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• Page: 44• Title: Mendelian Genetics• Date: 11-18-14• Essential Question: Can genetic outcomes

be predicted with 100% accuracy?**Do NOT leave a summary space on the first page! We will be using multiple pages

today.**

Principle of Dominance: some alleles are dominant and others are recessive

Y = Dominanty = Recessive

• the dominant allele will always be expressed when it is present

• a capital letter is used to represent a dominant allele[

[

Standard: predict possible outcomes of various genetic

combinations (B.6F)

Trait: a specific characteristic that varies from one individual to another

For example…

Inheritance is determined by biological factors that are passed from one generation to the next.

In other words, which traits you pass on depends on what genes

you get from your parents.

Genes: chemical factors that determine traits

(small sections of your DNA strand…remember??)

Alleles: different forms of a gene

Principle of Dominance: some alleles are dominant and others are recessive

Y = Dominanty = Recessive

• the dominant allele will always be expressed when it is present

• a capital letter is used to represent a dominant allele

Y = Dominanty = Recessive

• the recessive allele will only be expressed when the dominant is not present

• a lowercase letter is used to represent a recessive allele

Phenotype: appearance

Genotype: the actual genes

*Two organisms can have the same phenotype but

different genotypes*

BB Bb bb

Brown Eyes vs Blue eyes

Homozygous = purebred

Heterozygous = hybrid

BB Bb bb

BB Bb bb

Principle of Independent Assortment: the way alleles separate during meiosis is completely random and cannot be

predicted

**This is why you never know for

sure which traits will be passed on

to which offspring!**

Probability: the likelihood that a

particular event will occur

We can predict possible genetic outcomes using

probability.

Punnett square: a diagram that shows the

probability of certain traits being passed on to

offspring

• The letters in the Punnett square

represent alleles passed on from parent

to child.

Punnett squares are used to predict and

compare the genetic variations that will result from a cross.

1st Step = Identify the trait and what letter will represent it

What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a

white flower (pp)?

“P” and “p”

How to complete a Punnett Square

2nd Step = Assign the dominant/recessive trait for your letters

What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a white flower (pp)?

P = PINK (dominant) p = WHITE (recessive)

How to complete a Punnett Square

3RD Step = Match the letters to the correct parent (if none are specified, assume the

FIRST one is dad)

What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a

white flower (pp)?

= PP = ppMOMDAD

How to complete a Punnett Square

Let’s sum it up…..1st = Identify the trait and what letter will represent it

2nd = Assign the dominant/recessive trait for your letters

3rd = Match the letters to the correct parent

4th = Now fill in your Punnett square

Punnett Square practice…1. What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a white flower (pp)?

P P

p

p

Pp Pp

Pp Pp

P = Pink p = White

DAD = PPMOM = pp

**When using the letters like “P and p” OR “C and c”, draw the lowercase letter in cursive or just make sure you make them look different. Otherwise, you might

confuse the dominant for the recessive **

2. Long fingers are dominant (F) to short fingers (f). Complete the Punnett square for a homozygous

recessive mom and a heterozygous dominant dad.

F f

f

f

Ff ff

Ff ff

F = Longf = Short

DAD = FfMOM = ff

3. In a plant, long stems are dominant (L) to short stems (l). If a homozygous dominant flower and a homozygous recessive

plant are crossed, what would be the phenotypic ratio of their offspring?

L L

l

l

Ll Ll

Ll Ll

L = LongL = Short

DAD = LLMOM = ll

4. Straight hair (C) is dominant to curly hair (c). What would be the probability that a child would have curly

hair if both parents are heterozygous dominant?

C c

C

c

CC Cc

Cc cc

C = Straightc = Curly

DAD = CcMOM = Cc

5. Having a hitchhiker's thumb is a dominant trait (T). If a woman with a straight thumb has a child with a man who is heterozygous for the trait, what are the chances

their child will have a hitchhiker's thumb?

T t

t

t

Tt tt

Tt tt

T = Hitchhikert = Straight

DAD = TtMOM = tt

6. What would the phenotypic and genotypic ratios be for two purple (Pp) flowers that were bred together?

P p

P

p

PP Pp

Pp pp

P = Purplep = White

DAD = PpMOM = Pp

Can you identify your own genotypes and phenotypes?

Hairline:

Widow’s peak is dominant tostraight hairline

Eye Shape:

Almond eyes is dominant to round eyes

Tongue Rolling:

CAN roll the tongueis dominant to cannot

Eyelash Length:

Long eyelashes is dominant toshort eyelashes

Lip Thickness:

Thick lipsare dominant to thin lips

Hitchhiker’s Thumb:

Hitchhiker’s thumb is dominant tostraight thumb