1. MENDELIAN GENETICS One Factor Crosses

2. LEARNING GOALS: I can… …understand how chromosomes are arranged during meiosis …use the terms dominant and recessive & homozygous and heterozygous correctly …use a Punnett square to determine the possibility and probability of gene combinations between parents and the resulting traits

3. I.Determining Genotypes genotype phenotype A.Every living organism has a genotype that determines their phenotype. an individual’s collection of genes Genotype – an individual’s collection of genes an individual’s observable traits Phenotype – an individual’s observable traits their parents and is found in the nuclei (eukaryotic) of their cells (DNA) 1.An organism’s genotype comes from their parents and is found in the nuclei (eukaryotic) of their cells (DNA) their genotype 2.An organism’s phenotype then comes from their genotype “The genes of an organism determines the organism’s phenotype”

4. alleles B.For almost every gene there is more than one kind or form, called alleles. a variant form of a gene Allele – a variant form of a gene code for the same trait (for example: eye color) but come in different formsblueeye color or browneye color 1.You must remember that alleles code for the same trait (for example: eye color) but come in different forms (blue eye color or brown eye color) dominantrecessive 2.Alleles can either be dominant or recessive. a trait that is phenotypically expressed whenever one copy of the allele is inherited Dominant – a trait that is phenotypically expressed whenever one copy of the allele is inherited a trait that is phenotypically expressed only when two copies of the allele are inherited Recessive – a trait that is phenotypically expressed only when two copies of the allele are inherited

5. sexually asexually C.Organisms can reproduce sexually or asexually. genetically identical to their parents UNLESS their DNA is mutated 1.Organisms that reproduce asexually will be genetically identical to their parents UNLESS their DNA is mutated different from either parent because their genotype is a combination from two different people PLUS mutations can occur. 2.Organisms that reproduce sexually will be different from either parent because their genotype is a combination from two different people PLUS mutations can occur.

6. gametes are made with half the number of chromosomes of somatic cells (haploid) D.During meiosis gametes are made with half the number of chromosomes of somatic cells (haploid) only genes on the same chromosome are inherited together. 1.Because of the LAW OF INDEPENDENT ASSORTMENT only genes on the same chromosome are inherited together. chromosomes separate and arrange themselves randomly. 2.Because of the PRINCIPLE OF SEGREGATION chromosomes separate and arrange themselves randomly. two gametes will fuse randomly with a combination of alleles E.When fertilization occurs two gametes will fuse randomly with a combination of alleles homozygous 1.If an organism inherits two of the same allele for one trait they are said to be homozygous. heterozygous 2.If an organism inherits two different alleles for one trait they are said to heterozygous.

7. II.Using Punnett squares to determine gene combinations A.When biologists choose symbols to represent genes they usually take the first letter of the dominant trait. The upper case form of that letter represents the dominant allele the lower case form of that letter represents the recessive allele.

8. Practice determining symbols for traits: green is dominant over white G = green g=white round is dominant over wrinkled R = roundr=wrinkled tall is dominant over short T = tallt = short brown is dominant over blue B = brownb = blue

9. The symbols can then be used with a Punnett square to determine gene combinations Red flowers are dominant over white flowers PARENT #1 = homozygous red PARENT #2 = homozygous white (Follow the example on the board)

10. Use the information provided and a Punnett square to determine the possible gene combination from the following one factor crosses. Then, determine the probability of an offspring having a given gene combination. Finally, determine the probability of an offspring have the dominant or recessive trait. For your information: smooth is dominant over wrinkled brown is dominant over blue brown is dominant over blonde tall is dominant over short 1.homozygous brown X homozygous blonde 2.homozygous brown X homozygous brown 3.heterozygous tall X heterozygous tall