Genetic Crosses - EG

Gametes

specialized reproductive cells

• sperm, egg

How many chromosomes do gametes carry?

they carry half the number of chromosomes

• haploid (n) = 23

How many chromosomes are there in a human?

23 → number 1 through 23

• each carry unique set of genes

Majority of human cells are…

diploid (2n) = 46

• 23 chromosomes from sperm cell

• 23 chromosomes from egg cell

Each pair of chromosomes is called…

homologous chromosomes

• there are 23 pairs

Homologous chromosomes

carry the same genes at the same location on their chromosomes

Allele

different version of the same gene

Phenotype

physical (observable) trait of an organism

• Ex. hair color, eye color

Genotype

genetic makeup of an organism which influences phenotype

Dominant allele

expresses its trait even if only one copy is present

Recessive allele

expresses only when both recessive copies are present

Punnett square (monohybrid cross)

diagram used to predict the possible genetic outcomes

• genotypes and phenotypes

• based on what happens during meiosis

What do you need in order to see all possible genotypes and phenotypes?

you need F2 generation