M8 Recap Blog Post at Sahm-I-Am
(1) p. 227-233, 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.
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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.
Cross-Pollination
Self-pollination
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.
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(2) p. 233-236, Updating the Terminology
You will 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 that are different forms of that trait. 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 gene.
►Dominant vs. Recessive
Alleles can be dominant or recessive. When both dominant and recessive alleles are present, a dominant allele will always be seen over a recessive allele. For instance, brown eyes are dominant over blue eyes. Tall plants are dominant over short.
Recessive alleles can be seen if there are only recessive alleles present.
Dominant alleles are always represented by a capital letter, and recessive alleles are represented by a lowercase letter.
►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 gene, you always have an allele from your Mom and an allele from your Dad, so there are two alleles present for each particular gene. Your Mom and Dad got an allele from each of their parents for each particular gene. Your children will have one allele from you and one from your spouse for each gene.
Homozygous alleles are the same. So they will either be 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 will have 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.
►►Go see this hilarious picture of "heterozygoats." They're just allele uneven. Hahaha!
---So if a genotype is homozygous, we know the letters of the genotype are the same, whether they are both capital or both lowercase. If a genotype is heterozygous, there is one capital and one lowercase.
►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.
If you are asked for the phenotype, you will need to use words to explain what you mean. Green eyes, a tall plant, a purple flower, etc.
♦A genotype that is homozygous dominant means the letters are the same, and they are capital.
♦A genotype that is homozygous recessive means the letters are the same, and they are lowercase.
♦A genotype that is heterozygous means there is one dominant allele (capital) and one recessive allele (lowercase).
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(3) p. 236-238, Punnett Squares
Punnet Square with rabbits
Example 1
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| The homozygous bean in this example is homozygous recessive because the letters are lowercase. |
Example 2
After studying thru p. 238, you should be able to do these:
► 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.)
Read carefully, and do as many as you can correctly. Reread your textbook if necessary.
As you get further into the chapter, you may be able to do more on this site. There are a lot!
Learning this will help you to be able to do your Experiments.
Thanks to Julie at Mindful Wanderings for these links. =)
►Listen to more about Gregor Mendel's experiments at this link from HippoCampus.org. There are five segments, numbered at the top.
To read along, click the Topic Text button to the right.
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(4) p. 238-242, Pedigrees
Pedigree Instructions, Part 1
Pedigree Instructions, Part 2
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(5) p. 242-246, 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
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.
The genotype alleles from each parent will produce a gamete. One allele from each parent's various genotypes (eyes, hair, skin, different features). That is why we are all so different. =)
Dihybrid Cross
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 traits, they can pass on these recessive traits to some of their pups.
Another short one:
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(6) p. 247-249, Sex and 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.
Sex-Linked Traits
Terminology
Genotype is the combination of alleles an organism has. Genotype is the "type o' genes" you have. It's your genotype that determines you phenotype, which shows on the outside of your body.
Linked Genes and Crossing Over
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(7) p. 250-252, A More Complete Understanding of Genetics
Polygenetic Inheritance
Around 1 minute, notice he says IF melanin production were controlled by one gene...
Co-dominance, Incomplete Dominance
Recessive Single Gene Disorders (cystic fibrosis, sickle-cell anemia)
Understanding Blood Types - ABO and Rh - very good explanation!
Type AB blood is the universal recipient -- they can receive from types O, A, B, or AB.
Type O blood is the universal donor -- they can donate to types O, A, B, or AB.
So Melanie with type B blood can donate to Jill with type AB blood.
But Jill cannot donate to Melanie.
Valerie with type O blood can donate to both the other girls, but cannot receive from either of them.
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(8) p. 252b-255, Genetic Disorders and Diseases
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
I could find no videos for this section.
Heterozygoats! HA! I'm putting that in the science section of our next homeschool newsletter. = )
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