In the exposed lethal genes cause the individual's death during embryionic development before being born. H0m0zyg0us dominant individuals do <u>not get born</u>. Yellow: 2/3. Grey: 1/3. Phenotypic ratio: 2:1
<h3>What is complete dominance?</h3>
When the dominant allele completely masks the expression recessive allele, we talk about complete dominance.
This is the case of individuals that are heter0zyg0us for a particular gene and express the dominant trait.
The dominant allele is hiding the expression of the recessive allele.
<h3>What are the lethal genes?</h3>
Refer to genes that impede the normal development of the individual.
- They can cause death during embryo development <u>before the individual gets born, </u>
- They can cause the individual's death after being born and <u>before reaching </u><u>sèxual maturity</u><u>. </u>
Let us assume that mice color is coded by a single diallelic gene that expresses complete dominance.
<u>Available data</u>:
- Yellow color is dominant over grey color.
- Yellow is coded by the dominant allele Y
- Grey is coded by the recessive allele y
- Genotype YY → Yellow and lethal
The cross would be as follows,
Cross: Yy x Yy
Gametes) Y y Y y
Punnett square) Y y
Y YY Yy
y Yy yy
F1) Considering ONLY the successfully born individuals
<u></u>
<u>Genotype</u>
2/3 = 50% of the progeny is expected to be heter0zyg0us, Yy.
1/3 = 25% of the progeny is expected to be h0m0zyg0us recessive, yy.
<u></u>
<u>Phenotype </u>
2/3 = 50% of the progeny is expected to be yellow, Yy.
1/3 = 25% of the progeny is expected to be grey, yy.
The phenotypic ratio is 2:1
You will learn more about lethal genes at
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