Introduction to Genetics

Gregor Mendel Gregor Mendel is the “father of modern genetics” Austrian monk who did genetic experiments with pea plants Defined basic units of heredity 1822-1844

Mendel used pea plants to conduct experiments Mendel used pea plants to conduct experiments. He concentrated on petal color and shape of peas. Experiments led to basic genetic understandings such as: What happens when two different plants breed? How traits are passed from parents to offspring? Basic understandings of dominant and recessive traits?

Different traits Mendel observed:

Why Peas? Mendel could do two experiments a year Lacked modern technology Today scientists use organisms that reproduce quickly such as drosophila (fruit fly) which reproduces in 2 weeks or bacteria such as E. coli which reproduces within hours.

Genetics DNA are the blue-prints of all of your genetic information. DNA is tightly wound into chromosomes Your genetic information is on genes Genes are located on chromosomes

Your Genes and DNA You are a combination of your parents. You have ½ of your mom’s and ½ of your dad’s DNA Remember Meiosis? You have 23 pairs (one from each parent) to make a total of 46 chromosomes.

Human Chromosomes

Genetic Traits Genes you get from your dad are “paternal” and genes you get from your mom are “maternal” These make up your traits. Trait: characteristic determined by genes Example: I have the trait for blue eyes

Alleles Each trait is carried on a chromosome stripe. These stripes are called alleles. Allele: form of a gene on a specific region of a chromosome

Alleles for flower color Maternal Chromosome Paternal Chromosome

Which of Your Parents Traits Will You Get? Based on probability For example, eggs have X chromosomes and sperm have either X or Y chromosomes. XX= girl XY= boy What is the probability offspring will be a girl?

Boy or Girl 50% chance or 1 out of 2 Only two different combinations! XX or XY Determining the sex of a baby is one example of probability. But…it doesn’t always work that way…

Dominant Alleles vs. Recessive Alleles Certain traits are stronger then others. This means that they will more likely be expressed. For example: If I mix black paint with white paint, what color will paint most likely be? Black! It is a “stronger color”. Dominant allele: one that is expressed physically (what organism looks like)

Dominant Alleles vs. Recessive Alleles What about the white paint? Recessive allele: one that is masked or hidden by the dominant allele. White paint would be an example of the “recessive color”. There is still white paint in the mixture, but it looks black.

Terms To Know Genotype: combination of two alleles Homozygous: When the genes are identical Heterozygous: When the genes are different Phenotype: The observable trait (the trait you see)

Boy: XY Girl: XX What is the genotype for girl? Is boy homo or heterozygous? Heterozygous XY (different letters) Homozygous XX (same letters) What is the dominant allele (X or Y?) Y How do you know? Wherever Y is means a boy will form

How genes are expressed If an organism carries any combination of dominant genes, it will be expressed in an organism. Recessive genes are only expressed when there are two recessive genes Example XX in girls