Unit 6: Inheritance Part 1: Simple (Mendelian) Inheritance.

Unit 6: Inheritance

Part 1: Simple (Mendelian) Inheritance

Vocab review

• Homologous chromosome pair• Sister chromatid• Diploid, haploid• Independent assortment• Gamete• Gene• Allele

Gregor Mendel

Mendel's experiments• Characters and traits• Self-fertilization• True-breeding• Cross-fertilization

(monohybrid cross)

Mendel's results: flower color

P generationF1 generation, hybridF2 generationgenotypephenotype

Mendel's Results

What did Mendel’s findings mean?• Some traits mask others

– purple & white flower colors are separate traits that do not blend • purple x white ≠ light purple• purple masked white

– dominant allele • masks other alleles

– recessive allele • no noticeable effect when

inherited with the dominant allele homologous

chromosomes

I ’ll speak for both of us!

Punnett squaresPp x Pp

P pmale / sperm

P

p

fem

ale

/ eg

gs

PP

75%

25%

3:1

25%

50%

25%

1:2:1

%genotype

%phenotype

PP Pp

Pp pp pp

Pp

Pp

1st

generation(hybrids)

phenotype & genotypecan have different

ratios male female

Mendel's hypotheses• There are alternate versions of genes (alleles) that result in

variation in heritable characteristics.• For each character, an organism inherits two alleles (one from

each parent).– Homozygous – Heterozygous

• If the two alleles differ, one is dominant over the other (determines the organism's appearance). The other has no effect and is called recessive. – Complete dominance

• A sperm or egg carries only one allele because alleles segregate (separate) from each other during gamete production – Law of Segregation– What phase of meiosis does this occur during?

PRACTICE!

Monohybrid crosses

Allele key

Genotype key

Packet p. 2-3

Vocab Check

• P, F1, F2 generations• dominant allele• recessive allele• genotype• phenotype• homozygous• heterozygous• complete dominance

Genotype mystery• Sir Snowy Penguini Shackleton is a three-time “Best in Show” winner at the

Annual Antarctic International Penguin Show

• His owner would like to capitalize on this success and breed Sir Snowy to make more orange-footed penguins.

• The problem is that he doesn’t know Sir Snowy’s genotype. In show penguins, the dominant allele for foot color, O, results in orange feet, but the recessive allele, o, codes for green feet, which disqualifies a penguin from shows.

• Sir Snowy will earn lots more money if his owner can prove that Sir Snowy’s offspring will have only orange feet.

• Questions:

– What genotype does Sir Snowy have to be to guarantee all orange-footed offspring?

– How can his owner prove that Sir Snowy is that genotype?

Testcross exampleSir Snowy's genotype could be OO or Oo. To know for sure, Sir Snowy will be bred with a female that has green extremities.

Gametes will include only a little o allele since the female is homozygous recessive.

X

Oo Oo

Oo Oo

o o

O

O

Oo Oo

oo oo

O

o

o o

100% orange

50% orange

50% green

If the offspring all have orange feet, what genotype is Sir Snowy? What if some offspring have

green feet?

O? oo

Testcross: genotype detective tool• Crossing an individual of unknown genotype with

a homozygous recessive individual to determine the genotype.

Organisms have more than 1 trait!

• After monohybrid crosses, Mendel looked at seed shape and color together.

• Found that they were inherited separately (not dependent on each other).

• This led to the Law of Independent Assortment.

Law of Independent Assortment

RrYy x RrYy

Possible gametes:

RY

rY

Ry

ry

Possible gametes:

RY and ry

RRYY x rryy

PRACTICE!Dihybrid crosses

Using probability to solve genetic problems

• Rule of multiplication: probability of 2 or more events both happening.– Each heterozygous parent will

have half her/his gametes with B and half with b.

– The probability of B from the mother combining with B from the father is ½ x ½ = ¼

– Multiply individual probabilities– What is the probability that the

couple will have a girl with the genotype bb?

– ½ x ¼ = 1/8

Using probability to solve genetic problems

• Rule of addition: probability of an event happening via two different ways.– What is the probability that an

offspring will be heterozygous if both of the parents are heterozygous?

– Two combos of gametes will yield a heterozygote.

– ¼ + ¼ = ½

• You will probably use this less frequently than the Rule of Multiplication (mostly for working with two heterozygous parents as in the above example).

Practice!

Complete the problems on page 6 in your packet.

Practice

In dragons, the allele for fire breathing (F) is dominant to the allele for non-fire breathing (f) and the allele for wings (W) is dominant to the allele for a wingless body (w).

1. If a homozygous dominant dragon mates with a homozygous recessive dragon, what will the genotype(s) and the phenotype(s) of the offspring be?

2. If two of the offspring from the F1 generation are crossed, what are the potential combinations of alleles in the gametes?

3. Make a Punnett square to show the potential genotypes of the F2 generation.

4. How many potential genotypes are there for the F2 generation?

5. What is the ratio of possible phenotypes for the F2 generation?

FfWw

FW, Fw, fW, fw

9

9:3:3:1 (fire & wings: no fire & wings: fire & no wings: no fire & no wings)

On scrap paper