lab exam 2 - Unit 9 Genetics

Punnett Square

A chart that shows all the possible combinations of alleles that can result from a genetic cross between two parents. Punnett squares can only predict an offspring's genotypes and phenotypes, but not show the actual offspring. A Punnett Square can determine probability in offspring's genotypes and phenotypes.

1. Define a gene and an allele. What is the difference between a genotype and a phenotype? What information can be obtained from a Punnett Square? What genetic information cannot be determined from a Punnett square?

Genes are small sections of DNA within the genome that code for proteins. Genes vary in size in humans. In relation to genes, an allele is an alternative form of a gene that arises by mutation.A Punnett square helps you to determine the possible percentages of different genotypes in the offspring of two parents. A Punnett square can show the probability of an offspring with a given genotype resulting from a cross ,although, it cannot show actual offspring.

Pedigrees

Show how a trait is passed through several generations in a family. Pedigree charts are often used to map genetic diseases in families. Pedigrees offer families a method to determine the probability that a son/daughter will be born with a genetic disease by tracing the disease through the family line and determining the genotypes of family members with/without the disease. By knowing the phenotypes of your family members, you can often infer the genotypes of your family members as well.

2. In pea plants, purple flower color (P) is a dominant allele, while white flower color (p) is a recessive allele. If a pea plant has the genotype Pp, what is its phenotype? Explain your answer.

The phenotype for this plant would be the purple flower color. This is because the white flower color is recessive, meaning in order for it to be expressed the genotype must be homozygous. Because the purple flower color is dominant, even though the genotype is heterozygous, the purple color flower will show.

3. Explain why not all families with 4 children have 2 boys and 2 girls, as predicted by a Punnett Square.

This is a good question for me to answer because I actually have three sibling and they are all boys. So I come from a family of three sons and one daughter. The reason situations like the one with my family don't turn out perfect (having an even amount of both genders) is because the gender of a child is completely random and doesn't really follow the patterns that a Punnett square does. A Punnett square is used to seek other characteristics in humans such as hair color, different genetic diseases, and many other things, not gender though. Although it does work out in some families, gender is really just a completely random thing to be determined and has nothing to do with a Punnett square

Homozygous recessive

because both of her alleles code for the non-dominant form of the gene. (bb)

A dominant trait is expressed if...

either one or both alleles are the dominant form of the gene. For a person to have dimples (even on only one side), he would need to have at least one copy of the dimple allele

A recessive trait is...

masked by the presence of a dominant gene and is only expressed if both alleles are the recessive form of the gene. For a person to have a lack of dimples, he must have two copies of the recessive form of the gene.

Heterozygous

meaning that one of each type of allele. ( Bb)

Homozygous dominant

means that his two alleles are of the same type (homozygous) and that those alleles are both the dominant version of the gene. (BB)