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Chapter 8 “Heredity”
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Learning Target(s):
ò I Can…….
ò A) explain the differences between dominant and recessive traits.
ò B) explain the differences between phenotypes and genotypes.
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Why don’t you look exactly like your parents?
ò You don’t look exactly like your parents because of what is known as “ heredity’.
ò Heredity is the passing of traits from parent to offspring.
ò You may have curly hair while both your parents have straight hair or blue eyes while both of your parents have brown eyes
ò People have investigated this question for a long time.
ò
ò About 150 years ago, Gregor Mendel performed an important experiment which helped find answers to many of our questions.
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Gregor Mendel (1822-1884)
Is credited for the theories that explain how are traits are inherited from generation to generation.
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Gregor Johann Mendel § Was an Austrian monk who studied the inheritance of traits in pea plants. He was also great in Math, which helped him to better understand his research.
§ He developed the laws of inheritance
§ He is known as the “Father of Genetics."
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Mendel’s Pea Plant Experiments
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Let’s look back for a second: remember that whole Reproduction
thing in Flowering Plants???? ò Pollen contains the male sex cell ( sperm). It is Produced by the _______.
ò The female sex cells (eggs) is called the _______. This is located inside _____ of the flower.
ò Flowers are able to reproduce with the help of bees and other living organisms.
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Stamen (anther)
ovule ovary
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Two types of fertilization in Flowering Plants
Pollen carries sperm to the eggs for fertilization. Fertilization can occur by:
a)______pollination can occur in the “same” flower.
b) ____ pollination can occur between two “different” flowers.
Self-
Cross-
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How Mendel Began Mendel produced pure strains of plants by allowing plants to “self-pollinate” for several generations
Mendel’s experiments…
ò From working with these plants, Mendel noticed that the patterns of inherited traits were not always clear.
ò Sometimes traits would appear in one generation and be absent in another generation. In generations afterwards, the trait would “reappear” again.
ò Mendel noticed this also occurred in other organisms as well, so he wanted to learn more about “what caused these patterns”
ò To keep his investigation simple, Mendel decided to study plant, since he had already done research on them before.
ò How do you think Mendel’s experiment relates to you and your family?
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Mendel studied only one characteristic at a time…
ò A characteristic is a feature that has different forms in a population. (ex: hair color)
ò What are some more examples of characteristics a person may have?
ò Any characteristic that can be passed from a parent to his/her offspring are called “Traits”. These traits can come in different forms such as red hair, brown hair, etc…
ò .
“Trying it all”….. Mendel used different
plants that had different traits for each of the
characteristics he studied.
Mendel’s First experiment:
ò Mendel used plants that were “true-breed” to get different traits for each characteristic.
ò (ex: purple flower + white flower)
The results:
ò All of the flowers were purple? Are you surprised?
ò What happened to the traits of the White flower?
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Dominant and Recessive..
ò Mendel noticed that from crossing the plants, one trait was always present and the other seemed to have disappeared.
ò Mendel chose to call these traits:
ò A) Dominant
ò B) Recessive
ò Dominant traits are those that appear or are “visible”.
ò Recessive traits are those that are “hidden”.
Back to Gregor Mendel…
ò Mendel knew that from his experiment there must be two sets of instructions (one given from each parent).
ò We now call these instructions “genes”.
ò Each parent gives one set of genes to the offspring. The offspring then has two forms of the same gene for every characteristic –(one from each parent)
ò .
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What’s in your “genes”…….
ò B= brown-eyed
ò b= blue-eyed
ò The different forms of a gene (such as “dominant” or recessive” is called an allele.
ò Dominant alleles are represented by a Capital letter.
ò Recessive alleles are represented by a lower-case letter.
Quick check:
ò How many genes make up an allele?
ò Where does each gene come from?
ò Scenario: You have “freckles”. Your mom has rosy cheeks, but dad has freckles also. What is the dominant gene in this example?
ò Now write an example of an allele to represent the freckles and an example to represent the rosy cheeks.
ò Possible Answer:
ò FF= freckles
ò ff= rosy cheeks
ò Ff= freckles
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Genes affect the traits of offspring….
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An organism’s “physical appearance” is known as its phenotype. ( ex: color of plants: purple or white Shapes : round or wrinkled
In humans phenotypes are little more complicated. (Ex: Albinism in humans is even considered a phenotype).
Describe the phenotype of this flower.
Red and Yellow
Genes affect the traits of offspring….
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An organism’s “genetic make-up appearance” is known as its genotype. All genes occur in pairs, so 2 alleles affect a characteristic
Possible combinations are:
Genotypes RR Rr rr Phenotypes RED RED YELLOW
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Genotypes § Homozygous genotype - gene combination
involving 2 dominant or 2 recessive genes Homozygous genotypes are also called “purebreed” genotypes.
§ (e.g. RR or rr)
§ Heterozygous genotype - gene combination of one dominant & one recessive allele. These are also called “hybrid” genotypes.
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If T is the allele for tall and t is the allele for
short, write the 3 possible genotypes.
Ready for the
Countdown!
Quick check: .
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Genotypes represent the “genetic make-up” of the organism
Remember!!!
Phenotypes represent the
“physical appearance” in the organism
Remember!!!
What are some words you can use to Describe the phenotypes in this slide?
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What does “homozygous” mean?
“Heterozygous”? How many of each
type is shown here?
Quickcheck????
Learning Target(s):
ò I Can…….
Use a punnet square to predict possible outcomes when crossing different traits.
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Punnett Squares: What are they and why do we use them?
1) Are used to help solve genetics problems
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2) It organizes all the possible combinations of offspring from particular parents.
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Y= yellow pea y= green pea
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Get some practice…. ò Create a Punnet Square
to predict the offspring of two plants that produce round seeds. The “genotype” for each parent is Rr.
ò Round seeds are dominant and wrinkled seeds are recessive.
ò R=round
ò r= wrinkled
ò What will the offspring look like?
Practice problem …. ò Trait: Seed Shape
ò Alleles: R – Round r – Wrinkled
ò Cross: Rr x Rr
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R
r
r R
RR
rr Rr
Rr
What will the offspring look like?
What are the Genotypes?:_________
What are the Phenotypes?:________
What percent is “round”? “Wrinkled”?
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Here’s your answer…. ò Trait: Seed Shape
ò Alleles: R – Round r – Wrinkled
ò Cross: Rr x Rr
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R
r
r R
RR
rr Rr
Rr
Three of the offspring are Round and one is wrinkled.
What are the Genotype?: RR, rr, Rr
What are the Phenotype?: Round & Wrinkled
What percent is round? Wrinkled? 75% Round 25% wrinkled
Sample Problem #1 ò Trait: Seed Shape
ò Alleles: R – Round r – Wrinkled
ò Cross:
ò “homozygous”Round seeds x “Heterozygous” Round seeds
ò RR x Rr
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What are the Genotypes?__________
What is the Phenotype(s)? _______________
What percent is round? Wrinkled? ________
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Sample problem #2: ò Trait: Seed Shape
ò Alleles: R – Round r – Wrinkled
ò Cross: Wrinkled seeds x Round seeds
ò rr x Rr
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What is the Genotype(s)?
What is the Phenotype(s)?
What percent is Round? What percent is Wrinkled?
More practice: on your notebook paper, predict the offspring of the plants
crossed below.
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Cross 2 Pure Plants TT x tt
a) What are your results?
b) What are your results by Crossing two of the offspring?
T= Tall plants t = short plants
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Here’s your Answer: How did you do????
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Cross 2 Pure Plants TT x tt
a) What are your results?
b) What are your results by Crossing two of the offspring?
All of the Offspring are (Tt)
3 Tall & 1 short (TT, Tt, & tt)
Nemo has had a small fin ever since he was a baby clown fish. He hopes that one day when he has baby fish of his own, none of them will have a small fin like him. If he marries a clown fish who is purebred for regular-sized fins, is it possible for any of the babies to have small fins? Use a Punnett Square to find your answer. Regular-sized fins: F Small fins: f (1) What are the genotypes of Nemo, the wife, and child?
Nemo’s Genotype: _______
Wife’s Genotype: _______ (2) What is the probability that their children will have a small fin?
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Nemo has had a small fin ever since he was a baby clown fish. He hopes that one day when he has baby fish of his own, none of them will have a small fin like him. If he marries a clown fish who is purebred for regular-sized fins, is it possible for any of the babies to have small fins? Use a Punnett Square to find your answer. Regular-sized fins: F Small fins: f (1) What are the genotypes of the Nemo, wife, and child?
Nemo’s Genotype: _______
Wifes’s Genotype: _______
Child’s Genotype: _______ (2) What is the probability that their children will have a small fin?
F
F
f f
Ff Ff
Ff Ff
ff
FF
Ff
0% chance
Objectives:
ò I can:
ò Analyze and interpret a pedigree chart.
ò Explain the differences in genetic disorders and sex-linked traits.
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RECESSIVE GENETIC DISORDERS….
ò Result in the mutation of a recessive genetic gene.
ò Many recessive gene disorders are rare.
Examples include:
ò A) Cystic fibrosis-in Caucasian-Americans
ò B) Sickle-cell Anemia
in African-Americans
Genetic Disorders…….
ò Cystic fibrosis
ò produces a “thick” fluid rather than “thin” to lubricate the lungs and digestion tract. It builds up and makes it hard to breathe. You usually get repeated bacterial respiratory infections. Can be fatal.
ò Sickle cell anemia
ò Occurs when abnormal shaped red blood cells that don’t add oxygen to the blood (with hemoglobin).
ò Can also be fatal.
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Other Human Genetic Disorders Of Interest
ò Tay-Sachs Disease
ò Hemophilia
ò Huntington’s Disease
ò Muscular Dystrophy
Sex-linked Traits
ò Are traits (genes) located on the sex chromosomes
ò Sex chromosomes are X and Y
ò XX genotype for females
ò XY genotype for males
ò Many sex-linked traits carried on X chromosome
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Sex-linked disorders….
ò Females have two “X” chromosomes. One is used as a back-up gene in case the other becomes damaged.
ò Males have only one copy of each gene on their one “X” chromosome. The other gene is a “Y” chromosome.
ò The genes for certain sex-linked disorders, are carried on the X chromosome. Men are more likely to have sex-linked disorders than women, because the gene is recessive.
Color Blindnesss….
ò Color blindness is an example of a “sex-linked” disorder.
ò People who are color blind have trouble distinguishing between shades of red and green.
ò To help the colorblind, some cities have added shapes to their street lights.
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Hemophilia
ò --Hemophilia is another example of a sex-linked disorder.
ò It prevents blood from clotting, and people with hemophilia bleed for a long time after small cuts.
ò Hemophilia can be fatal!!!!
ò If people worry they might pass a disease to their children, they may seek genetic counseling.
Sex-linked Genes
ò Common Examples include:
ò Baldness
ò Hemophilia
ò Color Blindness
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Pedigree Charts…
ò A pedigree chart is a tool for tracing a trait through generations of a family. It is used to predict if a person is a carrier of a particular disease (or trait).
ò You can even use a pedigree chart to trace how you inherited your hair color.
How to read a pedigree chart….
ò Vertical lines connect children to their parents.
ò A solid square or circle indicates a person has a certain trait.
ò A half-shaded circle indicates a person is a “carrier” of the trait.
ò Not shaded: they don’t have nor carry the recessive trait (homozygous dominant, TT)
SQUARES= MALES CIRCLES= FEMALES
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Examine the chart below: Was this a “sex-linked” trait?
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Yes, In this case the females were only “carriers”, but a male actually had it…
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Possibilities
ò What if ?
ò Both parents are homozygous dominant?
ò If at least one parent is recessive for the trait?
ò Both parents are homozygous recessive?
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- They can’t pass the disorder to their children
- Their children have to be a carrier for the trait (tt x TT or tt x Tt)
- Their children will be homozygous recessive too
