Unit 9.3: Monohybrid Inheritance
1. Define the terms genotype, phenotype, homozygous, heterozygous, dominant, and recessive.
Genotype: the genetic makeup of an organism in terms of the alleles present.
Phenotype: the physical or other features of an organism due to both its genotypes and its environment.
Homozygous: having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-breeding.
Heterozygous: having two different alleles of a particular gene (e.g. Tt or Gg); not pure breeding.
Dominant: an allele that is expressed if it is present (e.g. T or G)
Recessive: an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g).
Alleles are different forms of the same gene. For example, a certain gene controls eye colour but there are many eye colours out there. If you inherit two different alleles for a particular gene, one may be stronger than the other; the stronger one is the dominant allele while the weaker one is the recessive allele. The effect of the recessive will be masked by the dominant. Dominants are represented with capital letters (e.g. B for a dominant brown allele controlling eye colour) and recessives with lower case letters.
Following on with the eye colour situation: you've got a mother with brown eyes (Bb genotype (B for the dominant brown allele, b for the recessive blue allele)) and a dad with blue eyes (bb genotype). Like with multiplication, you can use a punnet square to calculate outcomes.
Let's use the eye colour problem again to describe heterozygotes and homozygotes. If an individual ended up with an Bb genotype, they are known to be heterozygotes because they have two different alleles that make up their eye colour. The individual with the bb genotype is known to be a homozygote because they have the same kind of allele that makes up their eye colour.
2. Calculate and predict the results of monohybrid crosses involving 1:1 and 3:1 ratios.
To understand this concept let's use an example involving flowers, because flowers are nice. We can take two red flowers and predict their breeding outcomes. One flower's genotype is RR, while the other is Rw; the latter flower contains a recessive white allele.
Say you take two purple flowers and and want to breed them to produce a flower. The genotype of the purple flowers would be Pw, where the dominant allele is purple and the recessive allele is white.
1. Define the terms genotype, phenotype, homozygous, heterozygous, dominant, and recessive.
Genotype: the genetic makeup of an organism in terms of the alleles present.
Phenotype: the physical or other features of an organism due to both its genotypes and its environment.
Homozygous: having two identical alleles of a particular gene (e.g. TT or gg). Two identical homozygous individuals that breed together will be pure-breeding.
Heterozygous: having two different alleles of a particular gene (e.g. Tt or Gg); not pure breeding.
Dominant: an allele that is expressed if it is present (e.g. T or G)
Recessive: an allele that is only expressed when there is no dominant allele of the gene present (e.g. t or g).
Alleles are different forms of the same gene. For example, a certain gene controls eye colour but there are many eye colours out there. If you inherit two different alleles for a particular gene, one may be stronger than the other; the stronger one is the dominant allele while the weaker one is the recessive allele. The effect of the recessive will be masked by the dominant. Dominants are represented with capital letters (e.g. B for a dominant brown allele controlling eye colour) and recessives with lower case letters.
Following on with the eye colour situation: you've got a mother with brown eyes (Bb genotype (B for the dominant brown allele, b for the recessive blue allele)) and a dad with blue eyes (bb genotype). Like with multiplication, you can use a punnet square to calculate outcomes.
| b | b | |
|---|---|---|
| B | Bb | Bb |
| b | bb | bb |
2. Calculate and predict the results of monohybrid crosses involving 1:1 and 3:1 ratios.
To understand this concept let's use an example involving flowers, because flowers are nice. We can take two red flowers and predict their breeding outcomes. One flower's genotype is RR, while the other is Rw; the latter flower contains a recessive white allele.
| R | R | |
|---|---|---|
| R | RR | RR |
| w | Rw | Rw |
The ratio of a heterozygous flower to a homozygous flower is 1:1.
| P | w | |
|---|---|---|
| P | PP | Pw |
| w | Pw | ww |
From the punnet table we see that the possibility of producing a purple flower is 3/4, while producing a white flower is 1/4. The ratio is 3 purples : 1 white.
this summaries are veryhelpful,thank you
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