Sex Determination Male = XY Female = XX 23 pairs of chromosomes (22 autosomes/body chromosomes, 1 sex) X chromosome----->large, rod shaped Y chromosome-----> smaller
Mating of male & female XY x XX X Y X XX XY 50% male X XX XY 50% female
Sex-Linked Traits -traits that are carried only on the the X --sex chromosomes -none of the examples are carried on the Y--sex chromosome (Y-linked) -the genes involved have nothing to do w/ sexual development -rarely seen in females EXAMPLES: Colorblindness (red-green)--don t see red & green colors normally Hemophilia--inability of blood to clot, traced back to Queen Victoria Juvenile Gout--increase amount of uric acid causing joint pain Duchenne Muscular dystophy--muscles waste away with age Agammaglobulinemia--has no immunity to infection (Boy in bubble disease)
Colorblindness (red-green) X C =Normal Color Vision - X c = Colorblind - - - -
If a woman heterozygous for normal color vision marries a man w/ normal vision what are the chances that they will have a daughter who is colorblind? A colorblind son? X C X c - x X C Y
X C X c - x X C Y X C Y X C X C X C X C Y X c - X C X c- X -c Y
What numbers/colors do you see?
What is a sex-influenced trait? A sex-influenced trait is a trait controlled by a pair of alleles found on the autosomal chromosomes (pairs 1 through 22) but it s phenotypic expression is influenced by the presence of certain hormones. (So not found on sex chromosomes, found on the body or autosome chromosomes) Sex-influenced traits can be seen in BOTH sexes, but will vary in frequency between the sexes, or in the degree of the phenotypic expression. Example:Pattern Baldness Pattern Baldness can occur in both males and females, however it is much more common in males. Why is this? Because the pattern baldness trait is influenced by the hormone testosterone!
Polygenic Traits -traits determined by several genes (2 or more) -none of the genes are dominant Examples * Skin color * Eye color * Height Disorders involving polygenic traits *Spina bifida-- spinal cord/vertebrae does not form properly *Cleft lip/palate-- lip or roof of mouth does not form properly
Multiple Alleles -involves 3 or more alleles for a trait - the 3 alleles controlling blood type are = A,B & O -Blood type is a trait determined by 3 different alleles, but remember a person can only carry 2 bits of info for every trait (1 from dad, 1 from mom) - I is used which represents Immunogen or antigen *Antigen= chemical name tag on cells including RBCs *Antibody= made by body to inactivate antigen and are found w/in the plasma of the blood (liquid part) I=dominant i= recessive
I A = Type A antigen on red blood cell(rbc), produces antibodies against Type B I B = Type B antigen on RBC, produces antibodies against Type A i o = no antigen on RBC, produces both A & B antibodies I A I B = has both A & B antigens on RBC, but has no antibodies against other types
Use a Punnett Square to cross the following parents: I A i o x I B i o
I A i o I B I A I B I B i o i o I A i o i o i o
Blood typing used in paternity suits -can only say that a man may be the father not that he definitely is -however, it can prove that the father is definitely NOT the father -i.e. A man I A i o (type A blood) could be the father of a child with Type O blood. But a man with type AB blood could not possibly be the father of a child with blood Type O Now DNA fingerprinting is used, get DNA from saliva, blood or hair samples.
Pedigree Charts -A record showing how a trait is inherited over several generations -Shows the phenotype of the family members over many generations *Open circle/square = dominant trait *Shaded circle/square = recessive trait *Half Shaded circle/square = carrier of trait
Twins- Fraternal (2 eggs), fertilized by different sperm so they are genetically different, can be male and female Identical (1 egg), which splits after fertilization from one sperm, so they have identical traits and are always the same sex Polydactylism- having extra fingers or toes, determined by single dominant alleles Nondisjunction- failure of a chromosome pair to separate during meiosis producing gametes that lack a chromosome or have an extra chromosome (22 or 24 chromosomes instead of the normal 23)
Nondisjunction (Continued) Examples: Trisomy-21 (Down-Syndrome) is where the individual has an extra 21st chromosome XXX vs XX for the 21st pair, therefore, the individual has a total of 47 chromosomes Klinefelter Syndrome- male with an extra X chromosome -egg (XX) + sperm (Y) = (XXY) nondisjunction -sterile (small testes) -mental retardation, breast development Turner s Syndrome- have only one X chromosome and no other sex chromosome (missing a sex chromosome) -(XO), these individuals are female and sterile -short and have thick, webbed necks -don t develop sexually
Amniocentesis- removing fluid with cells from the amnion, which is a sac surrounding the fetus by using a long needle and then doing various chemical tests and procedures to produce a karyotype of the individual-checks to see if individual has 23 pairs of chromosomes or abnormalities. -this is done the 14th or 15th week of pregnancy