#99-100 Class Notes: Genetics New sex cells are made during meiosis, determines what one will look like. • Chromosomes that are the same type and size are called homologous ( 23 chromosomes pairs). • In the first division of meiosis, homologous chromosomes separate. • In the second division of meiosis, sister chromatids separate. • Each sex cell (egg, sperm) has 1 chromatid. An organism inherits 1 chromatid form each parent. Each chromatids holds information for a trait or characteristic.
Animation of Meiosis • http://www.cellsalive.com/meiosis.htm
Heredity is the passing on the traits, or characteristics, from parent to offspring. • The units of heredity are called genes.
Genes and Alleles. Genes- are segments of DNA on the chromosomes. Genes control characteristics or traits. Alleles- are characteristics, or traits are different forms of the same gene. The combinations of a gene for each trait occur by chance.
Organisms have at least two alleles for each gene. One allele came from the sperm and the other allele came from the egg. • One allele may be dominant over the other.
-Examples: • Gene = Face shape • Alleles =Round or square • Gene =Freckles • Alleles =present or absent • Gene = Widow’s peak • Alleles =present or absent
Dominant Vs. Recessive Allele Dominant allele- -(Root word: stronger) -The form of the gene that, when present, cover up(masks) the appearance of the recessive allele. -Scientists write dominant traits with Uppercase letters. Example: ( R= round)
Dominant Vs. Recessive Allele Recessive Allele- -(Root word: weaker) -The form of a gene that is hidden by the dominant allele is present. -Scientist write recessive traits with lowercase letters. Example: ( r=square)
Genotype and Phenotype • Genotype- The alleles of a gene an organism contains (internal, DNA’s coding letters). • Phenotype- The form of a trait that an organism displays (external, the physical appearance, What you see).
Genotype: Example Homozygous- both alleles are the same. Heterozygous- both alleles are different or hydrid.
Example of Genotype : (RR or rr) For simple dominant /recessive inheritance, there are 3 main types: 1. Homozygous Dominant: (RR 2 uppercase alleles) 2. Homozygous Recessive: (rr 2 lowercase alleles) 3. Heterozygous : (Rr 1 uppercase and lowercase alleles)
Write this down • Codominant- When an organism that has both alleles of a gene displays both phenotypes at the same time.
Gender In human, the sex of an individuals is determined by the particular combinations of two chromosomes called sex chromosomes. Individuals who have two X chromosomes (XX) are females, whereas those who have a X and Y chromosomes (XY) are males.
Create a Baby Lab To determine the gender/sex of offspring Only “Dad” flips his coin, if coin is head up is X or tails up is Y. Then to determine the other alleles of the offspring. Both “Dad” and “Mom” flip coins If the coin is head up = DOMINANT and tails up= recessive. Uppercase lowercase