Meiosis Making Gametes

Mitosis Review Mitosis: Division of the Nucleus ProphaseMetaphaseAnaphaseTelophase How many times does the nucleus divide in mitosis?ONE

Mitosis Review Think in your head: What are the four stages of mitosis? What is the purpose of mitosis? Prophase – Metaphase-Anaphase-Telophase The first purpose of mitosis is growth. The second function of mitosis is repair. Cells are constantly wearing out and getting damaged and unless an organism replaces them at least as fast as they are lost, a gradual deterioration will occur. Slide # 2

Meiosis Making Gametes

Introductory Vocabulary 1. Somatic cell: body cell a. EX: skin or bone cell 2. Diploid: two sets of chromosomes; 2n a. EX: humans have 2 sets of chromosomes in each body cell; 1 set came from the sperm & the other set came from the egg Slide # 3 Mitosis results in 2 diploid cells Diploid (2n) somatic cell

About Meiosis 1. Purpose of meiosis: produce haploid gametes. 2. Haploid: having 1 set of chromosomes; 1n 3. Gametes- special cells used in sexual reproduction. a. EX: egg and sperm cells b. Gametes are ONLY produced by meiosis 4. Meiosis occurs in reproductive organs (ovaries and testes) Slide # 9

Meiosis- cell division that producing reproductive cells called gametes (or egg and sperm) Meiosis involves dividing the nucleus two times in steps called Meiosis I and Meiosis II. By dividing twice, the chromosome number is halved in gametes.

Overview of Meiosis 1. Interphase: cell duplicates its chromosomes 2. Chromosomes are only duplicated ONCE 3. Cell divides 2 times to produce genetically different 4 cells Slide # 10

Stages of Meiosis I Slide # 11

Prophase I 1. Chromatids pair up with their Homologous pair forming a tetrad. 2. Crossing over is a process where pieces of two homologous chromosomes switch places. Slide # 12

Prophase I of Meiosis I

Replicated Chromosome Sister Chromatid Slide # 13

Tetrad Maternal chromosome replicated Paternal chromosome replicated Slide # 14 These chromosomes are homologous

Homologous chromosomes sister chromatids Tetrad 14

Crossing Over: Occurs in Prophase I 1. Homologous chromosomes : a. Pair up alongside each other lengthwise b. Swap bits and pieces of their chromosomes, shuffling the genome 2. Crossing over ONLY happens in Prophase I & results in NEW chromosomes that did not exist before in either parent 3. Why crossing over is important: a. It creates the genetic diversity of ALL sexually reproducing organisms b. Yes, this means you too!

Metaphase I: Tetrads line up in center Slide # 13 Anaphase I: Tetrads separate Telophase I & cytokinesis Meiosis I

Metaphase I of Meiosis I Homologous pairs line up in the center of the cell.

Anaphase I of Meiosis I Spindle fibers pull the homologues away from each other.

Telophase I of Meiosis I The chromosome number in these cells divides in half; starting with an initial four and ending with two in each new cell.

Meiosis II : Similar to Mitosis In Meiosis II each chromosome lines up and sister chromatids separate from each other. Prophase II Metaphase II Anaphase II Telophase II

Stages of Meiosis II

Meiosis II Slide # 15 Prophase II: Chromatid pairs move to center Metaphase II: The chromatids line up at center of the cell Anaphase II: chromatid pairs separate Telophase II: cells divide, producing 4 haploid cells

Meiosis occurs in the testes and is called spermatogenesis and in the ovaries of female and is called oogenesis.

Results: In males, four sperm are produced and flagella soon develop. In females, one large egg survives and three smaller eggs die.

A.MEIOSIS --A form of cell division that halves the number of chromosomes when forming specialized reproductive cells, such as gametes. **Four cells are produced, each with half as much genetic material as the original cell.

Chapter 7 Meiosis and Sexual Reproduction MeiosisMitosis 2n2n n2n2n2n2n 2n2n n nnnn

C. Mitosis VS. Meiosis Mitosis Produce identical cells Produce diploid cells Occurs in: –Plants—stems, leaves, roots –Animals—skin, bones, digestive organs, etc. Meiosis Produce gametes (sex cells) Produce haploid cells Occurs in: –Plants—ovules, spores –Animals—ovules (eggs), sperm

2n n Homo sapiens (human)46 23 Mus musculus (house mouse)40___ Zea mays (corn or maize)20___ Drosophila melanogasterDrosophila melanogaster (fruit fly) ___ 4 Xenopus laevis (South African clawed frog) ___ 18 Caenorhabditis elegansCaenorhabditis elegans (microscopic roundworm) ___ 6 Saccharomyces cerevisiaeSaccharomyces cerevisiae (budding yeast)32 ___ Canis familiaris (domestic dog)78 ___ Arabidopsis thaliana (plant in the mustard family)10 ___ Muntiacus muntjac (its Indian cousin) ___ 3 Myrmecia pilosula (an ant) ___ 1 Parascaris equorum var. univalens (parasitic roundworm) 2 ___roundworm Cambarus clarkii (a crayfish)200 ___ Equisetum arvense (field horsetail, a plant)216 ___ Determine the Diploid or Haploid number of each organism:

--Two parents each form reproductive cells that have one-half the number of chromosomes—these cells are called gametes and the process that they are made is called meiosis. Sexual Reproduction

Passing on of Traits IV.Sexual Reproduction- reproduction where two gametes unite.

B.Chromosome Number in a Cell 1.Diploid number 2n—the number of chromosomes in a body cell of an organism. 2.Haploid number n—half of the diploid number. –The diploid number for a human is 46 (humans have 46 chromosomes in each body cell) –The haploid number for a human is ___ and is found only in the gamete cells (sperm/egg) 23

I.Terms Trait – characteristic of an organism Gene – a heredity unit that codes for a trait. Allele – different gene forms Dominant – the gene that is expressed whenever it is present Recessive – the gene that is “hidden”. It is not expressed unless a homozygous condition exists for the gene.

I.Terms Homozygous – two identical (same) alleles for a given trait (TT). Heterozygous – two different (opposite) alleles for a given trait (Tt). Gamete – sexual reproductive cell. Fertilization – the fusion of two gametes. Phenotype – physical trait of an organism. Genotype – the genes present in the cell.

MENDEL Go to Section:

Introductory Vocabulary 1. Character: inheritable feature of an organism a.Example of characters in pea plants: Plant height, flower color, seed color, seed shape 2. Trait: variation in an inheritable feature Slide # 2 CharacterTraits HeightTall or Short Flower ColorPurple or White Seed ColorYellow or Green Seed ShapeRound or Wrinkled

Introductory Vocabulary 3. Heredity: transfer of traits from parent to offspring a. Inherited traits: traits received from parents b. Acquired traits: traits done to an organism that alter the appearance of the organism 4. Genetics: study of heredity 5. Pure breeding: producing same traits each generation 6. Hybrid: offspring from mating 2 different purebreds Slide # 3 Character: Stem height Traits: Tall or dwarf

Gregor Mendel: The Father of Genetics 1. Gregor Mendel: Austrian monk a.Did genetics (breeding) experiments on garden pea plants. b.1866: Published paper on experiments Slide # 4 Gregor Mendel

Gregor J. Mendel, O.S.A., experimental garden (35x7 meters) in the grounds of the Augustinian Monastery in Old Brno. Its appearance before Courtesy of Villanova University Archives. The Monastery Garden with the greenhouse which Gregor J. Mendel, O.S.A., had built in Its appearance before Courtesy of Villanova University Archives. The Monastery Garden: Eight Years of Pea Experiments

Why Mendel Chose Pea Plants Mendel chose pea plants for several reasons a.Grow quickly; grow many generations in short time b.Produce many offspring c.Have distinct traits Tall or dwarf Yellow or green seeds d.Could strictly control pollination Slide # 5 Brushed pollen from a 2 nd flower onto carpel (holds eggs) of 1 st flower Cut stamens (holds pollen) off of one flower Carpel develops into a pea pod.

Experiments with Pea Plants The distinct “either or“ traits. Seed shape (Smooth or wrinkled)

Mendel’s Experiment 1. Began with pure breeding parents. 2. All traits were the same in BOTH plants EXCEPT the trait being crossed. 3. All F 1 generation flowers (first generation) had purple flowers – it appeared as though white trait was lost! Slide # 6 Purple Flowers X White Flowers 4. Allowed 2 F 1 ’s to self pollinate. In F 2 generation, Mendel counted 705 purple flowered plants and 224 white flowered plants. (3 purple:1 white ratio) 5. The white flower trait was not lost; it was masked by the purple flower trait!

Question: What were the offspring of this P cross between a white and a purple flowering pea plant? The F 1 generation plants all had purple flowers. Question: What happens when the F 1 generation of pea plants are allowed to self- fertilize? The white trait reappeared! Question: What was the ratio for purple to white flowering plants in the F 2 generation? 3 purple :1 white

Seed Shape Flower Position Seed Coat Color Seed Color Pod Color Plant Height Pod Shape Round Wrinkled Round Yellow Green Gray White Smooth Constricted Green Yellow Axial Terminal Tall Short Yellow Gray Smooth Green Axial Tall Go to Section: Only one trait showed up in F 1 ’s; & both traits appeared in F 2 ’s at a 3:1 ratio. Mendel Found a Similar Pattern in Other Traits Slide # 7 F1F1 P

Conclusions made by Mendel: 1. Each parent MUST contribute one gene for each trait to the offspring. –Evidence: F 2 ’s had white flowers (present but hidden in F 1 generation.) 2. Each parent must have two copies of a gene; and can have two different versions of that gene called alleles at the same time. -- Evidence: F 2 ’s had white flowers both parents must have had at least one white allele! Dominant: allele that is expressed when 1 or both are present (capital letter) Recessive: allele that is masked by presence of dominant allele (lower case) a. The individual MUST have both recessive alleles to show the recessive trait Slide # 9 The F 1 purple flowering plants must have a second hidden gene for white flowers!

Alleles 1. Alleles: alternate forms of a gene or trait a. Parents may have two of the same alleles or two different alleles b. Homozygous: having 2 identical alleles c. Heterozygous: having 2 different alleles 2. Alleles are located on chromosomes This plant has 2 different alleles for the flower color character. Slide # 8 Every organism has two copies of the same gene. One copy came from MOM in her egg, the other gene copy came from DAD in his sperm. MOM DAD FROM Homologous Chromosomes

Homologous Chromosomes: -are similar gene carrying chromosomes from the opposite-sex parents.

Match these in your head, be ready to share. Gene Chromosome Homologous Pair Allele Threadlike structures made of DNA found in nucleus Unit of inheritance One form of a gene Two chromosomes that carry the same genes, but just different versions of those genes. Vocabulary Review

Mendel Solves the Genetics Puzzle Mendel reasoned that each parent must have 2 possible alleles to contribute –Genotype: the alleles the organism has (two letters) –Phenotype: physical appearance of an organism Mendel reasoned that the two alleles separated when gametes (sex cells like eggs) formed. Mendel also reasoned that the alleles paired up again during fertilization (joining of egg &sperm) Genotypes: PP x pp Gametes: P ~ p Fertilization: Pp Genotype of F1: All Pp Slide # 10 Phenotype of F1: All Purple Phenotypes: Purple & White Purebred Hybrid

In Summary, Mendel’s Work Showed Each parent contributes one allele for each trait. The two alleles of each trait separate from each other when gametes form (in meiosis) and pair up again during fertilization. Male’s (sperm) and female’s (egg) contribute equally. Acquired traits are not inherited.

C. Mendel’s Laws of Heredity 1.Law of Segregation—the two alleles for a trait segregate (separate) during the formation of gametes (meiosis). 2.Law of Independent Assortment —the alleles of different genes separate independently of one another during gamete formation. *Ex. The alleles for height separate independently of the alleles for flower color

Punnett Squares To show possible outcomes of the genes the new generation will have

Gene Diagram – Flower color Alleles- P = Purple flower p = White flower All genes occur in pairs – so 2 alleles affect a characteristic – possible combinations are; genotypes PP Pppp PhenotypesPURPLE PURPLE WHITE

Gene Diagram – Flower color Malefemale Pp parent gamete P p P p Offspring genotype PP Pp pp Phenotype Purple White Purple Purple 3 purple : 1 white

A. Punnett Square 1.Determine the traits used. 2.Determine the dominant vs. recessive trait. 3.Determine the letters for each trait. 4.Express the cross and determine the gametes formed. 5.Set up Punnett Square.

Punnett Square Place the two female gametes across the top Place the two male gametes down the side. Determine the offspring by filling in the squares.

Punnett Square Another method of showing crosses

Ex. Problem Trait-Eye Color Brown is dominant to blue B = Brown b = blue *Cross a homozygous brown eyed male with a blue eyed female. BBbbx B B bb b bb bB BB B Genotypic ratio: ___:___:___ Phenotypic ratio:____:____

1. Determine what the alleles are. P=purple p=white 2.Parent genotypes are determined. --Both are Pp 3.Parent’s possible gametes are determined and placed one next to -or above each box. Pp Purple male Pp purple female Pp P p Complete the Cross PP Pp pp 3 purple and 1 white offspring 3:1 chance with these parents Punnett Square

Why the White Flowers Reappeared in the F 2 ’s Slide # 11 Genotype of F1: Pp x Pp Gametes: ½ P ½ P ½ p½ p F 2 Genotypes: 1 PP: 2 Pp: 1 pp F 2 Phenotypes: 3 Purple : 1 White

Many human traits are controlled by single genes that have dominant and recessive alleles. For some human traits multiple alleles exist for a single gene meaning there are three or more alleles for that particular gene. Some examples of traits with multiple alleles are eye color & blood types. Multiple Alleles

Multiple Alleles: ABO Blood Groups The four possible blood types are A,B, AB, & O. The three alleles for blood types are written as: I A I B and i (i=O) The A & B alleles are codominant- both show up The O allele is recessive to all others. (Type O blood) 1.Type A codes for Antigen A proteins on the surface of red blood cells. 2.Type B codes for Antigen B proteins on the surface of red blood cells. 3.Type O does not code for either of these proteins.

What does it look like?

RED BLOOD CELLS Explain what would happen if the wrong blood type was given to someone? The immune system produces antibodies against the foreign antigen on the blood cells which causes them to clump up - leading to death.

Blood Type Genotype Antigen(s) Present Type A I A I A or I A i A Type B I B I B or I B i B Type AB IAIBIAIB A and B Type O iiNone

To tell what type blood you have they drop your blood into an anti- A and an anti-B serum. Both clump- type AB Type A clump- type A Type B clump- type B Type O blood- no clumping. What is my blood type?

WHO CAN RECEIVE YOUR DONATED BLOOD? ABABO AYesNoYesNo B Yes No ABNo YesNo OYes Recipient Blood Type Donor Blood Type Type O- is the universal donor. Type AB+ is the universal recipient.

Problem 1: Stephanie and Scott just had their first baby, Cody. Both parents have type AB blood. What are the possible blood types (phenotypes) that Cody may have inherited? (Punnett) IBIB IAIA IBIB IAIA IAIAIAIA 25% chance Type A 50% chance type AB 25% chance type B IAIBIAIB IAIBIAIB IBIBIBIB

Problem 2: Stacey and Brad both have type B blood. Is it possible for them to have a baby with type O blood? Explain. (Punnett) ii IF both parents are heterozygous B (BO) then there is a 25% chance of the baby having type O blood. IF either parent was homozygous B (BB), then there is a 0% chance of the baby having type O blood. iIBIB i IBIB IBIBIBIB IBiIBi IBiIBi IBIB IBIB i IBIB IBIBIBIB IBIBIBIB IBiIBiIBiIBi

Rh Blood Groups (85% of population has Rh antigen) What does it mean when a person has Type O positive blood? –The red blood cells have Rh antigen proteins on them. What phenotype will Rh+Rh+ or Rh+Rh- produce? positive What genotype will produce a Rh negative person? Rh-Rh- Rh

Problems with Rh antigen can come about with a pregnant mother who is Rh negative and her unborn child is Rh positive. How could this be a problem? An O- mother and O+ child’s blood does not mix until birth. When the mother is exposed to the Rh antigen she starts to produce antibodies against this antigen. If she has a second baby that is O+, the mother’s antibodies cross into the babies blood and cause the baby’s blood to clump and the baby dies. (The first baby does not die.)

Type B Distribution

Type A Distribution

Type O Distribution

Blood Type Distribution Percentages blood type

CODOMINANCE: In codominance, neither phenotype is completely dominant. –Instead, the heterozygous individual expresses both phenotypes. –A common example is the ABO blood group system.ABO blood group system –The gene for blood types has three alleles: A, B, and ii causes O type (ii) is recessive to both A and B. The A and B alleles are codominant with each other. –When a person has both A and B, they have type AB blood.

For an autosomal recessive disorder: When both parents are carriers of an autosomal recessive trait, there is a 25% chance of a child inheriting abnormal genes from both parents, and therefore of developing the disease. There is a 50% chance of each child inheriting one abnormal gene (being a carrier). –Examples: Galactosemia (the inability to metabolize lactose), cystic fibrosis, phenylketonuria, xeroderma pigmentosa, Tay-Sachs disease, Sickle cell diseaseGalactosemia Tay-Sachs diseaseSickle cell disease INCOMPLETE DOMINANCE: A heterozygous condition in which both alleles are partially expressed, often producing an intermediate phenotype. (sometimes called partial dominance) –For example, when a snap dragon with red flowers is crossed with a snap dragon with white flowers, a snap dragon with pink flowers is produced….OR…Like in Caucasians, the child of straight haired parents and a curly haired parent will have wavy hair… Straight and curly hair are homozygous dominant traits and wavy hair is heterozygous and is intermediate between straight and curly

Inheritance of Sickle-cell Anemia An amino acid substitution results in the sickle shape of the red blood cells. This causes the red blood cells to have low oxygen carrying capacity, and deprive tissues of oxygen. This can be fatal. The cell shape is elongated and curved, hence the “sickle” name instead of biconcave disk shape of normal cells. This disease is found almost exclusively in the African- American population and affects about 1 out of every 623 A.A. infants born in the U.S. The disease exists in Homozygous (ss) individuals. Heterozygous (Ss) individuals do not exhibit symptoms of the disease, but are considered carriers and have a resistance to malaria

Human Inheritance Karyotypes, Nondisjunction, and Chromosome Disorders

“Looking at Your Traits” 1.Tongue Rolling

“Looking at Your Traits” 2.Earlobes

“Looking at Your Traits” 3.Earbump

“Looking at Your Traits” 4.Widow’s Peak

“Looking at Your Traits” 5.Hitchhiker’s Thumb

“Looking at Your Traits” 6. Polydactyly

“Looking at Your Traits” 7. Syndactyly

“Looking at Your Traits” 8. Cleft Chin

“Looking at Your Traits” 9. Hair Whorl

“Looking at Your Traits” WHAT DID YOU INHERIT FROM YOUR FAMILY???

MY FAMILY TREE: PARENTS, BROTHER, GRANDPARENTS, ME

Human Inheritance Notes Blood Types Karyotypes Karyotypes, Nondisjunction, and Chromosome Disorders

Genetic Disorders

Detecting Genetic Disorders Special techniques are required to gather cell samples from an unborn fetus: AMNIOCENTESIS- A procedure in which a small sample of amniotic fluid is drawn out of the uterus through a needle inserted in the abdomen. It can be used beginning at the 14th to 16th week –Fetal cells extracted from amniotic fluid are cultured and karyotyped to identify some disorders. –Other disorders can be identified from chemicals in the amniotic fluids.

Amniocentesis

AMNIOCENTESIS A procedure in which a small sample of amniotic fluid (with baby cells) is drawn out of the uterus through a needle inserted in the abdomen. It can be used starting at week 14th to 16th.

CHORIONIC VILLUS SAMPLING A medical procedure done during weeks of a pregnancy. placentaA needle is inserted into the placenta (sac around baby) and a small amount of fetal tissue is withdrawn for analysis.

Karyotype Chart Once the cells have been gathered, scientists will take a picture of the chromosomes and make a karyotype chart. Karyotypes show the 23 homologous pairs for the person in which the cells were taken. The pairs are put in order from longest to shortest and numbered from 1 to 23. Pairs 1-22 are called autosomes. Pair 23 are the sex chromosomes. Karyotype interactive

Karyotypes 1. Karyotypes show the 23 homologous pairs for the person in which the cells were taken. 2. The pairs are put in order from longest to shortest and numbered from 1 to Pairs 1-22 are autosomes. 4. Pair 23 are sex chromosomes What is the sex of this individual? Male

Karyotypes 1. Karyotypes show the 23 homologous pairs for the person in which the cells were taken. 2. The pairs are put in order from longest to shortest and numbered from 1 to Pairs 1-22 are autosomes. 4. Pair 23 are sex chromosomes What is the sex of this individual? Male

Nondisjunction Nondisjunction caused by an error during meiosis I when homologous pairs fail to separate. One gamete will end up with one extra chromosome, and another gamete will be left with one less chromosome.

What is aneuploidy? 1.Aneuploidy: When chromosomes fail to separate properly during meiosis, the gamete will have an abnormal number of chromosomes Monosomy: one gamete has 22 chromosomes and the other has 23; the zygote ends up with 45 chromosomes Trisomy: one gamete has 24 chromosomes and the other has 23; the zygote ends up with 47 chromosomes

Down Syndrome 1. Cells contain one extra copy of chromosome # This results in: a. characteristic facial features b. short stature c. mental retardation d. shorter life-span e. Increased risk for heart problems, immune system problems, and cancer.

Turner Syndrome 1. This female has only one X chromosome. 45,X 2. This results in a. a female who cannot have children because the ovaries do not fully develop. b. Short in stature c. Webbed neck d. Some mental disability

Klinefelter Syndrome 1. Results in a male who has one extra X chromosome. 47,XXY 2. This results in a. Sterile b. mental retardation. c. true male, but can have some female characteristics.

GENDER & AUTOSOMES/SEX CHROMOSOMES Gender is determined by the combination of sex chromosomes inherited in the zygote. It is the sex chromosome within the sperm that is the determining factor (it provides either an X or Y). Also, it has been discovered that the Y chromosome carries a single gene, TDF (Testis Determining Factor) that determines maleness. (Girl= XX, Boy= XY) There are 23 pairs of chromosomes in humans. 22 pairs are autosomes(body) 1 pair is the sex chromosome(gender) The X chromosome is larger than the Y and it has extra genes on it that code for regular body traits.

SEX CHROMOSOMES Females(XX) have two X chromosomes Males (XY) have one X and one Y chromosome The Male will determine the gender (Boy or Girl) of the child. Why? –The male will give the Y chromosome 50% of the time. There is a 50% chance of a baby being a male or female.

Pedigree Charts The family tree of genetics What is a pedigree? What is a pedigree? Constructing a pedigree Constructing a pedigree Interpreting a pedigree Interpreting a pedigree

What is a Pedigree Chart?  A Pedigree chart traces the inheritance of a particular trait through several generations.  One GOAL of using a pedigree chart is to figure out who are carriers of the trait, because this information is typically unknown.

Steps to Creating a Pedigree 1.A genetic counselor will first gather information regarding who the family members are and how are they related. This will go back a few generations. 2.The genetic counselor will then ask who has the trait of interest. (Shows the trait) 3.After researching, the genetic counselor uses all of this information to construct a Pedigree chart, with all the family members’ names and genotypes written below each symbol.

Constructing a Pedigree  Male  Female

 Married Couple- –Horizontal Line  Siblings (offspring) –Vertical line  More than one Sibling: –a horizontal line is drawn with a vertical line coming down for each sibling. Constructing a Pedigree

I II III Constructing a Pedigree Roman numerals to the left of the pedigree show the generations. Birth Order: children are listed in birth order with oldest on left and youngest on the right.

 Fraternal twins- –Two line branching from the same point –two eggs and two sperm cells.  Identical twins- –Also called Maternal Twins –Are drawn branching off of the same point, but are also connected by a horizontal line. –one egg and one sperm unite and later splits to form two babies Constructing a Pedigree

Two horizontal lines from the same person represent two marriages / matings. Example: This man first had a girl with the lady on the left, then had a boy and girl with the lady on the right. Constructing a Pedigree The diagonal line through a symbol means the person is deceased (dead).

More Symbols in a Pedigree Chart  Full Shaded: –Affected person who shows a disorder  Half shaded: –Autosomal carrier or heterozygous for the trait)  Circle with dot: –X-linked carrier –always female  Deceased

 Pedigrees are used to find out: –who are carriers of the disorder & –the probability of having a future child with the disorder.  To begin to interpret a pedigree, first determine if the disorder is: –Autosomal dominant –Autosomal recessive –Sex-linked (carried on the X chromosome) Predicting using Pedigree Charts

Example Problem:  Is deafness a dominant or recessive trait?_____  To show deafness, what genotype does this son have to have? _______  For two parents who have normal hearing to have a deaf son, they both must be carrier. What are the parent genotypes?________  Write the genotypes for the parents and son under the correct circle/boxes, half- shading carriers. Shaded=deaf (D) is normal hearing (d) is deaf recessive dd Dd dd

Interpreting a Pedigree Chart First ask: Is it a Sex-linked or Autosomal Disorder? –If there is a much larger number of males than females who are affected then the disorder is Sex-linked. –If there is a 50/50 ratio between males and females who are affected then the disorder is autosomal.

Interpreting a Pedigree Chart If it is autosomal disorder then ask: Is it dominant or recessive? –If two parents do not show the trait and their children do show it, then it is an autosomal recessive disorder  (parents are heterozygous) –If the disorder is autosomal dominant, then at least one of the parents must show the disorder.

Note:  The following pedigree charts show infected individuals only.  Carriers are unknown at this point.

Practice Examples Does this pedigree show a Does this pedigree show a Sex-linked or Autosomal disorder?

Answer: Sex-Linked Disorder much larger number of males are affected

Practice Examples Does this pedigree show a Does this pedigree show a Sex-linked or Autosomal disorder?

Answer: Autosomal Disorder 50/50 ratio between males and females

Practice Examples Does this pedigree show a Autosomal Dominant or Recessive disorder? Does this pedigree show a Autosomal Dominant or Recessive disorder?

Answer: Autosomal Dominant Disorder At least one parent of the affected children show the disorder

Practice Examples Does this pedigree show a Does this pedigree show a Sex-linked or Autosomal disorder?

Answer: Autosomal Disorder 50/50 ratio between males and females

Practice Examples Does this pedigree show a Autosomal Dominant or Recessive disorder? Does this pedigree show a Autosomal Dominant or Recessive disorder?

Answer: Autosomal Recessive Disorder Two parents do not show the trait and their children do show it (heterozygous parents)

dd Dd Autosomal Recessive Genotypes and Carrier determination D = Normal hearing d = deafness Dd D?

Generation: Example Pedigree