A pedigree is a representation of a family history tracking a trait and showing the inheritance pattern of the trait and its expression. The whole progeny expresses unattached earlobes.
The autosomal recessive trait is the characteristic that is coded by a gene located in an autosomal chromosome (this is, not a sex chromosome).
This trait is recessive because it is coded by the recessive allele, meaning that the dominant allele hides its expression.
The presence of only one dominant allele in the genotype is enough for the idividual to express free earlobes.
Genotype Phenotype
EE, Homozygous dominant Free earlobes
Ee, Heterozygous Free earlobes
ee, Homozygous recessive Attached earlobes
The pedigree is the representation of a family history conserning a certain trait. In this case, attached earlobes.
The pedigree shows the expression -and inheritance pattern- of the trait through several generations.
To correctly interpret a pedigree, we need to know that
Family members
→ Individuals are represented with geometrical figures.
→ Males are squares
→ Females are circles
Trait/Phenotype
→ Healthy/normal/not affected individuals are represented with empty figures
→ Affected/mutated individuals are represented with solid black figures
Generations
→ Each file is represented with a roman number, indicating the Generation.
In the exposed example, we will assume that
According to this pedigree,
I- 1- man with attached earlobes (shaded)
I- 2- woman with unattached earlobes (empty)
II-1 - man with attached earlobes (shaded)
II-2 -woman with unattached earlobes (empty)
II-3 - man with attached earlobes (shaded)
II-4- do not have information
II-5 - woman with unattached earlobes (empty)
III-1 - man with attached earlobes (shaded)
III-2 - woman with attached earlobes (shaded)
III-3 - man with attached earlobes (shaded)
III-4 - no information
III-5 - No information
III-6 - woman with unattached earlobes (empty)
Since we so not have enough information, we will assume
Individual III-6 is a woman that expresses unattached earlobes. Since we do not know her genotype (homozygous or heterozygous), we will represent it as E- ⇒ The symbol - represents either the dominant or recessive allele.
This woman marries a man who was homozygous for unattached earlobes, EE.
Cross:
Parentals) E- x EE
Gametes) E - E E
Punnett square) E -
E EE E-
E EE E-
F1) 50% homozygous dominant EE
50% is expected to be either homozygous dominant EE or heterozygous Ee
100% is expected to have unattached earlobes.
Their whole progeny is expected to express unatached earlobes, because the father (EE) can only provide dominant alleles, and the simple presente of a dominant allele is enought to express the dominant trait.
IMPORTANT NOTE:
Up to this point we consider shaded shapes as individuals carring the trait attached earlobes. So, according to this reasoning, all shaded individuals must express the recessive trait and genotype ee.
However, according to the provided explanation, shaded individuals express the dominant trait.
If this is the case, individual III-6 is homozygous recessive ee expressing attached earlobes.
When she marries a homozygous dominant man expressing unattached earlobes EE, their children will only be heterozygous Ee and express unattached earlobes.
You will find both options in the attaced files. In any case, the whole progeny expresses unattached earlobes.
You can learn more about pedigrees at
brainly.com/question/19516649
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