Presentation is loading. Please wait.

Presentation is loading. Please wait.

Mendel’s Conclusions & Dihybrid crosses DO NOW: 2/27 Objectives: 1.Use a Punnett square to predict the outcome of a dihybrid cross. 2.Define the Mendel’s.

Similar presentations


Presentation on theme: "Mendel’s Conclusions & Dihybrid crosses DO NOW: 2/27 Objectives: 1.Use a Punnett square to predict the outcome of a dihybrid cross. 2.Define the Mendel’s."— Presentation transcript:

1 Mendel’s Conclusions & Dihybrid crosses DO NOW: 2/27 Objectives: 1.Use a Punnett square to predict the outcome of a dihybrid cross. 2.Define the Mendel’s Law of Segregation and Law of Independent Assortment and explain how they relate to Punnett squares. Task (answer, don’t copy): Dwarfism is caused by a dominant allele (D) in humans, and albinism is caused by a recessive allele (a). If a man heterozygous for dwarfism and albinism reproduces with an albino woman who is not a dwarf, what is the probability they will have an albino dwarf child?

2 The Dwarf and the Albino

3 Here’s how you might solve it… First, find the probability of dwarfism by using a Punnett square. –50% chance Then, find the probability of albinism. –50% chance Finally, multiply the probability of the two events together to find the probability of both happening –25% chance.

4 Dihybrid crosses The cross just explained is a dihybrid cross: a cross in which two different traits are studied. The earlier crosses we have studied are called monohybrid crosses because they track only a single trait.

5 Dihybrid Crosses: A Better Way Pea plant cross: PpYy x PpYy Gametes: reproductive haploid cells (sperm and egg) One individual heterozygous for 2 traits can produce 4 possible combinations of alleles. YP Yp yP yp

6 Try a Dihybrid Cross! Predict the outcome of a dihybrid cross between two pea plants heterozygous for both flower color and seed color (PpYy)

7 Dihybrid Punnett Square PP YYPP YyPp YYPp Yy PP YyPP yyPp YyPp yy Pp YYPp Yypp YYpp Yy Pp YyPp yypp Yypp yy PYPypYpy

8 Ratios? PP YYPP YyPp YYPp Yy PP YyPP yyPp YyPp yy Pp YYPp Yypp YYpp Yy Pp YyPp yypp Yypp yy How many of each? Purple flowers + yellow seeds : Purple flowers + green seeds : White flowers + yellow seeds: White flowers + green seeds: 9:3:3:1

9 Mendel’s “Laws” of Heredity The two basic mechanisms of these genetic crosses are explained on the next two slides. It is important to note that these “laws” work under certain conditions: –Each gene is on a different chromosome –The organisms are diploid

10 Law of Segregation A pair of factors is segregated (separated) during the formation of gametes (sex cells) Yy For example: 50% Of Gametes 50% Of Gametes

11 Law of Independent Assortment Factors for different characteristics are distributed independently from one another. Yy For example: 25% Of Gametes 25% Of Gametes Tt 25% Of Gametes 25% Of Gametes YyTt

12 What do you know? Construct a Punnett square showing a dihybrid cross between two lemmings. –One parent is heterozygous for brown fur (Bb: Brown = dominant) and homozygous recessive for a short tail (tt) –The second parent is homozygous recessive for white fur and heterozygous for a long tail. Predict how many of the offspring will be double recessive (white fur + short tail) This may be collected!

13 Homework 9.5 AND 3 Dihybrid Practice Problems Big Problem Set due Wednesday, 2.29 (but we will work on it in class tomorrow, 2.28)


Download ppt "Mendel’s Conclusions & Dihybrid crosses DO NOW: 2/27 Objectives: 1.Use a Punnett square to predict the outcome of a dihybrid cross. 2.Define the Mendel’s."

Similar presentations


Ads by Google