Mendelian Genetics

Mendel laid the groundwork for genetics. Genetics is the study of inheritance patterns and variation. Gregor Mendel showed that traits are inherited as units.

is the passing of traits from one generation to the next. Heredity is the passing of traits from one generation to the next. A trait is a distinguishing characteristic or quality.

DNA Review….. DNA, deoxyribonucleic acid, is the set of chemicals that tells all of the cells in our body what to do. It is like a set of directions, and is what makes each individual unique. A chromosome is made up of DNA. It is the long chain of DNA that has been coiled up tightly. These chromosomes, or pieces of DNA, contain genes. Homologous chromosomes are chromosomes that have the same genes, in the same location. You get one of each chromosome in a homologous pair from each parent. EX: Chromosome #1 you have one from mom and one from dad, and they are homologous because they contain the same genes.

DNA Genes Alleles Genes are segments of DNA on a chromosome that has directions for specific traits. EX: Hair color An allele is an alternate (different) form of a gene. EX: allele for brown hair (H), allele for blonde hair (h)

Alleles Recessive allele Dominant allele An allele whose trait always shows up in the organism when the allele is present. The dominant allele is represented by a capital letter (Brown hair is dominant = H) Recessive allele An allele whose trait is hidden when paired with a dominant allele. The only way a recessive allele shows up is if the organism does not have a dominant allele. This is represented by a lowercase letter (blonde hair is recessive = h) Ended here with A

We use the same letter to represent BOTH alleles!!

There are two alleles for each gene… Homozygous Heterozygous This is the term used when an organism has two identical alleles for a trait. Ex: HH or hh This is the term used when an organism has two different alleles for a trait. Ex: Hh Stopped here with class D

Genotype vs. Phenotype Genotype: actual alleles from parents (letters; HH) Phenotype: physical appearance of organism (No letters. What does it look like? What traits does it have? Brown hair or blonde hair?)

Let’s Try! Let’s use freckles. Having freckles is dominant = F No freckles is recessive = f How would you show an individuals genotype if they were: Homozygous dominant for freckles? Homozygous recessive for freckles? Heterozygous for freckles?

Write the genotype for an individual that is: Brown eyes = B Blue eyes = b Write the genotype for an individual that is: Blue eyed:________________________ Homozygous dominant for eye color:____________ Heterozygous for eye color:___________________ Homozygous recessive for eye color:________ What genotypes can a person have if they have brown eyes?_____________ Ended here with C

A purebred is an organism that always produces offspring with the same form of a trait as the parent. This is also referred to as homozygous. A hybrid is an organism that has two different alleles for a trait. This is also referred to as heterozygous.

Only 1 allele from each parent is in each box. Each box ends up with 2 total alleles, one from the mother and one from the father.

__________X__________ Monohybrid Cross Cross involving one contrasting trait Use a Punnett square to predict probabilities… (let’s use F) Cross a heterozygous purple flower with a homozygous recessive white flower. __________X__________