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Genetics Part 1

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by

Carolyn Lowe

on 15 October 2015

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Transcript of Genetics Part 1

PRACTICE
Factors for different traits are passed on independently of each other; i.e., the trait of pea height is not related to pea color.
This law has been modified. We will discuss this later.
Law of Independent Assortment
Parents have two "factors" for each trait but when gametes are formed (sperm and egg, pollen and ovule) only one factor is passed on.
Law of Segregation
If there are two possible factors for a trait in a cell, only one will show up - i.e., one is "dominant" and the other is "recessive".
Has been somewhat modified. We will discuss this later.
Law of Dominance
From this data and other data having to do with whether the peas were wrinkled or smooth, the color of flowers, and the height of the plants, Mendel, after 7 years, created "laws of inheritance".
Mendelian Genetics
A parent pea has the genes Tt and is tall. Which letter represents tall; T or t?
The other parent has the genes tt. Is it tall or short?
Gregor Mendel
Make Punnett squares and predict the possible outcomes for each of the following (round peas, tall plants, yellow peas and green pods are all dominant).
Pure (homozygous dominant) round peas crossed with pure wrinkled peas (homozygous recessive).
Pure wrinkled peas crossed with the offspring of above.
Tt tall plants crossed with pure tall plants.
Yellow PODS crossed yellow PODS.
Yellow heterozygous (hybrid - Yy) peas with yellow heterozygous peas.
Carolyn Lowe, PhD
Was a monk in what is now the Czech Republic who studied the inheritance of pea plants
He noticed that, if he had pure bred yellow peas and pure bred green peas and he cross-pollinated these, all the offspring peas (F1 generation) were yellow.
However, if he crossed the yellow offspring (called the F1 generation), 25% of THEIR offspring (the F2 generation) would be green.
Some Vocabulary
Parental Generation: the first generation (your parents).
F1 Generation- filial 1 - first offspring of the parental generation (you and your siblings).
F2 Generation - filial 2 - second generation when those of the F1 generation are interbred (if you and your siblings had children - ick).
Hybrid - the results when the 2 genes for a trait are different in an individual (not the same meaning as in agriculture) - so Hh or Ff
From the pea experiment we know that all the yellow peas of the F1 generation had to also have a green factor. So, if Y represents yellow peas and y represents green peas then YY will be yellow, yy will be green, and Yy will be yellow because yellow is dominant.
A little about Conventions
Biologists use letters to represent different variations of the gene. Typically we use a capital letter for the dominant allele and a lower case letter for the recessive allele. Usually we choose the letter of the dominant gene (i.e., Y for yellow and y for green). Also we usually put the dominant allele first (Yy - not yY) although it really doesn't matter in the end.
Vocabulary
Allele: a possible form of a gene. In peas alleles for color can be yellow or green. For plant height the alleles are short or tall.
Gene - a code for 1 protein and what Mendel called a "factor".
Chromosome - a whole bunch of genes all linked together.
Gamete - egg or sperm
Haploid - has only one allele. Gametes are haploid.
Diploid - has two alleles for each trait. The resulting organism from fusion of an egg and a sperm is diploid. Your cells are diploid (except for egg and sperm of course).
Zygote - a fertilized egg.

Phenotype - what genes are expressed; the trait that "shows" up.

Genotype - what the genes actually are. In the case of a dominant phenotype could be Gg or GG.
Dominant trait - a trait that manifests itself even if an allele for a different trait is present.
Recessive trait - a trait that only shows up if both alleles are the same and are for the recessive trait.
Heterozygous - the two alleles are different
Homozygous - the two alleles are the same.

Homozygous dominant - the two alleles are both dominant

Homozygous recessive - the two alleles are both recessive
Making Punnett Squares
Step 1
Write the alleles of the parent generation:

Mom = for tongue rolling (which is dominant)
Dad = for tongue rolling (he can't roll his tongue)
Step 2: Draw a box and mark it into 4 sections
Step 3: Put one parent's alleles either down the side or across the top (it doesn't matter which) with one allele over each column or beside each row. Then add the other parent's alleles (note: I am using blue and pink here just for a demonstration).
Step 4: copy each allele either across or down so that each square has one allele from each parent.
Step 5: determine percent possibility of each trait showing up:
In this particular case the child has a 50% chance of being Tt and being a tongue roller and a 50% chance of being tt and not being able to roll their tongue.
Recessive Genetic Diseases
Cystic Fibrosis - most common among European descended people.

Sickle Cell Anemia - most common among African descended people.

Tay-Sacs - most common among Jewish and Eastern European descended people
Dominant Genetic Diseases
Huntington's Disease
Marfan's Syndrome
Sex-linked (X-linked) Conditions
Hemophilia
Color blindness
Fragile X
Some contribution to baldness
Duchenne Muscular Dystrophy
Trisomies
Down Syndrome (trisomy 21)
Cognitive disabilities, very specific appearance

XXY - Klinefelter Syndrome: male, usually sterile, tall, usually less muscle mass and coordination than other males

XXX - Triple X: female, normal

XYY Syndrome: male, normal

Trisomy 13 and 18: Severe birth defects and cognitive disabilities. Usually do not live long after birth.
Monosomy
Turner Syndrome - X
Juvenile Myoclonic Epilepsy
Intermediate Dominance
"co-dominance"
Two different alleles show up at the same time.
I.e., the proteins created both have an action.
Examples: A and B alleles of blood type.
Black and Orange of cats.
Red and white of some flowers.
Wavy hair (from text)
Polygenetic Traits
Traits in which more than one gene (may be on separate chromosomes) influences
the expression of a trait.
Examples: hair, eye and skin color

Found on the X chromosome. Usually passed from mother to son. A girl must have a mother who is at least a carrier and a father with the condition.
Female, usually short, usually sterile, webbed neck, some cognitive disabilities.
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