Biology 101, Chapter 7, The 6th Day – Biology History, Cells, Genetics [post 3/3]

Spud-Doodles!
Blog Posts for Chapter 7:
• Post 1/3 Cells
• Post 2/3 - DNA
• Post 3/3 - Genetics


In Addition to Biology 101:
• Apologia Biology Exp. 8.1, Making Your Own Earlobe Pedigree
• Apologia Biology Exp. 8.2, A Dihybrid Cross
• Apologia Biology Exp. 8.3, Sex-Linked Genetic Traits
• Build-a-Spud Workshop using these Spud Genes.
My directions, and thanks to Mr. McClung for the original idea and directions.
• Extra Punnett Square worksheets in class - some choices are here and here.

Other Study Links:
► Pass the Genes, Please - Help the Melonheads pass their genes on to their little Melvin.
► Genetics Practice Problems - Answer questions about genotypes (such as bb, Bb, or B and b, or b and b, etc), and fill in Punnett squares.  (Put the male genes at the top of the Punnett square, and the female genes on the left.)
►Listen to more about Gregor Mendel's experiments at this link from HippoCampus.org.  There are five segments, numbered at the top.
This link will only be available until June 24, 2014.  =(



Naturally after learning how meiosis provides the way for 
us to all be so different, now we learn about genetics! =)



Genetics



a. Mendel's Experiments

Self-pollination - when a plant pollinates itself.  Usually, the stamen that holds the pollen (in the anther) must be taller than the pistil (where the stigma is) so that the pollen can fall to the stigma.  Sometimes this is not necessary as you can see in a video below. 
Flower dissection from last year.

(Source)


Cross pollination is more common than self-pollination.
Cross-pollination - when pollen is delivered from a flower to a different plant.  This happens frequently with bees, or when the wind blows the pollen, or by other means.

(1) Pollination, Plants, and Insects - Cross-Pollination





(2) Plant Reproduction: Methods of Pollination - Self-pollination





(3) Mendel Single Trait Experiments
Gregor Mendel used pea plants because they do not lend themselves to cross-pollination naturally.  Gregor Mendel did this by hand.
Genes are made up of segments of DNA found on larger pieces of DNA called chromosomes.








b. Terminology

(4) Genotype (Terminology)
Genotype is the combination of alleles an organism has.  Genotype is the "type o' genes" you have (TT, Tt, or tt). It is your genotype that determines you phenotype (which is the trait you can actually see).




You need to know this terminology:

Genes vs. Alleles
(uh-LEELs) hear pronunciation
A gene is a section of DNA that codes for a particular trait.
A gene comes in alleles (choices) that are different forms of a particular trait.
There are hundreds of genes on each chromosome!

Alleles are different versions of the same type of gene.

The gene for hair color can have blond alleles, brown alleles, etc, and the gene for eye color can have green alleles, blue alleles, brown alleles, etc.  Plants can be tall or short.  Flowers can be different colors.  Lots of different alleles for any particular type of gene.


We're all allele different.  =)


Allele vs. Trait

Alleles make up a trait.  The "blue eye" trait will contain the alleles b and b (one contributed from each parent).  The "brown eye" trait will contain the alleles B and B, or B and b. (B is dominant over b, so even though b can be present, B will make a person have brown eyes.)
Two alleles make up the blue eye trait [bb] or brown eye trait [BB or Bb].



Dominant vs. Recessive
Alleles can be dominant or recessive.  If you receive one allele for brown eyes and one for blue eyes (one from each parent - Bb), you will have brown eyes since brown eyes are dominant over blue eyes.  Tall plants are dominant over short.
So when both dominant and recessive alleles are present, a dominant allele will always be seen over a recessive allele.

Recessive alleles (blue eyes, etc.) can be seen in a person if there are only recessive alleles for that trait present on your DNA.  [bb]

Dominant alleles are always represented by a capital letter, and recessive alleles are represented by a lowercase letter. [Bb or BB]



Homozygous vs. Heterozygous
(home-oh-ZY-gus, het-er-oh-ZY-gus) Hear pronunciations here and here.
Alleles can be expressed in two different ways.  For each trait, you always have an allele from your Mom and an allele from your Dad, so there are two alleles present for each particular trait.  Your Mom and Dad got an allele from each of their parents for each particular trait.  Your children will have one allele from you and one from your spouse for each trait. 

Homozygous alleles are the same.  Homo means same; zygous comes from zygote, which is the initial cell formed when two gamete cells are joined.  (one from each parent)
So homozygous alleles will either be represented with two capital letters, or two lowercase letters.
TT can mean a tall plant, which is dominant, and tt can mean a short plant, which is recessive.

Heterozygous alleles are different.  (Different versions of the same type of gene)
Heterozygous alleles will be represented with one capital letter and one lowercase letter.
Bb means there is one allele for brown hair present and one allele for blond hair present.  But since brown is dominant, the person having these alleles will have brown hair.  This person may later have a child with brown or blond hair, depending on which allele is contributed from the other parent.

►So if a genotype is homozygous, we know the letters of the genotype are the same, and either they are both capital or both lowercase.  
If a genotype is heterozygous, there is one capital and one lowercase letter. 


Heterozygous and homozygous are adjectives.
Heterozygote and homozygote are nouns.



                                              This cracks me up!! =D                                 (source)



Genotype vs. Phenotype
--If you are asked to give the genotype, you will give the letters to represent the alleles.
BB, Bb, or bb, etc.
Genotype is the alleles inside you.
--If you are asked for the phenotype, you will use words to explain a visible characteristic.
Green eyes, a tall plant, a purple flower, etc.
Phenotype is what you see.

♦A genotype that is homozygous dominant means the letters are the same, and they are capital.  BB, TT, etc.
♦A genotype that is homozygous recessive means the letters are the same, and they are lowercase.  bb, tt, etc.
♦A genotype that is heterozygous means the letters are different, and there is one dominant allele (capital) and one recessive allele (lowercase).  Bb, Tt, etc.



Genotypes vs. Gametes vs. Zygotes
Genotypes:  TT, Tt, or tt, or PP, Pp, or pp.  Same letters.
Gametes:  TP, Tp, tP, tp.  Different alleles form a gamete (sperm or egg)
Zygotes:  Form when 2 gametes fuse during reproduction.

To clarify differences, here is an Example:
Gene - eye color
Allele - B or b
Genotype - BB, Bb, or bb
Trait or Phenotype - brown or blue eyes







c. Punnett Squares

(5) Gregor Mendel's Punnett Squares


Example 1
The homozygous bean in this example is homozygous
recessive
because the letters are lowercase.


 Example 2


(6) Introduction to Heredity - Heredity and classical genetics; dominant and recessive traits; heterozygous and homozygous genotypes.




Filling in a simple Punnett Square is just showing the different genotypes that 
are possible from the alleles of both parents through the process of meiosis.  


Now go back and read all the terminology definitions again.
I think you'll understand them better now.  =)



    Practice #1:
Pass the Genes, Please - Help the Melonheads pass their genes on to their little Melvin.
Genetics Practice Problems -
   Do the first 2 sections:
• "Monohybrid Cross" (comparing only one allele from each parent), and
• "TestCross" (crossing an unknown genotype and a homozygous recessive [dd] genotype to determine what the unknown genotype is.)
Read carefully!  You will see in TestCross, the first question tells you the female dog is deaf [dd], but you will see that the owner isn't sure if the hearing male dog is DD or Dd.
--Answer questions about genotypes (such as bb, Bb, or B and b, or b and b, etc), and fill in Punnett squares.  (Put the male genes at the top of the Punnett square, and the female genes on the left.)

►Remember, this is a computer, so it will want things in a certain order.
When you check your answers, DO NOT CHECK THE BOX that says "prevent this page from creating additional dialog."  This will cause the program to stop telling you whether an answer is correct or not.  And if you refresh your page, it will remove all previously done answers. =(







d. More Complex Crosses 

monohybrid cross - a cross between two individuals, concentrating only on one definable trait
dihybrid cross - a cross between two individuals, concentrating on two definable traits (this gives four possibilities)

If one were talking about the two traits of color of a plant -- purple or white, and the height of a plant -- tall or short, there would be four possibilities.
(1) A Tall Purple plant
(2) A Tall white plant
(3) A short Purple plant
(4) A short white plant

This would involve a dihybrid cross that concentrates on two definable traits.
The possibilities listed above would be these gametes:  TP, Tp, tP, tp.

►These ↑ are not genotypes; they are gametes.  
Genotypes are TT, Tt, or tt, or PP, Pp, or pp.  (Same letters.)


(7) Biology - Punnett Squares - simple (monohybrid cross) to more complex (dihybrid cross).  And I like that his use of the correct terminology will get you more familiar with it.

►At 5:45, he is talking about a "standard 9:3:3:1 ratio." 
You can see that the gametes across the top and on the side of the Punnett square are the same.  In a dihybrid cross (4x4 Punnett square) with mom and dad having identical gametes, this will always result in 9 offspring that are the same, two sets of 3 that are each the same, and one in the bottom right corner that is unique.  And if you write the mom's and dad's gametes in the same order, you will see this exact pattern on your grid.




(8) Dihybrid - Dihybrid Cross, meaning comparing not one, but two traits.

At 5:30, also note that three of the pups are carriers for a spotted and/or red coat.
Pup #2 is a carrier for a spotted coat, pup #3 is a carrier for a red coat, and pup #4 is a carrier for both a spotted and a red coat.
If any of these dogs mates with a dog who is homozygous recessive (ss or bb) for these particular traits, they can pass on these recessive traits to some of their pups.




(9) Punnett Square Fun - dihybrid crosses; independent assortment; incomplete dominance; co-dominance and multiple alleles.




Blood Types
Type AB blood is the universal recipient -- it can receive from types O, A, B, or AB.
Type O blood is the universal donor -- it can donate to types O, A, B, or AB.
So Melanie with type B blood or Kathy with type A blood can both donate to Jill with type AB blood.
But Jill cannot donate to either Melanie or Kathy.
Valerie with type O blood can donate to all three girls, but cannot receive from either of them.
(This is a simple explanation and does not include Rh)




(10) A Beginner's Guide to Punnett Squares - actually pretty fast, so a good review.
►At 06:50 --he shows a mistake that one might make with dihybrid crosses.  Watch out! =)




    Practice #2:
► Genetics Practice Problems 
Read and Do the 3rd and 4th sections:
• "Incomplete Dominance" (when two dominant traits blend), and
• "Dyhibrid Cross" (comparing not one, but two traits, resulting in 4 possibilities.)
Read carefully!  
--Answer questions about genotypes (such as bb, Bb, or B and b, or b and b, etc), and fill in Punnett squares.  (Put the male genes at the top of the Punnett square, and the female genes on the left.)

►Remember, this is a computer, so it will want things in a certain order.
When you check your answers, DO NOT CHECK THE BOX that says "prevent this page from creating additional dialog."  This will cause the program to stop telling you whether an answer is correct or not.  And if you refresh your page, it will remove all previously done answers. =(







e.  Pedigrees 

(11) Pedigree Instructions, Part 1





(12) Pedigree Worksheet, Part 2








f.  Sex-Linked Genetic Traits 

autosomes - chromosomes that do not determine the sex of the individual
sex chromosomes - chromosomes that determine the sex of the individual

Remember, humans have 23 homologous pairs of chromosomes.  Only one pair is the sex chromosomes; the other 22 are autosomes.

The female XX pair of chromosomes are perfectly homologous.  The male XY pair of chromosomes are not perfectly homologous.  There are fewer genes on the male's Y chromosome than there are on the X.
Sex-linked characteristics are not written in the same way you have learned so far because we need to distinguish that the Y chromosome does not have certain traits that can only exist on the X chromosomes of
males and females.
So we write both the X's for the female with the allele as a superscript, and only the X chromosome of the male (and not the Y) will have a superscript.  A superscript is written like an exponent, like this: X¹X² and X³Y, but instead of numbers the allele is either a capital or lowercase letter. 


(13) Sex-Linked Traits





(14) Sex-Linked Genes





(15) Chromosomes Crossing Over - Linked Genes








g. More about Genetics 

(16) Polygenetic Inheritance 
Around 1 minute, notice he says IF melanin production were controlled by one gene...





(17) Co-dominance - Incomplete Dominance





(18) Recessive Single Gene Disorders (cystic fibrosis, sickle-cell anemia)




There are at least five means by which genetic abnormalities occur.
1.  autosomal inheritance 
2.  sex-linked inheritance
3.  mutation
4.  changes in chromosome structure
5.  changes in chromosome number

None are truly beneficial.


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