Transcript Genetics II
Two copies of each autosomal gene affect phenotype (physical). • Mendel studied autosomal gene traits, like hair texture. Autosome – chromosome with genes not related to sex of organism (body cells) Several methods help map human chromosomes. • Karyotype - a picture of all chromosomes in a cell. XY • Karyotypes can show changes in chromosomes. – deletion of part of a chromosome or loss of a chromosome – large changes in chromosomes – extra chromosomes or duplication of part of a chromosome Karyotype The arrangement of all the chromosomes found in a cell. Includes: Autosomes: chromosome pairs 1-22 Sex Chromosomes: chromosome pair 23 Female = XX Male = X Y 23rd pair Female sex chromosomes XX Write down three different statements you could use to describe the difference between autosomes and sex chromosomes. Process Box Amniocentesis A medical technique used to collect the chromosomes of a developing fetus. It is done by inserting a needle into the womb and gathering cells in the amniotic fluid. FEMALE “Autosomes” MALE Sex Chromosomes (they determine male or female) Who determines the sex of the offspring? Father – he can provide an X or Y chromosome Egg X X XX XX X X Body Cell X XX XX XY XY X XY Body Cell Y Y Sperm 1female:1male We were all female • Genes on sex chromosomes are called sex-linked genes. . – Y chromosome - male characteristics . – X chromosome - genes affects many traits. Males can pass on X or Y Females only pass on X King Henry VIII is known for being ‘angry’ with his wives and blamed them for not producing a son. Explain why King Henry VIII should have found fault with himself. Process Box • Males have an XY genotype. – All of a male’s sex-linked genes are expressed. – Males have no second copies of sex-linked genes – Y chromosome is much smaller Females can carry sex-linked genetic disorders. • Males (XY) express all of their sex linked genes. • Expression of the disorder depends on which parent carries the allele and the sex of the child. X chromosome carries about 1100 genes while the Y carries about 250 Sex-linked disorder: Color Blindness 1. Genetic disorder found on the sex chromosome X 2. Known as a “sex-linked” because its found on chromosome 23 3. Normal Color Vision (N) = Dominant Colorblindness (n) = Recessive 2. Can’t distinguish between colors 3. More boys, than girls, are color blind…..WHY? • Color blindness is a problem in which red or green look like shades of gray or other colors. • The gene is carried on the X chromosome and is a recessive trait. XCXC = normal female XCXc = female, normal vision (carrier) XCY = normal vision male XcY = color blind male XC XC Y Xc XCXC XCXc XCY XcY Sex-linked disorder: Color Blindness XC XC Color blind Dad and Normal mother produces…. Two normal sons XC XC XC XC XC Y XC Y XN XN 2 “carrier” daughters (NOT color blind) XC Y Xn XN XN XNXn Normal Dad and Carrier mother produces…. 1 color blind son, 1 normal son 1 “carrier” daughter, 1 normal daughter Y XN Y Xn Y What is the only way to get a color-blind daughter?? Sex-linked disorder: Hemophila 1. Recessive genetic disorder found on the sex chromosome X 2. Disease in which blood doesn’t clot properly. 3. Normal Blood Clotting (N) = Dominant Hemophila (n) = Recessive Sex-linked disorder: Hemophila XH XH Affected dad and Normal Mother produces…. Two normal sons Xh XH Xh XH Xh Y XH Y XH 2 “carrier” daughters XH Y Xh Normal Father and Carrier Mother produces…. XH XH XH XH Xh 1 color blind son, 1 normal son 1 “carrier” daughter, 1 normal daughter Y XH Y Xh Y What cross will ALWAYS yield you 100% affected sons? – Carrier – has an allele for as trait or disease that is not expressed. – Carrier does not have disease symptoms but can pass it on to offspring. Dominant allele disorders are rare. Huntington’s disease is an example of a disease caused by a dominant allele. (dominant) • Some traits are neither totally dominant nor totally recessive. • Incomplete dominance - when neither gene is totally dominant to the other - Heterozygous phenotype is intermediate between the two homozygous phenotypes – Example: White flowers and red flowers produce pink flowers Incomplete Dominance X Straight Curly Pink There is a third color that exists in the heterozygous type. It’s a. mixture between the two homozygous types. Incomplete Dominance Incomplete Dominance Incomplete Dominance Incomplete dominance • Codominant - alleles will both be completely expressed. – Codominant alleles are neither dominant nor recessive. – The ABO blood types result from codominant alleles. Example – red and white flower produce a flower with BOTH colors • Many genes have more than two alleles. Co-dominance Heterozygous type shows BOTH phenotypes exist TOGETHER Co-dominance Co-dominance Co-dominance Sickle Cell Anemia • Disease in which the body makes sickle-shaped red blood cells. Sickle-shaped cells don’t move easily through your blood vessels. They’re stiff and sticky and tend to form clumps and get stuck in the blood vessels •The disorder is found on chromosome 11. and is therefore not sex-linked. • The Oxygen carrying hemoglobin can not carry oxygen as efficiently and the odd-shaped cells can easily clot and break. Fatigue, pain, and organ failure due to lack of oxygen supply are common symptoms of sickle cell anemia. • It is common in the African community Actual blood cells Sickle Cell Anemia Codominance Practice • Genes for blood cells: • R = Round blood cells • R’ = Sickle Cells R R’ Genotypes for blood cells RR = normal blood R RR’ = some sickle cells, some normal cells R’R’ = has sickle cell anemia R’ RR RR’ RR’ R’R’ Complete the following crosses, Report the genotypes and phenotypes of the offspring R = round blood cell R’ = sickle shape RR: Round cells RR’ = sickle cell trait R’R’: sickle cell anemia Mixed Cells x Hybrid ---------- x ---------R’ R Round Blood Cells x Hybrid ---------- x ---------EXPECTED R R EXPECTED R’ R’ R’ R RESULTS 1 sickle cell anemia -------------------------- R’ R’ R R’ R R R’ R RR 2 mixed cells -------------------------1 normal cells -------------------------- R RR RR R’ Sickle Cell Anemia x Pure Round ---------- x ---------R’ R’ R R’ R R’ R R R’ R R’ R EXPECTED RESULTS 4 mixed cells -------------------------- 2-------------------------normal cells -------------------------- Round Blood Cells x Sickle ---------- x ---------R’ R --------------------------------------------------- RESULTS 2-------------------------mixed cells R R’ R R’ R’ R EXPECTED RESULTS 4-------------------------mixed cells -------------------------- R’ R R’ R -------------------------- 1. Blood Type 4 different blood types • there are _________________________ Blood Type Genes Blood Type A IAIA or IAi Blood Type B IBIB or IBi Blood Type AB IAIB Blood Type O ii Which blood types are compatible for transfusion?? Yes or No ? O B A AB B Yes A No AB Yes A No Yes O AB IB IB IA IA I AIB IAIB IAIB IAIB 4___________ type AB blood IB ___________ ___________ i IA i IAIB IBi IAi ii IA IB IAi IBi 1-AB blood 1-hetero A blood ___________ 1-hetero B blood 1-pure O blood ___________ ___________ IA IA I AIA IB IAIB IA i IB IAIB IBIB i i IAi IAi ii ii i 1-pure A blood ___________ 2-AB blood i 1-pure B blood ___________ IA ___________ 2-hetero A blood i 2O blood ___________ IAi IBi IA i IAIA IAi 2-hetero A blood ___________ 2-heteroB blood ___________ IAi ii ___________ 2-hetero A blood ___________ 2- O blood Blood type statistics… • If there are 100 people in the room: 39 will be O+ 7 will be O34 will be A+ 6 will be A9 will be B+ 2 will be B3 will be AB+ and only 1 in 200 will be ABNote: The + and – is the presence (or absence) of a third antigen (Rh). • Polygenic traits are produced by two or more genes. Order of dominance: brown > green > blue. • Epistatic gene - can interfere with the expression of all other genes. Mice have 5 genes that control fur color. 2 genes for general color 1 for shading 1 for spots 1 epistatic gene for color that overrrules all other genes • Phenotype is a combination of genotype and environment. • The sex of sea turtles depends on both genes and the environment. Warm eggs develop into females • Height is an example of a phenotype strongly affected by the environmental factors such as early nutrition and health care. • Linked genes are not inherited together every time. • Chromosomes exchange homologous genes during meiosis. Linkage maps – map of location of genes on a chromosome. • The closer together two genes are, the more likely they will be inherited together. • Cross-over frequencies are related to distances between genes. • Cross-over frequencies can be converted into map units. – gene A and gene B cross over 6.0 percent of the time – gene B and gene C cross over 12.5 percent of the time – gene A and gene C cross over 18.5 percent of the time Pedigree - chart for tracing genes in a family. • Phenotypes are used to infer genotypes on a pedigree. • Autosomal genes show different patterns on a pedigree than sex-linked genes. Widow’s peak: W = widow’s peak w = non widow’s peak • If the phenotype is more common in males, the gene is likely sex-linked. Colorblindness: M = normal vision m = colorblindness Some examples of human codominant traits include: blood groups: ABO, Duffy, Kell, Kidd, MNS, Rhesus red cell enzymes: acid phosphatase, adenylate kinase serum proteins: haptoglobulins cell surface antigen: human leucocyte antigen (HLA)