GeneticsGenetics

• Heredity – characteristics inherited from parents to offspring through genes

• Genetics - The study of genes and heredity

Traits • Characteristics that are inherited through genes– Genes are a portion

of an organism’s DNA– Each organism has

two copies of each gene

– Genes have different forms called alleles

Gregor Mendel• A monk in the 1800s• First to identify

heredity• Studied the traits in

garden peas– Tall/short– Round/wrinkled– Green/yellow pods– Purple/white flowers

• Why peas???

Parent or “P” Generation

• The 2 organisms that are used to reproduce

F1 Generation

• The offspring - babies

F2 generation• The babies of the F1 or the

grandchildren of the P generation– Mendel noticed that in his peas, the

white trait that disappeared with the F1 generation reappeared, but in a very small ratio compared to the purple trait

The Rule of Dominance• There are two contrasting traits/alleles

– Ex: tall or short– Another example pod color – green/yellow

• Alleles can be either dominant or recessive (strong or weak)– Dominant alleles are observable– Recessive alleles are not observable when

the dominant allele is present – they are hidden (masked) by the dominant allele

The Law of Segregation• The two allleles for a gene

separate when forming a sperm and egg

Law of Independent assortment

• Alleles for different genes are distributed to sperm and egg independently and randomly– Different alleles do not affect

each other• Could be

– tall and fat– Short and thin– Tall and thin– Short and fat

• Why all siblings do not look exactly alike

Genotype• Created after fertilization of an egg

by sperm• The copies of alleles or genes that

an organism has• Genetic make-up• ontrols the phenotype• Ex: BB, Bb, bb

Phenotype• The way an organism physically

looks– Ex: Brown hair, tall– Determined by the genotype

How can three genotypes only produce two phenotypes?

Homozygous – (Homo: same)

• Pure/true breeding• When an organism has 2 copies of

the same allele• BB – homozygous dominant• bb – homozygous recessive

Heterozygous (Hetero: different)

• Hybrid• When an organism has 2 different

alleles for a gene• one capital; one lower case• Bb, Gg etc.

Punnett Square

• A chart used to predict the probability of traits represented among offspring

• Why it is only a prediction?

Monohybrid

• One cross because you are looking at only one trait

Monohybrid Punnett Square Problems

• Height – tall is dominant to short• Symbol for tall _______• Symbol for short _____• Phenotype –

– Homozygous tall male X short female

• Genotype– Male _____ X Female ______

P1 Punnett Square

– F1 genotype ratio

– F1 phenotype ratio

Monohybrid Punnett Square Problems

• Height – tall is dominant to short• Symbol for tall _______• Symbol for short _____• Phenotype –

– Heterozygous male and female

• Genotype– Male _____ X Female ______

F1 Punnett Square

– F2 genotype ratio

– F2 phenotype ratio