punnett squares. a punnett square illustrates how the parents alleles might combine in offspring. a...

Punnett SquaresPunnett Squares

Punnett Squares

A Punnett square illustrates how the A Punnett square illustrates how the parents’ alleles might combine in offspring. parents’ alleles might combine in offspring.

The top of the Punnett Square are one of the The top of the Punnett Square are one of the parent’s alleles, the side of the Punnett parent’s alleles, the side of the Punnett square shows the other parent’s alleles for square shows the other parent’s alleles for the trait the trait

HeterozygousHeterozygous: having dissimilar pairs of : having dissimilar pairs of alleles for any hereditary characteristicalleles for any hereditary characteristic

HomozygousHomozygous: having identical pairs of : having identical pairs of alleles for any given pair of heredity alleles for any given pair of heredity characteristicscharacteristics

Mendel’s Laws of Inheritance1. Law of Dominance: In heterozygous genotypes,

dominant alleles hide recessive alleles when both are inherited by an organism. (Hh means the dominant trait will show up in the phenotype)

Mendel’s Laws of Inheritance

1. The Law of Segregation (separation): Each organism has 2 alleles for a gene. Only one allele from each gene pair will be passed on to the offspring.

Homozygous/Heterozygous

Cross a homozygous Cross a homozygous dominant tall plant dominant tall plant with a homozygous with a homozygous recessive short plant. recessive short plant.

What letters would you use to represent this cross?

Dominant trait = tall Dominant trait = tall

Recessive trait = shortRecessive trait = short

T = tall T = tall t = short t = short

Hmzg / Htzg

What is the genotype of a homozygous What is the genotype of a homozygous dominant tall plant?dominant tall plant?

GenotypeGenotype

% % TTTT

% % TtTt

% tt% tt

TT TT

TT x ttTT x tt

What is the genotype of a homozygous What is the genotype of a homozygous recessive short plant?recessive short plant? tt tt

t t

T

T

PhenotypePhenotype

% tall% tall

% % shortshort

Tt Tt

Tt Tt

0

100

0

0

100

2. Cross a heterozygous brown haired rabbit 2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired with a homozygous recessive white haired rabbit.rabbit.

o What letters would you use to represent this cross?

Dominant trait = Dominant trait = brown hairbrown hair

Recessive trait = Recessive trait =

white hairwhite hair B = brownB = brown b = whiteb = white

What is the genotype of a heterozygous What is the genotype of a heterozygous brown haired rabbit?brown haired rabbit?

GenotypeGenotype

% % BBBB

% % BbBb

% % bbbb

Bb Bb

Bb x bbBb x bb

What is the genotype of a homozygous What is the genotype of a homozygous recessive white haired rabbit?recessive white haired rabbit? bb bb

b b

B

b

PhenotypePhenotype

% % brownbrown

% % whitewhite

bb bb

Bb Bb

0

50

50

50

50

3.. Cross a homozygous dominant 3.. Cross a homozygous dominant long haired guinea pig with a long haired guinea pig with a heterozygous long haired guinea pig.heterozygous long haired guinea pig.

o What letters would you use to represent this cross?

Dominant trait = Dominant trait = long hairlong hair

Recessive trait = Recessive trait =

short hairshort hair L = longL = long l = short l = short

What is the genotype of a homozygous What is the genotype of a homozygous dominant long haired guinea pig?dominant long haired guinea pig?

GenotypeGenotype

% % LLLL

% % LlLl

% ll% ll

LLLL

LL x LlLL x Ll

What is the genotype of a heterozygous What is the genotype of a heterozygous long haired guinea pig?long haired guinea pig? Ll Ll

L l

L

L

PhenotypePhenotype

% long% long

% % shortshort

LL Ll

LL Ll

50

50

0

0

100

4. Cross a heterozygous wrinkly 4. Cross a heterozygous wrinkly elephant with another heterozygous elephant with another heterozygous wrinkly elephant.wrinkly elephant.

What letters would you use to represent this cross?

Dominant trait = Dominant trait = wrinkly skinwrinkly skin

Recessive trait = Recessive trait =

smooth skinsmooth skin W = wrinklyW = wrinkly w = smooth w = smooth

What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant?

GenotypeGenotype

% % WWWW

% % WwWw

% % wwww

WwWw

Ww x WwWw x Ww

What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant? WwWw

W w

W

w

PhenotypePhenotype

% % wrinklywrinkly

% % smoothsmooth

Ww ww

WW Ww

25

50

25

25

75

PhenotypePhenotype

% round% round

% % wrinkledwrinkled

5. A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have

wrinkled seeds?

RR x RrRR x Rr

R r

R

R

RR Rr

RR Rr

R = round

GenotypeGenotype

% % RRRR

% Rr% Rr

% rr% rr

r = wrinkled

50

50

0

0

100