1. Presented by Kesler Science
Genetics
Created by Kesler Science – More 5E lessons at KeslerScience.com
Presented by Kesler Science

2. Essential Questions: What is genetics?
How are Punnett Squares used to describe the genetic relationship between parent to offspring?

3. Genetics
Genetics
The study of heredity, which is a biological process where a parent passes certain genes onto their offspring.
Genes are inherited from both parents through sexual reproduction.
These genes express specific traits or characteristics.
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4. Gregor Mendel Genetics “Father of modern genetics” Born in 1822
A monk from Austria
Discovered the basic principles of heredity
Experimented on pea plants and showed that their traits follow a particular pattern
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5. Genetics
Review
Chromosomes are found in the nucleus of a cell and carry genes.
Genes are segments of DNA on a chromosome and are responsible for inherited traits.
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6. Quick Action – Genetics
With a partner orally answer these questions.
What is genetics?
Who is considered the father of genetics?
Sketch a drawing of the nucleus of a cell, a chromosome and indicate the gene.
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7. Vocabulary Genetics Genotype - the genetic makeup of an organism.
Phenotype – the appearance of an organism based on its genotype, plus environmental factors
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8. What does the allele indicate in this pair of homologous chromosome?
Genetics
Alleles
Variants (differences) in a gene
Occurs on a fixed spot on a chromosome
In humans an allele might indicate blood type, colorblindness, or many other traits.
What does the allele indicate in this pair of homologous chromosome?
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9. Dominant/Recessive Genetics
Describes how likely it is for certain phenotype traits to pass from parent to offspring
Dominant Alleles – show their effect with only one copy of the allele
Recessive Alleles – show their effect with two copies of the allele
Blue Eyes - Recessive
Brown Eyes - Dominant
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10. Inherited Traits Genetics Genetically determined characteristics
Come from both parents, so offspring has a combination of both parents’ genes.
Examples: skin, hair, and eye color, height, and freckles
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11. Genetics
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12. Quick Action – Genetics
Work with a partner and determine how many of these dominant and recessive traits you have.
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13. Quick Action – INB Template
Genetics INB Template
Cut out the templates (there are 2)
Glue them into your INB per your teacher’s instruction.
Wait for further instruction.
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14. Genetics
Vocabulary
Homozygous Dominant – carries two copies of the same dominant allele (BB)
Homozygous Recessive – carries two copies of the same recessive allele (bb)
Heterozygous – carries two different alleles (Bb)
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15. Punnett Square Genetics
Parent 2
Punnett Square
A diagram used by geneticists to determine the probability (chance) of an offspring having a particular phenotype.
If the A represents red flowers and a represents green flowers, what are the chances of the flowers being green?
Probability is expressed in a percentage.
25%
25%
Parent 1
25%
25%
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16. Punnett Square (cont.) Genetics
Parent 2
Punnett Square (cont.)
Examines just one of the many genes that get passed on during sexual reproduction
Shows all possible way the offspring could inherit the gene from two parents.
25%
25%
Parent 1
25%
25%
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17. Genetics
In this Punnett square the B (Dominant) stands for brown eyes and the b (recessive) for blue eyes. The father’s alleles are on the top of the square and the mother’s along the side.
Both parent have brown eyes because their genetic make-up is Bb, and only one copy of a Dominant gene needs to be present to show its effect. Now, look how they have crossed the genotypes and filled in the information. We can see the probabilities of the phenotype of the offspring. There are 3 chances he/she will have brown eyes (BB, Bb, Bb) and only 1 chance for blue eyes (bb). So the probability of these parents having a blue-eyed child is 1 in 4 or 25%.
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18. Quick Action – Genetics
Let’s create our own Punnett Square
Draw a box with 4 squares leaving room at the top and side.
Choose a letter to represent your genes, one capital and one lower case. In this example we’re using choose T = tall and t = short.
3. Let’s say you have a short father
and tall mother. Set up your
table as such. t t T t
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19. Quick Action – Genetics
Now fill in the boxes with the
genotype combinations.
Figure out the percentage for
each box.
What percentage of the children are going to be tall? short? t t t T T t T t
25%
25% t t t t t
Note: We didn’t use T for tall and s for short because that would show two different genes which code for two different traits. A genotype contains two codes for the same trait, so we use two forms of the same letter.
25%
25%
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20. Quick Action – Genetics
Practice
Father is homozygous dominant (SS)and Mother is homozygous recessive (ss)
If S = freckles and
s = no freckles
What percent of the children will have freckles?
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21. Quick Action – Genetics
Practice
Both parents are heterozygous for black hair (Bb).
If B = black hair and
b = brown hair
What percent of the children will have black hair?
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22. Quick Action – Genetics
Practice
Father is heterozygous for dimples (Dd) and Mother is homozygous recessive for no dimples (dd).
If D = dimples and
d = no dimples, complete the square and determine what percent of the children will have dimples?
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23. Check for Understanding
Can you…
Define genetics?
Explain how Punnett Squares are used to describe the genetic relationship between parent to offspring?
Clear up any confusion and answer questions.
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