Genetics PPT PDF - Inheritance, Alleles, and Punnett Squares

Genetics The Study of Inheritance  Inheritance Inheritance refers to the characteristics that are passed on from parent to offspring. Some characteristics are very visible and some are not. It has been discovered that genes are the controlling factors of these characteri...

Genetics The Study of Inheritance  Inheritance Inheritance refers to the characteristics that are passed on from parent to offspring. Some characteristics are very visible and some are not. It has been discovered that genes are the controlling factors of these characteristics.  Gregor Mendel tidepool.st.usm.edu/ crswr/103inheritance.html  The Laws of Inheritance The Law of Dominance: Some traits are controlled by genes that are dominant over other genes for the same trait. The Law of Segregation: During gamete formation, the two genes for each trait are separated (segregated). The Law of Independent Assortment: Alleles for different genes usually separate independently of one another.  Mapping a Chromosome Chromosomes are the carriers of genes which control very specific traits. A gene is a factor that determines traits. Alleles are more specific forms of genes. Both are located on a chromosome  Alleles Alleles are always inherited in pairs. One of the pair is inherited from each parent as the result of sexual reproduction. The types of alleles inherited is called an organism’s GENOTYPE. The physical expression of these alleles is the organism’s PHENOTYPE.  Dominance and Recesiveness Alleles that are dominant are written as uppercase letters. Ex; B or H Alleles that are recessive are written as lower case letters. Ex; b or h When allele pairs are both identical (BB or bb) the organism is said to be homozygous. When allele pairs are different (Bb) the organism is heterozygous.  Inheriting Alleles The inheritance of alleles can be predicted by studying the alleles carried on gametes of both parents. The prediction is not a statistical analysis of what WILL happen, but a prediction of what COULD happen. The prediction of inheritance of one trait (gene) is called a monohybrid test cross.  Monohybrid Test Cross In creating a monohybrid test cross the alleles carried by both parents are arranged on a Punnett square: mother’s alleles on the top, father’s alleles on the left side. Mother Father  For Example The gene being predicted is height (H). A mother who is homozygous tall is mated with a father who is heterozygous tall. What are the probable genotypes and phenotypes of an offspring produced by these parents?  The Process Step One: Determine the genotype for each parent. Mother: HH Father: Hh  The Process Step Two: What are the alleles of each parent when segregated into gametes? Mother: H or H Father: H or h  The Process Step Three: Set up the Punnett Square H H H h  The Process Step Four: Write all possible combinations of alleles for the offspring. H H H HH HH h Hh Hh  The Process Step Five: Analyze the allele combinations and predict the genotype and phenotype possibilities. Genotype: HH - 2/4 or 50% Hh – 2/4 or 50% Phenotype: 4/4 or 100% tall  Example #2 The trait is eye color. Brown (B) is dominant over blue (b). A blue-eyed mother is mated with a heterozygous brown-eyed father. How likely will their child have blue eyes? Follow the five steps to answer this question.  Answer: Example #2 Mom: bb Dad: Bb b b B Bb Bb b bb bb Genotype: 2/4 or 50% heterozygous, 2/4 or 50% homozygous recessive. Phenotype: 50% chance of brown eyes, 50% chance of blue eyes.