Genetics is the study of inheritance. How does one generation pass traits to the next generation?
In genetics we refer to the Parents as P (the parental generation is often called, P1). Here are my
parents:
X
If we cross this female and this male of the human species, they will give rise to offspring with certain traits that were inherited from each parent; for a set of chromosomes- 1/2 of the set comes from the mother, and the other 1/2 is inherited from the father.
Remember that chromosomes come in pairs. Humans have 23 pairs- 46 total- humans are 2n (diploid)- 2(23)=46.
photo courtesy of : www.cancersupportivecare.com
Here is a photograph of me...I am my parents' offspring, and I have retained certain features of my parents. I have a gap in my teeth, like my mother (she had braces in her 50's to close it as she said it was getting too wide), and I am tall, like most people on my father's side of the family.
The P generation (parental) gives rise to the first filial (Latin word for son) generation or the F1 generation.
The basic unit of inheritance/heredity is known as the gene. Genes are located on chromosomes and are made of DNA.
The photo shows that your DNA (deoxyribonucleic acid) is in the nucleus of your cells.
The DNA is compacted in the form of chromosomes as you can see in the diagram; the DNA is coiled around
structural proteins called histones; there is further coiling that results in the chromosome structure.
Here is a problem from my Molecular Biology class with Dr. Shedlock at CofC last semester:
The DNA content of a human diploid nucleus (2 X 23 chromosomes) is 6 X 109 base pairs.
What would be the length of the DNA if the molecules were laid out end-to-end?
(3.4 Å/bp) x (6 x 109 bp) = 2.04 x 1010Å = 2.04 m
In a different post, I'll explain how if we unraveled the DNA in our nuclei (plural for nucleus), we would be able to stretch it from Charleston, SC to Austin, TX.
So, it's kind of amazing the way that so much DNA is compacted into the nucleus!
The genome consists of all the genetic information within an organism. The diagram indicates the entire set of chromosomes in an organism as the genome.
The chromosomes are composed of tightly wound DNA.
The genes are segments of the DNA strand that encode messages for making proteins.
I will make an entire post on proteins alone.
diagram is courtesy of www.broadinstitute.org
Try using Microsoft paint or go "old school" and use markers, colored pencils or real paint to draw this diagram out yourself. It will help you to understand the order of things.
A gene can exist in multiple forms called alleles (the alternative forms of a gene).
The genetic makeup of certain traits expressed by an individual organism is known as the genotype. The phenotype is the physical expression of the genotype.
For example, we may denote brown eyes as BB (homozygous dominant) or Bb (heterozygous for brown eyes), and bb (homozygous recessive) may denote blue eyes.
B is the dominant allele, expressing brown eyes...even if only one copy is present b is the recessive allele, expressing blue eyes only when two copies are present (which is why it's recessive because in the presence of the B allele, it doesn't express blue...it gets masked).
So, if two individuals produce offspring with brown eyes in the heterozygous form:
Bb- the genotype
Brown- the phenotype - physical expression of the genotype
Remember that genetics is not as simple as B and b...some phenotypes correspond to one genotype while others are more complex-corresponding to multiple different genotypes.
I will go into further detail in a later post.
