Terms you’ve gotta know BASIC GENETICS TERMS Terms you’ve gotta know

GENE Gene: a section of DNA that codes for a trait A chromosome is a chunk of DNA and genes are parts of chromosomes

ALLELE Allele: the different options for a gene Example: attached or unattached earlobes are the alleles for the gene for earlobe shape

DOMINANT/RECESSIVE Dominant: an allele that blocks or hides a recessive allele Recessive: an allele that is blocked by or hidden by a dominant allele Question: Using purebred crosses, how did Mendel figure out that genes are either dominant or recessive?

HOMOZYGOUS/HETEROZYGOUS Homozygous: When a person’s two alleles for a gene are the same Heterozygous: When a person’s two alleles for a gene are different You get one allele from your mom and one from your dad. If you get the same alleles from your mom and dad, you are homozygous for that trait. If your mom gave you a different allele than your dad, you are heterozygous for that trait

Tt GENOTYPE Genotype: A person’s set of alleles (gene options) Genotype is written in letters It is usually the first letter of the dominant allele to make it easier Choose a letter for each of these traits. Write both the dominant and the recessive genotype allele letters Attached Earlobes Freckles Dimples Tongue-roller

GENOTYPE Now, using your letters from before write a genotype for a person without freckles (Freckles are dominant) Write a genotype for a person with freckles

GENOTYPE-HETEROZYGOUS AND HOMOZYGOUS A Heterozygous genotype means an organism has both the dominant and the recessive allele (e.g. Aa) Homozygous recessive means an organism has 2 recessive alleles (e.g. aa) Homozygous dominant means an organism has 2 dominant alleles (e.g. AA) Write a heterozygous genotype for handedness Write a homozygous dominant and a homozygous recessive genotype for handedness

PHENOTYPE Phenotype: A person’s physical features because of their genotype What you look like (your phenotype) is based on what your genotype is (your genes) What will the phenotype of these genotypes be: WW, Ww, ww (Widow’s Peak dominant over straight hair line) HH, Hh, hh (Hitch hiker’s thumb is dominant over a straight thumb) CC, Cc, cc (Curly hair is dominant over straight hair)