Mendelian genetics and heredity

http://learn.genetics.utah.edu/content/begin/traits/

Chromosomes, genes and alleles

Definitions Genotype Phenotype Genes Locus Alleles Dominant/recessive/codominant Homozygous/heterozygous Test cross

Monohybrid crosses A red flower is crossed

with another red flower. Some of the offspring are white. What does this mean?

A. One flower cheated on the other

B. The white flower is a mutant

C. It´s not possible D. Something else

Practice questions Tongue rolling (T) is dominant over non-tongue rollling (t). A heterozygous male crosses with a homozygous recessive female. They have four children. What ratio of phenotypes do you expect in their children?

Show your working using Punnet grids.

Practice question 1. Pea plants have two phenotypes, short leaves

and long leaves. Long leaves are the dominant trait and short leaves the recessive trait.

Assuming that D is the allele for dominant and d is the allele for recessive write the possible genotypes for a plant with long leaves and a plant with short leaves plant.

Using a Punnet grid establish the offspring of the plants produced by the next combinations, Dd X dd , DD X Dd ,

DD X dd , dd X dd. Write the genotypes for each offspring and the phenotype ratio.

BLOOD TYPES

Blood type is an example of a gene which can de CODOMINANT.

This means that two alleles can be equally strong –so when we caary one of each we get a mixed phenotype:BOTH ALLELES ARE EXPRESSED.

How is blood type inherited?

Sex chromosomes and gender

Sex chromosomes and gender

XX XY

X X X Y

XX XX XY XY