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Genetics Using Punnett Squares PowerPoint Presentation

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Description : Check out this medical titled "Genetics Using Punnett Squares”.

This medical is about Punnett squares, a useful tool in genetics for predicting the outcome of offspring from the mating of two individuals. They are based on the principles of Mendelian genetics, which describe how traits are passed from parents to offspring.

To use a Punnett square, you first need to determine the genotypes of the parents. The genotype refers to the genetic makeup of an individual, which includes the alleles (different versions of a gene) they possess.

Next, you create a square with the alleles of one parent along the top and the alleles of the other parent along the side. Then, you fill in the boxes with the possible combinations of alleles for their offspring.

For example, lets say that one parent has the genotype Aa and the other has the genotype aa. In this case, the top of the Punnett square would have the letters A and a, and the side would have the letter a twice. You would then fill in the boxes with the possible combinations of alleles: Aa and aa.

The resulting Punnett square would look like this:

| A | a

--|---|--

a | Aa | aa

a | Aa | aa

From this, you can see that there are two possible genotypes for the offspring: Aa and aa. You can also determine the probability of each genotype occurring by counting the number of boxes that contain each genotype. In this case, there are two boxes with Aa and two boxes with aa, so each genotype has a 50% chance of occurring.

Punnett squares can be used to predict the outcome of more complex genetic crosses as well, such as those involving multiple genes or incomplete dominance. However, the basic principles remain the same: determine the genotypes of the parents, create the Punnett square, and use it to predict the possible genotypes and probabilities of the offspring.

Tags : Genetics, Punnett Squares, Mendelian genetics, genotypes, Medical Genetics, Medical Genetics

Published on : Jun 01, 2023 | Views : 963 | Downloads : 0

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Slide 1-

Genetics Using Punnett Squares
Slide 2-

Early Genetics The study of genetics began with observations made by Gregor Mendel. After noticing that the flowers his pea plants were either violet or white, Mendel began to study the segregation of heritable traits. Between 1856 and 1863 he cultivated and tested at least 28,000 pea plants. Remember that Mendel worked almost 150 years ago when nobody knew about genes or even the structures (chromosomes) that carry genes.
Slide 3-

Here are some traits observed by Mendel:
Slide 4-

Lets consider a single gene… A gene carries information that determines your traits. Traits are characteristics you inherit from your parents. Genes are located in chromosomes. Chromosomes come in pairs and there are thousands, of genes in one chromosome.
Slide 5-

Continued… In humans, a cell’s nucleus contains 46 individual chromosomes or 23 pairs of chromosomes. Half of the chromosomes come from one parent and half come from the other parent. This is a human karyotype representing the 23 pairs of chromosomes in a male Here is the detailed structure of a chromosome
Slide 6-

Definitions Allele- discrete version of the same gene Genotype- the genes of an organism for one specific trait Phenotype- the physical appearance of a trait in an organism
Slide 7-

Definitions Dominant trait refers to a genetic feature that “hides” the recessive trait in the phenotype of an individual. The term "recessive” describes a trait that is covered over (or dominated) by another form of that trait and seems to disappear. Homozygous= two alleles that are the same for a trait (Pure) Heterozygous= two different alleles for a trait (Hybrid)
Slide 8-

Practice We use two letters to represent the genotype. A capital letter represents the dominant form of a gene (allele) and a lowercase letter is the abbreviation for the recessive form of the gene (allele). Example below: P=dominant purple and p= recessive white The phenotype for this flower is violet while its genotype (if homozygous) is PP. The phenotype for this flower is white while its genotype is pp (to be white the flower must have two of the recessive copies of the allele).
Slide 9-

Punnett Squares The Punnett square is the standard way of working out what the possible offspring of two parents will be. It is a helpful tool to show allelic combinations and predict offspring ratios.
Slide 10-

Before we go further lets review how to set up a Punnett Square… We begin by constructing a grid of two perpendicular lines.
Slide 11-

Next, put the genotype of one parent across the top and the other along the left side. For this example lets consider a genotype of BB crossed with bb. B B b b Notice only one letter goes above each box It does not matter which parent’s genotype goes on either side.
Slide 12-

Next, fill in the boxes by copying the column and row head-letters down and across into the empty spaces. B B b B B B B b b b b b
Slide 13-

Punnett Squares Now that we have learned the basics of genetics lets walk through some examples using Punnett Squares.
Slide 14-

Lets say: W- dominant white w- recessive violet W w W Parents in this cross are heterozygous (Ww). Note: Make sure I can tell your capital letters from lowercase letters. What percentage of the offspring will have violet flowers? ANSWER: 25% (homozygous recessive) Usually write the capital letter first w W W W w W w w w
Slide 15-

Red hair (R) is dominant over blond hair (r). Make a cross between a heterozygous red head and a blond. R r r r What percentage of the offspring will have red hair? 50%
Slide 16-

Let’s try some more… In pea plants, tall pea plants (T) are dominant over short pea plants (t). Construct a Punnett Square for a heterozygous tall pea plant and a short pea plant. T t t t What are the percentage of phenotypes? 50% tall 50% short
Slide 17-

Black eyes (R) is dominant over red eyes (r) in rats. Make a cross between a homozygous rat with black eyes and a rat with red eyes. R R r r What is the possibility of a red eye off springs? 0% 
Slide 18-

References http://www.athro.com/evo/gen/punnett.html http://www.kidshealth.org/kid/talk/qa/what_is_gene.html http://brookings.k12.sd.us/biology/ch%2011%20genetics/punnettpractice.ppt#1 http://www.usoe.k12.ut.us/CURR/Science/sciber00/7th/genetics/sciber/punnett.htm http://www.biotechnologyonline.gov.au/images/contentpages/karyotype.jpg