Review - Part 1

Classify each item as being an allele, a genotype, or a phenotype.

1. Six fingers 2. W 3. Paired flagella 4. Kk 5. q

Review - Part 1

What are the alleles in each of these genotypes?

6. KK 7. jj 8. Qq 9. Aa

Review - Part 1

Rewrite each of these to be a correct genotype.

10. dD 11. E 12. TGtg

Review - Part 1

If R is the allele for spots and r is the allele for no spots, what will be these individuals’ phenotypes?

13. RR 14. Rr 15. rr

Review - Part 1

Suppose that Y is the allele for a long tail, and y is the allele for a short tail.

16. If zygote’s father has a short tail, what could his genotype be?

17. If the zygote’s mother has a long tail, what could her genotype be?

Review - Part 1

What gametes will each of these individuals make?

18. HH 19. ii 20. Ee

Section 11-2Probability & Punnett Squares

General Terms: Zygote - A fertilized egg. New offspring.

Homozygous – genotype with two identical alleles ex: TT – homozygous dominant or tt – homozygous recessive

Heterozygous – genotype with two different alleles ex: Tt

Practice

Identify each of these genotypes as being homozygous or heterozygous.GG ____________Yy ___________kk ____________Ss ____________Vv ____________

Practice

Identify each of these genotypes as being homozygous dominant, homozygous recessive, or heterozygous.ee ____________QQ ___________Ll ____________pp ____________CC ____________

Practice

Suppose that the I allele codes for orange fins and the i allele codes for yellow fins. The heterozygous genotype: __ The homozygous dominant genotype: __ The homozygous recessive genotype: __ A fish with yellow fins must have a _____________

genotype. A fish with orange fins could be either

_____________ or ___________________.

Genetics and Probability

Figuring out offspring is a matter of chance.Because not every gamete a parent

makes is the same, which alleles are passed to the baby are random.

An example, using coins:

Punnett Squares

Using the letter H to stand for heads…If you flip a coin that’s heads (H) on both sides,

what are the chances that it will come up heads (H)?

Punnett Squares

If it’s a normal coin, heads (H) on one side and tails (h) on the other…What are the odds that it will come up heads

(H) on a flip?

Punnett Squares

If you flip TWO normal coins, what are the odds that you will get heads (H) on both flips?

Punnett Squares

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

Punnett Squares

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

Punnett Squares

These are the possible combinations that he could have produced:

Punnett Squares

These are the possible combinations that he could have produced:

Punnett Squares

These are the possible combinations that he could have produced:

Punnett Squares

These are the possible combinations that he could have produced:

Punnett Squares

These are the possible combinations that he could have produced:

H

H H H H

H

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 What are the odds of getting heads on

one flip, tails on the other?

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 you flip two different coins:One coin has two headsThe other is normal, one heads and

one tails

What are the odds of getting heads on both flips?

Punnett Squares

This is called a Punnett Square. Punnett Squares display possible gametes and

possible offspring.

H H

H

h

H H H H

H h H h

Punnett Squares

The top and side boxes show possible gametes. The middle boxes show possible zygotes (offspring) they would create.

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Punnett Squares

Sample problem: What are the chances that a heterozygous brown-eyed father and a homozygous recessive blue-eyed mother would have a blue-eyed child? (Use letters B/b)

Step-By-Step Instructions: 1. Figure out Mom and Dad’s genotypes.

In the example: Dad = ___, Mom = __

Punnett Squares

2. Figure out Mom and Dad’s gametes. Dad’s gametes = __ and __ Mom’s gametes = __ and __

3. Set up a square. For a monohybrid cross (studying only one

gene), make a normal tic-tac-toe board.

Punnett Squares4. Write Dad’s gametes on one side, and Mom’s

on the other.• It doesn’t matter whether Mom or Dad is on the side vs top, just

keep both eggs together and both sperm together.

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Punnett Squares

4. (continued) Like a genotype, if there’s a dominant allele, put it first.

A a

A

a

A

A

a a

Punnett Squares

5. Complete zygote genotypes.Remember to put dominant allele first,

if there is one.

6. Write out all the zygote genotypes as fractions.I.e. 1/4, 2/4, 3/4, 4/4

Punnett Squares

7. Reduce fractions if possible, and convert fractions to percentages.For instance, if two of the four zygotes

are AA, the probability of genotype AA is 2/4 = 1/2 = 50%

8. If applicable, rewrite offspring genotype results as phenotype results.

Practicing with Punnett Squares

Parents – Tt and tt

Offspring:

Parents – TT and Tt

Offspring:

Practicing Punnett Squares

Show a monohybrid cross, with all genotype and phenotype probabilities, for parents who are HH and hh.

Practicing Punnett Squares

Show a monohybrid cross, with all genotype and phenotype probabilities, for parents who are Ll and Ll.

Practicing Punnett Squares

If Dad’s genotype is Rr and Mom is homozygous recessive, what are the odds of having homozygous dominant offspring?

Practicing Punnett Squares

If both parents are heterozygous, and they have ten offspring, approximately how many of those offspring would you expect to be homozygous recessive?

Practicing Punnett Squares

Suppose black fur is dominant and white fur is recessive. Two parents, one with black fur and one with white fur, have many offspring. Half of their babies are black-furred, and half are white-furred. What were the genotypes of the parents? Hint: when a question asks you to figure out parental

genotypes, make test crosses, Punnett Squares for every possibility, then see which one gives you offspring results that fit.

Pedigrees

Pedigree = A diagram that shows the phenotypes of everyone in an entire family.

Pedigrees

Key

7’s daughter is _.1’s great grandson-in-law is _.Amongst 4’s nieces and nephews, _ is older than _. Both of them are _____.

Section 11.3Exploring Mendelian Genetics

Mendel’s Fourth Conclusion!

4. Mendel’s Law of Independent Assortment: Genes for different traits (can) segregate independently of each other in meiosis.Which allele from gene 1 goes into a

sperm cell does not affect which allele from gene 2 the sperm will get.

Example:

Mendel’s Fourth Conclusion!

• If Dad has brown eyes (Bb) and a widow’s peak (Ww), his genotype is BbWw.• Half of his sperm will get the dominant B

allele from the eye color gene.• But that does NOT force those sperm to also get

the dominant W allele from the other gene. Some of them will get B and W, some of them will get B and w.

• He will make four different kinds of gametes: BW, Bw, bW, and bw.

Dihybrid Crosses

Dihybrid Cross = Punnett Square made for two genes at the same time.

Cross: RRYY X rryy [homozygous dominant round yellow peas (RRYY)

and homozygous recessive wrinkled green peas (rryy)]

Result: F1 offspring were all RrYy [heterozygous round yellow peas]

Mendel let the F1 plants self pollinate: RrYy X RrYy

Dihybrid Crosses

9:3:3:1 9/16 = 56% yellow round 3/16 = 19% yellow wrinkled 3/16 = 19% green round 1/16 = 6% green wrinkled

In a dihybrid cross, all three laws can be observed.Law of Dominance = Rr zygotes have round seeds.Law of Segregation = Each gamete has only one allele from each gene.Law of Independent Assortment = If a gamete has a dominant allele from one gene, it doesn’t have to also have a dominant allele from the other gene.

Patterns of Inheritance So far, we’ve only studied simple dominance, where

a gene has two alleles, one dominant and one recessive.

Most genes aren’t like that, and have more complicated patterns of inheritance. You must be able to recognize five more advanced

patterns on sight, and be able to make monohybrid crosses for three of them.

Patterns of Inheritance Polygenic Traits – The phenotype is determined by

more than one gene at once. Example: Eye color, in reality, doesn’t just come from

one B/b gene. There’s a gene for blue vs green tint, a gene for dark vs light, a gene for tan vs gold tint, a gene for color density, a gene for outlying vs inlying rings… and your exact eye color depends on all of them.

Patterns of Inheritance Multiallelic Trait – A single gene has more than two

possible alleles. Example: In cats, coat color is partly determined by the

browning gene, which has THREE alleles. B is the allele for black, b is the allele for chocolate brown, and bl is the allele for cinnamon brown.

• Possible genotypes for this gene are: BB, Bb, Bbl, bb, blbl, bbl.• If you cross a Bb cat with a blbl cat, what are the offspring

genotype probabilities?

Patterns of Inheritance Incomplete Dominance – neither allele is completely

dominant, the heterozygous phenotype is a blending of the other two. Example: four o’clock flowers - red flower crossed

with white flower produces pink flower

Patterns of Inheritance Incomplete Dominance Practice

If B is the allele for blue feathers, and Y is the allele for yellow feathers, what are phenotype probabilities if you cross a blue-feathered bird with a yellow-feathered bird?

Patterns of Inheritance Codominance - Two alleles are equally dominant,

and the heterozygote’s phenotype is both at the same time.

• Example: A black chicken (BB) crossed with a white chicken (WW) produces a heterozygous chicken (BW) that has black AND white feathers.

• Show the Punnett Square for a BB x BW cross:

Patterns of Inheritance Codominance AND Multiple Alleles

• Example: Blood type is determined by the A, B, and O alleles. O is recessive, A and B are codominant.

Genotype Phenotype

AA Type A

AO

BB Type B

BO

OO Type O

AB

Patterns of Inheritance

Sex-Linked Traits - Gene for the trait is on a sex chromosome. As a result, the trait doesn’t affect boys and girls equally. Sex chromosomes = X and Y, chromosomes

that males and females don’t have the same pairs of

Autosomal chromosomes = Normal chromosomes that everyone has a pair of.

• Any trait that’s not sex linked = Autosomal trait

Patterns of Inheritance

Sex-Linked Traits Example: Hemophilia is a recessive

sex-linked bleeding disorder, the gene is on the X chromosome.

If a mother with hemophilia has children with a healthy father:

Xh Xh

XH

Y

XHXh

XhY

XHXh

XhY

50% of offspring will be sick, but:Both daughters will be healthy.Both sons will have hemophilia.

Practice Identify each example as displaying sex-linkage, incomplete

dominance, codominance, multiple alleles, or polygenic traits. 1. A heterozygous wombat has striped brown and grey fur. 2. The gene for flagella length has alleles for very long, long,

medium, and short flagella. 3. Skin color is determined by the melanin gene, carotene

absoprtion gene, carotene deposition gene, and several genes that affect the number and thickness of skin capillaries.

4. Crossing a blue-nosed Dad with a red-nosed Mom produces purple-nosed babies.

5. Crossing a yellow-eyed Dad with a white-eyed Mom produces white-eyed sons, but not all daughters have white eyes.