Activating Prior Knowledge

Activating Prior Knowledge
Human Genetics Notes

Proteins Elements: Carbon, Hydrogen, Oxygen, Nitrogen
Monomer: amino acid (20 different kinds) Each amino acid has a central carbon atom bonded to 4 other atoms or functional groups

Nucleic Acids Large, complex organic compounds that store information in cells, using a system of four compounds to store hereditary information, arranged in a certain order as a code for genetic instructions of the cell. Elements: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus Monomer: Nucleotide Phosphate group (Phosphoric Acid) 5-carbon (pentose) sugar (Deoxyribose or Ribose) Nitrogenous Base

There are 4 Nitrogenous Bases
There are FOUR Nitrogen bases

Nitrogen bases pair according to certain rules:
a) Purines pair with pyrimidines b) Guanine pairs with Cytosine and Thymine pairs with Adenine The nitrogen bases are held together by hydrogen bonds.

DNA Replication Because each of the two strands of the DNA double helix has all of the information to reconstruct the other half, the strands are said to be complementary. Each strand of the double helix serves as a template to make the other strand.

S Phase: DNA Replication
In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated.

3 differences between DNA and RNA:
1. RNA is single stranded, DNA is double stranded 2. RNA contains uracil in place of thymine 3. 5-carbon sugar is ribose in RNA, deoxyribose in DNA Amoeba Sisters: DNA vs. RNA (4:43)

RNA Synthesis: Transcription
All 3 types of RNA are synthesized from DNA in the nucleus and then used to synthesize proteins in the ribosome. Protein synthesis is a two step process: 1) Transcription: DNA  mRNA (nucleus) 2) Translation: mRNA  amino acids  proteins (ribosome) DNA Transcription and Protein Assembly (3:01)

Protein Synthesis: Translation involves mRNA, rRNA, and tRNA.
Transfer RNA (tRNA) carries the amino acids to the ribosome (different tRNA for each amino acid) Ribosomal RNA (rRNA) makes up the major part of the ribosome. Three sequential nucleotides on a tRNA molecule are called an anticodon. The anticodon on the tRNA is complementary to the codon of mRNA.

Protein Synthesis: There are 64 different codons.
Each codon specifies a particular amino acid that is to be placed in the polypeptide chain. AUG is the “initiator” codon. There are 3 “stop” codons.

Diploid Cells A cell that contains both sets of homologous chromosomes is diploid, meaning “two sets.” The diploid number of chromosomes is represented by 2N. For humans, the diploid number is 46 (2N = 46)

Haploid Cells Some cells contain only a single set of chromosomes = a single set of genes. Such cells are haploid, meaning “one set.” The gametes (egg and sperm) of sexually reproducing organisms are haploid. For humans, the haploid number is 23 (N = 23).

Formation of Gametes – Egg and Sperm
Spermatogenesis Oogenesis Forms 4 haploid sperm Forms 1 ovum (egg) and 3 polar bodies Oogenesis (3:53)

Cell Division Anaphase Prophase Telophase Metaphase
The chromosomes separate and begin to move to opposite sides of the cell The chromosomes become visible. The centrioles take up positions on opposite sides of the nucleus. A nuclear envelope reforms around each cluster of chromosomes. The nucleolus becomes visible in each daughter nucleus. The chromosomes line up across the center of the cell. Anaphase Prophase Telophase Metaphase

Mitosis or Meiosis Meiosis Mitosis
Four new cells are formed from each original This process makes sperm cells Two new cells are produced from each original New skin cells are made this way This type of reproduction helps you grow This type of cell reproduction makes egg cells Makes cells with half the original chromosome number Makes cells with the same chromosome number as the original.

Segregation – Anaphase I & II
During anaphase I, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell. During anaphase II, the paired chromatids separate.

Prophase I The cells begin to divide, and the chromosomes pair up, forming a structure called a tetrad, which contains 4 chromatids. As homologous chromosomes pair up and form tetrads, they undergo a process called crossing-over.

Genotype vs. Phenotype:
Genotype: Genetic make-up of an organism (Ex: Aa, BB, cc) Phenotype: Physical characteristics of an organism (Ex: flower color, eye color)

Homozygous (Purebred) vs. Heterozygous (Hybrid):
Organism that has two identical alleles for a particular trait. (Ex: AA, bb, CC, dd) Organism that has two different alleles for the same gene. (Ex: Aa, Bb, Cc, Dd)

Human Genetics Section 13.3: Mutations Section 14.1: Human Chromosomes
Section 14.2: Human Genetic Disorders

Mutations Section 13.3

Vocabulary Mutation Germ Mutation Somatic Mutation Gene Mutation
Chromosomal Mutation Point Mutation Frameshift Mutation Deletion Duplication Inversion Translocation Nondisjunction Monosmy Trisomy Polyploidy

Mutations Mutations are heritable changes in genetic information.
A mutation results from a mistake in duplicating genetic information (DNA replication).

Types of Cells Affected
Germ Mutation - affects a reproductive cell (gamete or sperm/egg) Does not affect the organism Passed to offspring Somatic Mutation – affects body cells (all cells except gametes) Not passed to offspring

Ameoba Sisters – Mutations (7 min)
Types of Mutations All mutations fall into two basic categories: Those that produce changes in a single gene are known as gene mutations. Those that produce changes in a part of a chromosome, whole chromosomes, or sets of chromosomes are known as chromosomal mutations. Ameoba Sisters – Mutations (7 min)

Animated Intro to Cancer
Mutagens Mutations can be caused by chemical or physical agents (mutagens) Chemical – pesticides, tobacco smoke, environmental pollutants Physical – X-rays and ultraviolet light Animated Intro to Cancer

Gene Mutations Mutations that involve changes in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence. They generally occur during replication. If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.

Gene Mutations Point mutations include substitutions, insertions, and deletions.

Substitution Silent Mutation Missense Mutation Nonsense Mutation

Substitution

Sickle Cell Anemia

Frameshift Mutation Insertions and deletions are also called frameshift mutations because they shift the “reading frame” of the genetic message. Frameshift mutations can change every amino acid that follows the point of the mutation and can alter a protein so much that it is unable to perform its normal functions.

Muscular Dystrophy Both Duchenne muscular dystrophy and Becker muscular dystrophy result from mutations of a gene on the X chromosome that codes for the dystrophin protein in muscle cells; this protein helps to stabilize the plasma membrane during the mechanical stresses of muscle contraction. About 2/3 of cases are due to deletion mutations. If the number of nucleotides deleted in the mRNA is not a multiple of three, this type of frameshift mutation results in a severely defective or absent version of the protein, resulting in more rapid breakdown of muscle cells and the more severe Duchenne muscular dystrophy. If the number of nucleotides deleted in the mRNA is a multiple of three, the mutation does not cause a frameshift and this typically results in a less defective version of the protein, less rapid breakdown of muscle cells, and the milder Becker muscular dystrophy. Up to one-fifth of cases of Duchenne muscular dystrophy are caused by a nonsense mutation (a point mutation that results in a stop codon).

Muscular Dystrophy Because the dystrophin gene is on the X chromosome and because the alleles for defective dystrophin are recessive, both of these types of muscular dystrophy are much more common in boys than in girls. Duchenne muscular dystrophy affects one in every male babies.

Karyotypes A karyotype shows the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size. To see human chromosomes clearly, cell biologists photograph cells in mitosis, when the chromosomes are fully condensed and easy to view.

Karyotypes A karyotype from a typical human cell, which contains 46 chromosomes, is arranged in 23 pairs.

Sex Chromosomes Two of the 46 chromosomes in the human genome are known as sex chromosomes, because they determine an individual’s sex. Females have two copies of the X chromosome. Males have one X chromosome and one Y chromosome.

Sex Chromosomes This Punnett square illustrates
why males and females are born in a roughly 50 : 50 ratio. All human egg cells carry a single X chromosome (23,X). However, half of all sperm cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y). This ensures that just about half the zygotes will be males and half will be females.

Sex Chromosomes More than 1200 genes are found on the X chromosome, some of which are shown. The human Y chromosome is much smaller than the X chromosome and contains only about 140 genes, most of which are associated with male sex determination and sperm development.

Autosomal Chromosomes
The remaining 44 human chromosomes are known as autosomal chromosomes, or autosomes. The complete human genome consists of 46 chromosomes, including 44 autosomes and 2 sex chromosomes. To quickly summarize the total number of chromosomes present in a human cell, biologists write 46,XX for females and 46,XY for males.

Summary of Mendel’s Principles
Law of Dominance: Some alleles are dominant and others are recessive. Law of Segregation: Each adult has two alleles for each gene but they can only pass on one. Law of Independent Assortment: Each gene is inherited independently of each other.

Independent Assortment
How do alleles segregate if more that one gene is involved? Does the seed shape gene influence the seed color gene? Blue eyes, blonde hair? Brown hair, brown eyes? Principle of Independent assortment – genes for different traits can segregate independently during the formation of the gametes Seed shape & color gene do not influence each other

Orange eyes – defect in white gene
Gene Linkage NORMAL Thomas Hunt Morgan discovered that many genes in fruit flies were inherited together. Ex: Flies with reddish-orange eyes almost always had miniature wings This seemed to violate the principle of independent assortment. Vestigial wing Gene Map – shows the location of a variety of genes on chromosome 2 of the fruit fly. Orange eyes – defect in white gene

Linked Genes Morgan’s findings lead to 2 conclusions:
Each chromosome is a group of linked genes Chromosomes assort independently, not the individual genes.

When two genes are close together on the same chromosome, they do not assort independently and are said to be linked.

Gene Mapping Gene Maps: show the relative location of each gene on a chromosome. Looking at the parents chromosomes, explain why short legs and purple eyes are more likely to be inherited together than short legs and vestigial wings.

Gene Mapping Scientist realized that the further apart the two genes were on a chromosome, the more likely that crossing over would occur between them. They could used the frequency of crossing over between genes to determine their distance from each other. If genes were close then a crossover between them would be rare. If genes were far apart then a crossover between them would be more likely.

Chromosomal Mutations

Chromosomal mutations involve changes in the number or structure of chromosomes. These mutations can change the location of genes on chromosomes and can even change the number of copies of some genes.

Deletion involves the loss of all or part of a chromosome.

Chromosomal Deletion Example: Cri-du-chat (5p minus) – a piece of chromosome 5

Cri du chat (“cry of the cat”)
named for the distinctive cry affected infants make due in part to malformations of the larynx intellectual disability/delayed development small head size (microcephaly), low birth weight weak muscle tone (hypotonia) in infancy widely set eyes (hypertelorism) low-set ears a small jaw a rounded face heart defect

Jacobsen’s caused by a loss of genetic material from chromosome 11 - deletion occurs at the end of the long arm of chromosome 11 The signs and symptoms vary: delayed development, including the development of motor skills (such as sitting, standing, and walking) and speech. cognitive impairment and learning difficulties. behavioral problems and attention deficit-hyperactivity disorder (ADHD). small and low-set ears, widely set eyes) with droopy eyelids, skin folds covering the inner corner of the eyes a broad nasal bridge, downturned corners of the mouth, a thin upper lip, and a small lower jaw, large head size and a skull abnormality, which gives the forehead a pointed appearance. bleeding disorder called Paris-Trousseau syndrome - causes a lifelong risk of abnormal bleeding and easy bruising. heart defects, feeding difficulties in infancy, short stature, frequent ear and sinus infections, and skeletal abnormalities, can also affect the digestive system, kidneys, and genitalia. The life expectancy of people with Jacobsen syndrome is unknown, although affected individuals have lived into adulthood.

Williams Syndrome Williams syndrome is caused by the deletion of genetic material from a portion of the long (q) arm of chromosome 7. The deleted region includes 26 to 28 genes, and researchers believe that the characteristic features of Williams syndrome are probably related to the loss of several of these genes. williams-syndrome

Duplication produces an extra copy of all or part of a chromosome.

Chromosomal Duplication

Fragile X - Most people have 5-40 "repeats" at this end of their X-chromosome, those with Fragile X have over 200 repeats due to duplications

Fragile X FMR1 gene where a DNA segment, known as the CGG triplet repeat, is expanded The abnormally expanded CGG segment inactivates (silences) the FMR1 gene, which prevents the gene from producing a protein called fragile X mental retardation protein. Loss of this protein leads to the signs and symptoms of fragile X syndrome. Both boys and girls can be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely. Boys will have moderate mental retardation, a large head size, a long face, prominent forehead and chin and protruding ears, loose joints. Affected boys may have behavioral problems such as hyperactivity, hand flapping, hand biting, temper tantrums and autism. Other behaviors in boys after they have reached puberty include poor eye contact, perseverative speech, problems in impulse control and distractibility. Physical problems that have been seen include eye, orthopedic, heart and skin problems. Girls will have mild mental retardation. Family members who have fewer repeats in the FMR1 gene may not have mental retardation, but may have other problems. Women with less severe changes may have premature menopause or difficulty becoming pregnant.

Fruit flies experience a change in eye size of when duplication occurs.

Inversion reverses the direction of parts of a chromosome.

Chromosomal Inversion

Inversions The most common inversion seen in humans is on chromosome 9. This inversion is generally considered to have no harmful effects, but there is some suspicion it could lead to an increased risk for miscarriage or infertility for some affected individuals. An inversion does not involve a loss of genetic information, but simply rearranges the linear gene sequence.

Translocation occurs when part of a chromosome breaks off and attaches to another. Segments from two different chromosomes have been exchanged. Example: acute meyloid leukemia

Translocation Acute Meyloid Leukemia (AML)
Between chromosome 8 and 21; 15 and 17 is a cancer of the myeloid line of blood cells characterized by the rapid growth of abnormal WBC that accumulate in the bone marrow and interfere with the production of normal WBC Dermatofibrosarcoma – rare skin cancer Between chromosome 17 and 22 Somatic mutation – acquired during a person’s lifetime

Chromosomal Translocation

Chromosomal Mutation Insertion occurs when a portion of one chromosome has been deleted from its normal place and inserted into another chromosome

Chromosomal Disorders
The most common error in meiosis occurs when homologous chromosomes fail to separate. This mistake is known as nondisjunction, which means “not coming apart.” Nondisjunction may result in gametes with an abnormal number of chromosomes, which can lead to a disorder of chromosome numbers.

Nondisjunction Chromosomal mutations that involve whole chromosomes or complete sets of chromosomes results from a process known as nondisjunction This is the failure of homologous chromosomes to separate normally during meiosis.

Nondisjunction

Effects of Nondisjunction
If one chromosome is involved, the condition of one extra chromosome is called trisomy or one less chromosome is monosomy

Down Syndrome (Trisomy 21)
National Down Syndrome Society One in every 691 babies in the US is born with Down syndrome Down syndrome the most common genetic condition. ~400,000 Americans have Down syndrome and ~6,000 babies with Down syndrome are born in the US each year.

If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of that chromosome. This condition is known as a trisomy, meaning “three bodies.” The most common form of trisomy, involving three copies of chromosome 21, is Down syndrome, which is often characterized by mild to severe mental retardation and a high frequency of certain birth defects.

Patau Syndrome (trisomy 13) - serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months

Edward’s Syndrome (trisomy 18) - almost every organ system affected 1:10,000 live births. Children generally do not live more than a few months

Trisomy X (XXX) females. 1:1000 live births - healthy and fertile - usually cannot be distinguished from normal female except by karyotype

Klinefelter Syndrome (XXY)
In males, nondisjunction may cause Klinefelter’s syndrome, resulting from the inheritance of an extra X chromosome (XXY), which interferes with meiosis and usually prevents these individuals from reproducing. Affects male sex organs (small testes, sterile). feminine body characteristics. Normal intelligence.

Monosomy X (aka Turner Syndrome)
Nondisjunction of the X chromosomes can lead to a disorder known as Turner’s syndrome (Monosomy X). the only viable monosomy in humans only 45 chromosomes A female with Turner’s syndrome usually inherits only one X chromosome. genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence 98% of these fetuses die before birth

Jacob’s Syndrome (XYY)
XYY syndrome is a rare chromosomal disorder that affects males. It is caused by the presence of an extra Y chromosome. Individuals are somewhat taller than average and often have below normal intelligence.

There have been no reported instances of babies being born without an X chromosome, indicating that this chromosome contains genes that are vital for the survival and development of the embryo.

Nondisjunction If nondisjunction involves a set of chromosomes:
The condition in which an organism has extra sets of chromosomes is called polyploidy. Triploid (3n) Tetraploid (4n) Polyploid (many sets)

Harmful and Helpful Mutations
The effects of mutations on genes vary widely. Some have little or no effect, some produce beneficial variations, and some negatively disrupt gene function. Whether a mutation is negative or beneficial depends on how its DNA changes relative to the organism’s situation. Mutations are often thought of as negative because they disrupt the normal function of genes. However, without mutations, organisms cannot evolve, because mutations are the source of genetic variability in a species.

Beneficial Effects Plant and animal breeders often make use of “good” mutations. When a complete set of chromosomes fails to separate during meiosis, the gametes that result may produce triploid (3N) or tetraploid (4N) organisms.

Beneficial Effects Polyploid plants are often larger and stronger than diploid plants. Important crop plants— including bananas, limes, strawberries —have been produced this way. Many species are thought to be polyploids at some point, but it is most common in plants, with the highest occurrence in ferns and flowering plants.

Beneficial Effects Some of the variation produced by mutations can be highly advantageous to an organism or species. Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments. Mutations have helped many insects resist chemical pesticides. Some mutations have enabled microorganisms to adapt to new chemicals in the environment.

Harmful Effects Sickle cell disease is a disorder associated with changes in the shape of red blood cells. Normal red blood cells are round. Sickle cells appear long and pointed. Sickle cell disease is caused by a point mutation in one of the polypeptides found in hemoglobin, the blood’s principal oxygen-carrying protein. Among the symptoms of the disease are anemia, severe pain, frequent infections, and stunted growth.

Sex-Linked Inheritance
The genes located on the X and Y chromosomes show a pattern of inheritance called sex-linked. A sex-linked gene is a gene located on a sex chromosome. Genes on the Y chromosome are found only in males and are passed directly from father to son. Genes located on the X chromosome are found in both sexes, but the fact that men have just one X chromosome leads to some interesting consequences.

Sex-Linked Inheritance
For example, humans have three genes responsible for color vision, all located on the X chromosome. In males, a defective allele for any of these genes results in colorblindness, an inability to distinguish certain colors. The most common form, red-green colorblindness, occurs in about 1 in 12 males. Among females, however, colorblindness affects only about 1 in 200. In order for a recessive allele, like colorblindness, to be expressed in females, it must be present in two copies - one on each of the X chromosomes. The recessive phenotype of a sex-linked genetic disorder tends to be much more common among males than among females.

Can you see the numbers contained within this circle?
Colorblind Vision Tests

One or more sets of retinal cones that perceive color in light and transmit that information to the optic nerve are faulty. In a side-by-side comparison of a red Braeburn apple and green Granny Smith apple, a normal color vision person would see the apples as they appear on the top row. An individual who is red green color-blind would see those same apples as they appear on the bottom row and be unable to distinguish, by color, the Braeburn apple from the Granny Smith

Colorblindness Normal Vision Tritanopia

X-Chromosome Inactivation
If just one X chromosome is enough for cells in males, how does the cell “adjust” to the extra X chromosome in female cells? In female cells, most of the genes in one of the X chromosomes are randomly switched off, forming a dense region in the nucleus known as a Barr body. Barr bodies are generally not found in males because their single X chromosome is still active.

Human Pedigrees To analyze the pattern of inheritance followed by a particular trait, you can use a chart, called a pedigree, which shows the relationships within a family. A pedigree shows the presence or absence of a trait according to the relationships between parents, siblings, and offspring.

Human Genetic Disorders
Section 14.2

THINK ABOUT IT Have you ever heard the expression “It runs in the family”? Relatives or friends might have said that about your smile or the shape of your ears, but what could it mean when they talk of diseases and disorders? What is a genetic disorder?

Genetic Disorders Chromosomal Disorders Down Syndrome Turner Syndrome
Single Gene Disorders Down Syndrome Turner Syndrome Klinefelter’s Syndrome Jacobson’s Sickle Cell Disease Cystic Fibrosis Huntington’s Genetic Disorders

The most common error in meiosis occurs when homologous chromosomes fail to separate. This mistake is known as nondisjunction, which means “not coming apart.” Nondisjunction may result in gametes with an abnormal number of chromosomes, which can lead to a disorder of chromosome numbers.

Karyotype: Autosomes: chromosome pairs 1-22
Sex Chromosomes: chromosome pair 23 Down Syndrome Turner Syndrome Klinefelter’s Syndrome Jacobson’s

Down Syndrome (Trisomy 21)
National Down Syndrome Society One in every 691 babies in the US is born with Down syndrome Down syndrome the most common genetic condition. ~400,000 Americans have Down syndrome and ~6,000 babies with Down syndrome are born in the US each year.

Trisomy 21

Nondisjunction of the X chromosomes can lead to a disorder known as Turner’s syndrome (Monosomy X). A female with Turner’s syndrome usually inherits only one X chromosome. Women with Turner’s syndrome are sterile, which means that they are unable to reproduce. Their sex organs do not develop properly at puberty.

the only viable monosomy in humans only 45 chromosomes genetically female, however, they do not mature sexually during puberty and are sterile Short stature and normal intelligence 98% of these fetuses die before birth

Nondisjunction of the X chromosomes can lead to a disorder known as Turner’s syndrome (Monosomy X). the only viable monosomy in humans only 45 chromosomes A female with Turner’s syndrome usually inherits only one X chromosome. genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence 98% of these fetuses die before birth

Affects male sex organs (small testes, sterile). feminine body characteristics. Normal intelligence.

In males, nondisjunction may cause Klinefelter’s syndrome, resulting from the inheritance of an extra X chromosome (XXY), which interferes with meiosis and usually prevents these individuals from reproducing. There have been no reported instances of babies being born without an X chromosome, indicating that this chromosome contains genes that are vital for the survival and development of the embryo.

In males, nondisjunction may cause Klinefelter’s syndrome, resulting from the inheritance of an extra X chromosome (XXY), which interferes with meiosis and usually prevents these individuals from reproducing. Affects male sex organs (small testes, sterile). feminine body characteristics. Normal intelligence.

Patau Syndrome (trisomy 13) - serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months

Edward’s Syndrome (trisomy 18) - almost every organ system affected 1:10,000 live births. Children generally do not live more than a few months

Trisomy X (XXX) females. 1:1000 live births - healthy and fertile - usually cannot be distinguished from normal female except by karyotype

Jacob’s Syndrome (XYY)
XYY syndrome is a rare chromosomal disorder that affects males. It is caused by the presence of an extra Y chromosome. Individuals are somewhat taller than average and often have below normal intelligence.

From Molecule to Phenotype
There is a direct connection between molecule and trait, and between genotype and phenotype. In other words, there is a molecular basis for genetic disorders. Changes in a gene’s DNA sequence can change proteins by altering their amino acid sequences, which may directly affect one’s phenotype.

Human Pedigrees To analyze the pattern of inheritance followed by a particular trait, you can use a chart, called a pedigree, which shows the relationships within a family. A pedigree shows the presence or absence of a trait according to the relationships between parents, siblings, and offspring.

Interpreting Pedigrees

What do these symbols mean?
Female unaffected Female affected Male unaffected Mating Male affected

Pedigree Interpretation

Pedigree #1 Dominant or Recessive?
Must be recessive because the parents do NOT have the trait but individual II, 1; and II, 3 has the trait. What is the genotype for each parent (I, 1 and 2)? Heterozygous Autosomal or Sex-linked? Autosomal

Pedigree #2 Dominant or Recessive?
Dominant, because BOTH parents have the trait, but they were able to have children (individuals II, 1 and II, 3) without the trait. Autosomal or Sex-linked? Autosomal because there are even number of males and females who have the trait. Which individuals must be heterozygous? Parents on the left

Pedigree #3 XT Xt Xt Y XT Xt XT Y Xt Y XT Xt XT Xt Xt Y XT Xt Xt Y
Dominant or Recessive? Autosomal vs. Sex-linked? Recessive, sex linked.

Pedigree #4 (Problem #6 in HW)
How many generations are represented on this pedigree? 3 Is this a recessive or dominant trait? How can you tell? Recessive Is this sex-linked or autosomal? How can you tell? Sex linked, but could be autosomal Genotypes - Can individual II, 4 be homozygous? Why or why not? No, she must be heterozygous (receives recessive allele from dad). Why do mothers of affected males often feel guilty? Moms can be carriers and pass on trait to boys. Which individual has a genotype/phenotype that is not possible for sex-linked traits?

Patterns of Inheritance
Autosomal Recessive Autosomal Dominant Sex-Linked (X-Linked)

Autosomal Recessive Pedigree
Examples: Sickle Cell Anemia, Cystic Fibrosis, Albinism,

Autosomal Recessive Pedigree
II III

Sickle Cell Anemia

Sickle Cell Tutorial (5 min)
Sickle Cell Anemia A missense mutation is the cause of the disease, sickle cell anemia. a change in one base pair alters one amino acid effects hemoglobin protein, causing red blood cells to take on a strange shape Hemoglobin = the oxygen-carrying protein in red blood cells. The defective polypeptide makes hemoglobin less soluble, causing hemoglobin molecules to stick together when the blood’s oxygen level decreases. The molecules clump into long fibers, forcing cells into a distinctive sickle shape, which gives the disorder its name. Sickle Cell (1 min) Sickle Cell Tutorial (5 min)

Sickle Cell Disease Sickle-shaped cells are more rigid than normal red blood cells, and they tend to get stuck in the capillaries. If the blood stops moving through the capillaries, damage to cells, tissues, and even organs can result.

Genetic Advantages Most African Americans today are descended from
populations that originally lived in west central Africa, where malaria is common. Malaria is a mosquito-borne infection caused by a parasite that lives inside red blood cells.

Genetic Advantages Individuals with just one copy
of the sickle cell allele are generally healthy, and are also highly resistant to the parasite, giving them a great advantage against malaria. The upper map shows the parts of the world where malaria is common. The lower map shows regions where people have the sickle cell allele.

Genetic Advantages Disorders such as sickle cell disease and CF are still common in human populations. In the United States, the sickle cell allele is carried by approximately 1 person in 12 of African ancestry, and the CF allele is carried by roughly 1 person in 25 of European ancestry.

Cystic Fibrosis Cystic fibrosis (CF) is most common among people of European ancestry. Most cases result from the deletion of just three bases in the gene for a protein called cystic fibrosis transmembrane conductance regulator (CFTR). As a result, the amino acid phenylalanine is missing from the protein.

Cystic Fibrosis CFTR normally allows chloride ions (Cl−) to pass across cell membranes. The loss of these bases removes a single amino acid— phenylalanine—from CFTR, causing the protein to fold improperly.

Cystic Fibrosis People with one normal copy of the CF allele are unaffected by CF, because they can produce enough CFTR to allow their cells to work properly. Two copies of the defective allele are needed to produce the disorder, which means the CF allele is recessive. Cystic Fibrosis (6:16)

Genetic Advantages More than 1000 years ago, the cities of medieval Europe were ravaged by epidemics of typhoid fever. Typhoid is caused by a bacterium that enters the body through cells in the digestive system. The protein produced by the CF allele helps block the entry of this bacterium. Individuals heterozygous for CF would have had an advantage when living in cities with poor sanitation and polluted water, and—because they also carried a normal allele—these individuals would not have suffered from cystic fibrosis.

Autosomal Dominant Examples: Huntington’s Disease, Achondroplasia, Polydactyly

Autosomal Dominant Pedigree
II III

Huntington's Disease - CA Stem Cell Agency (3:50)
Huntington’s disease is caused by a dominant allele for a protein found in brain cells. The allele for this disease contains a long string of bases in which the codon CAG — coding for the amino acid glutamine - repeats over and over again, more than 40 times. Despite intensive study, the reason why these long strings of glutamine cause disease is still not clear. The symptoms of Huntington’s disease progressive breakdown (degeneration) of nerve cells in the brain broad impact on a person's functional abilities and usually results in movement, thinking (cognitive) and psychiatric disorders namely mental deterioration and uncontrollable movements usually does not appear until middle age. The greater the number of codon repeats, the earlier the disease appears, and the more severe are its symptoms. Huntington's Disease - CA Stem Cell Agency (3:50)

Achondroplasia a skeletal disorder, which is characterized by the failure of normal conversion of cartilage into bone that begins during fetal life and causes dwarfism. About 80 percent of people with achondroplasia have average-size parents; these cases result from new mutations in the FGFR3 gene. Achondroplasia (2:39)

Polydactyly a condition in which a person has more than five fingers per hand or five toes per foot

Sex-Linked Pedigree Examples: Colorblindness, Hemophilia, Muscular Dystrophy

Sex-Linked Pedigree I II III

Sex-Linked Pedigree

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