Upload
griffin-young
View
219
Download
0
Embed Size (px)
Citation preview
Gregor Mendel
Born in 1822 in Czechoslovakia.Became a monk at a monastery in 1843.Taught biology and had interests in statistics.Also studied at the University of Vienna
Mendel’s experiments
The first thing Mendel did was create a “pure” generation or true-breeding generation.He made sure that certain pea plants were only able to self pollinate, eliminating unwanted traits.He did this by cutting away the stamen, or male part of each flower
Genes and dominance
Trait : a characteristicMendel studied seven of these traitsAfter Mendel ensured that his true-breeding generation was pure, he then crossed plants showing contrasting traits.
He called the offspring the F1 generation or first filial.
What will happen when pure yellow peas are crossed with
pure green peas?All of the offspring were yellow.
Hybrids = the offspring of crosses between parents with contrasting traits
What did Mendel conclude?
Inheritance is determined by factors passed on from one generation to another.
Mendel knew nothing about chromosomes, genes, or DNA. Why?
These terms hadn’t yet been defined.
What were Mendel’s “factors”
The ‘factors” that Mendel mentioned were the genes.
Each gene has different forms called alleles
Mendel’s second principle stated that some alleles are dominant and some are recessive.
Mendel’s second cross
He allowed the F1 generation to self-pollinate thus producing the F2 generation.
Did the recessive allele completely disappear?
What happened when he crossed two yellow pea hybrid (F1) plants?
Results:
¾ of the peas were yellow, ¼ of the peas were green.During the formation of the sex cells or gametes, the alleles separated or segregated to different gametes. (pollen and egg)
11-2 Probability
The likelihood of a particular event occurring. Chance
Can be expressed as a fraction or a percent.
Example: coin flip.
Punnett Square
Developed by Reginald Punnett.
A diagram used to show the probability or chances of a certain trait being passed from one generation to another.
Reading Punnett squares
Gametes are placed above and to the left of the square
Offspring are placed in the square.
Capital letters (Y) represent dominant alleles.
Lower case letters (y) represent recessive alleles.
Homozygous = when an organism possesses two identical alleles. ex.YY or yy
Heterozygous = when an organism possesses different alleles. ex.Yy
Phenotype vs genotype
Genotype The genetic makeup Symbolized with
letters Tt or TT
Phenotype
Physical appearance of the organism
Expression of the trait
Short, tall, yellow, smooth, etc.
Probability and statistics
No one event has a greater chance of occurring than another.
You cannot predict the precise outcome of an individual event.
The more trials performed, the closer the actual results to the expected outcomes.
11-3 Independent Assortment
The two factor cross. Example: color and shape of peas.
F1 cross to produce the F2 generation
Ex RRYY x rryy
Round yellow mated with wrinkled green• Offspring would all be hybrid for both
traits (RrYy)
Some exceptions to Mendel’s principles:
Some alleles are neither dominant nor recessive.
Many traits are controlled by more than one gene (polygenic traits)
Incomplete dominance
A situation in which neither allele is dominant.
When both alleles are present a “new” phenotype appears that is a blend of each allele.
Alleles will be represented by capital letters only.
Japanese four-o-clock flowers
Red flower plant genotype = RR
White flower plant genotype = WW
Pink flower plant genotype = RW
What happens when a red flower is crossed with a
white flower?
According to Mendel either some white and some red or all offspring either red or white.All are pink
Codominance
When two alleles both appear in the phenotype.
Usually signified using superscripts.
example: color of hair coat in cattle.
crcr = red hairs
cwcw = white hairs
crcw = roan coat (mixture of both colors)
Multiple allele inheritance – Blood Types
When two or more alleles contribute to the phenotype.
Human blood types: A,B,O and AB
A and B are codominant to each other.
Both A and B are dominant over O.
Human Blood types: Type AB
TYPE AB
genotype = IAIB
Blood cells contain both types of antigens
Known as universal recipient
Human Blood types: Type O
TYPE OAllele = i No antigens on the surface of the blood cellsKnown as universal donor
Sample Problem:
A man with type AB blood marries a woman with type B blood whose father has type O blood. What are the chances that they have a child with type A blood? Type AB?
11-4 Meiosis
A method of cell division similar to mitosis.
2 main differences:
1. There are two divisions to produce 4 daughter cells
2. The cells produce contain ½ the chromosomes as the original cell
Chromosome number
All cells of an organism contain a specific number of chromosomes.
Most cells are diploid (2n) meaning they have two copies of each chromosome
Events of Meiosis I
During prophase I, each chromosome pairs with its homologous chromosome to form a tetrad
Crossing-Over
Crossing-over: an exchange of genetic material between sister chromatids
Results in greater variation
Meiosis II
Neither cell replicates its chromosomes.
Each cell splits (similar to mitosis)
Produces four daughter cells.
Animation
Net result:
Spermatogensis
4 mature sperm
Each sperm has exactly half the number of chromosomes as the father.
Oogensis
1 mature ova or egg.
Each egg has exactly half the number of chromosomes as the mother.
11-5 Gene Linkage
Are genes “linked” to each other on chromosomes?
Morgan found that many genes are linked together.
It was determined that chromosomes, not genes, assort independently during meiosis.
Gene Maps
First developed by Sturtevant in 1911.The farther apart two genes are, the more likely they will be separated in meiosis.
• There are twenty different amino acids that build proteins
• There are 64 different triplets/codons• Each amino acid is coded for by more than
one triplet/codon
The Players
mRNA:messenger RNA - carries protein recipe from the nucleus
tRNA: transfer RNA -brings amino acids to the ribosome
Ribosome: the site of protein synthesis - made of rRNA (ribosomal RNA ) and Protein
The Process of TranslationmRNA takes recipe to the ribosome in cytoplasm
ribosome attaches to the mRNA
TranslationThe ribosome moves along the mRNA until it reaches the “Start” codon
Start codon = AUG signals the start of the recipe
AUG also codes for the amino acid methionine
The process of Translation•A molecule of transfer RNA brings the amino acid called for by the mRNA to the ribosome
•transfer RNA = tRNA
The process of TranslationA second tRNA brings the second amino acid to the ribosome
The amino acids are joined together to begin the protein
THE PROCESS OF TRANSLATION CONCLUDED
The ribosome moves over 1 codon and another tRNA molecule brings another amino acid
The process continues until the stop codon on the mRNA is reached
-the stop codon = the end of the protein recipe
Meet tRNAeach molecule of tRNA carries a specific type of amino acid
- each tRNA molecule can only carry one type of amino acid
The tRNA has a group of 3 nucleotides at the base called the anticodon
How does tRNA know which amino acid goes where?
The anticodon on tRNA is complementary to a mRNA codon
the amino acid that a tRNA molecule carries is the amino acid that the complementary mRNA codon codes for
Example:
mRNA codon = GAC = aspartic acid
tRNA anticodon = CUG carries only aspartic acid