Download Modern Genetics Notes

Question: Why do some traits exhibit a large number of phenotypes?
COMPLEX PATTERNS OF INHERITANCE
Incomplete dominance — when neither allele of the parents is completely dominant, the
phenotype of the heterozygous offspring is a mix of parents.
Ex. red snapdragons x white snapdragons
pink snapdragons
Codominant alleles — both alleles show equally
Ex. black chicken x white chicken
speckled chicken
Multiple alleles — there are more than two alleles for a genetic trait
Ex. a rabbit’s coat color — four possible colors
Humans have 23 pairs of chromosomes. 22 pairs of homologous chromosomes are called
autosomes. The 23rd pair is called the sex chromosomes, which are indicated by X for
females and Y for males.
Sex — linked traits — traits controlled by genes located on sex chromosomes.
Ex. color blindness
Polygenic inheritance — inheritance pattern of a trait that is controlled by two or more
genes. Ex. skin color and height
*Nutrition, light, chemicals, and infectious agents such as bacteria, fungi, parasites and
viruses can all influence how genes are expressed.
Question: What does mRNA and tRNA stand for?
THE GENETIC CODE
Gene — a section of a DNA molecule that contains the information to code for one
specific protein.
The order of the nitrogen bases (guanine, cytosine, adenine and thymine) along a gene
forms a genetic code that specifies what type of protein will be produced.
RNA — (ribonucleic acid) genetic “messenger” which carries genetic code from the DNA
inside the nucleus into the cytoplasm
Messenger RNA — copies coded message from DNA and carries message to ribosome
in the cytoplasm.
Transfer RNA — carries amino acids to the ribosome and adds them to growing
protein
# Strands
SUGAR
NITROGEN BASES
DNA
2
deoxyribose
A, G, C, T
vs.
RNA
1
ribose
A, G, C, U (Uracil)
Mutation — any change in a gene or chromosome
Let’s say…original DNA sequence reads:
THE RED HAT
substitution
THE RED CAT
deletion
THE REC AT
Question: How are genetic disorders diagnosed?
addition
THE READ HAT
HUMAN GENETIC DISORDERS
Genetic disorder — an abnormal condition that a person inherits through genes or
chromosomes that are caused by:
1. mutations in the DNA of genes
2. changes in the overall structure or number of chromosomes
Pedigree — diagram or family
tree of genetic inheritance
used by geneticists to map
genetic traits
Karyotype — photograph of a person’s chromosome arranged in pairs and can reveal
whether a person has correct number of chromosomes
SOME GENETIC DISORDER CAUSED BY ABNORMAL
CHROMOSOME #
DISORDER
CHROMOSOME
DESCRIPTION
Down Syndrome or
Trisomy 21
# 21
47 chromosomes, intellectual disability,
heart defects, respiratory infections
Edward’s Syndrome
or Trisomy 18
# 18
47 chromosomes, severe intellectual
disability, characteristic malformations
Turner’s Syndrome
Single X in female
45 chromosomes, females only, are
infertile, no secondary sex
characteristics
Klinefelter’s
Syndrome
Extra X in male
45 chromosomes, males only, sterile,
small testicles, otherwise normal
appearance
Question: Can you give an example of selective breeding?
ADVANCES IN GENETICS
Selective breeding — process of selecting organisms with desired traits to be parents of
next generation—two techniques include:
Inbreeding — involves crossing two individuals that have similar characteristics
Hybridization — breeders cross two genetically different individuals in hopes of
offspring having best traits from both parents
Clone — organism that has exactly the same genes as the organism from which it was
produced
Genetic Engineering — genes from one organism are transferred into the DNA of
another organism (ex. bacteria producing insulin or cows producing milk with blood—
clotting protein for hemophiliacs)
Gene Therapy — involves inserting copies of a gene directly into a person’s cell
The Human Genome Project — project to identify the DNA sequence of every gene in the
human genome
Genome — all the DNA in one cell of an organism