Genotypic Ratios and Phenotypic Ratios for Punnett Squares
Summary
TLDRThis video explains how to determine genotype and phenotype ratios using a Punnett square. It covers calculating genotype ratios (homozygous dominant, heterozygous, homozygous recessive) and converting them into percentages. Then, it discusses phenotype ratios, focusing on the dominant and recessive traits (e.g., tall vs. short, red vs. white). A final example introduces codominance, where both traits are equally expressed, and the ratio of genotypes and phenotypes is explained. The video provides clear steps for calculating and understanding genetic outcomes in different inheritance scenarios.
Takeaways
- 🔬 The video focuses on determining genotype and phenotype ratios using a Punnett square.
- 🧬 The genotype ratio includes homozygous dominant, heterozygous, and homozygous recessive types.
- 📊 In the example, the genotype ratio is 1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive.
- 📉 Percentages for genotype are calculated based on the Punnett square, with each box representing 25%.
- 🌱 For the example involving tall and short traits, the genotype percentages are 25% homozygous dominant, 50% heterozygous, and 25% homozygous recessive.
- 🌿 Phenotype ratio refers to the observable traits, with 75% tall (dominant) and 25% short (recessive) in the first example.
- 🌸 In the second example, involving red and white flowers, heterozygous parents result in a 50% red and 50% white phenotype ratio.
- 🌻 The genotype ratio in the flower example is 50% heterozygous and 50% homozygous recessive.
- 🐓 The final example discusses codominance in chickens, where black, white, and spotted traits are expressed.
- 📑 Codominant genotype ratio in the chicken example is 1 black, 2 spotted, and 1 white, which corresponds to a 25%, 50%, and 25% ratio respectively.
Q & A
What is the difference between genotype and phenotype?
-Genotype refers to the genetic makeup or code (e.g., homozygous dominant, heterozygous, or homozygous recessive), while phenotype refers to the physical expression of that genetic code (e.g., tall or short in plants).
How do you calculate the genotype ratio using a Punnett square?
-To calculate the genotype ratio, count the occurrences of each genotype: homozygous dominant, heterozygous, and homozygous recessive. Then, express them as a ratio. For example, if there is 1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive, the ratio would be 1:2:1.
How is the percentage for each genotype determined?
-Each box in a Punnett square represents 25%. So, for each genotype, count how many times it appears, multiply by 25%, and you'll get the percentage. For example, if a genotype appears in 2 boxes, it accounts for 50%.
What is the genotype ratio for a heterozygous parent crossed with a homozygous recessive parent?
-The genotype ratio would be 0 homozygous dominant, 2 heterozygous, and 2 homozygous recessive. This can be simplified to a 1:1 ratio of heterozygous to homozygous recessive.
How do you calculate the phenotype ratio?
-To calculate the phenotype ratio, determine which traits are expressed. For example, if the dominant trait is tall, count how many offspring have that trait. The ratio is determined by comparing the dominant to the recessive phenotypes.
What is the phenotype ratio for a cross where tall is dominant over short?
-If tall is dominant over short, and there are 3 tall and 1 short offspring, the phenotype ratio would be 3:1. This corresponds to 75% tall and 25% short.
How would you express a genotype ratio as a percentage?
-To express a genotype ratio as a percentage, divide the occurrences of each genotype by the total number of squares (4 in a Punnett square) and multiply by 100. For example, if 2 boxes show heterozygous, it accounts for 50%.
What is the phenotype ratio in a case of codominance, such as black and white spotted chickens?
-In codominance, both traits are expressed equally. For example, if you cross black and white spotted chickens, the phenotype ratio could be 1 black, 2 spotted (black and white), and 1 white, resulting in a 1:2:1 ratio.
What happens in a cross between heterozygous red flowers and homozygous white flowers?
-In this cross, red is dominant, so half of the offspring will be heterozygous red (50%) and the other half will be homozygous white (50%), resulting in a phenotype ratio of 1:1 or 50% red and 50% white.
What does a 1:2:1 phenotype ratio indicate in a codominance situation?
-A 1:2:1 phenotype ratio in codominance indicates that one trait is expressed fully in 1 offspring, both traits are expressed in 2 offspring (showing the codominant trait), and the other trait is fully expressed in 1 offspring.
Outlines
🧬 Understanding Genotype and Phenotype Ratios
In this section, the speaker introduces the topic of genotype and phenotype ratios using a Punnett square. The focus is on calculating these ratios and percentages, particularly in an example where tall (dominant) is crossed with short (recessive). For genotype, the ratios are presented as 1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive. The percentages are calculated as 25% homozygous dominant, 50% heterozygous, and 25% homozygous recessive. For phenotype, tall (dominant) occurs in 75% of cases, while short (recessive) occurs in 25%.
🌸 Genotype and Phenotype Ratios in a Flower Cross
This example examines a flower cross where red (dominant) is crossed with white (recessive). A heterozygous parent is crossed with a homozygous recessive parent. The genotype ratios are explained as 0 homozygous dominant, 2 heterozygous, and 2 homozygous recessive. When simplified, the genotype ratio is 1:1 (50% heterozygous, 50% homozygous recessive). The phenotype ratio shows that red and white each make up 50%, emphasizing the inheritance of dominant and recessive traits in this scenario.
🐔 Co-dominance Example in Chickens
The final example explores a co-dominance scenario involving chickens, where the phenotypes include black, spotted (speckled), and white. The genotypes are represented as BB (black), BW (spotted), and WW (white). The genotype ratio is 1:2:1, meaning 25% black, 50% spotted, and 25% white. Similarly, the phenotype ratio mirrors this distribution, demonstrating how co-dominance results in a blend of traits in the offspring.
Mindmap
Keywords
💡Genotype
💡Phenotype
💡Homozygous Dominant
💡Heterozygous
💡Homozygous Recessive
💡Punnett Square
💡Dominant Trait
💡Recessive Trait
💡Codominance
💡Percentage Calculation
Highlights
Introduction to calculating genotype and phenotype ratios using a Punnett square.
Explanation of genotype, which refers to the genetic code, and phenotype, which refers to physical traits.
Example 1: Tall is dominant over short in a plant. The Punnett square is used to determine genotype and phenotype ratios.
Genotype ratio for Example 1: Homozygous dominant (1), heterozygous (2), and homozygous recessive (1).
Explanation of converting genotype ratios to percentages: 25% homozygous dominant, 50% heterozygous, 25% homozygous recessive.
Phenotype ratio for Example 1: 75% tall and 25% short.
Example 2: Red flowers are dominant over white flowers. A heterozygous parent is crossed with a homozygous recessive parent.
Genotype ratio for Example 2: 0 homozygous dominant, 2 heterozygous, and 2 homozygous recessive (1:1 ratio).
Genotype percentages for Example 2: 50% heterozygous and 50% homozygous recessive.
Phenotype ratio for Example 2: 50% red and 50% white.
Example 3: Codominant situation involving chickens with black, spotted, or white feathers.
Genotype ratio for Example 3: BB (1), BW (2), and WW (1), or 1:2:1 ratio.
Genotype percentages for Example 3: 25% BB, 50% BW, and 25% WW.
Phenotype ratio for Example 3: 1 black, 2 spotted, 1 white (1:2:1).
Summary of using Punnett squares to determine genotype and phenotype ratios across different genetic examples.
Transcripts
math and science in this video I'd like
to talk about figuring out the genotype
and phenotype ratio okay so let's go
ahead and get started so we have
completed the punnett square and I've
got it drawn out here and now we need to
calculate how to figure out the ratio
and also maybe the percent and in this
particular example tall is dominant over
short whenever you write the genotype
ratio and remember the genotype is the
genetic code you will write the
homozygous dominant then the
heterozygous then the homozygous
recessive so let's go ahead and write
this out first let's look for homozygous
dominant we have one of those alright of
one and now for heterozygous we have one
two and then for your homozygous
recessive we have one now if we would
like for this to be a percent for your
genotype percent remember each box is
25%
so that would be 25% 50% for
heterozygous and 25% for homozygous
recessive okay so we have 25 percent for
homozygous dominant 50% for heterozygous
25% for homozygous recessive okay
now let's look at the phenotype and the
phenotype will be how many will be tall
and how many will be short so tall will
be anytime it is the dominant trait so
it will be 1 2 3 because anytime you
have a capital letter you get the
dominant trait and then 1 for short
which is the recessive trait and if we
would like you to write that into a
percentage that will be 75% tall and 25%
short ok so there we go let's look at
another example and it has something you
may want to consider okay so we have
let's say red and we'll these will be
flowers red is dominant over
and we have a heterozygous parent
crossed with a homozygous for the
recessive trait so homozygous recessive
there so first let's look for homozygous
dominant for our genotype remember
genotype is your cold and there is zero
for heterozygous we have one two and
four homozygous recessive we have one
two now if you would like you can drop
the zero and that would be 2 to 2 or 1
to 1 now if we want to convert that to a
percentage that would be 1 2 or 50
percent would be heterozygous and 50
percent would be homozygous recessive
okay now let's look at phenotype
remember we're trying to see which one
is red and the percentage or the ratio
of white so the percentage of red to
white and so the red is dominant so that
would be 1/2 and then the white will be
1/2 and if we want to convert that to a
percentage that would be 5050 okay and
finally let's look at one more example
very quickly say you have a codominant
situation and in this particular example
we have a chicken in it can be black
spotted or white spotted is another word
for speculum so here we go I've kind of
set this up to pick up the pace a little
bit
so now instead we will have the ratio of
the genotype B be the genotype B W in
the genotype ww and so that would be 1
be B to be W in 1w or that would be 25
percent 50 percent or 25 percent and the
phenotype ratio kind of the same thing
this will be black this will be
spot it in this will be white so it's a
1 to 2 to 1 so there we go
I hope that helps in setting up a
genotype and phenotype ratio thanks for
watching and moving math uploads a new
math and science video every day please
subscribe and share
Посмотреть больше похожих видео
An Introduction to Mendelian Genetics | Biomolecules | MCAT | Khan Academy
Genetics vocabulary | Inheritance and variation | Middle school biology | Khan Academy
Co-dominance and Incomplete Dominance | Biomolecules | MCAT | Khan Academy
Introduction to Cytogenetics (Filipino) Genes Alleles Chromosomes
Monohybrid Cross Explained
Dihybrid cross and the Law of Independent Assortment | High school biology | Khan Academy
5.0 / 5 (0 votes)