Download G01 - Introduction to Mendelian Genetics.notebook

G01 ­ Introduction to Mendelian Genetics.notebook
January 31, 2014
UNIT 1 ­ GENETIC PROCESSES
INTRODUCTION TO GENETICS
Why do we not all look alike? What is it about people that make one person look different from another?
The answer is that we have different traits. A trait is a distinguishing physical feature (or characteristic/ability) that we inherit from our parents. WHAT IS GENETICS?
Genetics is a branch of Biology that deals with heredity and variation in organisms.
More specifically, genetics is the study of how traits get passed from generation to generation (heredity) and why organisms are different from each other (variation).
GENETICS VIEWPOINTS THROUGH TIME
Ancient Greece: Hippocrates (460­377 BCE) believed that every part of the parents’ bodies were involved in the creation of a child. Aristotle believed that male and female semen mixed to create a child.
Middle Ages Europe: William Harvey (1500's) believed in epigenesis. He thought that the embryo developed in stages and its development was affected by stimuli inside and outside the womb. Anton van Leeuwenhoek (1632­1723) believed that an embryo was present in male sperm and that females were just incubators for children to be born.
Dec 3­12:46 PM
Pangenesis started in Ancient Greece, where it was believed that males and females formed 'genes' in every organ. Genes then moved through the blood to the genitals and then into the children. Charles Darwin proposed this theory in the 1800's and his cousin, Francis Galton, disproved it.
In the 19th century it was believed that the sperm and egg simply blended together and offspring would have a mixture of the parents’ traits, known as the blending theory of inheritance.
Some of the most brilliant minds in Science couldn't explain the basics of heredity.
It wasn’t until a monk with a green thumb came along that we would have concrete data on trait inheritance.
Dec 4­9:45 AM
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G01 ­ Introduction to Mendelian Genetics.notebook
January 31, 2014
What do you already know about inheritance?
Jan 25­9:22 AM
TERMINOLOGY OF GENETICS
Traits are coded for by ___________, which are grouped together on ____________________. The macromolecule that makes up genes and chromosomes is called ____________________________________. This material is stored in the ________________ of our cells.
genes
nucleus
chromosomes
deoxyribonucleic acid (DNA)
Our traits are a physical expression of our genes, this is known as our ___________________. The genetic code (genes) you have that code for that trait is called your _________________________.
phenotype
genotype
Jan 25­9:23 AM
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G01 ­ Introduction to Mendelian Genetics.notebook
January 31, 2014
Humans have ______ chromosomes.
We get ______ from each parent.
Cells with the normal number of chromosomes for that organism are said to be __________________ (i.e. ______________________)
Some cells have half the number of chromosomes are said to be __________________ (i.e. ___________________________)
23
46 haploid
egg and sperm cells
skin cells
diploid
Jan 25­9:43 AM
• The 23 chromosomes from each parent are of the same type, just different variations, so each child has 23 pairs of similar chromosomes.
• 22 chromosome pairs contain important genes and have no influence on gender, these are called autosomes.
• The 23rd pair of chromosomes have fewer genes and have more of an influence on gender. These are known as the sex chromosomes. There are two types, known as _______ and _________.
• A female's cells carry 22 autosome pairs and ________________________
• A male's cells carry 22 autosome pairs and _______________________________
an X and Y chromosome
2 X chromosomes
Y
X
Jan 25­9:30 AM
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G01 ­ Introduction to Mendelian Genetics.notebook
January 31, 2014
Homework: Read Secons 4.1 and 4.2 in the text book, P 120 – 127
• Start a glossary for Unit 1; define: • genecs, heredity, variaon, trait, gene, purebred, P generaon, first filial (F 1) generaon, second filial (F2) generaon, hybrid, dominant, recessive, principle of dominance, allele, law of segregaon, homozygous and heterozygous, Jan 25­10:02 AM
MENDELIAN GENETICS
THE FUNDAMENTAL QUESTION
What is the relationship between genes (genotypes) and physical traits (phenotypes)? Phenotype = Genotype + environment
MENDEL'S WORK
Mendel studied pea plants to determine how traits get passed on from generation to generation.
To prevent pea plants from pollinating themselves, he emasculated the flowers and transferred the pollen manually.
Dec 3­12:46 PM
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G01 ­ Introduction to Mendelian Genetics.notebook
January 31, 2014
He chose pea plants for four main reasons:
1. They were commercially available throughout Europe
2. They are easy to grow and matured quickly
3. The sex organs are enclosed in the flowers
4. Different varieties had different traits
Mendel examined seven different characteristics. Each characteristic was present in only TWO forms.
Note how the seeds are either round or wrinkled. It is important to note that each of these seeds is part of a new generation – seeds are not of the same generation as the plant that bears them. They are considered to be the offspring (or what will become the offspring).
Dec 4­10:33 AM
MENDEL'S FIRST EXPERIMENT
Mendel crossed two purebred plants of varying height. These represent the parent generation (P). The seeds represent the 1st filial generation (F1 ). All offspring were tall. He then harvested and planted the seeds of F1 .
After pollination, three quarters of the plants of the 2nd filial generation (F
2 ) were tall while one quarter were short.
Parental Generation (P)
Purebred Tall Plants × Purebred Short Plants
First Filial Generation (F1)
All Tall Plants
Second Filial Generation (F2)
787 Tall Plants : 277 Short Plants
2.84 : 1.0
74% : 26%
Dec 4­10:46 AM
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G01 ­ Introduction to Mendelian Genetics.notebook
January 31, 2014
Mendel followed the same procedure for each of the seven traits he was experimenting with. These were his results:
MENDEL'S CONCLUSIONS
Mendel realized that since 75% of the F2 generation were tall, this had to be a dominant trait (always expressed).
The opposing trait, therefore, should be recessive (only expressed if it is the only allele present). This conclusion led to the discovery of the principle of dominance:
When individuals of contrasting traits are crossed, one trait is always dominant over the other. The offspring will therefore express only the dominant trait.
Dec 4­10:56 AM
EXPLAINING THE RESULTS
factors” • 1.Contrasting traits, such as tallness and shortness, are caused by internal “
that pass from parent to offspring by way of the gametes.
, one from the male • 2.Each offspring inherits 2 factors for each characteristic
(pollen) and one from the female (ovule, or egg). These factors separate in the gametes, known as the Law of Segregation
.
.
• 3.Purebred pea plants inherit 2 identical factors
, a different one from each parent.
• 4.Hybrid offspring inherit 2 contrasting factors
• 5.When both contrasting factors are present, only the dominant one shows, known as the Principle of Dominance
.
Dec 4­11:10 AM
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G01 ­ Introduction to Mendelian Genetics.notebook
January 31, 2014
MENDEL'S FACTORS
We know that Mendel’s “factors” are actually called genes. Every gene occurs in an alternate form, called an allele.
Alleles are codes for a specific trait. Two alleles combine to form a gene. If the alleles are identical, the gene is said to be homozygous. If the alleles are different, the gene is said to be heterozygous.
Dec 4­11:37 AM
Homework: Read Secons 4.1 and 4.2 in the text book, P 120 – 127
• Start a glossary for Unit 1; define: • genecs, heredity, variaon, trait, gene, purebred, P generaon, first filial (F 1) generaon, second filial (F 2) generaon, hybrid, dominant, recessive, principle of dominance, allele, law of segregaon, homozygous and heterozygous, Jan 25­10:40 AM
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