weird alleles, and intro to punnett squares 1. bring your allele worksheet up to me to be stamped!...

Weird Alleles, and Intro to Punnett

Squares

1. Bring your Allele Worksheet up to me to be stamped!

2. Pick up handouts.

Homework

Alleles worksheet #2 due tomorrow. Reminder, big project coming up soon.

Review Homework

Allele Conventions

Most of the time in this class, we’ll use the allele convention you’ve learned already, where one letter = one allele.

But most of the time in real-world science, scientists (naturally!) use a more complicated route.

Allele Convenions

There are SO MANY organisms, so many genes, and only 26 letters in the alphabet. To be specific, scientists usually use more than one letter for an allele.

They typically use a normal capital letter to stand for the gene, and then a superscript big or little letter for the allele. Like this:

Allele Conventions

The gene for coat color may have the dominant allele CB and the recessive allele Cb.

The gene for tail curling may have the dominant allele TC and the recessive allele Tc.

The gene for coat consistency may be BCH or BCh.

I’ll be sticking to just the normal allele convention to help you learn. But this more accurate convention is one that will come back a bit next week, and MCAS may choose to use it. So just be aware that these are alleles just like any other, they still just stand for different base sequences coding for different versions of proteins, they’re just written by scientists to be more specific.

Punnett Squares

A cool skill to have is the ability to predict the base sequences of relatives and future offspring. Knowing the alleles of living organisms can tell you about the genes and alleles of organisms that have long been dead! For simplicity, we’ll stick with one or two generations rather than thousands or millions.

Here is how it works.

Punnett Squares

In The Dark Knight, Harvey Dent had a coin with the same thing on both sides, heads and heads (H and H).

When he flipped that coin, what were the chances that it would come up heads (H)?

QuickTime™ and a decompressor

are needed to see this picture.



Punnett Squares

He acquired a coin that was heads (H) on one side, and damaged (we’ll call it h) on the other side. NOW what were the odds that, on one flip, it would come up heads (H)?





Punnett Squares

There is a scene where he flips it twice. The other two people in the scene are really hoping that it comes up heads (H) both times. What are the odds that it would?

Here’s how to set it up…





Punnett Squares

The first flip will be either heads (H) or damaged heads (h):





Punnett Squares

The second flip will also be either heads (H) or damaged heads (h):





Punnett Squares

These are the possible combinations that he could have produced:

























Punnett Squares

1 in 4 possible outcomes would be both heads (HH). 1/4 = 25% = .25

H h

H

h

H H H h

H h h h

Punnett Squares

The actual outcome was one heads and one damaged heads (Hh). What were the odds?

H h

H

h

H H H h

H h h h

Punnett Squares

2 of 4 possible outcomes = 1/2 = 50% = .5

H h

H

h

H H H h

H h h h

Punnett Squares

What if he’d had two coins somehow, one with two normal heads (HH) and one with one normal and one damaged side (Hh). Then, he flipped both at the same time. What are the odds that both coins would land with normal heads up (HH)?

Punnett Squares

This is called a Punnett Square. It’s a way of mathematically determining the probability of an outcome with some randomness (which side will land up?) and some non-randomness (which sides are possible?) What could this have to do with gametes and genes?

H H

H

h

H H H H

H h H h

Punnett Squares

Mom has two of every kind of chromosome, so, two alleles for every gene. Each egg has only of each kind of chromosome, so, one

allele. Half of her eggs have allele 1, half have allele 2. Dad has two of every kind of chromosome, so, two

alleles for every gene. Each sperm has only one of each kind of chromosome, so,

one allele. Half of his sperm have allele 1, half have allele 2.

And, it’s random which egg and which sperm fuse to create the offspring.

Punnett Squares

If you know Mom’s genotype, and Dad’s genotype, you can predict the likelihood that their offspring would have a certain genotype just like you could predict the likelihood of some coin tosses!

Punnett Squares are simple once you’ve got the idea, you just need to adhere to the conventions.

Punnett Squares

It doesn’t matter whether Mom or Dad is on the side, just keep both eggs together and both sperm together.

















Punnett Squares

Just like before, if something is heterozygous, write the dominant allele (capital letter) first.

A a

A

a

A

A

a a

Punnett Squares

Take out your color-coded Meiosis Guides, and with your partner, try to answer this question: If Meiosis makes four gametes for each parent, why do we make a Punnett Square with only two gametes per parent?

Punnett Squares

Results can be in two formats. Genotype Ratios or Probabilities = The likelihood

of offspring with different genotypes.

You and your partner, make a Punnett Square for this cross: Tt x tt

Punnett Squares

Phenotype Ratios or Probabilities: Same thing, but with phenotypes. In the example you just tried, suppose that the T

allele in spiders codes for long legs and the t allele codes for short legs.

Practice

Whiteboards out, one per table pair. Take turns writing, be kind to the markers.

Construct a monohybrid cross for YY x YY. Give genotype probabilities.

Practice

Construct a monohybrid cross for HH x Hh. Give genotype probabilities.

Practice

Construct a monohybrid cross for Rr x rr. Give genotype probabilities.

Practice

Construct a monohybrid cross for Dd x Dd. Give genotype probabilities.

Practice

Construct a monohybrid cross for kk x kk. Give genotype probabilities.

Practice

You cross a homozygous dominant tall pea plant (TT) with a homozygous recessive short pea plant (tt). What are the odds of an offspring being a short plant?

Practice

You cross a homozygous white flower with a homozygous red flower. Red is dominant to white. What are the odds of the offspring being a red flower? (note: when the problem doesn’t tell you what letters to use for the genotype, feel free to use any letter you want)

Practice

A male human is crossed with a female human. Males are XY, females are XX. What are the odds of a child being a girl?

Practice

You cross two heterozygous tall pea plants (Tt x Tt). What will be the phenotype probabilities for these offspring?

Practice

You cross two tall pea plants with each other, a homozygous dominant (TT) with a heterozygous (Tt). The pea plants produce 1000 offspring. How many of those offspring do you predict will be heterozygous?

Punnett Squares

Use the remaining time to work on your homework.

Monohybrid Crosses

Bring homework up to be stamped. Pick up handouts.

Homework

Worksheet due tomorrow.

Review Homework

Mendel

Read the handout about the life of the scientist who first outlined these principles, and for whom this kind of analysis (Mendelian genetics) is named.

When you’re done, look up so I can help you fill out the end.

Mendel’s Laws of Inheritance

Law of Dominance: In a cross of parents that are pure (homozygous) for contrasting traits, offspring will only have one of those traits. What is this describing that you’ve already

learned? Could you rephrase it to make more sense to

you?


Law of Segregation: A parent’s allele pair separates during gamete formation, and alleles randomly unite in fertilization. What is this describing that you’ve already


you?


Law of Independent Assortment: Alleles of different genes separate independently during gamete formation. Therefore, traits pass to offspring independently of each other. What is this describing that you’ve already


you?

Mendelian Genetics Practice

With your partner, read the paragraphs at the top of page 2. Make Punnett Squares demonstrating these two crosses, showing why Mendel got the results that he did.

Mendelian Genetics Practice

See the seven traits that Mendel studied in peas. Use this information to create seven practice problems for another pair. Be creative in how you word and set up the problem, see if you can challenge them!

Monohybrid Crosses

Bring homework up to be stamped. Pick up handouts.

Homework

Baby Lab (beginning today) will be due next week.

Homework Review

Baby Genetics Lab

Genetic Individuality Quiz. We are going to determine your phenotype.

The numbers are the numbers of different chromosomes. A real chromosome contains thousands of genes, we’ll just look at one each.

The phenotype on top for each chromosome is the dominant version. If you have the dominant version, play rock-paper-scissors

against your partner. If you win, you are homozygous dominant. If they win, you are heterozygous.

1. Tongue rolling (R & r) Rollers Non-rollers

2. Eye color (B & b) Non-blue eyes Blue eyes

3. Hair line (W & w) Widow’s peak No peak

4. Ear lobes (E & e) Free lobes Attached lobes

5. Big toe length relative to 2nd toe (T & t) Second toe shorter Big toe shorter

6. Thumb bend (G & g) Straight thumb Hitchhiker’s thumb

7. Little finger bend (J & j) Bent Straight

8. Thumb position (F & f) Left on top Right on top

9. Third finger length (S & s) Short Long

10. Sex (X & Y) Male Female

11. Fingernail curvature (N & n) Curved convex Straight convex

12. Mid-digit hair (ring finger) (H & h) Hair No hair

12. Freckles (F & f) Freckles No freckles

13. Nose bridge angle (P & p) Convex Concave

14. Chin dimple (D & d) Dimpled No dimple

15. Comptodactyly (Q & q) Flexed Straightened

weird alleles, and intro to punnett squares 1. bring your allele worksheet up to me to be stamped!...

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