GeneticsBiology 6(F)

Learning Objectives• Understand basic genetics vocabulary• Predict outcomes of monohybrid crosses• Predict outcomes of dihybrid crosses

Using Punnett Squares

B

B b

b

BB Bb

Bb bb

Different DNA (genetic material)

Why do people look different from one another?

What is Genetics?

Different proteins(appearances)

Genetics Vocabulary

Traita version of a character

Charactera recognizable feature controlled by genetics

fur color seed shape white fur wrinkled seeds

Genetics Vocabulary

Allelethe section of DNA that codes for a specific trait

B b

Genetics Vocabulary

Genotypean organism’s genetic makeup for a character

Phenotypean organism’s appearance for a character

white fur wrinkled seedshomozygous

recessiveheterozygous

bb Ww

Genetics Vocabulary - Genotype

Heterozygous“different”

Homozygous“same”

RRhh

BB

ww ss

TT

RrHh

Bb

Ww Ss

Tt

Phenotypes of heterozygous individuals can vary

• Complete dominance – same as

homozygous

• Incomplete dominance – an intermediate

• Codominance – both phenotypes shown

Genetics Vocabulary - Dominance

Genetics Vocabulary - Genotype• Individuals can be homozygous for some

characters and heterozygous for others• What determines an organism’s

genotype?

hh

ww

TT

Rr

Bb

Ss

Test Cross

A homozygous red-flowering plant is crossed with a homozygous white-flowering plant. What genotype will the offspring have?

RR rr

Rr

Test Cross

A homozygous red-flowering plant is crossed with a homozygous white-flowering plant. If red is dominant, what phenotype will the offspring have?

RR rr

Rr

red flowers

Monohybrid Cross

Two heterozygous red-flowering plants are crossed. What genotypes could the offspring have?

Rr Rr

R rR

r

RR Rr

Rr rrRR, Rr,

rr

Monohybrid Cross

Rr Rr

Two heterozygous red-flowering plants are crossed. If red is dominant over white, what is the most likely phenotype in the offspring?

R rR

r

RR Rr

Rr rrRed

Monohybrid Cross

Rr Rr

Two heterozygous red-flowering plants are crossed. If red is dominant over white, what are the average genotypic and phenotypic ratios?

R rR

r

RR Rr

Rr rr

Genotypes1 RR : 2 Rr :

1rrPhenotype

s3 red : 1 white

Monohybrid Cross

Rr Rr

Two heterozygous red-flowering plants are crossed. If red color is incomplete dominance, what is the most likely phenotype in the offspring?

R rR

r

RR Rr

Rr rrPink

Using Punnett Squares

Any genetics problem can be worked using the five steps below

Dihybrid Crosses

Two heterozygous red-flowering and heterozygous tall plants are crossed. If both characters are completely dominant, what fraction of their offspring will be tall and red-flowering (on average)? RrTt x RrTt

RT Rt rT rt

RT

Rt

rT

rt

RRTT

RRTt

RRTt

RrTT

RrTt

RrTT

RrTt

RRtt RrTt

RrTt rrTT

rrtt

Rrtt

rrTt

rrTtRrtt

9/16

Dihybrid Crosses

Two heterozygous red-flowering and heterozygous tall plants are crossed. If both characters are completely dominant, what are the average genotypic and phenotypic ratios?RT Rt rT rt

RT

Rt

rT

rt

RRTT

RRTt

RRTt

RrTT

RrTt

RrTT

RrTt

RRtt RrTt

RrTt rrTT

rrtt

Rrtt

rrTt

rrTtRrtt

Phenotypicred/tall red/shortwhite/tall white/short

- 9- 3- 3- 1

GenotypicRRTTRRTtRRttRrTTRrTtRrttrrTTrrTtrrtt

- 1- 2- 1- 2- 4- 2- 1- 2- 1

Using Punnett Squares

Any genetics problem can be worked using the five steps below

Learning Objectives• Understand basic genetics vocabulary• Predict outcomes of monohybrid crosses• Predict outcomes of dihybrid crosses

Using Punnett Squares

B

B b

b

BB Bb

Bb bb