Unit. V. Genetics
Terms that are important in genetics.
ï trait- a characteristic of an organism
ï gene- a segment of a chromosome which codes for a trait
ï allele- a specific type of gene which codes a particular trait quality
I. Meiosis & Sexual Reproduction
A. Sexual Reproduction- 2 parents
-gametes- sex cells - OVUM (OVA) and SPERM -haploid cell (N)
-somatic cell- diploid cell (2N). Any body cell other than the gametes
-zygote- a fertilized egg. (Union of 2 haploid cells making a diploid)
B. Meiosis
-objective: create a haploid gamete with complete genetic representation
-Karyotype- the set of chromosomes for an organism. Karyotypes for different sexes in humans
-gene & allele- Each gamete made must have one gene for every trait.
1. Interphase- growth & development of gamete precursor
2. Meiosis I-
a.) Prophase I-
-homologue, synapsis, tetrad/bivalent
-sister chromatid/centromere, nonsisters/chiasma
b.) Metaphase I-
c.) Anaphase I
d.) Telophase I & Cytokinesis
3. Interkinesis- No DNA replication
4. Meiosis II-
-analogous to Mitosis- but only produces 23 chromosome (instead of 46)
a.) Prophase II
b.) Metaphase II
c.) Anaphase II
d.) Telophase II & Cytokinesis
-Meiosis produces 4 haploid daughter cells where mitosis produced 2 diploid daughter cells
Image: Comparing Mitosis to Meiosis
Resource: Meiosis Tutorial
Resource2: Meiosis Tutorial
Resource3: Meiosis Tutorial
Practice: Mitosis vs. Meiosis
Vocabulary: Meiosis
II. Structure of DNA- Deoxyribonucleic Acid
Resource: What is DNA
James Watson & Francis Crick- 1954- deduced structure of DNA
DNA is a polymer made from Nucleic Acids in a double helix form.
A. Nucleotide
1. Phosphate
2. Sugar (Deoxyribose)
3. Nitrogen base
a. Purines- double ringed nitrogen bases
i. Adenine ( A )
ii. Guanine ( G )
b. Pyrimidines- single ringed nitrogen bases
i. Thymine ( T )
ii. Cytosine ( C )
B. Double Helix
1. Strand- Single chain of nucleotides
2. Double Helix
a. two strands in anti-parallel orientation
b. nitrogen bases bonded by Hydrogen bonds
C. Complementary Base Pairing
1. Complements Pairs- Purines = Pyrimidines
a. Adenine / Thymine- these form 2 hydrogen bonds between the bases
b. Guanine / Cytosine- these form 3 hydrogen bonds between the bases
III. Functions of DNA
1. Be able to store information that is used to control the development and metabolic activities of the cell and organism.
2. Be able to replicate with high accuracy during cell division and must be transmitted from generation to generation.
3. Be able to undergo mutations- causes genetic variability (Evolution)
IV. Replication
-process of replicating DNA molecules into exact copies- ìLike begets Likeî.
A. Process
1. The 2 strands unwind and ìunzipî. Helicase
2. New complementary nucleotides bind with existing strands
3. New nucleotides are bonded causing formation of 2 new strands.
** Semi-conservative model**
Resource: Simple View of Replication
Resource: Detailed View of Replication
V. Protein Synthesis
Ribosome- site of protein synthesis in the cell. There are two types: ìfreeî and ìboundî
A. Process- (Transcription and Translation)
1. Transcription- RNA is produced from DNA (transcribe = same language)
a. RNA- Ribonucleic Acid
differences from DNA
-pentose sugar is ribose (deoxyribose-DNA)
-nucleotide Uracil replaces Thymine
-single strand (double helix-DNA)
b. types:
-messenger RNA (mRNA). made from DNA, contains code for protein, sent to the ribosomes
-transfer RNA (tRNA). contains RNA code to match mRNA with appropriate amino acid
-ribosomal RNA (rRNA). RNA that is used to make ribosomes (with proteins)
b. Steps:
1. Initiation- RNA polymerase attaches to DNA
2. Elongation- RNA chain is built- complement nucleotides
3. Termination- code in DNA stops RNA synthesis
**This produces mRNA- carries code from nucleus (DNA) to cytoplasm where the ribosomes are found.
Animation: Transcription
2.Translation- ribosomes take RNA code and produces protein (translate = one language to another)
a.Steps:
1. Initiation- ribosome attaches to mRNA
2. Elongation- RNA code is read and polypeptide chain is built-
** tRNA attach and deposit Amino Acid- (Codon-Anticodon)
3. Termination- Stop codon on mRNA halts protein production
** UGA, UAG, UAA
Animation: Translation
B. Regulation of Gene Expression
Resource: Prokaryotic gene expression
VI. Mendel & Genetics
Gregor Mendel was born 1822 in Austria- first to establish Laws of Inheritance
A. History
-Austrian monk who experimented on garden pea (Pisum sativum).
**Previous experiments by Koelreuter (hybridization of tobacco plants)- c.1760
and T.A. Knight (true-breeders of garden pea) c. 1790
1. Segregation of traits in offspring
a. traits can be masked in one generation and reemerge in the next
b. traits segregate among the offspring of a cross
c. some traits are more likely to be represented than their alternatives
2. True-breeders were available
3. small & easy to grow
4. male and female reproductive organs are contained within the flower
a. self-fertilization
b. cross- fertilization
1. Established true-breeders by self fertilizing. Produced offspring with the same characteristics
2. Cross-breeding of true-breeders with different traits. Produced offspring with one characteristic.
3. Cross hybrid plants and keep track of 2nd generation offspring
Parent --> 1st Filial (F1) --> 2nd Filial (F2)
C. Results
1. First filial (F1) didnít show a ìblendingî of traits; exhibited single parent trait
a. dominant trait- the trait that is always expressed
b. recessive trait- the trait that is often masked by the dominant trait
2. Second filial (F2) showed a mixture of original parent traits
a. 75% were dominant trait : 25% were recessive trait (3:1 ratio- Mendelian Ratio)
b. Of the F2 dominant- 2/3 were true breeder and 1/3 were hybrids
therefore: º dominant true- breeders
º recessive true-breeders
‡ hybrids - produced both traits when self fertilized
D. Mendelís Hypothesis
1. Parents send ìfactorsî to offspring which codes for traits-
-These factors are now called genes- a segment of DNA which is defined by a locus
2. For each trait an organism contains 2 ìfactorsî that code for a trait, but can only
send 1 factor to an offspring, not both- Haploid gamete formation
3. Alternative forms of ìfactorsî that code for a trait-
-We now call alternative traits expressed from one gene alleles
a. homozygous- when a organism has two of the same alleles for a trait
b. heterozygous- when an organism has two different alleles for a trait
4. The two alleles forming a trait do not affect the other- remain separate
5. Not all ìfactorsî are expressed- some dominant, some masked (recessive)
a. genotype- description of an organisms alleles for a trait
b. phenotype- the expression of a genotype
E. Mendelís Laws
1. Law of Segregation
a. the alternative forms of a trait are encoded by alternative alleles
b. when a gamete is formed the two alleles segregate independently
c. each gamete has an equal probability of either allele
2. Law of Independent Assortment
-genes located on different chromosomes assort independently of one another
resource: Mendelian Genetics
F. Genetic Tools
1. Punnett Squares-
a. Monohybrid crosses- Analysis of offspring looking at 1 trait.
1. homozygous-homozygous- produces all homozygous offspring
2. homozygous-heterozygous- 1/2 dominant, 1/2 recessive phenotype ratio, same with genotype
3. heterozygous-heterozygous- produces a 3:1 phenotype ratio & 1:2:1 genotype ratio
Practice: Identifying gametes
practice: Monohybrid crosses
b. Dihybrid crosses- Analysis of offspring looking at 2 traits
Practice:: Dihybrid Crosses
2. Test crosses- differentiates homo dominant and heterozygous by crossing with homo recessive
Practice: Incomplete dominance
Practice: Linked genes
Practice: Crossing over
Practice: Sex-Linked genes
Vocabulary: Genetics
Review: Mendelian Genetics
Resources:
DNA from the beginning. Dolan Institute
