Punnett square Examples [Athro, Limited: Genetics]

Working out Punnett Square Examples

Using Punnett squares you can work out the probabilities that children of the parents in each example will have particular phenotypes and genotypes.

Monohybrid Crosses

Dominant B and recessive b
Cross between Heterozygous (Bb) parents

	B	b
B	BB	bB
b	Bb	bb

Dominant B and recessive b
Cross between a Homozygous dominant (BB) parent and a Heterozygous (Bb) parent

	B	B
B	BB	BB
b	Bb	Bb

Test cross
Dominant T and recessive t
Dominant T allele produces tall phenotype, homozygous recessive (tt) produces short phenotype
Cross between homozygous recessive (tt) and tall parents
In this test cross, the offspring may be able to tell you what the tall parent's genotype is.

	t	t
T	t T	t T
?	t ?	t ?

If you have 9 offspring and the offspring are

then the tall parent's genotype is:

Monohybrid cross with incomplete dominance

Dominant B and recessive b
Heterozygous Bb genotype produces phenotype intermediate to those produced by BB and bb
Cross between two Heterozygous (Bb) parents

	B	b
B	BB	Bb
b	Bb	bb

Dihybrid crosses

A dihybrid cross with two hetrozygous parents
Gene 1: A-dominant, a-recessive
Gene 2: C-dominant, c-recessive
Parents are heterozygous for both genes
Parent 1: Genotype=AaCc
Parent 2: Genotype=AaCc

Gene 1 Gene 2	A C	A c	a C	a c
A C	AA CC	AA Cc	Aa CC	Aa Cc
A c	AA Cc	AA cc	Aa Cc	Aa cc
a C	Aa CC	Aa Cc	aa CC	aa Cc
a c	Aa Cc	Aa cc	aa Cc	aa cc

Thus in this case, the probablity of a child having
is:

A dihybrid cross with one hetrozygous parent and one homozygous recessive parent
Gene 1: A-dominant, a-recessive
Gene 2: C-dominant, c-recessive

Parent 1: Genotype=AaCc
Parent 2: Genotype=aacc

Gene 1 Gene 2	A C	A c	a C	a c
a c	Aa Cc	Aa cc	aa Cc	aa cc
a c	Aa Cc	Aa cc	aa Cc	aa cc
a c	Aa Cc	Aa cc	aa Cc	aa cc
a c	Aa Cc	Aa cc	aa Cc	aa cc

A dihybrid test cross
Mendel's round, wrinkled, yellow, and green pea seeds
Gene 1: W-dominant: Wrinkled (wri) seeds, w-recessive: round (rou) seeds
Gene 2: G-dominant: Yellow (yel) seeds, g-recessive: green (gre) seeds

One homozygous recessive parent and one heterozygous or homozygous dominant parent
Parent 1: Genotype=wwgg Phenotype=round green seeds
Parent 2: Genotype=W?G? Phenotype=wrinkled yellow seeds

Gene 1 Gene 2	W G	W ?	? G	? ?
w g	Ww Gg	Ww g ?	w ? Gg	w ? g ?
w g	Ww Gg	Ww g ?	w ? Gg	w ? g ?
w g	Ww Gg	Ww g ?	w ? Gg	w ? g ?
w g	Ww Gg	Ww g ?	w ? Gg	w ? g ?

Sex Chromosomes

Sex Linked Trait

Sources:

Part of the Athro, Limited web site.
Copyright © 2000 Athro, Limited. All Rights Reserved.
Written by Paul J. Morris mole@morris.net
Maintained by Athro Limited
Date Created: 6 Jan 2000
Last Updated: 4 Dec 2007