E. GENETICS PROBLEMS When we \"solve a genetics problem\", what we are really do
ID: 201358 • Letter: E
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E. GENETICS PROBLEMS When we "solve a genetics problem", what we are really doing is predicting the proportion of offspring from a single pair of parents that will have different forms of a trait. For example, a curious pair of parents might wonder what the chances are that their unborn baby will have blue eyes. Or in more serious cases, a couple might want to know the probability that their child will inherit a certairn genetic disease that is present in their family history. We can make these predictions using a statistical tool called the Punnett Square (named for British geneticist and professor, Reginald Crundall Punnett). If we know the genotypes of two parents, we can determine the frequency of different all example, a parent who is heterozygous for freckles has one "F" allele and one "" allele of Segregation, these alleles segregate during for this gene locus. Therefore, based on Mendel's Law meiosis and half of their gametes will carry the "F" allele and half will carry the "" allele. We insert these allele/gamete proportions for each parent into the Punnett Square and can predict how random fertilization will result in different frequencies of genotypes in the offspring. Your instructor demonstrate the use of the Punnett Square using the example genetics problems be Show your work for all problems. 1. In humans, the allele for long eyelashes is dominant (L). Carol Brady is homozygous for long eyelashes. Her husband, Mike, has short eyelashes. a. b. c. What is the Mike's genotype? What is the Carol's genotype? Determine the predicted genotype and phenotype frequencies of their offspring. allele for dimples is dominant (D). Mr. and Mrs. Petrie (Rob and Laura) are both us for this trait. 2. In humans a. What is the Rob's genotype b. What is the Laura's genotype? c. Determine the predicted genotype and phenotype frequencies of their offspring.Explanation / Answer
Short eyelashes genotype: ll
Now, Carol Brady is homozygous for long eyelashes. Hence her genotype would be LL.
But her husband has short eyelashes; hence his genotype would be ll.
Punnett square:
l
l
L
Ll
Ll
L
Ll
Ll
All the offspring will be having long eyelashes with heterozygous in nature.
While person recessive for dimples has genotype dd.
Hence, Rob’s phenotype is Dd and Laura’s phenotype is also Dd.
D
d
D
DD
Dd
d
Dd
dd
Offspring phenotype is 3:1 (3 having dimples and 1 is recessive for this character)
Genotype is 1:2:1 (1 is homozygous for dimple; 2 is heterogeneous for dimple; 1 is recessive
for dimple)
Dan Connor doesn’t have Freckles; hence his phenotype would be ff.
F
f
f
Ff
ff
f
Ff
ff
From Punnett square, it is clear that half of the offspring will be having Freckles (heterogeneous in nature) and half will not.
l
l
L
Ll
Ll
L
Ll
Ll
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