Genetics

A Punnett square is a ​ (a)   that allows you to easily determine the expected ​ (b)   of different ​ (c)   in the ​ (d)   of two parents. An example of a Punnett square for pea plants is shown here. In this example, both parents are ​ (e)   for flower color (Pp).

• chart
• percentage
• genotypes
• offspring
• heterozygous

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NGSS.HS-LS3-1

In a broad sense, the term "genotype" refers to the ​ (a)   of an organism; in other words, it describes an organism's ​ (b)   . In a more narrow sense, the term can be used to refer to the ​ (c)   , or variant forms of a ​ (d)   , that are carried by an organism.

• genetic makeup
• complete set of genes
• alleles
• gene

The presence of ​ (a)   at a particular ​ (b)   . A ​ (c)   genotype may include one ​ (d)   and one mutated allele or two different mutated alleles (compound heterozygote).

• two different alleles
• gene locus
• heterozygous
• normal allele

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NGSS.MS-LS3-1

Gene locus is the physical site or location of a specific ​ (a)   on a ​ (b)   .

• gene
• chromosome

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NGSS.HS-LS3-1

We all have two alleles, or versions, of each gene. Being ​ (a)   for a particular gene means you inherited two identical versions. It's the opposite of a ​ (b)   genotype, where the alleles are different. People who have recessive traits, like blue eyes or red hair, are always homozygous for that gene.

• homozygous
• heterozygous

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NGSS.HS-LS3-1

NGSS.HS-LS3-2

The gametes produced by the ​ (a)   are at the top of the chart, and the gametes produced by the ​ (b)   are along the side. The different possible combinations of alleles in their offspring are determined by filling in the cells of the ​ (c)   with the correct letters (alleles). 

 

• female parent
• male parent
• Punnett square

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NGSS.HS-LS3-1

NGSS.HS-LS3-2

A ​ (a)   is a scoring of the type of variant present at a given location (i.e., a locus) in the genome. It can be represented by ​ (b)   . For example, BB, Bb, bb could be used to represent a given variant in a gene.

• genotype
• symbols

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NGSS.HS-LS3-1

In the cross shown above, you can see that ​ (a)   (25 percent) has the genotype PP, one out of four (25 percent) has the genotype pp, and ​ (b)   (50 percent) have the genotype Pp. These percentages of genotypes are what you would expect in any cross between ​ (c)   Of course, when just four offspring are produced, the actual percentages of genotypes may vary by chance from the expected percentages. However, if you considered hundreds of such crosses and thousands of offspring, you would get very close to the expected results, just like tossing a coin.

• one out of four offspring
• two out of four
• two heterozygous parents.

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NGSS.HS-LS3-1

NGSS.HS-LS3-2

​ (a)   are always expressed when the connected allele is dominant, even if only one copy of the dominant trait exists. ​ (b)   are expressed only if both the connected alleles are recessive.

• Dominant traits
• Recessive traits

A Punnett square can also be used to determine a ​ (a)   based on the other genotypes involved in a cross. Suppose you have a parent plant with purple flowers and a parent plant with white flowers. Because the p allele is r​ (b)   , you know that the white-flowered parent must have the genotype pp. The purple-flowered parent, on the other hand, could have either the PP or the Pp genotype. The Punnett square below shows this cross. The question marks (?) in the chart could be either P or p alleles.

• missing genotype
• ecessive

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NGSS.HS-LS3-1

NGSS.HS-LS3-2