Transcript 4.2 Patterns of heredity can be predicted

Chapter 4: Patterns of
Heredity
4.1 Living things inherit traits in patterns
4.2 Patterns of heredity can be predicted
4.3 Meiosis is a special form of cell division
4.2 Before you learned:
Genes are passed from parents to
offspring
Offspring inherit genes in predictable
patterns
4.2 Now, you will learn:
How Punnett squares can be used to
predict patterns of heredity
How ratios and probability can be used to
predict patterns of heredity
Punnett squares show possible outcomes of
inheritance
• Understanding patterns of heredity graphically:
– Punnett Square: how the parents’ alleles might combine in
offspring
– Each parents has two alleles for a particular gene
– An offspring receives one allele from each parent
Punnett Squares
• The top of the Punnett square shows one parent’s alleles for
this trait
• Add two dominant regular alleles (DD) on top
• Two recessive dwarf alleles (dd) on the side
• Each potential offspring would have the same genotype: one
dominant and one recessive allele (Dd)
• The phenotype would show the dominant allele: regular height
Punnett Squares Recap
Setting up and using a Punnett square is quite simple once you
understand how it works.
You begin by drawing a grid of perpendicular lines:
Next, you put the genotype of one parent across the top and that of the other parent
down the left side.
For example, if parent pea plant genotypes were YY and GG respectively, the setup
would be:
In this example, 100% of the offspring will likely be heterozygous (YG).
Since the Y (yellow) allele is dominant over the G (green) allele for pea plants, 100% of
the YG offspring will have a yellow phenotype, as Mendel observed in his breeding
experiments.