Science - Lesson #1: Alleles

Lesson #1:

Alleles

Dominant/Recessive and Homozygous/Heterozygous

Learning Intention:

Students will be able to explain how alleles are inherited from parents and determine traits, applying this knowledge to real-world genetics, including LULU and NANA, the CRISPR twins.

Success Criteria:

I can accurately define and distinguish between alleles, dominant and recessive traits, homozygous, and heterozygous.
I can explain how probability applies to genetic inheritance and use a coin flip activity to model the random assortment of alleles.
I can use a Punnett square to predict the probability of offspring inheriting a dominant or recessive trait (e.g., widow’s peak) from two parents.

Standards:

HS-LS3-3:

Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.

Reminders:

Part 1

Warm-Up

(5 min)

Directions: Tell the A.I. everything you know so far about DNA. This will determine whether we can move on to the next lesson.

SchoolAIAI-Powered Tutors and Learning Activities

Part 2:

Slow Reveal Graphs

(10 min)

Slow Reveal Graph - Alleles

Part 3:

Mini-Lesson / Stop n' Jot

(8 min)

Alleles are different versions of the same gene. They determine traits like eye color or having a widow's peak.

An allele can be dominant or recessive.

You inherit one allele from each parent.

A dominant allele is one that expresses its trait even if only one copy is present (e.g., brown eyes from the Bb or BB).

A recessive allele only expresses its trait when two copies are present (e.g.,Blue eyes from bb).

Part 4

Search and Unseen

Cengage Style

(10 min)

Mendel’s Observations

Mendel discovered hereditary units, which we now call genes, almost a century before the discovery of DNA. Today, we know that individuals of a species share traits because their chromosomes carry the same genes.

Diploid cells have pairs of homologous chromosomes. Thus, they have two copies of each gene. The two copies may be the same, or they may differ. If the two alleles at a specific locus on a chromosome are the same, the alleles are homozygous. If they are different, the alleles are heterozygous. A genotype is the particular set of alleles an individual carries. A genotype results in a phenotype. Phenotype refers to the individual’s observable traits. Mendel studied seven traits in garden pea plants (Table 12-2).

Modeling Genetic Crosses

The phenotype of a heterozygous individual for a particular trait depends on its two different alleles. In many cases, the effect of one allele influences the effect of the other, and the outcome is reflected in the individual’s phenotype. A dominant allele is the allele that is expressed when two different alleles or two dominant alleles are present. A recessive allele is the allele that is expressed only when two copies are present. A dominant allele is often represented by a capital letter, in this case F. A recessive allele is represented by a lowercase letter, such as f (Figure 12-19).

A grid called a Punnett square is helpful for predicting the outcomes of crosses (Figure 12-20). This grid was developed by British geneticist R. C. Punnett in the early 1900s to track the combination of alleles possible from parental gametes to their offspring. In sexually reproducing organisms, fertilization occurs when a male and female gamete fuse. The gametes are haploid, but the resulting zygote is diploid. A Punnett square is a useful model to show this fusion and the probable outcomes for a specific gamete combination.

Search Question

🔍 Based on Mendel’s observations, what is the difference between a genotype and a phenotype? Provide an example using dominant and recessive alleles.

Unseen Question

🧬 In a certain species of flowers, red petals (R) are dominant over white petals (r). A gardener notices that two red-flowering plants produced some offspring with white flowers. Explain how this is possible using your understanding of dominant and recessive alleles.

Part 5

Stop n Jot

Phenotype
The physical traits you can see, like eye color, hair color, or height.

Genotype
The genetic makeup of an organism, or the combination of alleles it has for a trait.

Allele
A different version of a gene (for example, a gene for eye color can have a brown allele or a blue allele).

Dominant
An allele that always shows up in the phenotype if at least one copy is present.

Recessive
An allele that only shows up in the phenotype when two copies are present.

Homozygous
Having two of the same alleles for a trait (AA or aa).

Heterozygous
Having two different alleles for a trait (Aa).

Punnett Square
A chart used to predict the possible genotypes and phenotypes of offspring from a genetic cross.

Part 6

Real-World Application

Imagine if Travis Kelce and Taylor Swift had a baby 🤮. Make a punnett square to determine the probability it has a widow's peak.

Widows Peak - Dominant (TT or Tt)

No Widow's Peak- Recessive (tt)

Possibility 1

Possibility 2

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