in brain development and other functions
• Usually severely affects males more than females
• mental retardation

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Missing Pieces of Chromosomes

Prader-Willi Syndrome

• part of chromosome 15 is missing, intellectual disability is common

Wolf-Hirschhorn Syndrome

• part of chromosome 4 is missing
• Children with this syndrome have profound intellectual disability

Cri du chat syndrome (cat's cry syndrome)

• part of chromosome 5 is missing
• heart defects are common

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Detecting Genetic Disorders

• Amniocentesis is removing and testing a sample of amniotic fluid (the liquid that surrounds a fetus).
• Karyotype

• Can see if there are the correct number of chromosomes
• Ultrasound (sonogram) is using sound waves to determine the position and anatomy of the offspring.
• Fetoscopy is the direct observation of the fetus and surrounding tissues.

***FYI: The term intellectual disability is now used instead of mental retardation.

Unit 11: Applied Genetics Notes, Vocabulary, and Study Guide

Unit 10 and 11 Combined Vocabulary: https://quizlet.com/_1ypks5

Unit 11 Vocabulary: https://quizlet.com/_ve9xc

Unit 11 Study Guide: https://quizlet.com/_1e9w1s

Unit 11: Applied Genetics CONCISE Notes

2.       Dihybrid Cross – crossing two traits between parent organisms (16 square) - See Dihybrid Crosses

a.       Determine the alleles for the parents

b.      Use the FOIL method to mix up the alleles - multiply the first, outside, inside, last in the group

c.       Put them around the Punnett Square

d.      Multiply (cross) the alleles beside the square with the alleles above the square

e.      Determine the possible genotypes of the offspring in fraction, percent, and ratio

f.        Determine the possible phenotypes of the offspring in fraction, percent, and ratio

                                                               i.      Ex. Right handedness is dominant to left handedness. Freckles is dominant to no freckles. Cross two parents that are heterozygous for both traits: RrFf x RrFf

                                                             ii.      FOIL: RrFf = RF, Rf, rF, rf (same for both since they are the same)

Then complete the Punnett Square just as you would a 4 square one.

Video: FOIL and Dihybrid Cross

Video: How to Complete a Dihybrid Cross - Go to 4:09

3.       Incomplete Dominance – when neither allele is completely dominant, a third phenotype - a trait that exists that between the two traits

a.       Ex. Cross Red Snapdragon and White Snapdragon flowers

b.      RR = red; R’R’ = white; RR’ = pink

c.       Cross a Red snapdragon (RR) with a White snapdragon (R’R’)

d.      All of the offspring are Pink (RR’)

Video: How to Complete an Incomplete Dominance Punnett Square - Go to 4:37

4.       Codominance – both alleles are dominant, so both show up - are produced

a.       Ex. Cross Black feathered chickens and White feathered chickens

b.      B = black feathers; W = white feathers

c.       Cross a black feathered chicken (BB) with a white feathered chicken (WW)

d.      All of the offspring are Black and White feathered (BW)

Video: How to Complete a Codominance Punnett Square

5.       Multiple Alleles – when there are more than two alleles in the gene pool for a trait

a.       Ex. Blood Type; Three alleles: A, B, O; Four Main Blood Types = A, B, AB, O (positive and negative types are different)

b.      If a person receives the wrong blood type in a transfusion they could die because the cells would clump together causing a clot

Video: How to Complete Blood Type Punnett Square Problems

6.       Polygenic Traits – traits controlled by two or more genes

a.       Eye color, skin color…

Video: Polygenic Traits

7.       Linked Genes – when genes are close together on a chromosome and tend to be inherited together (bends the Law of Independent Assortment)

a.       Linkage map (chromosome map)

                                                               i.      Shows the location of genes on a chromosome

                                                             ii.      Genes that cross over frequently must be farther apart than genes that cross over rarely

b.      Ex. Red hair and freckles seem to be linked

Video: Linked Genes

8.       Sex-Linked Genes – when linked genes are found on the sex chromosomes (sex-linked traits)

a.       Thomas Hunt Morgan experimented with fruit flies and found that one pair of chromosomes controlled the sex of the organism

                                                               i.      XX – Girl

                                                             ii.      XY – Boy

                                                            iii.      Autosomal chromosomes (autosomes) are the other 22 pairs of chromosomes in humans
                                         iv. The 23rd pair of chromosomes are the sex chromosomes and determine if you are male or female

•                                  See Unit 10: The Chromosome Theory of Inheritance

Video: Chromosome Theory of Inheritance and The Fruit Fly

b.      X chromosome contains more genes than the Y chromosome

                                                               i.      This means that a male is more likely to inherit a recessive gene if it is located on the X chromosomes and not found on the Y chromosome

c.       Main kinds of sex linked genes in humans

                                                               i.      Hemophilia – a rare bleeding disorder in which the blood doesn't clot normally; people bleed longer than others; usually occurs in males

                                                             ii.      Color Blindness - people cannot tell the difference between red and green

1.       Carried on the X chromosome

2.       X^B is normal; X^b is colorblind; Y does not have the allele

3.       Females have two alleles for the genes, males only have one
True of all recessive X-linked traits:
1. If the mother has the trait, all of her sons will have it.
2. If the father has the trait but the mother does not carry the trait, then all of their daughters will carry the trait.
3. If the mother is a carrier and the father does not have the trait, daughters have a 50% chance of being a carrier and sons have a 50% chance of having the trait.
4. Males cannot carry the trait, they either have the trait or they do not.

Video: How to Complete X-Linked Punnett Squares - Go to 5:46

Video: X-Linked Traits: Hemophilia

9.       Pedigrees – shows how traits are inherited in a family; like a family tree of genetic inheritance

a.       Males are represented by squares

b.      Females are represented by circles

c.       Affected persons (show the trait) are shaded

d.      Carriers – someone who is heterozygous for a trait; they do not have the trait but can pass is to offspring -  are shown by a half shaded circle or square

e.      Roman numeral I is the parent generation (P1)

f.        The youngest generation is at the bottom

g.       Roman numeral II are the children of the P1 parents and their spouses (F1)

h.      Roman numeral III are the children of the F1 children and their spouses (F2)

i.         A horizontal line between a circle and square represents parents

j.        A vertical line between the parents show the offspring of those parents

k.       You must determine if the trait is dominant or recessive and figure out the genotype of different individuals by making Punnett Squares and using all of the skills you have learned thus far.

10. Autosomal Dominant and Autosomal recessive Diseases:

a. Some diseases are carried by dominant alleles (B), some are carried by recessive alleles (b).

b. If the disease is carried by a dominant alleles, then the offspring need only inherit one allele to express the disease (BB or Bb).

c. If the disease is carried by a recessive allele, then the offspring needs two recessive alleles to express the disease (bb).

d. If a person has just one defective gene (Bb), then the person is known as a carrier. They will not express the disease but can pass it to their offspring. Only recessive alleles can be carried.
e. With autosomal recessive inheritance, all affected individuals will be homozygous recessive.

f. With dominant inheritance, all affected individuals will have at least one dominant allele. They will be either homozygous dominant or heterozygous.

11. Sex-Linked Diseases

a. With sex-linked inheritance, more males (XY) than females (XX) usually have the trait. Sex-linked inheritance is usually recessive. 

Videos: Solving Pedigrees 1 - 3

1

2

3

10.   Testing For Genetic Diseases

a.       Amniocentesis is removing and testing a sample of amniotic fluid (the liquid that surrounds a fetus).

b.      Ultrasound (sonogram) is using sound waves to determine the position and anatomy of the offspring.

c.       Fetoscopy is the direct observation of the fetus and surrounding tissues.

Video: Ultrasound Amniocentesis

Other Disorders

11.   Muscular Dystrophy – sex-linked - cause muscle weakness and loss of muscle tissue, which get worse over time; tends to form in early childhood

12.   Icthyosis Simplex (vulgaris) – sex-linked - a common skin disorder passed down through families that leads to dry, scaly skin

13.   Sickle Cell Anemia – codominant autosomal recessive-  red blood cells have a crescent shape blocking small blood vessels causing pain and anemia (low red blood cell count); common in African Americans

14.   Pedigree – a diagram used by geneticists to chart a trait from one generation to the next

15.   Chromosome abnormalities – caused by the addition or deletion of a chromosome or part of a chromosome during meiosis or mitosis; a birth defect

16.   Down Syndrome – an extra chromosome in the 23^rd pair; causes mental retardation, slanted eyes, thick tongue, poor muscle tone, abnormal palm and footprints

17.   cri du chat syndrome (cat's cry syndrome) – part of chromosome 5 is missing; heart defects are common

18.   Prader-Willi syndrome, part of chromosome 15 is missing, intellectual disability is common

19.   Wolf-Hirschhorn syndrome, part of chromosome 4 is missing. Children with this syndrome have profound intellectual disability

20.   Cystic Fibrosis (CF) – autosomal recessive – is a disease that forms thick mucus in the lungs and digestive track. It is one of the most common genetic disease in white Americans. It can be treated with physical therapy, special diets, drug therapies, and gene therapy.

21.   Tay Sachs – autosomal recessive – Common in Jewish people; this disease is caused by a missing enzyme that breaks down a lipid produced and stored in the tissues of the central nervous system. The child dies by the age of 2 or 3; no cure

22.   Phenylketonuria (PKU) – autosomal recessive – caused by a missing enzyme; can cause severe mental retardation but all babies in U.S. are tested soon after birth. Children that have this disease must have a special diet that does not have phenylalanine in it until they reach around 5 or 6. (look at the side of a Coke can)

23.   Huntington’s disease – autosomal dominant – the tissue in the middle of the brain begins to die; symptoms begin between ages of 30-50; these people lose control of their muscles.

Crossing over - the exchange of genes between homologous pairs of chromosomes
Cancer - uncontrolled cell division
Karyotype - a chart of matched chromosomes used to determine if there is an unusual number of chromosomes

Unit 11: How to Complete Diyhybrid Crosses

Dihybrid Crosses

A dihybrid cross is a way to study two traits at a time. When studying two traits at a time, Mendel's Law of Independent Assortment comes into play. Most traits are inherited independently of each  other. For instance, being right handed does not mean you will have freckles. Example: Being right-handed (R) is dominant to being left-handed (r). Having freckles (F) is dominant to not having freckles (f). Cross a mother who is heterozygous for right-handedness (Rr) and  heterozygous for freckles (Ff) with a father who is also right-handedness (Rr)  and heterozygous for freckles (Ff).  In order to complete a dihybrid cross,  -the first step is to identify the genotypes of the two traits in each organism:  RrFf x RrFf. -The next step is to FOIL (mathmatically) each organisms alleles.  To do so, Multiple the First term of each pair, the Outside term of each pair, the Inside term of each pair, and the Last term of each pair. Next, place each pair of alleles from the FOIL on a different square of the  Punnett diagram. Then place each allele with its partner from the side of the  square. To determine the genotypic ratio, count how many of each kind of genotypes  there are, beginning with the dominant genotypes: RRFF, RRFf, RrFF, RrFf, RRff, Rrff, rrFF, rrFf, rrff =1, 2, 2, 4, 1, 2, 1, 2, 1 The genotypic ration for the above problem is 1:2:2:4:1:2:1:2:1 To determine the phenotypic ratio, count how many of each kind of phenotypes there are, beginning with the dominant phenotype and proceeding in this order: Dominant Dominant = Right-handed with freckles RRFF, RRFf, RrFF, RrFf = 9 Dominant Recessive = Right-handed no freckles RRff, Rrff = 3 Recessive Dominant = Left-handed with freckles rrFF, rrFf = 3 Recessive Recessive = Left-handed no freckles rrff = 1 The phenotypic ratio for the above problem is 9:3:3:1. In fact, anytime both  parents are heterozygous for both traits then the phenotypic ratio will always  be 9:3:3:1! For more information, see the Bozeman Science video "A Beginner's Guide to Punnet Squares".