Genetics

Ms MahoneyMCAS 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 SynthesisMaking 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 DNA2. 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 thecytoplasm1.RNA attaches to the ribosome2.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. Figure out what the parent alleles are2. Place in parent alleles3. Fill in the offspring alleles4. Determine the genotype and phenotype

possibilities

Example: a tall parent has offspring with another tall parent. Each has a genotype of Tt.

GENOTYPES¼ = _____½ = _____¼ = _____

T t

T

t

T T T t

T t t t

PHENOTYPES ____ or ____% _________ ____ or ____% _________

TT

75

Tt

tt

3/41/4 SHORT

TALL

25

Pedigree

Sex linked Pedigree