Life Science Chapter Five Genetics Heredity Punnett Squares Dominant Recessive Mendel Human Genetics

Heredity Defined The passing of traits from parents to offspring Traits are controlled by genes that are made of DNA and genes are found on chromosomes At the end of meiosis each cell ends up with one of the two forms of the gene T—dominant or t- recessive

Alleles Defined Are the different forms a gene may have Signified by letters for simplicity T—dominant t-recessive TT, Tt, tt

Genetics Defined Study of how traits are inherited through the action of alleles Father of Genetic Gregor Mendel

Genetics Definitions Purebred Organism that always produces the same trait Has two of the same alleles TT or tt

Genetics Definitions Dominant It always dominates or covers up the recessive form of the gene Signified with a capital letter T, A, H etc.

Genetics Definitions Recessive Shows up only when there are two alleles for the recessive type tt or aa

Probability Ratio of offspring Branch of mathematics that helps you predict the chance that something will happen Scientific research is based on repeatable results

Punnett Square Dominant Capital letter Always written in front of small letter Recessive Small letter Genotype Genetic makeup Both alleles are known AA or Aa or aa

Punnett Square Phenotype Physical trait Trait that shows Don’t always know both alleles Examples Genotype—t or T Phenotype—short or tall

Punnett Square Always two or more alleles for every trait! Homozygous TT or tt Two of the same allele Both recessive or both dominant

Punnett Square Heterozygous Tt Two different alleles One dominant and one recessive Write dominant in front or recessive trait Move parent traits down and across

Punnett Square TT tTt t

Punnett Square Tt TTTTt t tt

Punnett Square First square 100% tall--phenotype 100% Tt—genotype Second Square 25% TT 50% Tt 25% tt 75% tall 25% short

Mendelian Inheritance 1. Traits are controlled by alleles on chromosomes 2. An allele may be dominant or recessive in form 3. When a pair of chromosomes separate during meiosis, the different alleles for a trait move into separate sex cells

After Mendel Incomplete Dominance The production of a phenotype that is intermediate to those of the two homozygous parents Red with white give pink offspring Blending of the two traits

After Mendel Multiple Alleles A trait controlled by two alleles Co-dominance Blood types A and B are co- dominant O is recessive

Blood Types GenotypePhenotype ABAB—universal acceptor BOB AOA AAA BBB OOO—universal donor

After Mendel Multiple Genes Combination of many genes Polygenic Inheritance When a group of gene pairs act together to produce a single trait Examples, height, body build, weight, shape of lips, eyes, ears, eye color, hair color, skin color

Human Genetics Sickle-cell anemia Homozygous recessive disorder Sickle-cell blood cells can’t deliver enough oxygen to the cells in the body

Human Genetics Cystic fibrosis Homozygous recessive Thick mucus instead of thin fluid to lubricate the lungs and intestinal tract Makes it hard to breathe

Human Genetics Sex determination Up to male Provides either a X or a Y Female only has X and X

Human Genetics Sex-linked disorders Those genes contained on sex chromosomes (X or Y) Color blindness Male pattern baldness

Human Genetics Sex-linked gene An allele inherited on a sex chromosome Females must be homozygous recessive and have two recessive alleles to have a sex-linked disorder

Human Genetics Sex-linked gene Males only need one on the X chromosome

Human Genetics Hemophilia Another example Blood does not clot properly Located on X- chromosome Females need two genes Males need one gene

Pedigrees A tool for tracing the occurrence of a trait Squares are males Circles are females Colored in shapes Person has the trait Half-colored shapes Person is carrier on X- chromosome Open/not colored shape Person does not have disease

Genetic Engineering Scientists experiment with biological and chemical methods to change the DNA sequence Helps to make medicine Improve crops