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Answer:
1. The shape of the earlobe is determined by a single autosomal gene, with two alleles: the dominant allele (F) expresses a detached (or free-hangning) earlobe, whereas the recessive allele (f) determines an attached earlobe. The potential dominant/recessive combinantions can yield different patterns of inheritance depending on what the allele combination is present in the progenitors (e.g. if both parents are FF, 100% of the progeny will be FF and presenting free earlobes; if one parent is Ff and the other is ff, then the inheritance pattern will be 50% free earlobes 50% attached earlobes.
2. Like the earlobe trait, the inheritance pattern of blood type depends on the combination of alleles, in this case THREE: A, B, and O. A and B are dominant, O is recessive. The Rh factor is determined by the presence (Rh+) or absence (Rh-) of a particular gene (RHD), and is independent from blood type.
3. Joseph's blood Rh factor is +, and his blood type is
Explanation:
1. This is a case of simple Mendelian inheritance. During meiosis, each chromosome will take with it one copy of the allele (e.g., in an individual with Ff genes, one gamete will end up carrying F, the other will end up carrying f). Since this sorting out of alleles is random, there is a random chance that either an F carrying gamete or an f carrying gamete to fuse with a gamete of the opposite gender (carrying in time F or f) to produce the zygote. A Punnett square can be used to show the resulting probabilities (see Question 3).
2. In this case we have two different types of patterns. One given by three allele versions of the same gene, A, B (the dominants), and O, resulting in types A (alleles AA or AO), B (BB or BO), AB (both AB alleles present) and O (OO). The blood type depends on a series of antigens expressed in the cellular membrane, with O alleles expressing none. In the case of the Rh factor, it is inherited independently from blood type as it is coded in a different gene.
3. Joseph's blood factor is Rh+ as some of his progeny with an Rh- partner is Rh +. His blood type is BO, since, even though none of Joseph and Rita's sons or daughters is blood type O, one of their daughters (A type) married a B type and had an O type son. This means that both parents had to have an recessive O allele masked by the dominant allele. Claire has to have inherited this O allele from Joseph as Rita is blood type AB. Punnett square below illustrates this
Joseph
B O
Rita A AB AO
B BB BO
this explains all four blood types from their progeny, with genotypes AO and BO yielding A and B blood types respectively.
In complete dominance, the dominant allele hides the expression of the recessive allele. In codominance, both alleles are expressed. 1. Complete dominance / 2. Complete dominance and codominance / 3. Genotype: IBi +- and Phenotype B Rh+.
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1. Explain the inheritance pattern of the ear lobe attachment trait. Explain bow you determined this.
Earlobe attachment is controlled by a single, autosomal, diallelic gene. Let us say that
- E is the dominant allele that codes for free-hanging earlobes
- e is the recessive allele that codes for attached-earlobes
The inheritance pattern of the earlobe attachment is simple Mendelian inheritance showing complete dominance.
According to allelic combination, each individual will express a phenotype that is the product of a mixture between both parents' genetic charges.
Following the first Mendel principle, each individual has a pair of alleles, and each allele codes for an alternative form of the same trait -for instance, attached and free-. These alleles independently segregate during gamete formation.
In complete dominance, the dominant allele completely masks the recessive allele expression. This is evident in heter0zyg0us individuals that carry both alleles but only express the dominant phenotype.
2. Explain the two inheritance patterns of blood type.
The gene that determines the ABO blood type of a person is a triallelic gene.
According to the allelic combination, the inheritance pattern might be either complete dominance or codominance.
Alleles are IA, IB, and i.
- IA express complete dominance over i. The person presents A type of antigens.
- IB express complete dominance over i. The person presents B type of antigens.
- IA and IB are codominant. The person presents both types of antigens, A and B.
- i is the recessive allele. The person does not present any antigen.
→ H0m0zyg0us dominant or heter0zyg0us Individuals IAIA or IAi will express the A blood type.
→ H0m0zyg0us dominant or heter0zyg0us Individuals IBIB or IBi will express the B blood type
→ Individuals with h0m0zyg0us recessive genotype, ii will express the 0 blood type.
→ Individuals carrying IA and IB alleles will express the AB blood type.
The Rh factor expresses complete dominance, where the + allele is dominant over the - allele. So whenever the + allele is present, either in h0m0zyg0us or heter0zyg0us state, the individual will express Rh+ factor.
3. What did you determine Joseph's blood type to be?
We know that
- Joseph is Rh+ and expresses blood type B.
- Rita is Rh- and expresses blood type AB
- Some of their progeny are Rh+
- One of their daughters is heterozygous for blood type A, IAi.
Rh factor
- If Joseph is Rh+, he could be either ++ or +-. So he could provide either + alleles or - alleles to his children.
- Rita is Rh-, meaning that her genotype is --, h0m0zyg0us recessive. She could only provide - allele to the progeny.
- The fact that some of their progeny are Rh+, suggests that the rest are be Rh-. If this is the case, then Joseph is heter0zyg0us for Rh+.
Cross: Joseph x Rita
Phenotypes) Rh+ x Rh-
Parentals) + - x --
Gametes) + - - -
Punnett square) + -
- +- --
- +- --
F1) 50% of the progeny is Rh + ⇒ heter0zyg0us genotype +-
50% of the progeny is Rh - ⇒ h0m0zyg0us genotype --
ABO
- Joseph has blood type B. He could be either IBIB or IBi
- Rita is AB. Her genotype is IAIB
- Their daughter is IAi, which means that she inherited IA allele from Rita -who is the only one carrying the IA allele- and the recessive alle i from Joseph.
- In this case, Joseph is heter0zyg0us for blood type B. He is IBi.
Cross: Joseph x Rita
Phenotypes) B x AB
Parentals) IBi x IAIB
Gametes) IB i IA IB
Punnett square) IB i
IA IAIB IAi
IB IBIB IBi
F1) 25% of the progeny is AB ⇒ Genotype IAIB
50% of the progeny is B ⇒ 25% IBIB + 25% IBi
25% of the progeny is A ⇒ Genotype IAi ⇒ The daughter
So, Joseph's blood type is B and Rh+
- Genotype: IBi +-
- Phenotype B Rh+
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