Genetics Study of heredity Heredity is the study of how offspring get their traits from their parents. Traits are physical characteristics: Height, hair color, flower color

Where do traits come from? Traits are controlled by genes. Genes are found on chromosomes Chromosomes are wound up DNA

Chromosomes Humans have 46 chromosomes They are organized into 23 pairs

Chromosomes and Genes Every chromosome contains thousands of genes Each gene has 2 parts These parts are called alleles One allele comes from each parent from each parent

Alleles There are two kinds of alleles Dominant and recessive Dominant alleles are more powerful They can hide recessive alleles when paired together. DOMINANT ALLELES ARE SHOWN WITH CAPITAL LETTERS recessive alleles are shown with lower case letters

Alleles and Traits The combination of alleles an organism has determines what it will look like. 2 capital alleles (QQ) will show the dominant trait 2 lower case alleles (qq) will show the recessive trait 1 dominant and 1 recessive allele (Qq) combination will show the dominant trait

How does this work? Each parent give the offspring 1 allele. Q q

However… Each parent has 2 possible alleles to give. But only one will be given to their offspring Q Q q q

Parents and Offspring The alleles the parents can give the offspring determine what the offspring will be.

Offspring possibilities The alleles given by the parents will determine what the offspring has. Q q + = Qq

Defining allele combinations If the alleles given to the offspring by the parents are the different it is called heterozygous or hybrid. Q q + = q Q + = Qq

Defining allele combinations If the alleles given to the offspring by the parents are the same it is called homozygous or purebred. Q Q + = q q + = QQ qq

Types of Homozygous/purebred combinations If the 2 alleles given by the parents are dominant alleles it’s called homozygous dominant or a dominant purebred. Q Q + = QQ

Types of Homozygous/purebred combinations If the 2 alleles given by the parents are recessive alleles it’s called homozygous recessive or a recessive purebred. qq q q + =

Genes and physical appearance The genetic code found on the chromosomes is referred to as the genotype. QQ, Qq, qq The physical trait that results is referred to as the phenotype.

Predicting the possible offspring The tool geneticists use to predict the possible offspring is called a Punnett Square

Reading a Punnett Square A Punnett square show the probability that parents will have certain offspring. Phenotypes: 75% chance the offspring will be tall 25% chance the offspring will be short Genotypes: 25% chance the offspring will be homozygous dominant/dominant purebred 25%chance the offspring will be homozygous recessive/recessive purebred 50% chance the offspring will be heterozygous/hybrid