For "JOYMERCY" Only!!! Assign #4
AlphaMann
geneticsunit22_bio-studyguide3.pdf
12/15/2011
1
Gene and Chromosomes
Chromosomes determine sex in many species
• X-Y system: Humans
• X-O system: grasshoppers, roaches, other insects – Females XX, males XO
• Z-W system: fishes, butterflies, birds – Males ZZ, females ZW
• Chromosome number: ants, bees – Females diploid, males haploid
• Temperature: turtles, other amphibians – Depending on incubation temp, females or males
12/15/2011
2
Sex-linked genes exhibit a unique pattern of inheritance
• Sex-linked gene: occurs on a sex chromosome
• These genes are not related to femaleness or maleness
Sex-linked disorders affect mostly males
• Males only get one X, so if they get a recessive allele, that’s the only one they get
• Sex linked alleles:
– Red-green color blindness
– Hemophilia
– Duchenne muscular dystrophy
12/15/2011
3
Sex-linked crosses
• Autosomes versus sex chromosomes.
• The “X” chromosome carries genes that the “Y” chromosome does not.
• A good example of a sex-linked cross is colorblindness.
– The colorblind gene is located on the “X.” • C = normal vision. • c = colorblind vision.
• Why do you think there are more colorblind men than women?
• Is it possible for a woman to be colorbind?
Cross a normal male (XCY) and a normal carrier female (XCXc).
XCXC
XCY
XCXc
XcY
XC Y
XC
Xc
G.R. = 1:1:1:1
P.R. = 2:1:1
Can you see why?
12/15/2011
4
Chromosomes Determine Sex (Gender) in Many Species
The X-Y system
44 + XY
44 + XX
Parents
22 + X
22 + Y
22 + X
Sperm Ova
44 + XX
44 + XY
Zygotes (offspring)
• In humans and other mammals
– There are two varieties of sex chromosomes, X and Y
Chromosomes Determine Sex (Gender) in Many Species
• X-Y system: Humans
• X-O system: grasshoppers, roaches, other insects
– Females XX, males XO
• Z-W system: fishes, butterflies, birds
– Males ZZ, females ZW
• Chromosome number: ants, bees
– Females diploid, males haploid
22 + XX
22 + X
76 + ZZ
76 + ZW
16 (Haploid)
16 (Diploid)
(b) The X–0 system
(c) The Z–W system
(d) The haplo-diploid system
Temperature: turtles, other amphibians depending on incubation temp, females or males
12/15/2011
5
Sex-Linked Genes Exhibit a Unique Pattern of Inheritance
• Sex-linked gene: occurs on a sex chromosome
• These genes are not related to femaleness or maleness
Sex-Linked Genes Exhibit a Unique Pattern of Inheritance
12/15/2011
6
Sex-Linked Genes Exhibit a Unique Pattern of Inheritance
Sex-Linked Genes Exhibit a Unique Pattern of Inheritance
12/15/2011
7
Sex-Linked Disorders Affect Mostly Males
• Males only get one X, so if they get a recessive allele, that’s the only one they get
• Sex linked alleles:
– Red-green color blindness
– Hemophilia
– Duchenne muscular dystrophy
Y ask Y?
12/15/2011
8
Central Dogma of Cell & Molecular Biology
DNA
RNA
Protein
Cellular Functions!!!
Who discovered DNA? Friedrich Miescher (1844-1895) 1869
Found: 1) Nuclei of WBC contained material that was rich in – P O N C H
Interested in studying the nuclei of cells – what’s in the nucleus?
2) Material was acidic NUCLEIC ACID
Location Chemical Properties
12/15/2011
9
What is the Evidence that Chromosomes Contain the Genetic Material?
1) All somatic cells in the body have the same number of chromosomes
2) Gametes (sperm, eggs) have half the ‘normal’ number of chromosomes
3) Prior to cell division, the number of chromosomes in the cell doubles – allowing for each new cell to have the ‘normal’ number of chromosomes after cell cell division
So, chromosomes seem to be important – but what are they?
Scientists knew: - chromsosomes are located in the nucleus - DNA was located in the nucleus
1920 – DNA was identified as a part of chromosomes therefore: its in the right location to be the genetic material but -
Chromosomes
DNA Protein
Also in the right location to be the genetic material
Genetic Material: DNA or Protein?
Support for: DNA - All cells from the same organism have the same amount of DNA. i.e. the amount of DNA is constant - When an animal or cell is starved, the lipids (fats), carbohydrates and PROTEIN all get metabolized in an attempt to keep the organism alive. DNA is never metabolized
Protein - DNA is just too boring (simple)! Only four monomers (G,A,T,C) responsible for all the diversity in nature?! - Proteins were different among organisms and different among tissues in the same organism
12/15/2011
10
Evidence that DNA is the Genetic Material
Experiment #1: Griffith (1929) used pneumococcus bacteria (one of the leading causes of death in 1929)
smooth strain (virulent) – ‘smooth’ due to polysaccharide coat rough strain (not virulent) – not polysaccharide coat
Transforming Factor
Oswald Avery
Maclyn McCarty
Smooth cells
Experiment #2 – Avery, McCloud & McCarty (1944)
DNA protein lipid carbos
mix with rough cells
Isolate
alive alive alive DEAD
What is Griffith’s ‘transforming factor’?
12/15/2011
11
Think about this…
• Remember “the birds and the bees?”
– Don’t laugh but many students try to cross two XY individuals or two XX individuals.
• Could two normal people have a colorblind child?
– What would its sex be?
• Try these crosses at home. Make up some more!
– A normal male and a colorblind female.
– A colorblind male and a carrier female.
– A colorblind male and a colorblind female.
Some interesting genetic facts:
• Some genes are dominant, but don’t always
express themselves.
• The environment can also impact how genes express themselves.
• Many traits have so many genes, that you can’t isolate one.
12/15/2011
12
Polydactyly is a dominant trait. But not everyone shows it.
Temperature can change what genes are expressed.
12/15/2011
13
Traits that have many genes are hard to “pin down.”
That is it!
• There is one word, when it comes to your understanding genetics.
• PRACTICE!
• Have a wonderful day!
