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CHAPTER 7 - GENETICS AND INHERITANCE

________________________ - The passing of traits from parents -> offspring.

________________________ - The scientific study of heredity.

In the 1860's, a monk named ___________________________________, the "father of genetics," performed experiments on garden peas. Previous experiments were done in genetics, but Mendel's research was different because he took a ________________________ approach to his research. He _______________________ the _________________ and ________________ of offspring resulting from his crosses of garden peas.

 

WHAT MENDEL DID:

He did this by allowing a population of pea plants to ____________________________ for many generations

This is the ________________________________ Generation

He did this by taking pollen from the anthers of purple flowers, and placing it on the stigmas of white flowers

This is the ________________________________ Generation

This is the ________________________________ Generation

RESULTS: 705 plants with purple flowers
              + 224 plants with white flowers
                929   Total Plants

 

Mendel studied more than flower color in garden peas: (Table 7-1)

 

 Mendel Developed a Model to Explain his Results

The following rules summarize Mendel's ideas about inheritance:

  1. Parents transmit information or "___________________" about traits to their offspring
  2. Each individual has 2 factors, or ___________________ for each trait, one from each parent
  3. _____________________________ - 2 factors have the same information. (Ex: If both factors have information to make purple flowers)

    _____________________________ - 2 factors have different information. (Ex: One factor codes for purple flowers, one codes for white flowers)

  4. _____________________________ - A segment of DNA that carries instructions for producing a specific trait
  5. _____________________________ - Alternate forms of a factor, or gene.

    _____________________________ - The many factors that an organism possesses

    _____________________________ - An organisms physical appearance, determined by its combination of alleles. This reflects all of the traits actually expressed by the organism

  6. An individual possesses _______ alleles for each trait - one from their ___________________ and one from their _____________________. During _________________ ____________________, alleles ____________________ randomly so that a gamete receives a copy of one allele or another.
  7. ________________________________________ - An allele that is expressed in an individual. Dominant traits appear in every generation of offspring.

________________________________________ - An allele in an individual that is present but remains unexpressed (it is masked by dominant allele).

In Mendel's ______________________________, the purple flower color was caused by a dominant allele (purple - expressed), masking a recessive allele (white - unexpressed)

 

Visualizing Mendel's Model

________________________ are used to represent alleles.

________________________ alleles are represented by _________________ case letters (Ex: w for white flowers = recessive trait)

________________________ alleles are represented by _________________ case letters (Ex: W for purple flowers = dominant trait)

A plant that is ____________________________, or _________________________ for recessive white flower color is designated __________.

A plant that is ____________________________, or _________________________ for dominant purple flower color is designated __________.

A ___________________________ plant would be designated __________.

 

A PUNNETT SQUARE can help you VISUALIZE crosses & PREDICT the outcome of crosses

Cross a true breeding Purple flower (WW) with a true breeding White flower (ww):

 

   
   

 

 

Genotypic Ratio:

 

  

Phenotypic Ratio:

 

 

_____________________________ - The likelihood that something will happen (in this case, what will be the genotype & phenotype of the individual?)

 

# Individuals with that Trait
Total # of Individuals in Population

Ex: Toss a coin…what is the probability that the coin will land heads up? 1/2 = 50%, or 1:1

Because of __________________________________________, the probability that an egg or sperm cell in one of Mendel's heterozygous pea F1 plants (Ww) will contain the allele W is 50%, or 1/2, just as in a coin toss.

 

Now Cross 2 Heterozygous Plants (Ww) X (Ww)

 

   
   

 

 Genotypic Ratio:

 

  

Phenotypic Ratio:

 

  

Mendel's Conclusions

This describes how traits can disappear & reappear in a certain pattern from generation -> generation

 

Predicting the Outcomes of a Cross

_______________________________________ - A simple Punnett Square which illustrates a cross focusing on only one trait, such as flower color.

_______________________________________ - A Punnett Square that illustrates a cross that focuses on two traits of interest.

 

We will consider the following TWO traits in our Dihybrid Cross:

 

Shape of Pea:

 

Color of Pea:

 

 

Cross 2 heterozygous yellow, round peas: (YyRr) X (YyRr)

  

       
       
       
       

 

Possible Genotypes:

 

 

 

Possible Phenptypes:

 

 

 

From this dihybrid cross, Mendel developed the ______________________________________________________

Other Factors that Influence Heredity

Many genes do not follow the simple inheritance pattern of inheritance described by Mendel.

  1. ______________________________________________________ - Intermediate forms of a trait are visible.
  2. Ex: A cross between homozygous Red Snapdragons (RR) & homozygous White Snapdragons (rr) produce Pink Snapdragons (Rr)

     

       
       

     

    Genotypic Ratio:

     

     

    Phenotypic Ratio:

     

     

  3. ______________________________________________________ - Both genes in a heterozygote are fully expressed.
  4. Ex: Homozygous Red Coated Horse (RR) X Homozygous White Coated Horse (rr) -> Roan Coated Horse (Rr)

    Both colors of hair are found on the horse

     

       
       

     

    Genotypic Ratio:

     

     

    Phenotypic Ratio:

     

     

  5. ______________________________________________________ - When traits are controlled by genes that have more than two alleles. Combinations of any two of these alleles can produce different phenotypes.
  6. Ex: ABO Blood types in Humans

    Phenotype (Blood Type)

    Genotype

    Type A

    IAIA, IAi

    Type B

    IBIB, IBi

    Type AB

    IAIB

    Type O

    ii

    Only two alleles are present in the genotype, but various _________________________ occur depending upon which __________________________ are _____________________________.

    Cross a Type A Heterozygote (Iai) X Type AB

     

       
       

     

    Genotypic Ratio:

     

     

    Phenotypic Ratio:

     

     

  7. ______________________________________________________ - Traits that are controlled by alleles carried only on the X chromosome. X-linked genetic disorders occur mostly in males.
  8. Ex: Colorblindness, Hemophilia, and Baldness

    Cross a Normal Male (XY) X a Female carrier of Colorblindness (XXc)

     

       
       

    Genotypic Ratio:

     

     

    Phenotypic Ratio:

     

     

     

  9. ______________________________________________________ - A trait controlled by more than one pair of genes.
  10. Ex: Height, weight, eye color, hair color, skin color

  11. ______________________________________________________ may affect gene expression.

Ex: Arctic Fox

 

 

Human Genetic Disorders

_____________________________ - A change in a gene. Mutations are a source of the variation a species needs in order to adapt to changing conditions & evolve over time.

____________________________________________ - The harmful effects that some mutations produce.

 

Types of Genetic Disorders

Ex: ___________________________________

A mutation exists for a gene that codes for a protein responsible for transporting Cl- ions. In a homozygous condition (Both copies of the gene are missing), cells are unable to export Cl- out of cells. This causes water to diffuse into lung cells, making it difficult to remove mucus from the lungs, resulting in infections and difficulty breathing.

 

   
   

 

Ex: __________________________________

A mutation exists in the gene that codes for hemoglobin, a protein in RBCs that carries oxygen throughout the body. In homozygous condition (both copies of gene are missing), the body builds an abnormal form of hemoglobin, which gives the cell an abnormal "sickled" appearance. Sickle cells get caught in blood vessels & restrict blood flow to tissues. Anemia (low RBC count), fatigue, muscle cramps, kidney & heart failure result. Evolution has favored the sickle cell gene because people with this disease are resistant to malaria

 

   
   

 

 

This mutation is expressed in heterozygous individuals. Only those that are homozygous recessive for NOT having this mutation aren't affected. The mutation is passed down to 50% of offspring when one parent is heterozygous (affected), and one parent is unaffected.

Ex: Dwarfism

 

   
   

 

These patients have an entire extra chromosome or are missing an entire chromosome.

Ex: _______________________________________

These patients have an extra copy of chromosome 21

Characteristic features include:

* extra folds in upper eyelids
* Broad, flattened nose
* short stature
* Mental retardation

 

Genetic Counseling & Gene Therapy

If one family member is affected by a genetic disorder, it may be possible that other family members are heterozygous carriers of the gene causing the disorder.

____________________________________________ - People who use a family tree, or pedigree to identify parents at risk for having children with genetic disorders. They assist these parents in deciding whether or not to have children.

_____________________________ - A record that shows the occurrence of a trait over several generations.

Ex: Two phenotypically normal parents have 4 children; 2 boys and 2 girls. One boy is a hemophiliac, one is normal, and both girls are normal. Hemophilia is a Sex-Linked trait.

The following pedigree, developed by a genetic counselor, helped the parents determine each family member's genotype, and the parents' risks of having another child with hemophilia.

Key: (Pedigree)

 

 

 

What do the question marks above the female children indicate?

 

 

Prepare a Punnett Square to predict the probability of these parents having another child with hemophilia

 

   
   

 

Genotypic Ratio:

 

 

Phenotypic Ratio:

 

 

 

____________________________________________ - A new technique in which faulty genes are replaced with functional genes, which are "spliced" into an individuals genome. This has been used in several individuals with genetic disorders to treat the disease.

   

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