Genetic Crosses Genotype vs Phenotype Genotype An organisms

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Genetic Crosses

Genetic Crosses

Genotype vs Phenotype �Genotype: An organism’s genetic makeup which consists of the alleles that

Genotype vs Phenotype �Genotype: An organism’s genetic makeup which consists of the alleles that an organism inherits from it’s parents (ex: Ee, EE, or ee) �Phenotype: The physical appearance of an organism’s genotype.

Homozygous vs Heterozygous �Homozygous: When both alleles of a pair are alike for a

Homozygous vs Heterozygous �Homozygous: When both alleles of a pair are alike for a specific characteristic. �An organism can be homozygous dominate (EE) or homozygous recessive (ee) �Heterozygous: When both alleles in the pair are different. (Ee)

Probability �Probability = # of times expected to happen # of times could happen

Probability �Probability = # of times expected to happen # of times could happen �Example: �In Mendel’s experiment the tominate trait of yellow seed color appeared in F 2 generation 6, 022 times. The recessive trait of green seed color appeared 2, 001 times. The total number of individuals was 6, 022+2001 = 8, 023. �What is the probability of the dominate trait?

Probability �Probability of dominate trait = 6, 022 =. 75 or 75% 8, 023

Probability �Probability of dominate trait = 6, 022 =. 75 or 75% 8, 023 �This can be expressed in either a percentage, fraction, or a ratio �Probability tells us that there are three chances in four that an offspring of two heterozygous individuals will have the dominate trait and one chance in four that the offspring will have the recessive trait.

Monohybrid Crosses �Monohybrid Cross: a cross that only one characteristic is tracked is monohybrid.

Monohybrid Crosses �Monohybrid Cross: a cross that only one characteristic is tracked is monohybrid. �Punnett Square: a diagram used to aid biologists in predicting the probable distribution of inherited traits in offspring. �Six Examples: 1. Homozygous X Homozygous 2. Homozygous X Heterozygous 3. Heterozygous X Heterozygous 4. Testcross 5. Incomplete Dominance 6. Codominance

Example One: Homozygous X Homozygous �There is a 100% probability that the offspring will

Example One: Homozygous X Homozygous �There is a 100% probability that the offspring will have one specific genotype, thus producing the same phenotype.

Example Two: Homozygous X Heterozygous �Will produce an outcome 50% probability dominate or recessive.

Example Two: Homozygous X Heterozygous �Will produce an outcome 50% probability dominate or recessive.

Example Three: Heterozygous X Heterozygous �¼ BB, ½ Bb, ¼ bb �Genotypic Ratio: 1

Example Three: Heterozygous X Heterozygous �¼ BB, ½ Bb, ¼ bb �Genotypic Ratio: 1 BB: 2 Bb: 1 bb �Phenotypic Ratio: 3 Brown, 1 Blue

Example Four: Testcross �How can you determine if a guinea pig is homozygous (BB)

Example Four: Testcross �How can you determine if a guinea pig is homozygous (BB) or heterozygous (Bb)? �Perform a Testcross: taking an individual with an unknown genotype and crossing it with another individual who is homozygous

Example Five: Incomplete Dominance �Incomplete dominance occurs when the phenotype of a heterozygote is

Example Five: Incomplete Dominance �Incomplete dominance occurs when the phenotype of a heterozygote is intermediate between the phenotypes determined by the dominant and recessive traits. � Pink flowers (Rr) come from a dominant homozygous red parent (RR) and a recessive homozygous white parent (rr).

Example Six: Codominance �Codominance occurs when both alleles for a gene are expressed in

Example Six: Codominance �Codominance occurs when both alleles for a gene are expressed in heterozygous offspring. �Neither allele is dominant or recessive, nor do the alleles blend in the phenotype (as in incomplete dominance).

Dihybrid Cross �Dihybrid cross: is a cross which two characteristics (genes) are tracked. �The

Dihybrid Cross �Dihybrid cross: is a cross which two characteristics (genes) are tracked. �The offspring of the animal being crossed in a dihybrid cross is called a dihybrid. �Two examples: 1. Homozygous X Homozygous 2. Heterozygous X Heterozygous

Example One: homozygous X homozygous �Review to page 185 �Two seeds with two different

Example One: homozygous X homozygous �Review to page 185 �Two seeds with two different genes being expressed: (1) round, yellow seed (RRYY) (1) wrinkled, green (rryy)

Example Two: Heterozygous X Heterozygous �Use the same procedure as in homozygous x homozygous.

Example Two: Heterozygous X Heterozygous �Use the same procedure as in homozygous x homozygous.