2 Chromosomes Determine Your Gender Humans have 23 pairs of chromosomes22 pairs are autosomes (chromosomes that are NOT involved in making gender)Also called homologous chromosome pairs1 pair are sex chromosomes (NOT HOMOLOGOUS; different genes)The sex chromosomes are “X” and “Y”“XX” is a girl“XY” is a boyXEgg cells ALWAYS have “X” chromosomeYXY
3 A karyotype5 µmPair of homologouschromosomesCentromereSisterchromatidsan ordered, visual representation of ALL chromosomes in a human cellArranged according to homologous pairs
5 What is a genetic disorder? What causes a genetic disorder? Caused by an abnormality in an individual’s DNAHow do these abnormalities occur?Non-disjunctionAddition or subtraction of chromosome or set of chromosomesMutationsChange to DNA sequence (gene)
6 Abnormal Chromosome Number When nondisjunction occursPairs of homologous chromosomes do NOT separate normally during meiosisGametes contain 2 copies or NO copies of a particular chromosomeWhat are some disorders caused by non-disjunction?Downs SyndromeTrisomy 21Klinefelter’s SyndromeXXYTurner SyndromeMonosomy X
7 What happens when meiosis goes wrong? NONDISJUNCTION!!!
8 Nondisjunction of sister chromatids in meiosis II Figure 15.12a, bMeiosis INondisjunctionMeiosis IIGametesn + 1n 1n – 1n –1nNumber of chromosomesNondisjunction of homologouschromosomes in meiosis INondisjunction of sisterchromatids in meiosis II(a)(b)
9 AneuploidyResults from the fertilization of gametes in which nondisjunction occurredOffspring have an abnormal number of a particular chromosome
10 What are some disorders caused by non-disjunction? Downs SyndromeTrisomy 21Kleinfelter’s SyndromeXXYEdwards SyndromeTrisomy 18Patau SyndromeTrisomy 13Turner SyndromeMonosomy X
11 1.) Trisomy 18-Edwards Syndrome Half of infants with this condition do not survive beyond the first week of life. Some children have survived to the teenage years, but with serious medical and developmental problems.Trisomy 18 is a somewhat common syndrome. It is three times more common in girls than boys.kidney malformations, structural heart defects at birth, intestines protruding outside the body (omphalocele), mental retardation, developmental delays, growth deficiency, feeding difficulties, breathing difficulties, and arthrogryposis (a muscle disorder that causes multiple joint contractures at birth)
12 2.) Trisomy-13: Usually Fatal Trisomy 13 – Patau Syndrome More than 80% of children with trisomy 13 die in the first year.Mental retardation and motor disorderStructural eye defects including cleft iris,Cleft palate,PolydactylyPolydactyly (extra digits)Low-set earsProminent heelDeformed feet known as rocker-bottom feetOmphalocele (abdominal defect)Abnormal palm patternOverlapping of fingers over thumbKidney defectsHeart defects (ventricular septal defect)
13 3.) Klinefelter - XXY Klinefelters As babies and children, XXY males may have weaker muscles and reduced strength. As they grow older, they tend to become taller than average. They may have less muscle control and coordination than other boys their age.During puberty, the physical traits of the syndrome become more evident; because these boys do not produce as much testosterone as other boys, they have a less muscular body, less facial and body hair, and broader hips. As teens, XXY males may have larger breasts, weaker bones, and a lower energy level than other boys.By adulthood, XXY males look similar to males without the condition, although they are often taller. In adults, possible characteristics vary widely and include little to no signs of affectedness, a lanky, youthful build and facial appearance, or a rounded body type with some degree of gynecomastia (increased breast tissue). Gynecomastia is present to some extent in about a third of affected individuals, a slightly higher percentage than in the XY population. About 10% of XXY males have gynecomastia noticeable enough that they may choose to have cosmetic surgery.Affected males are often infertile, or may have reduced fertility. Advanced reproductive assistance is sometimes possible.
14 Klinefelter syndromea result of an extra chromosome in a male, producing XXY individuals1/2000 live births
20 Human Disorders Due to Chromosomal Alterations Down syndromeIs usually the result of an extra chromosome 21trisomy 21
21 What are some disorders caused by mutations? Sickle cell anemia (recessive)Cystic fibrosis (recessive)Maple syrup urine disorder (recessive)Congenital hypothyroidism (recessive)Huntington’s Disease (dominant)Maple syrup urine – found in mnemonites cant digest amino acids, so their urine smells sweet because the amino acids come out in urineDecrease in thyroid hormonal production/thyroid gland missing/thyroid gland not fully formed
22 Cystic Fibrosis Example of recessive disorder Affect mostly people of European descentSymptomsMucus buildup in the some internal organsAbnormal absorption of nutrients in the small intestine
23 Sickle Cell Anemia Another recessive disorder Affects one out of 400 African-AmericansHemoglobin is the O2 carrying protein in red blood cellsSCA is an inherited blood disease where hemoglobin clumps together causes red blood cells to stiffen and curl into a sickle/crescent shapeBecause of this, the RBC cannot transport O2 effectivelySymptomsPhysical weakness, pain, organ damage, and even paralysis
24 Human Chromosomal Disorders Recessive DisordersCystic FibrosisExcess mucus in lungs, digestive tract, liverMore susceptible to pneumonia, infectionEarly death ~ average age of 37Tay-SachsLipid accumulation in brain cells, mental retardationBlindness, death in childhoodDominant DisorderHuntington’s diseaseDeterioration of nervous system, uncontrollable movementsDevelops in middle age, death soon after
25 Dominantly Inherited Disorders Some human disordersAre due to dominant alleles only need 1 dominant alleleExample is achondroplasiaForm of dwarfism lethal when homozygous for the dominant allele
26 Another Dominant Disorder Huntington’s disease (HD)degenerative disease of nervous systemNo obvious phenotypic effects until about 35 to 40 years of ageHDNormal
Your consent to our cookies if you continue to use this website.