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Notes:MYP Genetics Notes |
Nature vs Nurture
Nature: what our DNA codes for
Nurture: the environment we grew up in The discovery of DNA in the 1950s intensified the debate around nature vs nurture. Are we simply the product of our DNA? OR Are we the product of your environment (where you live, what you eat, who your parents and grandparents are, etc)? OR is who we are more complicated that an either or senario? Article To study this question more closely: psycologists, sociologists, and geneticists have used the only tool we have to get as close to identical human beings as possible--> identical twins.
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Watch the video: can you tell what is a product of nature vs nurture?
The jury is still out, but the more we learn the more we realize it is a lot more complicated than even scientists initally thought! |
Gregor Mendel's Experiment
Gregor Mendel (1822-1884) was born in Mordovia (now modern day Czech Republic) to a poor farming family. He was a bright student and wanted to pursue further education.
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Mendel's Experiment:
Using pea plants, Mendel crossed two true breeding plants (only produced the same trait over and over) that were opposites in traits. Examples:
Story Story of Gregor Mendel |
Mendel's 3 Laws of Inheritance
1. Law of Segregation: No two alleles of the same gene from one individual can be inherited together. The two alleles in a person a "segreated" or seperated from each other.
First Law (Segregation) |
2. Law of Independent Assortment: Alleles from two different genes are not inherited together, they are inherited independently of each other. Both genes alleles are segregated having nothing to do with the other, therefore they are inherited independently.
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3. Law of Dominance: That some alleles overpower the expression of other alleles within an organsim. So the presence of a dominant (A) alele and a recessive (a) allele in the same organsims (Aa) results in the dominant phenotype always being expressed.
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Understanding Terminology
Characteristic/ Trait: Some physical aspect that is coded for in DNA (ex. flower color)
Gene: a sequence of DNA that codes for a specific protein within the body. Leads to traits. Allele: a variation of a gene (ex. purple or white) The number of variations of a specific gene vary from two to dozens.
Recessive: an allele that is overshadowed by a different allele (identified with a lower case letter) Homozygous: Having two the same allele of one gene within one individual (AA or aa) Heterozygous: Having two different alleles of one gene within one individual (Aa) Phenotype: The physical characteristics of an organsim (ex. purple flowers Genotype: The genetic make up of the organsims, represented through letters (ex. AA, Aa, aa) |
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Inheritance Basics
Humans have 23 pairs of chromosomes (or 46 total chromosomes). [You have two of every chromosomes] The last pair of the 23 is referred to as the sex chromosomes (XY). Having two X chromosomes designates at female. Having and X and a Y designates as male, as the genes on the Y chromosome turn on many of the genes that code for males genes on the rest of the chromosomes.
If mom has 46 chromosomes and dad has 46 chromosomes, and you have 46 chromosomes, how does that work?
Why is this important?
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Introduction to Punnett Squares
Rules of a punnett square:
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Punnett Squares: Monohybrid Crosses
Monohybrid crosses= genetic crosses with 1 gene.
Example Problem: Blue skin is dominant to green skin in smurfs. If two heterozygous blue smurfs marry what is the genotypic and phenotypic ratio for the next generation?
Example Problem: Blue skin is dominant to green skin in smurfs. If two heterozygous blue smurfs marry what is the genotypic and phenotypic ratio for the next generation?
Steps:
Monohybrid Crosses (practice problems) |
Punnett Squares: X-Linked Crosses
X-linked crosses = genetic crosses with genes found on the X chromosomes.
Because male and female play such an important role in this form of inheritance it is important to indicate genotypes as either male or female. XX= female XY= male Women who are heterozygous for recessive X-linked traits are often said to be a carrier of this disorder. While they themselves do not show the trait (normal) they carry the gene to be able to pass it down to the next generation.
Example problem: Color-blindness is an X-linked recessive disorder. If a woman who is a carrier for color-blindness has children with a normal seeing man. What is the probability of them having a child who is color blind? A female who is color-blind? A male who is color blind?
Because the genes are carried on the X chromosomes, females have the normal two copies of genes, but males only have one copy. Due to males having only one copy, X-linked recessive genes appear more often in males than in females. (see Pedigrees/ Family trees below for more information.) |
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Introduction to Pedigrees/ Family Trees
A pedigree (or family tree) is a way of tracking human inheritance of traits. Because human generations occur relatively slow (~ every 60 years), the only way to determine inheritance (dominant/ recessive/ x-linked etc) is by looking at how traits are carried through a family lineage.
Rules:
By analyzing how a specific trait is passed down through the generations, and using Punnett squares with predictive ratios, we can determine the method of inheritance.
Practice building and analyzing pedigrees Practice Problems + the answer key |