NON-MENDELIAN GENETICS: CODOMINANCE || GRADE 9 SCIENCE _ BIOLOGY

Summary

In this educational video, we explore co-dominance, a non-Mendelian inheritance pattern where both alleles are equally expressed. Using speckled chickens and blood group antigens as examples, we demonstrate how traits are visible in heterozygotes. A practical problem-solving session follows, where we predict offspring genotypes and phenotypes from crosses between white and red cattle. The lesson concludes with a Punnett Square exercise, illustrating the genotypic and phenotypic outcomes of these crosses, providing a clear understanding of co-dominance in genetics.

Takeaways

• 🔬 The lesson discusses co-dominance, a non-Mendelian pattern of inheritance where both alleles are expressed equally in the phenotype.
• 🐓 A speckled chicken is given as an example of co-dominance, where black and white feathers are both visible, illustrating the expression of both alleles.
• 🩸 Another example of co-dominance is in blood groups, specifically with the A and B antigens, where the presence of both results in an AB blood type.
• 📊 The lesson uses a Punnett Square to predict the genotypes and phenotypes of offspring from a genetic cross.
• 🐄 The first example problem involves crossing a white cow (ww) with a red bull (RR), resulting in heterozygous offspring (RW) with a phenotype of rowdy.
• 🐃 When two heterozygous rowdy cows (RW) are crossed, the offspring can be homozygous red (RR), heterozygous rowdy (RW), or homozygous white (ww), with a genotypic ratio of 1:2:1.
• 🌟 The phenotypes from the cross of two heterozygous rowdy cows are one red bull, two rowdy cows, and one white cow.
• 📝 The lesson emphasizes the importance of understanding and applying genetic principles to predict outcomes of genetic crosses.
• 👩‍🏫 The script is educational, aimed at learners interested in genetics, and encourages subscription for more content.
• 🔔 The channel invites viewers to subscribe and enable notifications to stay updated with new educational videos.

Q & A

What is the law of co-dominance in genetics?

The law of co-dominance states that both alleles are expressed equally in the phenotype of a heterozygote, meaning both traits are observed.

Can you provide an example of co-dominance from the script?

A speckled chicken is an example of co-dominance, resulting from a cross between a black and a white chicken, producing a chicken with both black and white feathers.

What is another example of co-dominance mentioned in the script?

The blood group AB is an example of co-dominance, where the A and B alleles are co-dominant, and a person with both antigen A and B will have the blood type AB.

What is the genotype of the white cow and red bull used in the example problem?

The genotypes of the white cow and red bull are ww and RR, respectively, indicating they are homozygous for their respective traits.

How is the genotype of the offspring determined in the example of crossing a white cow and a red bull?

The genotype of the offspring is determined using a Punnett Square, resulting in four heterozygous Rr offspring.

What is the genotypic ratio of the offspring when a white cow and a red bull are crossed?

The genotypic ratio of the offspring is 4 Rr (heterozygous) to 0, indicating all offspring will have the genotype Rr.

What is the phenotype of the offspring when a white cow and a red bull are crossed?

The phenotype of the offspring is all row one, which means they will all have a red and white mixed coat.

What happens when two heterozygous Rr cows are crossed according to the script?

When two heterozygous Rr cows are crossed, the offspring can have genotypes RR (homozygous red), Rr (heterozygous), and rr (homozygous white).

What is the genotypic ratio of the offspring when two heterozygous Rr cows are crossed?

The genotypic ratio of the offspring is 1 RR : 2 Rr : 1 rr, indicating one homozygous red, two heterozygous, and one homozygous white.

What is the phenotype of the offspring when two heterozygous Rr cows are crossed?

The phenotype of the offspring is one red bull, two row one (red and white mixed coat), and one white cow.

What is the significance of the Punnett Square in determining the offspring's genotype and phenotype in the script?

The Punnett Square is used to predict the genotypes and phenotypes of the offspring by illustrating the possible combinations of alleles from each parent.