Determine the probability of a couple having a child with a widow's peak if the conditions are as follows: The gene for widow's peak follows strict autosomal dominant-recessive inheritance. Widow's peak (W) is dominant, and no widow's peak (w) is recessive. The genotype of the mother is Ww, and the genotype of the father is ww.

Video transcript

Hi, everyone. Let's take a look at this practice problem together in a population of flower plants. There's a gene that determines flower color. The gene follows strict autosomal dominant recessive inheritance. Red color capital R is dominant, white color, lowercase R is recessive. A plant breeder has two parent plants. One with genotype capital R, lowercase R and another with genotype lowercase R, lowercase R. What is the probability that their offspring will have red flowers? The answer options are a 50%. B 25% C 75% and D 100%. So, recall that this type of problem is called a mono hybrid genetic cross because we are only concerned with one trait. So where do we begin? I'm going to put outline steps on the screen right now and talk through them. So the first step is that we need to identify the parent genotypes. Step two, we will use a punnet square and fill it in in order to determine offspring genotypes. And step three will determine how many offspring will have red flowers and then determine the probability. So starting with step one, the question told us that the flower color gene is autosomal dominant recessive inheritance. Meaning the gene has two copies or two alleles where one is completely dominant over the other A L red flower color represented by the capital R is the dominant A L white flower represented by lowercase R is the recessive a little. Now, we are told that parent one is heterozygous dominant genotype. So their genotype is capital R, lowercase R. They can produce two different gametes. One with the dominant a little and one with the recessive a little. Now, parent two, we're told is homozygous recessive lowercase R, lowercase R and they can only produce gametes that have the recessive a little. So now we've determined the parent genotypes and can move on to step two on the screen. I am putting up the completed punnett square. So to set it up and fill it out on the top column, on the top, we have two columns, one for each a little from parent one and on the left are two rows for each A lil of parent two. Then we fill in the corresponding columns and rows to determine the possible offspring genotypes. Now note that there are two possible genotypes for the offspring. We have the homozygous recessive and the heterozygous dominant genotypes. Now we can move on to step three. So in step three, we need to determine how many offspring have the red flowers. Now remember that offspring that will contain the dominant A L capital R will have red flowers. And there are two offspring with red flower color, the heterozygous Damon genotypes. Now, there are four possible offspring genotype outcomes. So to calculate the probability would be two divided by four, multiplied by 100% which equals 50%. Therefore, there is a 50% probability that offspring will have red flowers. So the correct answer is option a 50%. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.