Genetics
Ms Mahoney
MCAS Biology
• Central Concepts: Genes allow for the storage and
transmission of genetic information. They are a set
of instructions encoded in the nucleotide
sequence of each organism. Genes code for the
specific sequences of amino acids that comprise
the proteins characteristic to that organism.
• 3.1 Describe the basic structure (double helix,
sugar/phosphate backbone, linked by
complementary nucleotide pairs) of DNA, and
describe its function in genetic inheritance
DNA Structure
• Two strands (double helix)
• Sugar and Phosphate backbone
• Nucleic Acid
– Made of nucleotides
– 4 different kinds
•
•
•
•
Adenine : A
Guanine: G
Thymine: T
Cytosine: C
– A pairs with T
– G pairs with C
DNA Function
• Holds genetic information
– For you (now) and your kids (future)
• Code for proteins
• Central Concepts: Genes allow for the storage and
transmission of genetic information. They are a set of
instructions encoded in the nucleotide sequence of
each organism. Genes code for the specific
sequences of amino acids that comprise the proteins
characteristic to that organism.
• 3.2 Describe the basic process of DNA replication and
how it relates to the transmission and conservation
of the genetic code. Explain the basic processes of
transcription and translation, and how they result in
the expression of genes. Distinguish among the end
products of replication, transcription, and
translation.
Replication
• DNA make copies of itself when new cells are
being made
– Happens before mitosis and meiosis
– Very important that the copy is the SAME
Replication Steps
1. DNA unwinds (opens up)
2. DNA polymerase (enzyme) adds nucleotides
to the new strand (complementary)
3. Two new strands are formed
– Each strand has an old copy and a new copy
Protein Synthesis
Making of Proteins
• Also called gene expression
• Two parts: transcription and translation
• Transcription
– Make RNA from DNA for a certain protein
• Translation
– Make protein from RNA
Transcription
Transcription Steps
Happens in the nucleus
1. Polymerase (enzyme) attaches to DNA
2. RNA is made based on the DNA strand
RNA: one strand, nucleic acid, AUCG
Translation
Translation Step
Happens on the ribosomes on the ER or in the
cytoplasm
1. RNA attaches to the ribosome
2. tRNA “reads” the RNA and brings the
matching amino acid based on the codon
Codons
• 3 nucleotides on RNA
– Code for 1 amino acid
• Remember amino acids combine to make proteins
• You can use a code box to determine the
amino acid
• Central Concepts: Genes allow for the storage and
transmission of genetic information. They are a set of
instructions encoded in the nucleotide sequence of
each organism. Genes code for the specific sequences
of amino acids that comprise the proteins
characteristic to that organism.
• 3.3 Explain how mutations in the DNA sequence of a
gene may or may not result in phenotypic change in
an organism. Explain how mutations in gametes may
result in phenotypic changes in offspring.
How to talk about genes?
• Genotype
– DNA involved in the genes
– Two copies (one from each parent)
• Called alleles
– Example: BB, Bb, or bb
• Phenotype
– Physical appearance of the gene
– Example: brown hair, blue eyes, purple flowers
Mutations
• Mutations: change in the DNA
– Most mutations don’t do anything
– Some mutations are harmful
• Examples: change proteins, cause cancer
• Mutations in body (somatic) cells
– Affect the person
• Mutation in sex (gametes) cell
– Affect the children (offspring)
Mutations
• Mutation during REPLICATION
– DNA will have the mutation from now on
• RNA and protein made from this DNA will be mutated
• Mutation during TRANSCRIPTION
– RNA will be affected this one time
• Mutation during TRANSLATION
– Protein will be affected this one time
• Central Concepts: Genes allow for the storage and
transmission of genetic information. They are a set
of instructions encoded in the nucleotide sequence
of each organism. Genes code for the specific
sequences of amino acids that comprise the
proteins characteristic to that organism.
• 3.4 Distinguish among observed inheritance
patterns caused by several types of genetic traits
(dominant, recessive, codominant, sex-linked,
polygenic, incomplete dominance, multiple alleles).
Inheritance
• Inheritance: passing of genes to offspring
– After meiosis, gametes from each parent fertilize
and make a zygote
• Alleles: different variations of the same gene
– Hair color: ________ or _________?
– Flower colors: _______ _______ ______?
– Homozygous: same alleles
– Heterozygous: different alleles
Alleles
• Dominant alleles
– Allele that when present is physically seen
– Shown as a Capital Letter
– Autosomal or sex linked
• Recessive alleles
– Allele that when present (in one copy) is not physically
seen
– If you have two copies, then it is seen\
– Shown as a lowercase letter
– Autosomal or sex linked
D vs r example
• Flower Color
– Red is dominant (capital R)
– White is recessive (lower r)
– If you have the genotype RR the flower color is
______________?
– If you have the genotype Rr the flower color is
______________?
– If you have the genotype rr the flower color is
______________?
Alleles
• Codominant
– Dominant and recessive alleles are mixed
– Red and white make ______________
• Incomplete dominant
– Dominant and recessive alleles are both seen
– Red and white make ___________________
Alleles
• Sex linked
– Found on the X or Y chromosome
• Males have a greater chance of having a disorder if the allele is on
the X because they have only one
• Polygenic
– Two more different genes work together to make a trait
– Example: Eye color is determined by 3 genes
• Multiple Alleles
– More than two types of alleles for a gene
– Example: Blood groups (A B and O)
• Central Concepts: Genes allow for the storage and
transmission of genetic information. They are a set of
instructions encoded in the nucleotide sequence of each
organism. Genes code for the specific sequences of amino
acids that comprise the proteins characteristic to that
organism.
• 3.5 Describe how Mendel’s laws of segregation and
independent assortment can be observed through patterns
of inheritance (e.g., dihybrid crosses).
• 3.6 Use a Punnett Square to determine the probabilities for
genotype and phenotype combinations in monohybrid
crosses.
Mendel’s Laws
• Apply to Meiosis
• Law of Segregation
– Chromosomes separate into different gametes
• Law of Independent Assortment
– Chromosomes randomly separate
– This helps create unique gametes with different
combinations of alleles
Punnett Square Basics
1.
2.
3.
4.
Figure out what the parent alleles are
Place in parent alleles
Fill in the offspring alleles
Determine the genotype and phenotype
possibilities
Example: a tall parent has offspring with another
tall parent. Each has a genotype of Tt.
T
t
T
TT
Tt
t
Tt
tt
GENOTYPES
TT
¼ = _____
Tt
½ = _____
tt
¼ = _____
TALL
3/4 or ____%
75
PHENOTYPES ____
_________
____
_________
1/4or ____%
SHORT
25
Pedigree
Sex linked Pedigree