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AP Biology Mendelian Genetics Part 4 • Important concepts from previous units: • Genes are located on chromosomes. • There are two types chromosomes associated humans – autosomes and sex chromosomes. • Chromosomes are inherited from the parents. One from EACH parent Sperm AND Egg Genes on Chromosomes • Linked Genes – – These are usually inherited as a linked unit because they are found on the same chromosome. This term usually is associated with genes on Autosomes (1-22). Autosomes and linked genes • Alfred Sturtevant – He was the pioneer of genetic mapping – locating the loci of genes. He used crossover rates to determine the loci on chromosomes. – • • • • The finished product is called a Linkage Map. The smaller the rate; the closer they are to each other on the same chromosome. The higher the rate; the farther apart they are from each other on the same chromosome. The loci are measured in Centimorgans or map units. Linkage Map based on Crossover frequency Recombination frequencies 9% 9.5% 17% b Chromosome cn vg Locus Gene Maps • Sex-Linked Genes – This term refers to genes found on the sex chromosomes; 95% of the time it mainly refers to the X chromosome. (Think X when it is seX linked.) • This is because both sexes have at least one X chromosome in their genome. • XX (Female and homologous) ; XY (Male and heterologous) – Sex chromosomes undergo very little crossover during Prophase I of Meiosis. Sex –Linked Female – TWO Xs Sex-Linked Male – ONE X – Sex of the organism will be determined at conception. This is when egg is fertilized by the sperm. You will either get a sperm containing an X chromosome or a sperm containing a Y chromosome. Everyone starts out female. (This is why we all have nipples.) – • • At about two months of age in the womb, the Y chromosome’s SRY gene goes active to make testosterone, from estrogen, to finish development of the male. (Remember, functional groups.) After development is complete, testosterone production is turned off until puberty. At puberty it is turned back on so as to make the secondary sexual characteristics, such as facial hair. Patterns of Inheritance and some Human Sex-Linked Genetic Disorders: (NO cure exists, because the problem is in the DNA.) • Color Blindness – This is the result of a faulty gene (recessive) on the X chromosome for making a particular type of light wavelength (color) absorbing protein in cones of the retina of the eye. – The most common type is Red/Green Colorblindness. (Red and Green appear gray.) • Hemophilia (Means “love of bleeding”) – These individuals CANNOT make (recessive) Antihemolytic Factor. (AHF for short.) – They may experience problems with possible bleeding to death. – This was a disorder associated with the “Royal BlueBloods of Europe” – They were inbreeding to keep the crown “In the Family”. – Treatment? These individuals have to keep AHF with them at all times in case they get hurt. If they do get hurt and start to bleed, they will require a shot of AHF to stop the bleeding. Even a bruise (bleeding under the skin) can possibly lead to death. • THE PATTERN ON A PEDIGREE: It will appear to mainly affect males (as they only have one X chromosome). This is because if the inherited X chromosome has a recessive gene on it; it will NOT be covered up by a dominant one on another X chromosome (as is the case in most females). Females can still get these disorders, but they must inherit two recessive X chromosomes. The females tend to be carriers, so they appear unaffected. So they tend to pass the recessive X on to their sons. The son will be a sufferer, if he gets the recessive X, of the disorder. It appears to skip a generation, because the mother is a carrier and the sons are showing the disorder. Pedigree of Color Blindness Pedigree of Hemophila • Genes associated with these two terms (linked genes and sex-linked genes) do not follow Mendel’s Laws of Inheritance and normal ratios. – – – This is because these terms are mostly referencing one chromosome and not inherited pairs of chromosomes. Variation on linked chromosomes is associated with crossover frequency with its homologous mate. Sex –linked is referencing the X chromosome only. Males have 1 and females two copies. AP Biology Mendelian Genetics Part 5 • Important concepts from previous units: • There are also gene errors – point mutations and reading frame mutations. • Chromosomal Errors than can occur: – These could occur during Mitosis or Meiosis. • • They would occur during the Anaphase Stages where chromosomes are moving. They could also occur during Crossover where gene DNA segments are moving. Non-Disjunction Down syndrome • Trisomy 21, because the person has three copies of chromosome 21 instead of two • Some of the characteristics of may include: – outwardly slanted eyes – exaggerated fold of skin on the inside of the eye – flat ears set low on the head – flattened face – small teeth – relatively short arms and legs. Edward syndrome • Trisomy 18, because the person has three copies of chromosome 18 – – – – – Some of the characteristics of Edward syndrome may include: defects of the kidneys, ureters, heart, lungs and diaphragm cleft lip or cleft palate small skull (microcephaly) malformations of the hands and feet – including missing thumbs, club feet and webbing between the fingers and toes (syndactyly) – neural tube defect, where the spinal cord, meninges and blood vessels protrude through a gap in the vertebrae (myelomeningocele) – malformations of the sex organs – survival beyond the neonatal period is uncommon. Patau Syndrome • Trisomy 13, because the person has three copies of chromosome 13 instead of two. • Some of the characteristics of Patau syndrome may include: – – – – – – – – small skull (microcephaly) an abnormal opening in the skull malformations of part of the brain structural defects of the eyes cleft lip or cleft palate additional toes or fingers (polydactyly) congenital heart disorders, such as ventricular septal defect neural tube defect, where the spinal cord, meninges and blood vessels protrude through a gap in the vertebrae (myelomeningocele) – malformations of the sex organs – survival beyond the neonatal period is uncommon. Triple X syndrome (XXX) • may be taller than average • Most females with triple X syndrome have normal sexual development and are able to conceive children. • Triple X syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills. Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), and behavioral and emotional difficulties are also possible, but these characteristics vary widely among affected girls and women. Seizures or kidney abnormalities occur in about 10 percent of affected females. XYY • may be taller than average • Most males with 47,XYY syndrome have normal sexual development and are able to father children. • XYY syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills. Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), hand tremors or other involuntary movements (motor tics), and behavioral and emotional difficulties are also possible • A small percentage of males with 47,XYY syndrome are diagnosed with autistic spectrum disorders which are developmental conditions that affect communication and social interaction Klinefelter (XXY) • Extra copies of genes on the X chromosome interfere with male sexual development, often preventing the testes from functioning normally and reducing the levels of testosterone. • A shortage of testosterone can lead to delayed or incomplete puberty, breast enlargement (gynecomastia), reduced facial and body hair, and an inability to have biological children (infertility) • Children with Klinefelter syndrome may have learning disabilities and delayed speech and language development. They tend to be quiet, sensitive, and unassertive, but personality characteristics vary among affected individuals. • Older children and adults with Klinefelter syndrome tend to be taller than their peers. Compared with unaffected men, adults with Klinefelter syndrome have an increased risk of developing breast cancer Turner (XO) • • • • • • monosomy X, which means each cell in the individual's body has only one copy of the X chromosome the most common feature of Turner syndrome is short stature, which becomes evident by about age 5. An early loss of ovarian function (ovarian hypofunction or premature ovarian failure) is also very common. About 30 percent of females with Turner syndrome have extra folds of skin on the neck (webbed neck), a low hairline at the back of the neck, puffiness or swelling (lymphedema) of the hands and feet, skeletal abnormalities, or kidney problems. One third to one half of individuals with Turner syndrome are born with a heart defect, such as a narrowing of the large artery leaving the heart (coarctation of the aorta) or abnormalities of the valve that connects the aorta with the heart (the aortic valve). Complications associated with these heart defects can be life-threatening. Most girls and women with Turner syndrome have normal intelligence. Developmental delays, nonverbal learning disabilities, and behavioral problems are possible, although these characteristics vary among affected individuals. – Two types of errors can occur: • Chromosomal Number (Aneuploidy means “Abnormal number of chromosomes”) – This is the result of non-disjunction. “Failure to separate” during Anaphase. – Trisomic - Three of 1 kind of chromosome.) – Monosomic - Missing one, the other half of the pair. (It is located in the Trisomic gamete.) – Polyploidy - Many extra sets of chromosomes. • • • i. 3n (triploid) - Three “halves” are in this cell. ii. 4n (tetraploid) - Four “halves” are in this cell. iii. Deadly in most animals; Plants not really affected because they are simple organisms. • Individual Chromosome Structure » These occur because of faulty crossover » Deletion – Chromosome segment is “missing”. It got stuck on the other homologous chromosome during crossover. » Duplication – A chromosome segment was “copied” twice. Two genes on one chromosome. It is “missing” from the other homologous chromosome. » Inversion – A chromosomal segment is “backwards”. It was inverted (“backwards”) during crossover. » Translocation – A chromosomal segment is attached to a different autosome. It accidentally broke loose and ended up on another chromosome. Cri-du-chat • Cri-du-chat (cat's cry) syndrome, also known as 5p- (5p minus) syndrome, is a chromosomal condition that results when a piece of chromosome 5 is missing. Infants with this condition often have a high-pitched cry that sounds like that of a cat. The disorder is characterized by intellectual disability and delayed development, small head size (microcephaly), low birth weight, and weak muscle tone (hypotonia) in infancy. Affected individuals also have distinctive facial features, including widely set eyes (hypertelorism), low-set ears, a small jaw, and a rounded face. Some children with cri-du-chat syndrome are born with a heart defect. Chromosome Structure Errors • Syndrome – This term refers to an organism “possessing” the identifying traits of a particular genetic disorder. Human Genetic Disorders due to two abnormal chromosomal number: – • Down’s Syndrome » » » » This affects about 1 in 700 births. This individuals possess an extra 21 Autosome (A.K.A. Trisomy 21) General syndrome features – mental retardation, flat face, squinted eyes, small. Mainly the result of women of advanced age having babies. Trisomy 21 • Extranuclear DNA (“extra” means “outside of”) – DNA that is located outside the nucleus in organelles. (These are Mitochondria, Chloroplasts, and Plastids.) Mitochondria inherited from the mother inside the egg. They are exactly alike. (Helps in Criminal Forensics cases trying to establish relationship between individuals.) Mitochondrial Myopathy - These mitochondria lack the ability to make large quantities of ATP because they posses faulty DNA for making some of the enzymes or proton pump proteins in the cellular respiration process.) – – • General Characteristics: These individuals are very tired all the time. Extranuclear DNA (This DNA CAN can affect an organism)