u7l4 heredity

Unit 7 Lesson 4 Heredity

Copyright © Houghton Mifflin Harcourt Publishing Company


Indiana Standards


• 8.3.3 Explain that genetic information is transmitted from parents to offspring mostly by chromosomes.

• 8.3.4 Understand the relationship between deoxyribonucleic acid (DNA), genes, and chromosomes.

• 8.3.5 Identify and describe the difference between inherited traits and physical and behavioral traits that are acquired or learned.

Give Peas a Chance


What is heredity?

• Traits, such as hair color, result from the information stored in genetic material.

• Heredity is the passing of genetic material from parents to offspring.


What did Gregor Mendel discover about heredity?• Gregor Mendel was an Austrian monk. In the

1800s, Mendel did the first major experiments in heredity.

• Mendel studied seven characteristics of pea plants.

• A characteristic is a feature that has different forms in a population.



What did Gregor Mendel discover about heredity?• The seven different characteristics Mendel studied

were plant height, flower and pod position, seed shape, seed color, pod shape, pod color, and flower color.

• Each characteristic had two different forms. These different forms are called traits.



What did Gregor Mendel discover about heredity?

• Mendel always started with plants that were true-breeding.

• True-breeding plants always produce offspring with the same characteristic if allowed to self-pollinate naturally.



What did Gregor Mendel discover about heredity?• Mendel crossed plants that were true-breeding for

producing yellow seed pods with plants that were true-breeding for green seed pods.

• All of the plants from the first generation produced green seed pods.

• Mendel called the green seed pod the dominant trait, and the yellow seed pods the recessive trait.



What did Gregor Mendel discover about heredity?• Next, Mendel let the first generation plants self-

pollinate.

• Out of the generation that resulted, called the second generation, about three-fourths had green seed pods and one-fourth had yellow pods.



What did Gregor Mendel discover about heredity?• The recessive trait had seemed to disappear in the

first generation, but it reappeared in the second generation.



What did Gregor Mendel discover about heredity?• Mendel hypothesized that each plant must have

two heritable “factors” for each trait, one from each parent.

• Some traits, such as yellow color, could only be observed if a plant had two of the same factors.

• A plant with two different factors would show the dominant factor but be able to pass on both factors to its offspring.



It’s in your genes!


How are traits inherited?

• Mendel’s ideas can be even further explained by our modern understanding of DNA.

• What Mendel called “factors” are actually segments of DNA known as genes.



• Genes are segments of DNA. They give instructions for producing a certain characteristic.




• The offspring has two versions of the same gene for every characteristic—one from each parent.

• Different versions of a gene are known as alleles.

• Dominant alleles are shown with a capital letter, and recessive alleles are shown with a lowercase version of the same letter.




• An organism with one dominant and one recessive allele for a gene is heterozygous for that gene.

• An organism with two of the same alleles for a gene is homozygous for that gene.




• The combination of alleles that you inherited from your parents is your genotype.

• Your observable traits make up your phenotype.

• The phenotypes of some traits follow patterns similar to the ones Mendel discovered.




• The dominant allele contributes to the phenotype if one or two copies are present in the genotype.

• The recessive allele contributes to the phenotype only when two copies of it are present.




• If one chromosome in the pair contains a dominant allele and the other contains a recessive allele, the dominant allele determines the phenotype.

• This is called complete dominance.




• Some characteristics are a result of several genes acting together.

• Sometimes, one gene influences more than one trait.

• For example, many genetic disorders, such as sickle-cell anemia, are linked to a single gene but affect many traits.




• Sometimes, the environment can influence an organism’s phenotype.

• Some traits are acquired only from one’s environment and are not inherited.

• For example, your ability to read and write is an acquired trait.



Bending the Rules


What are the exceptions to complete dominance?• Some traits do not follow the pattern of complete

dominance.

• For traits that show incomplete dominance and codominance, one trait is not completely dominant over another.


What are the exceptions to complete dominance?• In incomplete dominance, each allele in a

heterozygous individual influences the phenotype.

• The result of incomplete dominance is a phenotype that is a blend of the phenotypes of the parents.

• An example of this in humans is hair. A person with one allele for straight hair and one allele for curly hair will have wavy hair.



What are the exceptions to complete dominance?• For a trait that shows codominance, both of the

alleles in a heterozygous individual contribute to the phenotype.

• Heterozygous individuals have both of the traits associated with their two alleles.



What are the exceptions to complete dominance?• Human blood type is an example of codominance.

• Three alleles play a role in determining blood type.

• A person with an A allele and a B allele has type AB blood.



u7l4 heredity

Science

gregor mendel

mendel crossed plants

seed color

generation plants

green seed pods

yellow seed pods

seed shape

truebreeding plants