Genetics The Study of Heredity

What is Heredity? Heredity is the passing of traits from a parent to its offspring! Genetics is the study of heredity! Traits are physical characteristics represented by genes on the chromosome!

Why do some offspring look different from the parents? They inherit different genes! Parents only pass one of each pair of chromosomes to the offspring. When combined from each parent the offspring will have two of each (1 + 1 = 2)

Some things CANNOT be inherited! Things that are a result of the environment cannot be inherited! Example: Injuries or Practiced Skills

Review Which of the following cannot be inherited? Eye color Hair color Height Injuries

Where are the Genes? Genes are located on the chromosomes Chromosomes are inside the nucleus

Sex Cells vs. Body Cells Reproduce during mitosis Reproduce during a process called meiosis Female sex cells = eggs Male sex cells = sperm Sex cells are also called gametes.

Meiosis Gametes are formed during a process called meiosis. The cell divides into four cells New cell has ½ the number of chromosomes as the parent cell!

Review Which process produces sex cells? Mitosis Meiosis DNA replication Photosynthesis

Example EX. A grass hopper has 24 chromosomes How many chromosomes are in the sex cells? 12 chromosomes (1/2) Egg (12) + Sperm (12) = 24 chromosomes

EXAMPLE EX: A human has 46 chromosomes How many chromosomes does each gamete have after meiosis? 46/2 = 23

Mitosis vs. Meiosis Start with one cell End with two identical cells Parent cell has same number of chromosomes as daughter cells Produces body cells Start with one cell End with four cells Daughter cells have ½ the number of chromosomes as parent cell Produces sex cells (gametes)

Gregor Mendel 1851 A monk known as the father of genetics for his study of how traits are in inherited in pea plants Mendel wondered why some of the plants had different physical characteristics, or traits.

Mendel’s Pea Plants His research used hundreds of pea plants. Some of the plants grew tall and some grew short. Some of the plants produced green peas and some produced yellow peas Why Peas? yellow.

Mendel’s Observations Mendel observed that pea plants’ traits were often similar to their parents. Sometimes, however, the pea plants had different traits than their parents. Mendel’s work formed the foundations of GENETICS.

Purebred Plants A purebred is one that always produces offspring with the same trait as the parent. The offspring trait will always be identical to the parent trait in a purebred! Examples: purebred tall plants only produce tall offspring. Green peas only produce green pea offspring

Purebred or Hybrid? PP Purebred MM Tt Hybrid tt Qq

Mendel’s Experiment In his first experiment, Mendel crossed purebred tall plants with purebred short plants. Pure Tall X Pure Short He called this the parent generation (P generation) The offspring produced were called the F1 generation.

Results To Mendel’s surprise all of the offspring in the F1 were ALL TALL! The offspring produced are called hybrids. A hybrid is the result of crossing two purebreds

Mendel’s Conclusion The traits that an offspring gets depend on two gene factors. The female parent contributes one factor while the male parent contributes the other factor. Certain factors in a pair can mask or hide the other factor. EX. The tall factor was hiding the short factor in the F1

Alleles Different forms of genes are called alleles. Each parent has two alleles, but can only give one to the offspring! Offspring get one allele from mom and one allele from dad! Ex: Tall plant allele or Short plant allele can be inherited

Allele Demonstration The gene for hair color is represented by the letter “B” Brown hair is dominant: “B” Black hair is recessive: “b”

Dominant vs. Recessive Alleles The genes or alleles exist in two forms: A. Dominant B. Recessive A dominant allele is a stronger form of the gene and will ALWAYS show up in the organism when the allele is present. A recessive allele is a weaker form of a gene or allele will only show up if the dominant is not present.

Dominant vs. Recessive DD Dominant Dd dd Recessive Mn aa

Review Who is the father of genetics? Charles Darwin Watson Rosalind Franklin Gregor Mendel

Symbols in Genetics Scientist use symbols to write about the alleles for each of the crosses. They use letters instead of words Example: tall plants “T” short plants “t” Dominant allele is represented by capital letter Recessive allele is represented by a lower case version of the letter.

WHEN A PLANT INHERITS…. Two dominant alleles TT Purebred Tall Two recessive alleles tt Purebred Short One dominant and one recessive Tt Hybrid Tall

Genotype vs. Phenotype Genotype: the genes present The letter symbols Ex: Tt Phenotype: the physical or visible appearance A description! Ex: tall

What is the genotype? A hybrid smooth pea pod (dominant =smooth, recessive= pinched) Pp Purebred wrinkled pea seed (dominant= round, recessive=wrinkled) rr A hybrid tall pea plant (dominant=tall, recessive=short) Tt